Further observations on and novel products from acid-catalysed indole-pyrrole condensations: formation of pyrrolo2,3-bcarbazoles

摘要

J. CHEM. SOC. PERKIN TRANS. 1 1994 Further Observations on and Novel Products from Acid-catalysed Indole- Pyrrole Condensations: Formation of Pyrrolo2,3-bcarbazoles Laddawan ChunchatpraserP and Patrick V. R. Shannon *JJ a Department of Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen, 40002, Thailand School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, Cardiff CFI 3TB, UK The clay-catalysed reaction between indole and ethyl 5-acetoxymet hyl-4-acetyl-3-met hylpyrrole-2- carboxylate 1a has been shown to give 2-ethoxycarbonyl-3,4-dimethylpyrrolo3,2-bcarbazole 3a as the major product, accompanied by 3.9 of the isomeric pyrrolo2,3-bcarbazole 4a. The minor product was rationalised by the correspondingly small amount of indole-2-pyrrolylmethyl substituted product observed when an alternative pyrrole was used.The proportion of pyrrolo2,3-b -carbazole 4 formed was shown to increase with the presence of strongly electron-donating groups in the indole. In the case of 5-methylindole, which gave 6.4 of the 2,3-b isomer, when the reaction was run at a lower temperature, the intermediate 3-substituted pyrrolylmethylindole 7c could be isolated. Cyclisation of this, under the original reaction conditions gave only the pyrrolo3,2-b -carbazole 3h. There was no equilibration between the isomeric pyrrolocarbazoles under the reaction conditions. The electrophilic substitution of the pyrrolo3,2-bcarbazole 3a was examined. The pyrrolylmethyl and dimethylallyl cations, pyridine hydrobromide perbromide and Vilsmeier formylation all gave predominant, prior attack at the 10-position of the pyrrolo3,2-bcarbazole.For the 10-pyrrolylmethylpyrrolo 3,2-bcarbazole 6a bromination gave the 8- bromo and 6.8-dibromo derivatives. In a recent publication,' we described the clay-catalysed condensation between pyrroles of type 1 with the indoles 2a-d to give the pyrrolo3,2-bcarbazoles 3a-d. These compounds, like the structurally related ellipticines, have been demonstrated to have anti-tumour activity.2 For the original indoles 2a-d we isolated only the tetracyclic pyrrolo3,2-bcarbazoles Sand none of the isomeric 2,3-b systems, 4. In earlier work,3 however, we showed that the acid- catalysed reaction between indole and the pyrrole lc, gave, apart from the main 3-pyrrolylmethyl substituted product, 5 of the mono-2-pyrrolylmethyl indole 5.It would be expected that analogues of 5 derived from acylpyrroles of type 1 (R3 = Ac), would rapidly cyclise at the indolyl 3-position to give the alternative pyrrolo2,3-bcarba- zole systems 4 (see Scheme 1). We therefore re-examined the indole-pyrrole la reaction in detail. In the event, two new minor products were isolated by chromatography apart from the pyrrolocarbazole 3a. The least-polar was a pale yellow solid, M+ 306, clearly isomeric with the deeper yellow tetracycle 3a. In the 'H NMR spectrum all of the expected signals were present-but the chemical-shift difference between the aromatic 3 and 4 methyls (S3.17 and 2.95) was greater than for the isomer 3a (S2.91 and 2.90) and the 10-H singlet was at much higher field (S7.18; 6 7.85 in 3a).These two features were found to be characteristic differences between the 3,2-b and 2,3-b isomers. Further confirmation of the structure 4a of the by- product as the pyrrolo2,3-bcarbazole (3.9) was obtained by the NOE enhancements shown. As expected, isomer 4a showed in its UV spectrum shorter wavelength bands above 300 nm than 3a. The more polar of the two by-products gave a strong molecular ion at m/z 513. The 'H NMR spectrum showed all the signals characteristic of the pyrrolo3,2-bcarbazole 3a, but with the absence of the 10-H singlet. In addition signals due to a pyrrolylmethyl substituent were obvious. The orientation of the pyrrolocarbazole nucleus and the position of substitution of the pyrrolylmethyl unit were confirmed by the NOE enhancements shown in structure 6a.The presence of the pyrrolylmethyl group at the 10 position implied that the latter was the most reactive site in the pyrrolo3,2-bcarbazole towards electrophilic substitution and this was confirmed by the additional experiments described below. The use of K10 clay is not essential for the pyrrole-indole condensations and, in fact, toluene-p-sulfonic acid gave an enhanced yield of the pyrrolocarbazole 6a. Earlier on indoles has shown that 4- or 6-methoxy groups can increase the amount of electrophilic substitution at the 2-position. We therefore thought that 4-hydroxyindole would give an enhanced degree of 2-substitution by the pyrrolylmethyl group and hence a greater proportion of the pyrrolo2,3-bcarbazole 4b when compared with indole itself.In the event this proved to be so. Treatment of 4-hydroxyindole with K10 clay and the pyrrole la gave, as expected, a number of impure products including 3-, 5-and 7- pyrrolylmethyl substituted indoles. From the product mixture, however, crystallisation and chromatography of the mother liquors afforded the two pure pyrrolocarbazoles 3e (10.6) and 4b (4.3). The spectral properties of these isomers enabled an unambiguous structure assignment to be made. It is known' that N-methylation of indoles (and pyrroles) increases the rate of electrophilic substitution at the indole-3 (and pyrrole-5) positions.We therefore next investigated the pyrrole condensation with 4-methoxy-1 -methylindole 2f.* The main product (46) from 2f and pyrrole la was the pyrrolo3,2- blcarbazole 3f with no detectable amounts of the 2,3-b isomer. It would appear that the N-methyl group in the indole 2f restores the 3-position as the predominant site of electrophilic substutition. It is likely that, when predominant initial substitution at the indolyl3-position occurs (as for indole itself, and for the indole 20, a spirocyclic intermediate 7 is formed, as in the cyclisation of tryptamidesg followed by a highly regioselective migration of the C(Me)OH-pyrrolyl bridge leading to a predominance of the 3,2-b isomer (see Scheme 2).A minor product (4.6) from the reaction of the indole 2f was the 10-substituted pyrrolocarbazole 6b. 5-Hydroxyindole underwent reaction with the pyrrole la more slowly than with 4-hydroxyindole. The total yields of the two isomeric pyrrolocarbazoles obtained (3g,5.7 and 4c 1.1) R' .. la R' = Me, R2= Et, R3=Ac 2a all R=H g R~=OH b R' = Me, R2= CH2Ph, R3= Ac b R2=OMe h R2=Me c R' = Me, R2= CH2Ph, c R~=F i R2=@=OMe R3 = CH2CH2C02Me d R4=Me j p=R3=OCH20 6 R'=OH k R'=F f R'=OMe I R3=F R5=Me m R2=CI R" = H unless stated otherwise n R2=Br R' R7 3a R6 = Et b R2 = OMe, R6= Et c R2=F.R6=Et f R' = OMe, R5 = Me, R6 = Et g R2=OH, R6= Et 4a R6= Et h R2= Me, R6= Et b R' =OH, R6= Et i R2 = R3 = OMe, R6 = Et c R2=OH, R6= Et j R2 = R3 = OCH20, R6= Et d R2= Me, R6 = Et k R' = F, R6= Et e R2= R3= OMe, R6 = Et I R3=F,R6=Et f R2= R3= OCH20, R6= Et m R2= CI, R6= Et g R3=F,R6= Et n $=Br,R6=Et h F?=Me,R6=et o R6=CH2Ph I R2 = Br, R6 = Et p R7 = Me2C=CHCH2, R6= Et NOE differences shown for compound 4a H s R7 = CHO, R6 = Et ut R7 = CHO, R2= Me, R6 = Et 0-qixc02cH2phII Me2C=CHCH2, R6 = Et H v R7 = Br, R6 = Et y2 S;H2 C02Me 5 were less.It proved difficult to purify the products in the presence of large amounts of starting materials. The 3,2-b isomer 3g first co-crystallised with the pyrrole-but treatment of this mixture with additional 5-hydroxyindole and clay, -H+-H$14 Scheme 1 J.CHEM. soc. PERKIN TRANS. 1 1994 C02R6 )=./ followed by chromatography, afforded a pure sample of 3g. Its isomer 4c could not be separated on crystallisation from ca. 12 of 3g. It was clear that the isomer 3g was tenaciously adsorbed by the clay and the yields quoted do not necessarily represent the amounts or proportions actually formed. U 7 IH'+ H U Scheme 2 Small amounts of the 10-substituted compound 6c were also isolated as well as, significantly, the 3-monosubstituted intermediate 8a, the major product (1 1.5). The structure of the latter was evident from the molecular weight (M', 340, 100) and the presence of the indole 2 H (S 7.10, d, J 2.5 Hz) and the methylene bridge (S4.31, s) in the 'H NMR spectrum.8a R2=OH, R3= Et d R3= Et b R' = F, R3 = Et R2= CI, R3 = Et c R2= Me, R3 = Et f R2 = Br, R3= Et It appeared that electron-donating groups in the indole were linked with the formation of the 2,3-bpyrrolocarbazole isomer, and this proved to be the case with 5-methylindole- which gave the isomers 3h and 4d in the ratio 5 :1, respectively. The 1 0-pyrrolylmethyl derivative 6h was also isolated (1 2.9). Where two strongly electron-donating groups were present, this effect was larger. Thus, 5,6-dimethoxyindole gave, as well as the 10-substituted product 6d, both isomers 3i and 4e in the J. CHEM. SOC. PERKIN TRANS. 1 1994 ratio 8.1 :4.8. In fact, in the case of 5,6-methylenedioxyindole, the major product was the 2,3-b isomer 4f (9.2) with substantial amounts of the isomer 3j (7.4) and the 10-substituted product 6e.By contrast with the effect of the electron-donating groups in the indole, a series of halogenated indoles (2k-n) were also condensed with pyrroles la-but they gave predominantly the 3,2-bpyrrolocarbazoles with little or none of the 2,3-b isomers. Thus, 6-fluoroindole gave the 2,3-b isomer 4g (3.1) along with the 1 0-pyrrolylmethyl derivative 6f. These results paralleled those with 5-chloro- and 5-bromo-indoles. It is noteworthy that both 4-fluOrO- and 5-fluoro-indole 'gave none of the 2,3-b isomer. In the former case the 3,2-b isomer 3k (from 4-fluoroindole) was accompanied by the 3-mono- substituted derivative 8b. It can be seen from the above examples (a) that 10-pyrrolylmethyl substituted pyrrolo3,2-bcarbazoles often accompany the pyrrolo2,3-bcarbazole as reaction products and (b) there seems little doubt that the primary site of electrophilic substitution in the 3,2-b isomer is at C-10.In fact, when the pyrrolo3,2-bcarbazole 30was treated with toluene- p-sulfonic acid and 1 equiv. of the pyrrole lb, the major product (27.8) was the 10-pyrrolylmethyl derivative 6g. A second product was also isolated. This high melting point compound had M+ 906 and analysed for CS6H,,N,08. In the 'H NMR spectrum all the signals expected of a 10-pyrrolylmethyl-pyrrolo3,2-bcarbazole were seen, but, only two doublets and a triplet could be seen for the ring A aromatic protons.The 9 H doublet signal was at characteristically lowfield (6 7.70) and was shown by double resonance to be coupled to a triplet at 6 6.90 which, in turn, was coupled to a doublet at 6 6.83. The 6- position was, therefore, substituted by the second pyrrolyl- methyl group and this led to the 6,lO-disubstituted pyrrolo- carbazole structure 3r. Similar results were obtained by treatment of the pyrrolocarbazole 3a with the pyrrole la but using clay. In the light of the evident ease of substitution of the 3,2-b system of 3a by the pyrrolylmethyl group, we examined some additional electrophiles. Formylation of 3a under Vilsmeier conditions gave the 10- formyl derivative 3s in high yield; the methyl analogue 3h gave the aldehyde 3t in 54 yield.Similarly treatment of 3a with 2- methylbut-3-en-2-01lo and clay gave the 10-(2-methylbut-2- enyl) analogue 3p with unchanged starting material and a very minor by-product (0.6) shown by 'H NMR spectroscopy to be the 6-substituted product 3u. Bromination of 3a with 1 equiv. of pyridinium hydrobromide perbromide in dichloromethane gave the 10-bromo compound 3v as the major product, but significant quantities of the 8-bromo 3n and 8,lO dibromo derivative 3q were also formed. When 2 equiv. of the brominating agent were used only the 8,lO-dibromo compound 3q was isolated (68). The relative selectivity of the bromination was illustrated by treatment of the lo-pyrrolyl- methylpyrrolocarbazole 6a with 1 equiv. of the perbromide. The main product (42) was the 8-bromo compound 6i, but the 6,8-dibromo analogue 6j (16.5) was a minor but significant product.The circumstantial evidence that exists suggests that when the initial step in the indole-pyrrole condensation is formation of a 2-substituted indole, e.g. 5, cyclisation takes place very rapidly at the indole-3 position to give only the pyrrolo- 2,3-bcarbazole. In keeping with this, no 2-monosubstituted intermediates have been isolated, except in the case of 5 in which cyclisation on the indole is precluded by the absence of the pyrrole-3-carbonyl group. By contrast, we have been able to isolate the 3-substituted intermediates of the pyrrolo3,2-b- carbazoles. In these cases, if the mechanism shown in Scheme 2 is correct, treatment of the 3-substituted intermediate with clay should give only the pyrrolo3,2-bcarbazoles 1ven in cases where the reaction from pyrrole and indole gives both the 3,2-b and 2,3-b isomers.Such a case is that of 5-methylindole. We isolated both 3,2-b (31.5) and 2,3-b (6.42) isomers when the parent pyrrole la and the indole 2h with clay were the starting materials. By using a lower temperature for the reaction, we were able to isolate useful quantities (ca. 12) of the 3-substituted intermediate 8c. Treatment of the latter with clay under the conditions of the normal reaction and virtually quantitative recovery (92.5 weight) of the reaction components showed that no detectable amount of the 2,3-b product 4h was present.Whilst this experiment proves that no 2,3-b isomer 4h is formed from the 3-substituted indole 8c it does not rule out direct cyclisation at the 2-position of 8c as a pathway to the 3,2- b isomer. We attempted to trap a spirocyclic intermediate from the 3-substituted intermediate 8d using trifluoroacetic acid anh~dride,~and acetic anhydride, but this was unsuccessful. Finally, the unlikely possibility of equilibration of the 3,2-b and 2,3-b systems was ruled out. Treatment of either of the pyrrolocarbazoles 3h and 4h with clay under the original (pyrrole-indole) reaction conditions gave none of the alternative isomer. Experimental IR spectra were recorded on a Perkin-Elmer 1600 series FTIR; UV spectra were measured in ethanol on a Perkin-Elmer Lambda 2 UV-VIS spectrophotometer; and 'H NMR spectra were obtained on a Bruker WM 360-NMR spectrophotometer at 360 MHz.JValues are given in Hz. EI mass spectra were run on a Varian CH5D instrument. Flash column chromatography was carried out with Fisons, Matrex silica 60,35-70 pm. Light petroleum was of boiling range 40-60 "C. Synthesis of the Pyrrolo3,2-bcarbazoles3a, h,Pyrrolo-2,3-bcarbazoles 4a-i, and the 1O-Pyrrolylmethylpyrrolo3,2-blcarbazoles 6a-i: General Procedure.-A solution of each indole 2a, e-k (2.0 mmol) and the 5-acetoxymethyl-4-acetyl-pyrrole la (2.0 mmol) in 1,2-dichloroethane (20 cm3) was heated under reflux and stirred with Montmorillonite clay (2 g) for 4-7 h. The reaction was followed to completion by TLC.After the clay had been filtered off and washed well with 1,2- dichloroethane, evaporation of the combined filtrates under reduced pressure gave a yellow solid or an oil. Flash chromatography of this on silica, eluting with ethyl acetate in dichloromethane, gave the corresponding pyrrolo3,2-b- and pyrrolo2,3-b-carbazoles and 10-pyrrolylmethylpyrrolo-3,2-bcarbazole. Ethyl 3,4-Dimethylpyrrolo3,2-bcarbazole-2-carboxylate3a a/zd Ethyl 3,4-Dimethylpyrrolo2,3-bcarbazole-2-carboxylate 4a.-These compounds were obtained from indole and the 5-acetoxymethyl-4-acetylpyrrolela. Chromatographic separ- ation yielded the 3,2-b isomer 3a as a yellow solid (0.400 g, 65.4), m.p. 209.5-21 1 "c (lit.,' 209.5-21 1 "c); amp;('H6- DMSO) 11.22(1 H,s, 1-NH), 10.7(1 H,s,5-NH),8.06(1 H,d, J 7,9-H),7.85(1 H,s, 10-H),7.40(1 H,d, J7,6-H), 7.35(1 H, t, J7, 7-H), 7.08 (1 H, t, J7,8-H), 4.35 (2 H, q,OCH,CH,), 2.91 (3 H, s, CH,), 2.90 (3 H, s, CH,) and 1.35 (3 H, t, OCH,CH,); A,,(EtOH)/nm (log amp;,Jdm3 mol-' cm-') 410sh (3.69), 392.8 (3.74), 340.7 (4.67), 325sh (4.48), 310sh (4.23) and 268.8 (4.34); the 2,3-bisomer 4a was a pale yellow solid (0.024 g, 3.9), m.p.276278deg;C (Found: C, 74.45; H, 5.7; N, 9.0. ClgH18N202 requires c,74.49; H, 5.92; N, 9.15); ~H(~H~-DMSO) 1 1.10 (1 H, S, I-NH), 10.91 (1 H,s, 9-NH), 8.17(1 H, d, J7.5,5-H), 7.37 (1 H, d, J7, 8-H), 7.32 (1 H, dt, J 1.5 and 7, 7-H), 7.18 (1 H, s, 10-H), 7.1 1 (1 H, dt, J 1.5 and 7,6-H), 4.37 (2 H, q, OCH2CH,), 3.17 (3 H, s, 4-CH3), 2.95 (3 H, s, 3-CH3) and 1.39 (3 H, t, OCH,CH,); saturation of the 10-H at 6 7.18 enhanced singlets due to 1-NH at 6 11.10 (3.5) and 9-NH at 6 10.91 (3.579, and saturation of the 4-CH, at 6 3.17 enhanced the singlet due to 3- CH, at 6 2.95 (2.7) and 5-H doublet at 6 8.17 (13.5); m/z () 306 (80, M+)260 (loo), 232 (48) and 102 (10); A,,(EtOH)/nm (log e,/dm3 mol-' cm-') 380sh (49, 349 (4.21), 305.3 (4.95) and 260.2 (5.09); and the 1O-pyrrolylmethylpyrrolo3,2-bcar-bazole 6a as a yellow solid (0.034 g, 6.6), m.p.243-245 "C (decomp.) (Found: C, 69.9; H, 6.1; N, 8.1. C30H31N305 requires C, 70.16; H, 6.08; N, 8.18); ~H(~H~-DMSO) 10.85 (1 H, S, 5-NH), 10.15 (1 H, s, pyr-NH), 10.1 1 (1 H, s, 1-NH), 7.88 (1 H, d, J7.5,9-H), 7.46(1 H,d, J7.5,6-H), 7.36(1 H, t, J7.5,7-H), 7.03 (1 H, t, J 7.5, 8-H), 5.15 (2 H, S, 10-CH,), 4.27 (2 H, 9, 2- OCHZCH,), 4.1 1 (2 H, 9, 5'-OCH,CH,), 2.95 (3 H, S, 4-CH3), 2.90(3H,~,3-CH3),2.55(3H,~,4'-CH3),2.51(3H,s,COCH3), 1.34 (3 H, t, 2-OCH2CH,) and 1.13 (3 H, t, S-OCH,CH,); saturation of the 10-CH, at 6 5.15 enhanced the doublet due to 9-H at 6 7.88 (5) and the singlets due to pyr-NH at 6 10.15 (2.8) and 1-NH at 6 10.1 1 (2.8); m/z () 513 (88, M'), 487 (65), 439 (29), 322 (29) and 260 (28); A,,,(EtOH)/nm (log amp;,,,/dm3 mol-' cm-') 414sh (3.90), 398 (3.91), 339.6 (4.72) 323.5sh (4.51), 308.9sh (4.36) and 270.9 (4.62). Ethyl 9-hydroxy-3,4-dimethylpyrrolo3,2-bcarbazole-2-car-boxylate 3e and ethyl 5-hydroxy-3,4-dimethylpyrrolo2,3-b-carbazole-2-carboxylate4b.These compounds- were obtained from 4-hydroxyindole and the 5-acetoxymethyl-4-acetylpyrrole la.The 2,3-b isomer 4b,after recrystallisation from ethyl acetate, gave pale green crystals (0.028 g, 4.3), m.p. 251-254 "C (~~CO~P.);GH(~H~-DMSO)10.95(I H, S, 1-NH), 10.85 (1 H, S, 9-NH),9.89(1 H,s,OH),7.08(1 H, t, J7.5,7-H),7.07(1 H,s, 10- H),6.77(1 H,d, J7.5,8-H), 6.52(1 H,d, J7.5,6-H),4.32(2H,q, OCH2CH3), 3.44 (3 H, s, 4-CH,), 2.92 (3 H, s, 3-CH3) and 1.37 (3 H, t, OCH,CH,); m/z () 322 (65, M'), 276 (loo), 248 (88), 219 (15), 205 (lo), 191 (10) and 178 (5) (Found: M+,322.1317. Cl9HI8N2O3 requires M, 322.1317). Further elution gave the 3,2-b isomer 3e after recrystallisation from ethyl acetate-light petroleum as green crystals (0.0686 g, 10.6), m.p. 260-262 "C (~~CO~~.);~H(~H~-DMSO)11.13(1 H, S, 1-NH), 10.56(1 H, S, 5-NH), lO.OO(1 H,s,OH),8.02(1 H,s, 10-H),7.12(1 H, t, J7.5, J.CHEM. soc. PERKIN TRANS. 1 1994 Ethyl 9-methoxy-3,4,5-trimethylp~rrolo3,2-bcarbazole-2-carboxylate 3f. This compound, obtained from 4-methoxy-l- methylindole and the 5-acetoxymethyl-4-acetylpyrrolela,was a yellow solid (0.322 g, 46), m.p. 263-266 "C (Found: C, 71.8; H, 6.3; N, 7.9. C21H22N203 requires C, 71.98; H, 6.33; N, 8.00); dH(CDC1,)8.60(1 H, br,s,NH), 8.15 (1 H, s, 10-H), 7.40(1 H, t, J8,7-H),6.95(lH,d,J8,6-H),6.66(1H,d,J8,8-H),4.43(2H, q, OCH2CH3), 4.10 (3 H, s, OCH,), 4.04 (3 H, s, NCH,), 3.19 (3 H, s, 4-CH3), 2.98 (3 H, s, 3-CH3) and 1.46 (3 H, t, OCH2CH,); saturation of the N-CH, protons at 6 4.04 enhanced the signals due to 6-H at 6 6.95 (9.7) and 4-CH3 at 6 3.19 (3.2), and saturation of the 8-H proton at 6 6.66 enhanced the signals due to OCH, at 6 4.10 (2.4) and 7-H at 6 7.40 (7.3); m/z () 350 (74, M+),304 (loo), 276 (17), 233 (10) and 152 (10).The 10- pyrrolylmethylpyrrolo3,2-bcarbazole6b was a yellow solid (0.026 g, 4.59), m.p. 268-270 "C (Found: C, 69.1; H, 6.4; N, 7.8. Camp;,,N,O6 requires C, 68.92; H, 6.33; N, 7.54); dH(CDC13) 10.97 (1 H, br, s, pyr-NH), 9.65 (1 H, br, s, 1-NH), 7.45 (1 H, t, J8,7-H), 7.04(1 H, d, J8,6-H), 6.73 (1 H, d, J8,8- H), 5.27 (2 H, S, lO-CH,), 4.42 (2 H, q,2-0CH,CH,), 4.14 (2 H, 9, 5'-OCH2CH3), 4.03 (3 H, s,N-CH,), 4.00(3 H, s, OCH,), 3.14 (3H,~,4-CH3),2.93(3H,~,3-CH3),2.66(3H,~,4'-CH3),2.60(3 H, s, COCH,), 1.48 (3 H, t, 2-OCH2CH,) and 1.15 (3 H, t, 5'-OCH2CH3);m/z () 557 (100, M+),51 1 (22), 450 (16), 304 (13), 256 (14) and 233 (21). Ethyl 8-hydroxy-3,4-dimethylpyrrolo3,2-bcarbazole-2-car-boxylate 3g and ethyl 6-hydroxy-3,4-dimethylpyrrolo2,3-b-carbazole-2-carboxylate4c.These compounds were obtained from 5-h ydr ox yindole and the 5-ace t oxyme th y l-4-acetylpyrrole la. The chromatographic separation yielded starting 5-hydroxyindole (0.100 g, 37.6) and the pyrrole la (0.117 g, 21.91); the third fraction was a solid mixture of the 2,3-b- and 3,2-b-isomer and the starting pyrrole la (0.23 lg). Fraction 4 gave the 3-pyrrolylmethylindole 8a (0.078 g, 1 1 S), m.p.99-102 "C (Found: C, 66.9; H, 6.2; N, 8.0. Cl,H,oN,O, requires C, 67.04; H, 5.92; N, 8.23); GH(CDC1,) 8.84 (1 H, s, pyr-NH),8.14(1H,s,ind-NH),7.20(1H,d,J8,7-H),7.10(1H, d,J2.5,2-H),6.81(1H,d,J1.5,4-H),6.79(1H,dd,J8and1.5, 6-H), 5.60 (1 H, br, s, OH), 4.31 (2 H, s, 3-CH2), 4.21 (2 H, q, OCH,CH,), 2.58 (3 H, s, 4'-CH,), 2.48 (3 H, s, COCH,) and 1.27 (3 H, t, OCH,CH,); m/z () 340 (100, M'), 325 (44),2937-H),6.83(1H,d,J7.5,6-H),6.48(1H,d,J7.5,8-H),4.39(2H,(21), 279 (35), 266 (39,251 (31), 223 (25) and 196 (5). Fraction 5q,0CH2CH3), 2.87 (3 H, s,4-CH3), 2.85 (3 H, s, 3-CH3)and 1.38 (3 H, t, OCH,CH3); m/z () 322 (61, M'), 276 (loo), 248 (20), 219 (5) and 138 (11) (Found: M+ 322.1305. C1,H,,N,O, requires M, 322.1317).Next to be eluted was 4-hydroxy-5- pyrrolylmethylindole (0.033 g, 4.85) as an impure, light yellow solid, GH(CDC13) 9.00 (1 H, br, s, pyr-NH), 8.92 (1 H, s, OH), 8.11 (1 H, br,s, 1-NH),7.08(1 H,t, J2.5,2-H),7.03(1 H,d, J7.5, gave the 1O-pyrrolylmethylpyrrolo3,2-bcarbazole6c as a yellow solid (0.01 5 g, 1.4), 6H(2H,-DMSO) 10.48 (1 H, s, 5-NH), 10.13 (1 H, s, pyr-NH), 9.85 (1 H, s, 1-NH), 8.84 (1 H, s, OH), 7.28 (1 H, d, J8,6-H), 7.25 (1 H, S, 9-H), 6.93 (1 H, d, J8, 7-H), 5.1 1 (2 H, S, 10-CH,), 4.33 (2 H, q,2-OCH,CH3), 4.10 (2 H, 9, 5'-OCH,CH,), 2.93 (3 H, S, 4-CH3), 2.90 (3 H, S, 3-CH3), 7-H),6.91(1H,d,J7.5,6-H),6.63(1H,dt,J2.5and2,3-H),4.292.56 (3 H, S, 4'-CH3), 2.53 (3 H, S, COCH,), 1.35 (3 H, t, 2- OCH,CH,) and 1.13 (3 H, t, 5'-OCH,CH3); m/z () 529 (18, (2 H, q,OCH,CH,), 4.22 (2 H, S, 5-CH,), 2.58 (3 H, S, 4'-CH3), 2.55 (3 H, s, COCH,) and 1.33 (3 H, t, OCH,CH,); m/z () 340 (41, M'), 298 (20), 251 (13), 225 (28), 145 (100) and 133 (7) (Found: M+,340.1423.C19HZON204 requires M, 340.1423); similarly obtained was 4-hydroxy-7-pyrrolylmethyl-indole (0.032 g, 4.70); SH(CDC1,) 10.40 (1 H, s, pyr-NH), 8.91 (1 H, br,d,ind-NH),7.13(1 H,t, J2.5,2-H),6.94(1 H,d, J7,6- H),6.55(1H,t,J2.5,3-H),6.46(1H,d,J7,5-H),5.55(1H,br,s, OH),4.29(2H,~,7-CH,),4.26(2H,q,OCH,CHJ,2.61(~H,s, 4'-CH,) 2.55 (3 H, s, COCH,) and 1.30 (3 H, t, OCH2CH,); m/z () 340 (30, M'), 294 (lo), 267 (loo), 224 (70) and 125 (25); and the 4-hydroxy-3-pyrrolylmethylindole(0.03 18 g, 4.68); d~(cDC1,) 10.17 (1 H, S, pyr-NH), 8.08 (1 H, S, NH), 7.15 (1 H, d,J2,2-H),6.98(1H,t,J7,6-H),6.95(1H,dd,J7and1.5,7-H), 6.52 (1 H, br, s, OH), 6.45 (1 H, dd, J7 and 1.5,5-H), 4.52 (2 H, s, 3-CH,), 4.26 (2 H, 9, OCHZCH,), 2.55 (3 H, S, 4'-CH3), 2.50 (3 H, s, COCH,) and 1.32 (3 H, t, OCH,CH,); m/z ('A)340 (100, M+), 298 (20), 294 (30), 276 (36), 266 (20), 252 (88), 225 (80) and 145 (53).M'), 483 (25), 422 (17), 322 (28), 290 (25), 276 (loo), 248 (53) and 234 (20) (Found: M ,529.2220. C30H3 'N306 requires M,+ 529.221 1). Recrystallisation of the third fraction from ethyl acetate-light petroleum gave a mixture (9 : 1) of the 2,3-b isomer 4cand the 3,2-b-isomer 3g, respectively (1.1 1 and 0.12). The 2,3-b isomer 4c~howed6,(~H,-DMSO) 11.00 (1 H, s, 1-NH), 10.52 (1 H,s,9-NH),8.80(1 H,s,OH),7.59(1 H,s, 5-H),7.16(1 H,d, J 7.8,8-H), 7.1 1 (1 H, S, 10-H), 6.80(1 H, S, J7.8,7-H),4.35 (2H, 9, OCH,CH,), 3.13 (3 H, s, 4-CH,), 2.92 (3 H, s, 3-CH,) and 1.38 (3 H, t, OCH,CH,).Removal of the solvent and crystallisation of the residue from the remaining filtrate from methanol gave a 1 : 1 ratio mixture of the 3,2-b isomer 3g and the pyrrole la (0.067 g) which was further treated with 5-hydroxyindole (0.016 g, 0.12 mmol) and montmorillonite clay (40 mg) in 1,2-dichloroethane (5 an3)for 7 h. After the clay had been filtered off and washed well with 1 ,Zdichloroethane, evaporation of the combined filtrates gave a yellow solid. Crystallisation from 1769J.CHEM. soc. PERKIN TRANS. 1 1994 requiresmethanol yielded the 3,2-b isomer 3g as yellow crystals (decornp.) (Found C, 68.9; H, 6.1; N, 7.5. C20H22N204 (0.037 g, 5.69), m.p. 250 "c (decornp.); ~H(~H~-DMSO) C, 68.83; H, 6.05; N, 7.65);6~(~H,-DMSo) 11.15 (1 H, S, 1-NH), 10.36(1 H, S, 5-NH),7.73(1 H,s, lO-H),7.62(1 H,s,9-H), 11.11(1 H,s, 1-NH), 10.21(1H,~,5-NH),8.83(1H,~,OH),7.736.95 (1 H, S, 6-H), 4.37 (2 H, 9, OCH,CH,), 3.87 (6 H, S,(1 H,s, 10-H), 7.37(1 H,d, J2.5,9-H),7.21(1 H,d, J8,6-H),6.87 (1 H, dd, J 8and 2.5,7-H), 4.36 (2 H, q, OCH,CH,), 2.87 (3 H, s, 4-CH,), 2.84 (3 H, s, 3-CH3) and 1.38 (3 H, t, OCH,CH,); m/z () 322 (69, M+), 276 (loo), 248 (24), 220 (3) and 138 (5) (Found: M+, 322.1322. C19H18N,03 requires M, 322.1317). Ethyl 3,4,8-trimethylpyrrolo3,2-bcarbazole-2-carboxylate 3b and e th y 1 3,4,6-trimethy lpyrrolo 2,3 -b carbazo le-Zcarboxy -late 4d.These compounds were obtained from 5-methylindole and the 5-ace t oxymet hyl-4-ace ty lpy rrole 1a. Chromatographic separation yielded the 3,2-b isomer 3b as a yellow solid (0.201 g, 31.5), m.p. 215-216.5"C (Found: C, 74.8; H, 6.3; N, 9.0. C2oH2oNzOz requires c, 74.97; H, 6.29; N, 8.74); amp;(C2H6- DMSO) 11.19 (1 H, S, 1-NH), 10.47 (1 H, S, 5-NH), 7.86 (1 H, S, 9-H), 7.82 (1 H, S, 10-H), 7.29 (1 H, d, J8,6-H), 7.18 (1 H, dd, J 8 and 2, 5-H), 4.37 (2 H, q, OCH,CH,), 2.91 (3 H, s, 4CH3), 2.89 (3 H, s, 3-CH3), 2.46 (3 H, s, 8-CH3) and 1.39 (3 H, t, OCH2CH,); m/z () 320 (64, M'), 274 (loo), 246 (24), 137 (14) and 123 (10) (Found: M+, 320.1514.C20H20N202 requires M, 320.1524); the 2,3-b isomer 4d as a pale yellow solid (0.041 g, 6.42), m.p. 288-290 "C (Found: C, 75.2; 6.5; N, 8.6. C20HzoN202 requires c, 74.97; H, 6.29; N, 8.74); amp;('H6- DMSO) 11.05 (1 H, S, 1-NH), 10.76 (1 H, S, 9-NH), 7.98 (1 H, S, 5-H), 7.25 (1 H, d, J8,8-H), 7.15 (1 H, d, J8,7-H), 7.13 (1 H, S, lO-H), 4.36 (2 H, q,OCH2CH,), 3.17 (3 H, S, 4-CH3), 2.93 (3 H, s, 3-CH3), 2.49 (3 H, s, 6-CH3) and 1.39 (3 H, t, OCH,CH3); m/z () 320 (80, M+), 274 (loo), 246 (42), 149 (13) and 127 (15) +(Found: M , 320.1528. C20H20N202 requires M, 320.1524). The 1O-pyrrolylmethyIpyrrolo3,2-bcarbazole6b was a yellow solid (0.068 g, 12.9), m.p. 245-248 oC;amp;(2H6-DMSO) 10.68 (1 H, s, 5-NH), 10.41 (1 H, s, pyr-NH), 9.99 (1 H, s, 1-NH), 7.72 (1 H, S, 9-H), 7.35 (1 H, d, J7.5,6-H), 7.19 (1 H, d, J7.5,7-H), 5.16 (2 H, S, 10-CH,), 4.31 (2 H, q, 2-OCHzCH3), 4.12 (2 H, 9, 5'-OCH2CH,), 2.93 (3 H, S, 4-CH3), 2.89 (3 H, S, 3-CH3), 2.57 (3 H, S, 4'-CH3), 2.48 (3 H, S, COCH,), 2.38 (3 H, S, 8-CH3), 1.32 (3 H, t, 2-OCH,CH3) and 1.18 (3 H, t, S-OCH,CH,); m/z () 527 (100, M'), 481 (97), 435 (23), 420 (43), 218 (34), 202 (36) and 130 (18) (Found: M+, 527.2420.C31H33N305 requires M, 527.2420). 2 x OCH,), 2.90 (3 H, s, 4-CH3), 2.87 (3 H, s, 3-CH,) and 1.39 (3 H, t, OCH,CH,); m/z () 366 (loo), 320 (99), 305 (1 l), 277 (19), 249 (8), 183 (1 1) and 160 (29); and the starting pyrrole la (0.1687 g, 31.59). Ethyl 7,8-methylenedioxy-3,4-dimethylpyrrolo3,2- b carba- zole-Zcarboxylate 3i and ethyl 6,7-methylenedioxy-3,4-di-methylpyrrolo2,3-bcarbazole-2-carboxylate 4f.These com- pounds were obtained from 5,6-methylenedioxyindoleand the 5-acetoxymethyl4acetylpyrrolela. Chromatographic separ- ation yielded the 3,2-b isomer 3j as a yellow solid (0.052 g, 7.4373, m.p. 263-265deg;C (Found: C, 68.45; H, 4.95; N, 7.8. CzoH18N204 requires C, 68.56; H, 5.18; N, 8.00); SH(~amp;-DMSO) 11.13(1 H,s, 1-NH), 10.49(1 H,s,~-NH), 7.72(1 H,s, 10-H), 7.62 (1 H, S, 9-H), 6.95 (1 H, S, 6-H), 6.04 (2 H, S, OCHZO), 4.37 (2 H, q,OCH,CH3), 2.89 (3 H, S, 4-CH3), 2.87 (3 H, s, 3-CH,) and 1.39 (3 H, t, OCH,CH,); m/z () 350 (84, M'), 304 (loo), 276 (44),152 (22) and 138 (14). The 2,3-b isomer 4f was a pale yellow solid (0.0647 g, 7.43), m.p.270-270.5 "C (Found: C, 68.4; H, 5.1; N, 8.3. C20H18N204 requires C, 68.56; H, 5.18; N, 8.00); ~H(~H~-DMSO)11.00 (1 H, S, 1-NH), 10.78(1H,~,9-NH),7.66(1H,~,5-H),7.13(1H,~,8-H),6.98(1 H,s, 10-H),6.04(2H,~,OCH~O),4.36(2H,q,OCH~CH~),3.10 (3 H, s, 4-CH,) 2.91 (3 H, s, 3-CH,) and 1.38 (3 H, t, OCH2CH3); m/z () 350 (93, M'), 304 (loo), 276 (35) and 152 (30). The 1O-pyrrolylmethylpyrrolo3,2-bcarbazole 6e was a yellow solid (0.050 g, 8.92), m.p. 239-242 "C (decomp.); ~H(~H~-DMSO)10.73(1 H, s, 5-NH), 10.08 (2 H, s, 1-NH and pyr-NH), 7.33 (1 H, s, 9-H), 6.99 (1 H, s, 6-H), 6.02 (2 H, s, OCHZO), 5.08(2H,s, lO-CH2),4.32(2H,q,2-OCH2CH3),4.12 (2H, q, 5'-OCHzCH,), 2.92(3 H, S, 4-CH3), 2.90(3 H, S, 3-CH,), 2.58 (3 H, s, 4'-CH3), 2.54 (3 H, concealed by DMSO, COCH,), 1.35 (3 H, t, 2-OCH2CH,) and 1.17 (3 H, t, 5'-OCH,CH3); m/z PA) 557 (95, M'), 51 1 (loo), 465 (22), 450 (60), 350 (23), 304 (33) and 276 (28) (Found: M', 557.2160. C31H31N307 requires M, 557.2161).Ethyl 9-JE~ro-3,4-dimethylpyrrolo3,2-b~carbazole-2-carb-oxylate 3k and 3-(3'-acetyl-5'-ethoxycarbonyl-4'-methylpyrrol-Ethyl 7,8-dimethoxy-3,4-dimethy~yrrolo3,2-bcarbazole-2-2'-ylmethyl)-4-JEuoroindole8b. These compounds were obtained carboxylate3i and ethyl 6,7-dimethoxy-3,4-dimethylpyrrolo2,3-bcarbazole-2-carboxylate 4e. These compounds were obtained from 5,6-dimethoxyindole and the 5-acetoxymethyl-4-acetyl-pyrrole la. Crystallisation of the crude oil from dichloro- methane gave the 2,3-b isomer 4e as pale yellow crystals (0.035 g, 4.78), m.p.265-268 "C (Found: C, 68.2; H, 5.91; N, 7.38. C21H22N204requires c, 68.83; H, 6.05; N, 7.65); amp;(c2H6- DMSO) 11.00 (1 H, S, 1-NH), 10.65 (1 H, S, 9-NH), 7.68 (1 H, S, 5-H), 7.14 (1 H, S, 8-H), 6.97 (1 H, S, 10-H), 4.37 (2 H, q, from 4-fluoroindole and the 5-acetoxymethylpyrrole la. The pyrrolo3,2-bcarbazole 3k was a yellow solid (0.156 g, 24.0), m.p. 233-235.5 "C (Found: C, 70.5; H, 5.4; N, 8.5. ClgH17FN202 requires C, 70.36; H, 5.28; N, 8.64); d~(~H6- DMSO) 11.28(1 H, S, 1-NH), ll.OO(1 H,s, 5-NH), 7.91 (1 H,s, 10-H),7.36(1 H,dt, J5and7,7-H),7.24(1 H,d, J7,6-H),6.86 (1 H, dd, J 10 and 7,8-H), 4.39 (2 H, q, OCH,CH,), 2.93 (3 H, s, 4-CH,), 2.91 (3 H, s, 3-CH,) and 1.40 (3 H, t, OCH,CH3); m/z () 324 (58, M'), 278 (loo), 250 (22), 222 (9) and 139 (9).The 3- pyrrolylmethylindole 8b was an off-white solid (0.214 g, 31.3),OCH2CH3),3.87(3H,s,OCH3),3.85(3H,s,OCH,),3.15(3H, s, 4-CH,), 2.93 (3 H, s, 3-CH3) and 1.38 (3 H, t, OCH,CH,); m/z () 366 (97, M'), 320 (loo), 305 (21), 277 (21), 249 (14), 183 (14) and 160 (29). Crystallisation of the remaining filtrate from dichloromethane-light petroleum gave the 10-pyrrolylmethyl- pyrrolo3,2-bcarbazole 6d as yellow crystals (0.019 g, 3.31), m.p. 270-273 "C (decomp.); ~H(~H~-DMSO) 10.59 (1 H, S, m.p. 179-182 "C (Found: C, 66.7; H, 5.79; N, 7.96. C19H19FN203 requires C, 66.65; H, 5.59; N, 8.18););~(~H6-DMSO) 11.90(1 H,s,pyr-NH), ll.lO(l H,s,ind-NH),7.19(1 H,d,J7,7-H),7.04(1H,dt,J5and7,6-H),6.75(1H,dd,Jll and 7,5-H), 6.59 (1 H, br s, 2 H), 4.47 (2 H, s, CH,), 4.27 (2 H, q, OCH2CH3), 2.55 (3 H, s, 4'-CH,), 2.32 (3 H, s, COCH,) and 5-NH),10.30(1H,s,pyr-NH),10.12(1H,s,1-NH),7.23(1H,s,1.32 (3 H, t, OCH2CH3); m/z () 342 (100, M'), 327 (34), 295 9-H), 6.98 (1 H, S, 6-H), 5.16 (2 H, S, lO-CH,), 4.34 (2 H, 9, 2- (15), 281 (36), 268 (27), 253 (23) and 225 (17).OCH2CH3),4.08 (2 H,q, 5'-OCH2CH,), 3.85 (3 H, s,OCH,), Ethyl 7-JEuoro- 3,4-dimethylpyrrolo 3,2- b carbazole-2-curb- H,s,3.62(3H,s,OCH,),2.91(6H,s,4-CH3and3-CH,),2S4(3 oxylate 31 and ethyl 7-JEuoro-3,4-dimethylpyrrolo2,3-bcar-4'-CH3),2.48 (3 H,s,COCH,), 1.34(3 H,t,2-OCH2CH3)and 1.15(3 H, t, 5'-OCH2CH,); m/z () 573 (80, M+), 527 (loo), 466 (60), 366 (28), 320 (20), 240 (23) and 148 (16) (Found: M+ 573.2475.C3,H,,N,0, requires M +,573.2475). Chromato- graphic separation of the remaining filtrate yielded the 3,2-b isomer 3i as a yellow solid (0.0595 g, 8.l), m.p. 237-240 "C bazole-2-carboxylate 4g. These compounds were obtained from 6-fluoroindole and the 5-acetoxymethyl-4acetylpyrrolela. The 3,2-b isomer 31 was a yellow solid (0.305 g, 47.1), m.p. 231- 234 "C (Found: C, 70.45; H, 5.5; N, 8.7. CI9Hl7FN,O2 requires C, 70.37; H, 5.25; N, ~.H);~G,(~H~-DMSO) 11.27 (1 H, S, 1-NH), 10.82 (1 H, s, 5-NH), 8.90 (1 H, dd, J9 and 6,9-H), 7.85 (1 H,s, lO-H),7.12(1 H,dd, JlOand2,6-H),6.89(1 H,dt, J2and 9, 8-H), 4.37 (2 H, q, OCH,CH,), 2.89 (6 H, s, 4-CH3 and 3- CH,) and 1.39 (3 H, t, OCH,CH,); m/z PA) 324 (60, M'), 278 (loo), 250 (34), 222 (10) and 139 (7) (Found: M+, 324.1267.ClgHl7FN2O2 requires M, 324.1274). The 2,3-b isomer 4g was a pale yellow solid (0.020 g, 3.08), m.p. 262-265deg;C (decomp.); amp;('H6-DMSO) 11.14 (1 H, S, 1-NH), 11.06 (1 H, s, 9-NH), 8.12 (1 H, dd, J9 and 6, 5-H), 7.19 (1 H, s, 10-H), 7.15 (1 H, dd, J 10 and 2, amp;H), 6.92 (1 H, dt, J2 and 9,6-H), 4.36 (2 H, q,OCU,CH,), 3.13 (3 H, S,4-CH3), 2.93 (3 H, S, 3-CH,) and 1.39(3 H, t, OCH,CH,); saturation of the 10-H proton at 6 7.19 enhanced the signals due to 1 -NH at 6 1 1.14 (2.2) and 9-NH at 6 11.06 (2.2); m/z () 324 (72, M'), 278 (loo), 250 (39), 222 (9) and 139 (6) (Found: M+, 324.1280.C19H17FN202 requires M, 324.1274). The 1O-pyrrolylmethylpyrrolo3,2-bcarbazole6f Was a yellow solid, m.p. 283-285 "c(0.0156 g, 2.9); 6~('amp;- DMSO) 11.04 (1 H, s, 5-NH), 10.31 (1 H, s, pyr-NH), 10.12 (1 H, s, 1-NH), 7.86 (1 H, dd, J9 and 6,9-H), 7.17 (1 H, dd, J 10 and 2,6-H), 6.85 (1 H, dt, J2 and 9,8-H), 5.13 (2 H, s, 10-CH,), 4.19 (2 H, q, 2-0CH,CH,), 4.11 (2 H, q,5'-OCH,CH,), 2.93 (3 H, S, 4-CH3), 2.90 (3 H, S, 3-CH3), 2.56 (3 H, S, 4'-CH3), 2.5 1 (3 H, concealed by DMSO, COCH,), 1.34 (3 H, t, 2-OCH2CH,) and 1.16 (3 H, t, S-OCH,CH,); m/z () 532 (7, M'H), 486 (12), 325 (90), 210 (100) and 196 (40) (Found: MH+ 532.225. C3,H3,FN30, requires MH, 532.2249). J. CHEM. soc. PERKIN TRANS. 1 1994 2.95 (3 H, s, 3-CH,) and 1.40 (3 H, t, OCH,CH,); m/z () 386 (98, M+Cs1Br), 384 (98, M+C7'Br), 340 (91), 338 (loo), 312 (37), 310 (44), 312 (20), 229 (35) and 204 (16).The 3- pyrrolylmethyIindoIe8f was an off-white solid (0.406 g, 50.3), m.p. 222-225 "C (Found: C, 56.3; H,4.7; N, 6.8. ClgHl9BrN2O3 requires c, 56.58; H, 4.75; N, 6.95); amp;('H6-DMSo) 12.05 (1 H, s,pyr-NH), ll.OS(1 H,s,ind-NH),7.82(1 H,s,4-H),7.30 (1 H, d, J7.5,6-H), 7.16 (1 H, d, J7.5,7-H), 7.02 (1 H, d, J 1.5, 2-H), 4.29 (2 H, S, 3-CH2), 4.27 (2 H, q, OCH,CHj), 2.52 (3 H, concealedbyDMSO,4'-CH,),2.33(3H,s,COCH3)and1.33(3 H, t, OCH,CH,); m/z () 404(100, M+CS1Br), 402 (98, M+- C7'Br), 389 (38), 387 (43), 358 (15), 356 (14), 330 (31), 328 (30), 315 (20), 313 (22), 287 (12), 285 (lo), 234 (17), 206 (47), 194 (33) and 178 (31).Synthesis of 3-(3'-Acetyl-5'-ethoxycarbonyl-4'-methylpyrrol-2'-ylmethyl)-5-methylindoleamp;.-A solution af 5-methylindole (0.196 g, 1.5 mmol) and the 5-acetoxymethyl-4-acetylpyrrole la (0.400 g, 1.5 mmol) in dichloromethane (15 cm3) was gently heated at reflux and stirred with Montmorillonite clay (1.5 g) for 7 h. After the clay had been filtered off and washed well with dichloromethane, evaporation of the combined filtrates gave an oil. This was submitted to column chromatography on silica eluting with (0-20) ethyl acetate in dichloromethane to give (a) 5-methylindole (0.075 g, 38.1), (b) the pyrrolo3,2- Ethyl 8-chloro-3,4-dimethylpyrrolo3,2-bcarbazole-2-carb-blcarbazole 3h (0.037 oxylate 3m and 3-(3'-acetyl-5-ethoxycarbonyl-4'-methylpyrrol-2'-ylmethyl)-5-~hloroindole8e.These compounds were obtained from 5-chloroindole and the 5-acetoxymethyl-4-acetylpyrrole la.The pyrrolo3,2-bcarbazole 3m was a yellow solid (0.112 g, 16.4, m.p. 218-220deg;C (Found: C, 66.8; H, 4.85; N, 8.3. C1gH17ClN202 requires C, 66.96; H, 5.03; N, 8.22);6~(~amp;- DMSO) 11.33(1 H,s, 1-NH), 10.84(1 H,s,5-NH),8.19(1 H,s, 9-H), 7.93 (1 H, S, 10-H), 7.41 (1 H, d, J7,6-H), 7.36(1 H,dd, J7 and 2,7-H), 4.38 (2 H, q, OCH,CH,), 2.90 (6 H, s, 4-CH3 and 3- CH,) and 1.39 (3 H, t, OCH,CH,); m/z () 342 (20, M+37Cl), 340 (60, M'3'Cl), 296 (34), 294 (loo), 266 (19), 265 (1 l), 231 (lo), 230 (14) and 229 (10). The 3-pyrrolylmethylindole8ewas an off-white solid (0.251 g, 35.1), m.p.218-220 "C (Found: C, 63.8;H,5.2;N, 7.7. ClgHlgClN,0,requiresC,63.60;H, 5.34;N, 7.81);6,(C2H6-DMS0) 12.07 (1 H, s, pyr-NH), 11.03 (1 H, s, ind-NH),7.68(1H,d,J2,4-H),7.35(1H,d,J8,7-H),7.06(1H, dd, J 8 and 2,6-H), 7.05 (1 H, br, s, 2-H), 4.30 (2 H, s, 3-CH2), 4.28 (2 H, q, OCH,CH3), 2.53 (3 H, concealed by DMSO, 4'- CH,), 2.34 (3 H, s, COCH,) and 1.33 (3 H, t, OCH,CH,); m/z ()360(34,M+37Cl), 358(100,M+35Cl), 345(15), 343(51), 3 13 (1 3), 3 1 1 (1 8), 297 (36), 286 (1 2), 284 (36), 271 (8), 269 (24), 243 (8), 241 (1 7), 207 (1 3), 205 (9) and 15 1 (27). Ethyl 8-bromo-3,4-dimethylpyrrolo3,2-bcarbazole-2-carb-oxylate 3n, ethyl 6-bromo-3,4-dimethylpyrrolo2,3-bcarbazole-2-carboxylate 4i and 3-(3'-acetyl-5-ethoxycarbonyl-4'-methyl-pyrrol-2'-ylmethyl)-5-bromoindole8f. These compounds were obtained from 5-bromoindole and the 5-acetoxymethyl-4- acetylpyrrole la.The 3,2-b isomer 3n was a yellow solid (0.088 g, 11.479, m.p. 228-23 1 "C (decomp.) (Found: C, 59.2; H, 4.35; N, 7.5. C19H17BrN,02 requires C, 59.23; H, 4.45; N, 7.27); ~H(~H~-DMSO)11.34 (1 H, S, 1-NH), 10.85 (1 H, S, 5-NH), 8.33(1 H,d, J2,9-H),7.93(1 H,s, 10-H),7.48(1 H,dd, J8and2, 7-H), 7.36 (1 H, d, J8,6-H), 4.37 (2 H, q,OCH*CH,) 2.91 (6 H, s, 4-CH3 and 3-CH2) and 1.39 (3 H, t, OCH,CH,); m/z () 386 (69, M+CS1Br), 384 (70, M+C7'Br), 340 (94), 338 (loo), 312 (14), 310 (13), 231 (15), 229 (21) and 204 (11). The 2,3-b isomer 4i was a pale yellow solid (0.0182 g, 2.36), m.p. 280-281 "C (decomp.) (Found: C, 59.4; H, 4.7; N, 7.3.C19H17BrN,02 requires C, 59.23; H, 4.45; N, 7.27);6~(~H,-DMSO) 11.16(1 H,s, 1-NH), 11.11 (1 H,s,9-NH),8.25(1 H,s, 5-H),7.48(1H,dd,J8and1.5,7-H),7.34(1H,d,J8,8-H),7.22 (1 H, S, 10-H), 4.37 (2 H, 9, OCH,CH,), 3.15 (3 H, S, 4-CH3), g, 7.65) and (c) the pyrrolo2,3- blcarbazole 4d (0.009 g, 1.89) which were identical in all respects with the pyrrolo3,2-bcarbazole 3h and the pyr- rolo2,3-bcarbazole 4d from previous experiment respectively. Further elution gave the 3-pyrrolylmethylindole amp; (0.061 g, 12.1), m.p. 192-195 "C (Found: C, 70.8; H, 6.6; N, 8.4. C20H22N203 requires c, 70.98; H, 6.55; N, 8.28); amp;(C2H6- DMSO11.95(1H,s,pyr-NH),10.67(1H,s,ind-NH),7.35(1H, br, s, 4-H), 7.21 (1 H, d, J8,7-H), 6.90 (1 H, d, J8,6-H), 6.79 (1 H, br, s, 2-H), 4.29 (2 H, s, 3-CH2), 4.27 (2 H, q, OCH,CH,), 2.52 (3 H, concealed by DMSO, 5-CH3), 2.39 (3 H, s, 4'-CH3), 2.32 (3 H, s, COCH,) and 1.32 (3 H, t, OCH,CH,); m/z () 338 (100, M'), 323 (56), 277 (44),264 (33), 249 (26), 221 (25), 194 (13), 145 (24) and 131 (38); and the starting pyrrole la (0.152 g, 38).Cyclisation of the 3-Pyrrolylmethylindole 8c.-A solution of the 3-pyrrolylmethylindole amp; (0.034 g, 0.1 mmol) in 1,2-dichloroethane (5 cm3) was heated at gentle reflux and stirred with Montmorillonite clay (0.1 g) for 1.5 h. TLC showed that only one product had formed and the reaction was complete. After the clay had been filtered off and washed well with 1,2- dichloroethane, evaporation of the combined filtrates gave a yellow solid (0.029 g, 92.5) which was identical in all respects with the pyrrolo3,2-bcarbazole 3h of the previous experiment.There was no detectable pyrrolo2,3-bcarbazole 4d. Reaction of Indole and the 5-Acetoxymethyl-4-acetylpyrrole la with Toluene-p-suljbnic Acid.-Toluene-p-sulfonic acid (30 mg) was added to a solution of indole (0.1 17 g, 1.O mmol) and the 5-acetoxymethyl-4-acetylpyrrole la (0.267 g, 1 .O mmol) in 1,Zdichloroethane (10 cm3) and the reaction mixture was heated under reflux for 7 h. After cooling, the mixture was evaporated under reduced pressure and the remaining crude oil was submitted to column chromatography eluting with (5.35) ethyl acetate in light petroleum. This gave the pyrrolo3,2- blcarbazole 3a as a yellow solid (0.043 g, l4.l), m.p.209.5- 21 1 "C (lit.,l 209.5-21 1 "C) and the 10-pyrrolylmethylpyr-rolo3,2-bcarbazole 6a as a yellow solid (0.074 g, 28.8), m.p. 243-245 "C (decomp.) which was identical in all respects with the 1O-pynolylmethylpyrrolo3,2-bcarbazole 6a of the previous experiment. Reaction of the Pyrrolo3,2-bcarbazole 3a and the 5-Acetoxymethyl-4-acetylpyrrole la.-A solution of the pyr- J. CHEM. soc. PERKIN TRANS. 1 1994 rolo3,2-bcarbazole 3a (0.076 g, 0.25 mmol) and the pyrrole la (0.069 g, 0.25 mmol) in 1,2-dichloroethane (5 cm3) was heated under reflux and stirred with Montmorillonite clay (250 mg) for 7 h. After the clay had been filtered offand washed well with 1,2-dichloroethane, evaporation of the combined filtrates gave a yellow solid which was chromatographed, eluting with (amp;lo) ethyl acetate in dichloromethane.This gave starting pyrrolo3,2-bcarbazole 3a (0.029 g, 37.5) and the 10-pyrrolylmethylpyrrolo3,2-bcarbazole 6a (0.038 g, 29.9) which was identical in all respects to the 10-pyrrolylmethyl- pyrrolo3,2-bcarbazole 6a of the earlier experiment. Reaction of the Pyrrolo3,2-bcarbazole 30 and the 5-Acetoxymethyl-4-acety lpyrrole 1b.-Toluene-p-sulfonic acid (10 mg) was added to a solution of the pyrrolo3,2-bcarbazole 30 (0.074 g, 0.2 mmol) and the pyrrole lb (0.066 g, 0.2 mmol) in 1,2-dichloroethane (5 cm3)and the reaction mixture was heated under reflux for 7 h. Evaporation of the mixture under reduced pressure gave a yellow solid which was chromato- graphed eluting with (0.15) ethyl acetate in dichloromethane. This gave the starting pyrrolo3,2-bcarbazole 30 (0.014 g, 19.2); the lO-pyrrolylmethylpyrrol03,2-bcarbazole 6g as a yellow solid (0.035 g, 27.8), m.p.233-236 OC (Found: C, 75.5; H, 5.43; N, 6.42. C40H35N305 requires C, 75.33; H, 5.53; N, 6.59); ~H(~H~-DMSO) 10.89 (1 H, S, 5-NH), 10.50 (1 H, S, pyr-NH), 9.98 (1 H, s, 1-NH), 7.83 (1 H, d, J 8,9-H), 7.47-7.1 1 (12 H, m, 2 x ArH, 6-H and 7-H), 6.99 (1 H, t, J7.5,8-H), 5.39 (2 H, S, 2-OCH,Ph), 5.19 (2 H, S, 10-CH2) 5.10 (2 H, S, 5'-OCH,Ph), 2.96 (3 H, s, 4-CH,), 2.91 (3 H, s, 3-CH3) and 2.52 (6 H, s, 4'-CH3 and COCH,); m/z ()637 (25, M+), 529 (18), 108 (63), 91 (100) and 77 (36); and the 6,lO-dipyrrolylmethylpyr-rolo3,2-bcarbazoZe 3r (0.012 g, 12.8), m.p.254-256 "C (Found: c, 73.9; H, 5.72; N, 6.33. C56H50N408 requires c, 74.15; H, 5.56; N, 6.18); ~H(~H~-DMSO) 12.24 (1 H, S, 6-pyr-NH), 10.49 (2 H, s, 5-NH and 10-pyr-NH), 10.00 (1 H, s, 1-NH), 7.70 (1 H, d, J7.5,9-H), 7.49 (15 H, m, 3 x ArH), 6.90 (1 H, t, J 7.5, 8-H), 6.89 (1 H, d, J 7.5, 7-H), 5.38 (2 H, S, 2-OCH2Ph), 5.32 (2 H, s, 10-pyr-OCH,Ph), 5.16 (2 H, s, 10-CH2), 5.10 (2 H, s, 6-pyr-OCH2Ph), 4.62 (2 H, s, 6-CH2), 3.03 (3 H, s, 4-CH3), 2.92 (3 H, s, 3-CH3), 2.58 (3 H, s, 6-pyr-CH3), 2.50 (6 H, s, 10-pyr-CH, and COCH,) and 2.32 (3 H, s, 6-pyr-COCH,); saturation of the 10-CH, at 6 5.16 enhanced the signals due to 9-H doublet at 6 7.70 (23.7), 1-NH at 6 10.00 (3.9) and 10-pyr-NH at 6 10.49 (1 1.8); and saturation of the 6-CH2 at 6 4.62 enhanced the signals due to 7-H doublet at 6 6.89 (8.3), 6-pyr-NH at 6 12.24 (9.9) and 5-NH at 6 10.49 (1 1.6); m/z (FAB) M, 906.Vilsmeier Formylation of the Pyrrolo3,2-bcarbazoles 3a and 3:General Procedure.-The pyrrolo3,2-bcarbazole (0.3 mmol) was added to the solution of N-methylformanilide (0.037 cm3, 0.3 mmol) and phosphorus oxychloride (0.041 cm3,0.45 mmol) in trichloroethylene (1 an3),and the mixture was gently heated under reflux for 30 min. After cooling, aqueous sodium acetate (0.13 g in water 1.5 an3)was added to the mixture which was then heated further for 10 min. The reaction mixture was extracted with chloroform (3 x 10 cm3) and the combined extracts were washed with hydrochloric acid (0.1 mol dmP3; 3 x 10 cm3) and water (3 x 10 cm3) and then evaporated under reduced pressure to give a yellow solid.This was submitted to column chromatography eluting with (amp;lo) ethyl acetate in dichloromethane to give the 10-formylpyr- rolo3,2-bcarbazole. Ethyl 1O-formyl-3,4-dimethylpyrrolo3,2-bcarbazole-2-car-boxylate 3s was obtained from the pyrrolo3,2-bcarbazole 3a as a yellow solid (0.0646 g, 64.573, m.p. 292 "C (decomp.); 6H(2Hs-DMSO) 11.38 (1 H, S, 1-NH), 11.21 (1 H, S, CHO), 10.82(1H,s, 5-NH),8.52(1 H,d, J7.5,9-H)7.85(1 H,d,J7.5,6- H),7.52(1 H, t, J7.5,8-H),7.19(1 H,t, J7.5,7-H),4.12(2H,q, OCH,CH,), 3.02 (3 H, s, 4-CH,), 2.89 (3 H, s, 3-CH3) and 1.42 (3 H, t, OCH,CH,); m/z() 334 (100, M'), 288 (49), 260 (65), 231 (20) and 204 (12) (Found: M+ 334.1325.C20H18N203 requires M,334.1 3 17); v-(Nujol)/m-' 3449, 3275, 1687 and 1639. Ethyl 10-formyl-3,4,8-trimethylpyrrolo3,2- b carbazole-2- carboxylate 3t was obtained from the pyrrolo3,2-bcarbazole 3b as a deep yellow solid (0.056 g, 54.0"/,), m.p. 293-294deg;C; amp;('H6-DMSO) 11.24 (1 H, S, 1-NH), 11.17 (I H, S, CHO), 10.77 (1 H, S, 5-NH), 8.29 (1 H, S, 9-H), 7.45 (1 H, d, J8,6-H), 7.33 (1 H, d, J8,7-H), 4.40 (2 H, q, OCH,CH3), 2.99 (3 H, S, 4-CH,), 2.88 (3 H, s, 3-CH,), 2.50 (3 H, s, 8-CH3) and 1.42 (3 H, t, OCH2CH3); m/z ()348 (100, M'), 302 (52), 274 (54) and 245 (15) (Found: M+ 348.1465.C21H20N203 requires M, 348.1474); v,,,,(Nujol)/an-' 3446,3236, 17 16 and 1642. Reaction of the Pyrrolo3,2-bcarbazole 3a and 2-Methylbut- 3-en-2-ol.-A solution of the pyrrolo3,2-bcarbazole 3a (0.165 g, 0.54 mmol) and 2-methylbut-3-ene-2-01(0.093g, 1.08 mmol), in 1,Zdichloroethane (20 cm3)was heated under reflux and stirred with Montmorillonite clay (0.5 g) for 15 h. The clay was filtered off and washed well with 1,2dichloroethane and evaporation of the combined filtrates gave a brown oil. This was submitted to column chromatography eluting with (504) light petroleum in dichloromethane to give the 10-(2-methylbut- 2-enyl)pyrrolo3,2-bcarbazole3p as a yellow solid (0.047 g, 23.3), m.p. 168-171 "C (Found: C, 77.1; H, 7.18; N, 7.59.C24H26N~O2 requires c, 76.97; H, 7.00; N, 7.48); amp;('Ha- DMSO) 10.71 (1 H,s, 1-NH), 10.62(1 H,s,5-NH),8.00(1 H,d, J 7.5,9-H), 7.43 (1 H,d, J7.5,6-H), 7.35 (1 H, t, J7.5,8-H), 7.08 (1 H, t, J7.5, 7-H), 5.18 (1 H, br, t, J6, CH,CH=), 4.39 (2 H, q, OCH2CH,), 4.23 (2 H, br, d, J6, CH,CH=), 2.90 (3 H, s, 4-CH,), 2.89 (3 H, S, 3-CH3), 1.95 (3 H, S, -CCH3), 1.65 (3 H, S, =CCH3) and 1.39 (3 H, t, OCH2CH3); m/z () 374 (100, M'), 328 (a),313 (22), 300 (9), 299 (15), 285 (17), 284 (10) and 273 (24). Also obtained was the 6-(2-methylbut-2enyl)pyrrolo3,2-bcar-bazole 3U as a yellow solid (0.0012 g, 0.6); d~(~amp;-DMso) 11.22(1 H,s, 1-NH), 10.11 (1 H,s,~-NH), 7.91 (1 H,d, J7.5,9- H),7.85(1 H,s, 10-H), 7.14(1 H,d,J7.5,7-H), 7.03(1 H, t, J7.5, 8-H), 5.52 (1 H, br, t, J6, CH,CH=), 4.37 (2 H, q, OCHZCH,), 3.69 (2 H, d, J6, CH,CH=), 2.98 (3 H, S, 4-CH3), 2.91 (3 H, S, 3-CH,), 1.80(3 H,s,=CCH3),1.79(3 H,s,=CCH,)and 1.40(3 H, t, OCH2CH3); m/z r/,)374 (100, M'), 328 (93), 273 (14), 245 (18) and 243 (10); and the starting pyrrolo3,2-bcarbazole 3a (0.063 g, 38).Reaction of the Pyrrolo3,2-bcarbazole 3a with Pyridine Hydrobromide Perbromide.-Pyridine hydrobromide per-bromide (0.092 g, 0.3 mmol) was added to a solution of the pyrrolo3,2-bcarbazole 3a (0.096 g, 0.3 mmol) in dichloro- methane (10 an3), and the mixture was stirred and gently heated under reflux for 30 min. Evaporation of the mixture under reduced pressure gave a yellow oil which was submitted to column chromatography eluting with (54) light petroleum in dichloromethane.This gave the lO-bromopyrrolo3,2-bcar-bazole 3y as a yellow solid (0.034 g, 29.9), m.p. 248-251 "C (decomp.) (Found: C, 59.1; H, 4.6; N, 7.1. C19H17BrN,02 requires c, 59.23; H, 4.45; N, 7.27); amp;('amp;-DMSo) 11.03 (1 H, S, 1-NH), 10.48 (1 H, S, 5-NH), 8.64(1 H, d, J7,9-H), 7.50 (1 H, d, J7,6-H), 7.47 (1 H, dt, J7 and 2,8-H), 7.18 (1 H, dt, J7 and 2,7-H), 4.38 (2 H, q, OCH,CH,), 2.92 (3 H, s, 4-CH3), 2.89 (3 H, s, 3-CH3) and 1.40 (3 H, t, OCH,CH,); m/z () 386 (66, M+ "Br), 384 (65, M+'"Br), 340 (loo), 339 (30), 338 (97), 312 (13), 311 (lo), 310 (13), 231 (24), 230 (31) and 229 (29); the 8-bromopyrrolo3,2-bcarbazole 3n as a yellow solid (0.0076 g, 6.6) which was identical in all respects with the pyrrolo- 3,2-bcarbazole 3n in the previous experiment; the 8,lO- dibromopyrrolo 3,2-bcarbazole 3q as a greenish yellow solid (0.0122 g, 8.76) which was identical with the pyrrolo3,2- blcarbazole 3q of the next experiment; and the starting pyrrolo3,2-bcarbazole 3a (0.0247 g, 20.9).Synthesis of the 8,l O-DibromopyrroZo3,2-bcarbazoZe3q.-Pyridine hydrobromide perbromide (0.064 g, 0.2 mmol) was added to a solution of the pyrrolo3,2-bcarbazole 3a (0.0306 g, 0.1 mmol) in dichloromethane (6 cm3) and the mixture was stirred and gently heated under reflux for 30 min. After cooling of the mixture, the product crystallised and was filtered off to give the 8,l O-dibromopyrroZo3,2-bcarbazoZe3q as greenish yellow crystals (0.032 g, 68.8), m.p. 276-278 "C (Found: C, 49.0; H, 3.2; N, 5.8.C,,H,6BrN202 requires(=, 49.16; H, 3.47; N, 6.04); amp;(C2H,j-DMSO) 11-24 (1 H, S, 1-NH), 10.62 (1 H, S, 5-NH),8.75(1 H,d, J2,9-H), 7.60(1 H,dd, J8and2,7-H), 7.47 J. CHEM. SOC. PERKIN TRANS. 1 1994 requires M 79Br 669.047); and the 8-bromo-l O-pyrroZyZ-methyZpyrroZo3,2-bcarbazole 6i as a yellow solid (0.01 7 g, 41.8),m.p.240 "C(decomp.)(Found: C, 60.8; H, 5.1 1;N, 7.13. C30H30BrN305requiresC, 60.81; H, 5.10; N, 7.09);6H(2H,- D~S0)11.03(1H,s,5-NH),10.63(1H,s,pyr-NH),10.22(1H, S, 1-NH), 7.94(1 H, S, 9-H), 7.48 (1 H,d, J7.5,7-H), 7.40(1 H, d, J 7.5, 6-H), 5.13 (2 H, S, 10-CH2), 4.33 (2 H, q, 2-OCH2CH3), 4.14 (2 H, q, 5'-OCH2CH,), 2.95 (3 H, S, 4-CH3), 2.91 (3 H, S, 3-CH3), 2.58 (3 H, S, 4'-CH3), 2.48 (3 H, S, COCHj), 1.36 (3 H, t, 2-OCH2CH3) and 1.18 (3 H, t, 5'-OCH2CH,); m/z ?A) 593 (49, M+ 'lBr), 591 (48, M+ "Br, 513 (43), 202 (16), 181 (8), 134 (lo), 82 (50), 81 (51) and 79 (100).Acknowledgements We thank The Royal Society for a Developing Countries (1 H,d, J8,6-H),4.39(2H,q,OCH,CH3),2.91(~H,s,~-CH~),Fellowship (to L. C.) and Wellcome Laboratories Ltd, 2.88 (3 H, s, 3-CH3) and 1.39 (3 H, t, OCH,CH,); m/z () 466 (41, M+ "Br), 464 (79), 462 (41, M+ "Br), 420 (55), 418 (loo), 416 (57), 392 (8), 390 (14), 389 (ll), 340 (15) and 338 (16). Reaction of the 1O-PyrroZyZmethyZpyrrolo3,2-bcarbazoZe6a with Pyridine Hydrobromide Perbromide.-Pyridine hydro-bromide perbromide (0.0228 g, 0.07 mmol) was added to a solution of the pyrrolo3,2-bcarbazole 6a(0.035 g, 0.068 mmol) in dichloromethane (5 cm3), and the mixture was stirred and gently heated under reflux for 30 min. After cooling of the mixture, the solution was washed with water (10 cm3), dried (Na2S0,) and evaporated under reduced pressure to give an oil.This was submitted to column chromatography eluting with (0-10) ethyl acetate in dichloromethane to give the 6,8-dibromo- 1O-pyrroZyZmethyZpyrroZo3,2-bcarbazoZe6j as a yellow solid (0.0075 g, 16.5), m.p. 250-253 "C (decomp.); amp;(CDCl,) 10.50 (1 H,~,5-NH),8.98(1 H,s, l-NH),8.72(1 H,s, l-NH),8.63(1 H, S, 9-H), 7.52 (1 H, S, 7-H), 4.47 (2 H, q, 2-OCH2CH,), 4.42 (2 H, S, lO-CH2), 4.29 (2 H, q, 5'-OCH2CH,), 2.92 (3 H, S, 4-CH3), 2.87 (3 H, S, 3-CH3), 2.68 (3 H, S, 4'-CH3), 2.59 (3 H, S, COCH,), 1.48 (3 H, t, 2-OCH2CH3) and 1.34 (3 H, t, 5'-OCH2CH3); m/z () 671 (7, M+ C8'Br), 625 (8), 579 (12), 195 (40),134 (30) and 108 (100) (Found: M+ 79Br, 669.047. C30H29Br2N305 Beckenham, Kent, for the gift of chemicals. References 1 L. Chunchatprasert, K. R. N. Rao and P. V. R. Shannon, J. Chem. SOC.,Perkin Trans.I, 1992,1779. 2 Patent application no. WO 93/01512. 3 L. Chunchatprasert, A. H. Jackson, K. R. N. Rao and P. V. R. Shannon, J. Chern. Res., 1992, (S),258. 4 R. Iyer, A. H. Jackson, B. Naidoo and P. V. R. Shannon, Chem. Commun., 1972,461. 5 A. H. Jackson, R. Iyer, B. Naidoo and P. V. R. Shannon, J. Chem. SOC.,Perkin Trans.2,1973,872. 6 J. S. L. Ibaceta-Lizana, R. Iyer, A. H. Jackson and P. V. R. Shannon, J. Chem. SOC.,Perkin Trans.2,1978,733. 7 A. C. Tinker, Ph.D. Thesis, Cardiff, 1976. 8 A. H. Jackson, P. R. Jenkins and P. V. R. Shannon, J. Chem. SOC., Perkin Trans.I, 1977,1698. 9 K. M. Biswas,A. H. Jackson, M. M. KobaisyandP. V. R. Shannon, J. Chern. SOC.,Perkin Trans.I, 1992,461. 10 E. Collins and P. V. R. Shannon, J. Chern. SOC.,Perkin Trans.1, 1973,419. Paper 4/00705K Received 4th February 1994 Accepted 17th March 1994