A new convergent method for porphyrin synthesis based on a lsquo;3 + 1rsquo; condensation

摘要

WA new convergent method for porphyrin synthesis based on a mlsquo;3 + lrsquo;condensation nz IJ 7i-Arezki Boudif and Michel Momenteau* Institut Curie-Biologie, CNRS URA I387, B6t II2, Centre Uniuersitaire, 91405 Orsay, France A new methodology based on the lsquo;3 + 1rsquo; acid-catalytic condensation of tripyrranes and pyrrole- 2,5-dicarbaldehyde has been used, for the first time, for the synthesis of two types of porphyrins: vic- dipropionic ester porphyrins 30 and 31 including an analogue of the corallistin-A and vic-diacrylic ester porphyrins 32 and 34. For this purpose, synthesis of various tripyrranes and pyrrole-2,s-dicarbaldehydes have been reported and characterized. Studies by dynamic lsquo;H NMR of sterically hindered tripyrranes show conformational exchange, in solution.Structures of the new porphyrins have been confirmed by lsquo;H NMR spectrometry. Introduction of diacrylic ester groups in vicinal positions markedly influences the electronic spectra of compounds 32 and 34 which present an oxorhodo-type absorption pattern. Introduction In order to satisfy either symmetry factors or the nature of the substituents, a variety of approaches have been developed and are currently employed in the synthesis of porphyrins and related macrocycles. They are as follows. Stepwise condensation of monopyrroles with aliphatic or aromatic aldehydes. This procedure initiated and developed by Rothemund rsquo; and reinvestigated by Lindsey et al. is used to prepare rneso-arylporphyrins. Using a functionalized pyrrole, in a self-condensation reaction, this synthetic route was recently extended to the general synthesis of porphyrins bearing the same substituents at the P-positions and of meso-tetra-alkylp~rphyrins.~ lsquo;2 + 2rsquo; Synthesis.This procedure consists of the condensation of two dipyrromethanes or dipyrromethenes units. This method has an historical value since it was initially employed by Fi~cher.~It was later developed by MacDonald et a/.6and was employed to produce uro-, copro-, aetio-porphyrins and other centrosymmetric porphyrins. rsquo; Cyclization of linear tetrapyrrole compounds (bilanes, bilenes or biladienes). This procedure involves cyclization of tetrapyrroles obtained by multi-step condensation of pyrroles.rsquo; In this method, the presence of a transition metal is often required.Limitations and advantages of these methods have been discussed by D01phin.~ In a recent communication we reported the first example of the synthesis of a vic-diacrylic porphyrin using a new lsquo;3 + Irsquo; condensation strategy. lo The general path of this method consists of a condensation of a tripyrrane with a pyrrole-2,5- dicarbaldehyde in the presence of an acidic catalyst. Herein, we report the development of this new method (Scheme I) allowing OHC H++ + -H OHC C02H Scheme 1 the preparation of compounds that cannot be obtained using classical procedures. The synthesis and characterization of their precursors are also included. Results and discussion Synthesis of pyrrole-2,5-dicarbaldehydes The preparation of pyrrole-2,5-dicarbaldehydeshas recently been described.Since, however, the method reported was only applicable to the synthesis of one of the types of pyrrole which we needed, we decided to investigate the preparation of such starting materials by two other procedures which allow the introduction of aldehyde functions onto pyrroles. Formyl- ation can be achieved by the Vilsmeier-Haack reaction l2 or oxidation of cr-methyl groups.13 For the synthesis of porphyrins 30-32 and 34we needed three types of pyrrolecarbaldehydes 7 and 8 (Scheme 2) and 14.Synthesis of the pyrroledicarbaldehyde RI gH 1 R=H 3 R=H 2 R=Me 4 R=Me ii. iii I v or vi OHCdCH0H -OHCA$ycO2@H 7 R=H 5 R=H 8 R=Me 6 R=Me Scheme 2 Reugents and conditions: i, hv, UV, CuS0,-H,O, RT; ii, POC1,-DMF, CICH,CH,CI, 60-70 ldquo;C; iii, aqueous AcONa, reflux, 45 min; iv, NCCH,CO,Et, Et,N, toluene, reflux;v, 3 mol dm-3 aq.NaOH, reflux, 3 h; vi, KOH-MeOH-H,O, reflux, 30 min 7 has been reported by Olsson et a1.14 To obtain the pyrroledicarbaldelyde 8 from 11, we investigated the synthesis J. Chem. Soc., Perkin Trans. 1,1996 1235 of the latter from a-methyl pyrrole 9 l5 as a starting material. Thus, treatment of9 with Pb(OAc),-PbO, in acetic acid at room temperature for 3 days by the procedure described by Battersby et a1.13 gave compound 10 (73) (Scheme 3). However, Me Me i Me H 9 OHC H*10 COzEt + OHCdMe H 11 Scheme 3 Reagents and conditions: i, Pb(OAc),-PbO,, AcOH, RT, 3 days attempted saponification of the ester function and subsequent removal of the carboxylic acid group from 10 was unsuccessful.An alternative way to prepare 8 was by formylation of 2 (Scheme 2). The work of Bellamy et ~1.'~related to the photochemistry of aromatic N-oxides, shows the possibility of converting 4-substituted pyridine N-oxides into pyrrole-2- carbaldehydes by UV irradiation. Thus, aqueous 4-methylpyrid- ine N-oxide when irradiated in the presence of CuSO, with a 350 W high-pressure mercury vapour lamp effectively gave 2. The best yield (21) was obtained after 30 h of reaction. Protection of the aldehyde function at position 2 as an ethoxycarbonyl(cyano)vinyl group and subsequent formylation on carbon 5 were carried out as described above to give 6 (59).Cleavage of the protecting group to give the pyrroledicarbalde- hyde 8 was carried out using milder conditions than those used in the case of 5. Thus, the compound was obtained in 39 yield by treatment of 6, in methanol, with 1.5 mol dm-3 aqueous potassium hydroxide for 40min under reflux. A second improved method for the synthesis in good yield ( 70), of pyrrolecarbaldehydes is based on the oxidation of x-methyl groups. We have used this method to prepare pyrrole- 2,5-dicarbaldehydes bearing two electron-withdrawing groups at positions 3 and 4 (Scheme 4),starting from commercially available 2,5-dimethylpyrrole. Thus, treatment with POC1,- DMF (3 equiv.), in a Vilsmeier-Haack reaction, gave 12 (55).These functions react in a Wittig-type reaction to give the diacrylic pyrrole derivative 13 (62). Oxidation of the 2- and 5- methyl groups was carried out with Pb(OAc),-PbO, in acetic acid. Although this reaction is usLally very slow (reaction time 70 h),13 3 h was found sufficient to give the pyrrole dicarbaldehyde 14 (22). Synthesis of tripyrranes The synthesis of tripyrranes has already been described and used for the preparation of porphyrinoid derivatives which possess a thi~phene,'~ furan l7 or pyridine18 ring as a replacement for one of the pyrrole rings and in the preparation of extended macrocycles such as sapphyrins. 19,,0 As defined above, our strategy for the preparation of porphyrins is a convergent procedure which consists of condensation of tripyrrole units with pyrrole-2,5-dicarbaldehydes.We now describe the preparation of the different tripyrranes employed (Scheme 5).The pyrrole derivative 13 was converted, into the 2,5-di(acetoxymethyl)pyrrole 15, in good yield, when treated with lead tetraacetate (2.2 equiv.) in acetic acid. The pyrroles 16,,' 18 22 and 24 23 were prepared according to the literature. The pyrrole 16 was transesterified to afford 17. 1236 J. Chem. SOC.,Perkin Trans. 1,1996 i, ii EtOZC, ,COzEt I bsol;/ CHO Me' H H 1312 iv /' Ivi. Et02C, ,CO,Et Et02Cbsol; /C02Et H H 15 14 Scheme 4 Reagents and conditions: i, POC1,-DMF, ClCH,CH,Cl, 60-70 "C; ii, Aqueous NaOH, reflux, 15 min; iii, (EtO),POCH,CO,Et-NaH, THF, 60 "C; iv, Pb(OAc),, AcOH, RT, 1 h; v, Pb(OAc),-PbO,, AcOH, RT, 3 h The a-methyl group of the pyrrole 18 was oxidized to a carboxylic acid group by treatment with S02C1, followed by hydrolysis.The resulting carboxylic acid substituent was removed by iodination to give 19. Finally, iodine was removed by catalytic hydrogenation at 40"C in a mixture of THF- MeOH to afford the pyrrole 20 (68.6) which upon transesterification led to the benzyl ester 21. Following the same procedure, 24 was converted into compound 25 which was converted into the 2-(acetoxymethy1)pyrrole 26 (68). The tripyrrane 22 was prepared in 56 yield by a Montmorillonite K-10 catalysed condensation of the di(acetoxymethy1) pyrrole 15 with the pyrrole 17 (2 equiv.) in methylene dichloride.,, The tripyrrane 23 was prepared in 67.5 yield by a toluene-p-sulfonic acid catalysed condensation of 15 with the pyrrole 21 (2 equiv.) in hot absolute ethanol (Scheme 5).Following the procedure used for compound 22, the tripyrrane 27 was prepared in 64 yield by condensation of the pyrrole 26 with freshly distilled pyrrole. 'H NMR characterizationof tripyrranes The 'H NMR spectrum of the tripyrrane 29 showed two broad signals at 9.12 (1 H) and 10.85 (2 H) ppm, assignable to the NH resonance. P-Pyrrole protons of the central pyrrole gave a doublet at 5.85 ppm (weakly coupled with NH, JHH2.5 Hz) whilst singlets at 4.41and 3.66 ppm (both 4H) were identified as the benzylic CH, and bridge-CH, protons, respectively.In the case of the tripyrranes 22 and 23, there are P-ethyl acrylate substituents which exert an additional steric hindrance and affect the 'H NMR spectra. Except in the 2-5 ppm range, the spectra of these tripyrranes were well resolved. In addition to a quartet assignable to ethoxy group CH,, these spectra showed, in the 2-5 ppm range, unresolved and unassignable signals see Fig. l(a)and (b), T = 295 K the broadness and multiplicity of which, however, suggest the occurrence of slow conform- ational exchange. By use of 'H dynamic NMR spectroscopy in 2H8toluene rather than in CDCI,, the former allowing studies over a larger temperature range than the latter, assignments in the 2-5 ppm range for the tripyrranes 22 and 23 were made.At 295 K, the spectrum of 22 showed an unresolved signal at 2.33 ppm (4H), 4coalescent signals at 2.75 (4H), 3.1 (2 H), 3.9 (4H) and 4.5ppm (2 H). At the same temperature, the spectrum of 23 showed 3 coalescent signals at 3.2 (2 H), 4(4 H) and 4.5 ppm (2 'I LR2 H 16 R' =H, R2 =Et, R3 =Et 17 R' =H, R2 =Et, R3 =Bn 18 R' =Me, R2 =Me, R3 =Et 19 R' =I, R2=Me, R3 =Et 20 R' =H, R2 =Me, R3=Et 21 R' =H, R2 =Me, R3 =Bn + 15 i or iiI Et02C, ,CO,Et H H H 22 R2 =Et, R3 =Bn 23 R2=Me, R3 =Bn bsol; H H 24 R4 =Me, R5 =Et 25 R4 =Me, R5 =Bn 26 R4 =CH20Ac, R5 =Bn I ii H H H 27 R5 =Bn Bn =PhCH2 throughout Scheme 5 Reugents und condirions: i, Montmorillonite K-10 Clay,CH,CI,, 3 h, RT; ii, p-MePhSO,H, abs. EtOH 60-70 "C H).With an increase in temperature, in both cases, a gradual disappearance of the coalescence occurred. This was completed at 345 K where spectra were well resolved see Fig. l(a) and (b). From literature data for the 'H chemical shifts of tripyrranes 25 and from those obtained for the tripyrrane 27, we have assigned the signals in the spectrum of compound 22 as follows: quartets at 2.35 and 2.80 ppm correspond to p-ethyl methylene protons; singlets at CLC 3.6 and 4.5 ppm (both 4 H) present in the spectra of 22 and 23 were assigned to bridge and benzyl methylene protons. Wishing to know if the non-equivalence resulting from conformational exchange was due to a loss of symmetry relative to the central pyrrole or to the presence of another element of symmetry, we lowered the temperature in order to reduce conformational exchange rates.As shown on the spectra at 273 K see Fig. l(a) and (b),each singlet at 3.6 and 4.5 ppm on spectra recorded at 345 K, gave rise to two doublets. In addition, homonuclear coupling constant values (JHH16 Hz) determined from spectra were in agreement with those of r.... I". ',....,....,....,...-1 r ....,....,..,....,...., 5.0 4.5 4.0 3.5 3.0 2.5 2.0 5.0 4.5 4.0 3.5 3.0 2.5 6 (PPm) Fig. 1 2-5 pprn range 'H DNMR spectra (200 MHz, ZH8toluene)of the tripyrranes 22 (a)and 23 (b) geminal protons. In order to confirm this assumption, homo- nuclear decoupling experiments were carried out. Couplings of the protons at 3 and 4.45 ppm have been established by selective irradiation.From 'H DNMR studies in the case of the tripyrranes 22 and 23, we deduced that broadening of the signals corresponding to bridge-methylene protons and those of benzylic groups was really due to slow conformational exchange. In addition, results of decoupling experiments at low temperature (273 K) suggested that the two protons of each methylene group were magnetically different. The presence of these two non-equivalent protons either for bridge-methylene groups or benzylic ester substituents could be explained by a central symmetry type with respect to the central pyrrole. Formation of porphyrins The cyclization involves the acid-catalysed condensation of I, 14-unsubstituted tripyrranes with 1 equiv.of pyrrole-2,5-dicarbaldehydes. In a general procedure, protected benzyl tripyrrane- 1,14-dicarboxylates were deesterified by hydrogen- ation over Pd-C. Although decarboxylation of the resulting tripyrrane-dicarboxylic acids appears to occur spontaneously, they were used in the following step without other purification. Initially, condensation of the tripyrrane 28 with the pyrroledicarbaldehyde 7 was carried out in absolute ethanol, in the presence of an excess of zinc acetate, at room temperature for 1 day. Such conditions were chosen because it has been reported in the literature that the presence of metallic ion appears to facilitate cyclization by the template effe~t.~~,~' With a catalytic amount of toluene-p-sulfonic acid and after addition of DDQ to oxidize porphyrinogen, the work-up of the reaction mixture furnished the zinc complex of porphyrin 30 (5.5).The structure of Zn-30, as well as the other porphyrins whose synthesis is reported here, was characterized on the basis J. Chem. SOC.,Perkin Trans. 1,1996 1237 Table I Optimization conditions for the preparation of the porphyrin 30 Concentration of reagents (mmol) a' 1.6 b2 c 1.6 d 1.6 e 1.6 f 1.6 g2 Temperature Acidic Solvent ("C) EtOH RT TSA" CH,Cl, RT TSA CII,Cl, RT TSA CH,Cl, RT CH,Cl, RT CH,Cl, RT (CH,Cl), 40-50 TSA a In the presence of Zn(OAc),.2H,O. TSA = toluene-p-sulfonic acid. of 'H NMR spectral evidence. The presence of Zn" having little effect on the yield of the cyclization, we have tested different conditions but always in the absence of zinc sa the results are reported in Table 1.The concentration range (1.6-2 mmol) used was suggested by the procedure described by Sessler in the synthesis of sapphyrins.2' In all cases, the yields of 30 were higher after oxidation, chromatography and crystallisation than in the presence of Zn".Factors such as the nature of the acid catalyst, reaction time and temperature were varied. Use of trifluoroacetic acid instead of toluene-p-sulfonic acid in CH,Cl, increased the yields, (from 20 to 30) for 20 h reactions. An increase in the reaction time (from 70 to 80 h) but with no other changes, also gave increased yields; (from 53.5 and 61.5).An increased reaction temperature (50 "C in dichloroethane which has a polarity comparable to that of methylene dichloride) significantly decreased the yield (to 6.5). This result suggested that one of the two reactants or both are very unstable when the temperature is raised. Porphyrins 31, 32 and 34 were prepared under the conditions corresponding to the test f (Table 1) in 42.5,49 and 33 yields respectively. Porphyrin 32 is an analogue of corallistin-A. This free-base porphyrin was isolated from the demosponge Corallistes SP.,~Its synthesis as a dimethyl ester derivative was reported by Scott et ~1.~'and was obtained in 32 yield using Johnson's method by cyclization of appropriate a,c-biladiene. Our porphyrin 31 differs only by the substitution of one acetic acid side chain of the natural product by one propionic acid side chain, other peripheral substituents remaining unchanged.The porphyrins 32 and 34 bearing vicinal P-ethyl acrylic ester groups, are reported for the first time (Schemes 6 and 7), and are the first representatives of a new family which should be of interest in exploring physicochemical behaviour-electronic property relationships. UV-visi ble characterization From the UV-visible absorption patterns of the porphyrins synthesized two groups may be characterized. Porphyrins 30 and 31 show, in the visible region, an absorption spectrum of Zn.30 M = the well known etio-type (band IV I11 11 I). This is 30 M = 31 M =characteristic of P-alkyl substituted free-base porphyrins (see data in Experimental section).Porphyrins 32 and 34 form a Scheme 6 second group, the visible absorption spectra of which are CF,CO,H, characterized by four bands with relative intensities 111 I1 RT TV I. This sort of absorption pattern, known as the oxo-rhodo-type, was reported for free-base porphyrins bearing two electron-wi thdrawing groups on diagonally opposite pyrrole rings.30 Thus, porphyrins with vicinal diacrylic ester groups represent a further substitution pattern which is also characterized by the same oxorhodo-type visible spectra. Moreover, we observed a bathochromic shift of ca. 20 nm with respect to those of the dipropionic acid porphyrins 30 and 31, probably as the result of an extension of the IT delocalized system to the adjacent acrylic side chains.1238 J. Chem. SOC.,Perkin Trans. I, 1996 Duration Yield catalyst (hours) ( 24 5.5 20 20 20 22 F,CCO,H 20 30 F,CCO,H 70 53.5 F,CCO,H 80 61.5 20 6.5 22 or 23 li Et02C, ,C02Et H H H 28 R3 = Et 29 R3 =Me + 77..11 or 111 Et025 I Et02C t k02Et R2 32 R3=Et C02Et CO2Et Zn, R2 = H, R3= Et 2H, R2= H, R3= Et 2H, R2 =Me,R3 =Me Reagents and Conditions: i, H,, Pd-C (1 Ox),THF, RT; ii, distilled CH,Cl,, 72 h, RT; iii, p-MePhSO,H, abs. EtOH, Conclusion We have shown that a new general pathway based on a '3 + 1' condensation may conveniently afford a single porphyrin if at least one of the two components, pyrrole or tripyrrane, is symmetrical.The symmetry restriction which characterizes this method is balanced by its convergent character. By the reported technique we have directly synthesized for the first time uic-dipropionic and vie-diacrylic ester porphyrins. Porphyrins of / bsol;u / C02Et 34 27 R5= C02Bn ic 33 R5= C02H Scheme 7 Reugennts and condiitzons: i, H,, Pd-C (loo/,), THF, RT; ii, CF,CO,H, distilled CH,Cl,, RT the latter type have unusual oxorhodo electronic absorption spectra as a result of the chemical nature of the substituents and/or their peripheral positions. Studies of the effects induced by the presence of electron-withdrawing substituents on the physicochemical properties, mainly the redox behaviour of their metal complexes, are underway.Experimental 'H NMR spectra were obtained in the indicated solvents, with a Bruker AC 200 instrument. Chemical shifts are given in ppm relative to TMS. Coupling constants are given in Hz. Optical spectra were recorded using a Varian DMS 200 spectrophotom-eter. When dry CH,Cl, or (CH,Cl), is specified, these were distilled over CaH,. THF and diethyl oxide were respectively distilled over Na-PhCOPh and sodium. Ether refers to diethyl ether. 3-Methylpyrrole-2-carbaldehyde2 A solution of 4-methylpyridine-N-oxide (2 g, 18.3 mmol) and hydrated copper sulfate (CuSO,*SH,O; 45.2 g, 10 equiv.) in distilled water (800 cm3) was irradiated, at 24-27 "C for 24 h with a high-pressure Vapors-mercury Lamp (350 W, 1.6 A) after which it was saturated with sodium chloride and extracted with ether (450 cm').The extract was dried (Na,SO,) and evaporated to give the title compound 2 (0.42 g, 21) after chromatography on a silica gel column (Found: C, 60.94; H, 5.25; N, 9.75. Calc. for C,H,NO,: C, 61.31; H, 5.10; N, 10.22);6,(200 MHz, CDCI,) 9.65 (1 H, br, NH), 9.60 (1 H, s, CHO), 7.24 (1 H, t, 2-H), 6.11 (I H, t, 3-H) and 2.37 (3 H, s, CH,). 2-(2-Cyano-2-ethoxycarbonylvinyl)-3-methylpyrrole4 A mixture of the pyrrole 2 (2 g, 18.4 mmol), ethyl cyanoacetate (2 equiv.) and triethylamine (0.8 cm3)was heated under reflux in dry toluene (30 cm3) for 4 h after which it was evaporated. The residue was dissolved in the minimum of absolute ethanol and the solution frozen to give the product as yellow needles (2.52 g, 67.5);6,(200 MHz, CDCl,), 9.80 (1 H, br, NH), 8.01 (1 H, S, CH=), 7.12 (1 H, t, 5-H), 6.22 (1 H, t, 4-H), 4.25 (2 H, 9, OCH,CH,), 2.26 (3 H, s, CH,) and 1.34 (3 H, t, OCH2CH,).5-(2-Cyano-2-ethoxycarbonyIvinyl)-4-methylpyrrole-2-carb-aldehyde 6 A suspension of compound 4 (1.5 g, 7.35 mmol) in distilled dichloroethane (20 cm3) was added to a Vilsmeier complex generated by treating DMF (1.5 cm3) with POCl, (1.3 cm3). After the mixture had been heated under reflux for 0.5 h it was cooled and treated with saturated aqueous sodium acetate (50 cm3) and again heated to reflux for 1 h. After work-up, the crude product was chromatographed on a silica gel column eluted with CH2Cl, to give compound 6 (1.01 g, 59.5) as a yellow powder (Found: C, 61.8; H, 5.0; N, 11.8.Calc. for CI2H,,N2O,: C, 62.07; H, 5.17; N, 12.07); amp;(200 MHz, CDCI,) 10.22 (1 H, br, NH), 9.68 (1 H, s, CHO), 8.07 (I H, s, HC=), 6.81 (I H, d, 3-H), 4.35 (2 H, 9, OCHZCH,), 2.30 (3 H, S, CH,) and I .37 (3 H, t, OCH,CH,). 3-Methylpyrrole-2,5-dicarbaldehyde 8 The procedure described for compound 5 was used to prepare compound 6 in 59.5 yield, starting from the pyrrole 2. Cleavage of the aldehyde protecting group was carried out under mild conditions compared with those used for 5.A solution of the intermediate 6 (0.6 g, 2.6 mmol) in methanol (25 cm3)was treated with a solution of potassium hydroxide (3.4 g) in water (35 cm3) and the mixture was heated under reflux for 40 min under argon.The mixture was then evaporated to remove the methanol and the residue was diluted with water, acidified to pH 4.5 with 6 mol dm-, hydrochloric acid and extracted with ethyl acetate (ca. 300 cm3).The extract was dried (Na,SO,) and evaporated and the crude product was chromatographed on a silica gel column with CH,Cl,-Et20 (100: 5, vh) as eluent the pure title compound 8 as a white powder (I 37 mg, 39) (Found: C, 60.9; H, 5.25; N, 9.75. Calc. for C,H,NO,: C, 61.31; H, 5.10; N, 10.22). 0',(200 MHz, CDCI,) 9.87 (1 H, s, CHO), 9.68 (1 H, s, CHO), 6.76 (1 H, d, 3-H) and 2.41 (3 H, s, CH,). 2,5-Dimethylpyrrole-3,4-dicarbaldehyde12 Distilled 2,5-dimethylpyrrole (10.1g, 0.105 mmol) was added dropwise at room temperature to a Vilsmeier complex prepared from distilled DMF (50 cm3) and POCl, (34 cm3, 0.36 mol) added at 0deg;C under argon, and then stirred at room temperature for 1 h.The reaction mixture was warmed to and held at 50 "C for 2 h after which it was cooled (ice water-bath) and treated cautiously with 2 mol dm-, aqueous NaOH. This mixture was briefly heated under reflux and finally poured into ice-water (2 dm3).The title pyrrole 12was filtered off and dried (P205)overnight (9.2 g, 62);6,(200 MHz, CDCl,) 9.90 (1 H, br, NH), 10.22 (2 H, s, CHO) and 2.54 (6 H, s, CH,). 3,4-Di(2-ethoxycarbonylvinyl)-2,5-dimethy~pyrrole13 Triethyl phosphonoacetate (68 g) in freshly distilled THF (40 cm3)was added at room temperature to a dispersion of sodium hydride (60; 12 g) suspended in THF (60 cm3)under argon.A solution of compound 12(4.58 g, 30.3 mmol) in distilled THF (120 cm3) was added dropwise at room temperature to the reaction mixture which was then heated at 60 "C overnight. The solution when poured into ice-water (1.5 dm3) gave the diacrylic pyrrole 13 as a precipitate which was filtered off and recrystallized from hot absolute ethanol (6.75 g, 83.5) (Found: C, 65.7; H, 7.1; N, 4.7. Calc. for C,,H,,NO,: C, 65.98; H, 7.21; N, 4.81); 6,(200 MHz, CDC1,) 9.12 (1 H, br, NH), 7.75 (2 H, d, JHH16, CH=), 5.95 (2 H, d, JHH16, =CH), 9.22 (4 H, q, OCH,CH,), 2.31 (6 H, s, CH,) and 1.30 (6 H, t, OCH,CH,). 3,4-Di(2-ethoxycarbonylvinyl)pyrrole-2,5-dicarbaldehyde14 A suspension of compound 13 (0.5 g, 17.2 mmol) in glacial acetic acid (I5 cm3) was added to a mixture of Pb(OAc), (0.5 g, 2.2 equiv.) and of PbO, (0.98 g, 2.28 equiv.) in the same solvent (20 cm3) at room temperature.After being stirred at room temperature for 3 h, the mixture was treated with distilled water (20 cm3) and then heated under reflux for 20-30 min. It was then diluted with water (100 cm3) and CH,C1, (100 cm3) and the phases were separated. The aqueous layer was extracted several times with CH,Cl,. The combined organic phase and extracts were neutralized, washed with water, dried (Na,SO,) and evaporated. Chromatography of the residue on a silica gel column gave the pyrrole (0.12 g, 22) (Found: C, 59.2; H, 5.78; N, 3.91. Calc. for C,,H,,NO,: J. Chem.SOC.,Perkin Truns. I, 1996 1239 C, 60.18; H, 5.33; N, 4.38); dH(200 MHz, CDC1,) 10.62 (1 H, br, NH), 9.96 (2 H, s, CHO), 7.86 (2 H, d, JHH 16, CH=), 6.27 (2 H, d, JHH 16, =CH), 4.26 (4 H, q, OCH,CH,) and 1.32 (6 H, t, OCH,CH,). 3,#-Di(2-ethoxycarbonylvinyl)-2,5-di(acetoxymethyl)pyrrole 15 Compound 13 (3 g, 10.3 mmol) in glacial acetic acid (50 cm3) was added dropwise at room temperature to a solution of lead tetraacetate (9.6 g, 2.1 equiv.) in the same solvent (80 cm3). The mixture was stirred at room temperature for 90 min after which it was evaporated under reduced pressure. Work-up followed by precipitation in CH,CI,-heptane gave the pyrrole 15 (3.12 g, 74.5) (Found: C, 58.3; H. 5.9; N, 3.5. Calc. for C,,H,,NO,: C, 58.96; H, 6.14; N, 3.43); 6amp;00 MHz, CDCI,) 9.42 (1 H, br, NH), 7.71 (2 H, d, JHH16, CH=), 6.04 (2 H, d, JHH 16, =CH), 5.05 (4 H, s, CH,-pyrrol.), 4.24 (4 H, q, OCH,CH,), 2.08 (6 H, s, OCH,) and 1.31 (6 H, t, OCH,CH,); Benzyl-4-ethyl-3-methylpyrrole-2-carboxylate21 Sulfonyl chloride (6.6 cm3, 3.2 equiv.) was added dropwise to a solution of the pyrrole 18 (5 g, 25 mmol) (prepared according to the method described by Inhoffen et aZ.,,, based on a Knorr cyclization, and obtained in 52 yield) in freshly distilled ether (200 cm3).The mixture was stirred for 24 h, under argon, at room temperature after which it was evaporated. The residue was dissolved in acetone (100 cm3) and the solution diluted with distilled water (50 cm3). After the mixture had been heated under reflux for 45 min, the acetone was removed under reduced pressure and the aqueous layer was extracted several times with CH,CI, until no suspension remained.The combined extracts were evaporated and the residue was dissolved again in ether (300 cm3). This solution was then extracted with 10 aqueous NaHCO, (300 cm3) to remove the aldehyde by-product resulting from the non-quantitative formation of the trichloromethyl derivative. The aqueous solution was finally acidified with 6 mol dm-, hydrochloric acid to the pyrrolecarboxylic acid. This was filtered off and dried over P,O,; yield 4.42 g (76.5). The carboxylic acid (3 g, 13.33 mmol) was added to a solution of KHCO, (8 g) in water (100 cm3) to which a similar volume of ethanol was then added.Iodine (8 g, 2 equiv.) previously dissolved in a minimum of absolute ethanol, was then added dropwise at room temperature to the solution. This mixture was stirred for 2.5 h at 40 ldquo;C before being heated at 90 ldquo;C to remove thc excess of iodine. When poured into ice-water the mixture gave the iodide derivative 19 which was filtered off and dried over P,O, overnight; yield 3.74 g (91.5). Magnesium oxide (1 g) was added to a solution of compound 19 (3.5g, 1 1.4 mmol) in THF-EtOH (1 : 1; 60 cm3) and this was followed by Pd-C (10; 1 g). Hydrogen was bubbled into the vigorously stirred mixture and the reaction was monitored by TLC. On completion of the reaction, the catalyst was removed by filtration through Celite and the filtrate evaporated to give compound 21 (2.03 g, 98).Sodium (0.06 g) was added to benzyl alcohol (20 cm3) under argon and the solution was stirred for some minutes. After this the pyrrole 20 (2 g, 11 mmol) in benzyl alcohol (5 cm3) was added to it. The mixture was heated at 100 ldquo;C under reduced pressure (10 mmHg) for 4 h after which the alcohol was removed under reduced pressure. The residue was dissolved in CH,Cl, and the solution neutralized, dried (Na,SO,) and evaporated to give the pyrrole 21 in quantitative yield (2.6 g). Compound 20: dH(200 MHz, CDCI,) 8.78 (I H, br, NH), 6.65 (I H, d, JHH 2.5, 5-H), 4.29 (2 H, 9, OCHZCH,), 2.41 (2 H, 9, CHZCH,), 2.27 (3 H, s, CH,), 1.33 (3 H, t, OCH,CH,), 1.15 (3 H, t, CH,CH,).Compound 21:dH(200 MHz, CDCI,) 8.80 (1 H, br, NH), 7.45 (5 H, m, Ph), 6.65 (1 H, d, JHH 2.5), 5.29 (2 H, s, OCH,), 2.41 (2 H, q, CH,CH,), 2.28 (3 H, s, CH,) and 1.15 (3 H, t, CH,CH,). 1240 J. Chern. SOC.,Perkin Trans. I, 1996 Benzyl-3,4-diethylpyrrole-2-carboxylate17 The pyrrole 16 (9.1 g, 46.6 mmol), prepared according to the method described by Sessler 22 and obtained in 84 yield, was transesterified under similar conditions to those used for the preparation of 21 to give the pyrrole 17(1 1.4 g, 96lsquo;;/,) as a brown oil; 6amp;00 MHz, CDCI,) 9.29 (1 H, br, NH), 7.42 (5 H, m, Ph), 6.68 (1 H, d, JH112.5, 5-H), 5.37 (2 H, S, OCH,Ph), 2.85 (2 H, 9, CH,CH,), 2.51 (2 H, q, CH,CH,) and 2.25 and 2.21 (6 H, 2 t, 2 CH,H,). Benzyl5-acetoxymethyl-3-ethyI-4-methylpyrrole-2-carboxylate 26 The pyrrole 2424 (5 g, 25.6 mmol), transesterified by the method described above, gave the ester 25 which was then treated with lead tetraacetate in acetic acid according to the preparation of the pyrrole 15 to afford compound 26 (5.35 g, 78) (Found: C, 68.41; H, 6.45; N, 4.44. Calc.for C18H21N04: C, 68.57; H, 6.66; N, 4.44); amp;(200 MHz, CDCI,) 8.92 (1 H, br, NH), 4.65 (2 H, q, OCH,CH,), 2.70 (2 H, q, CH,CH,), 2.16 and 1.91 (6 H, 2 s, 2 CH,), 1.31 (3 H, t, OCH,CH,) and 1.08 (3 H, t, CH,CH,). 2,5-Bis(5rsquo;-benzyloxycarbonyl-3rsquo;,4rsquo;-diethylpyrrol-2rsquo;-ylmethyl)-3,4-di(2-ethoxycarbonylvinyl)pyrrole22 A solution of compounds 17 (2.52 g, 9.8 mmol) and 15(2 g, 4.9 mmol) in CH,Cl, (40 cm,) was stirred at room temperature in the presence of acidic Montmorillonite K-10 clay (4 g).After 3 h, the clay was filtered off and the solution was first shaken in the presence of aqueous NaHCO, and then washed with water and dried (Na,SO,). Evaporation gave the crude product which was chromatographed on a silica gel column. The starting pyrrole 17 was eluted with CH,C1, followed by elution of the tripyrrane 22 (2.21 g, 56) with a mixture of CH,Cl,-Et,O (100:3, v/v) (Found: C, 71.8; H, 6.7; N, 5.4. Calc. for C,,H,,N,O,: C, 71.91; H, 6.86; N, 5.24); dH(200 MHz, 2H,toluene) 11.51 (2 H, s, 2NH), 10.09 (I H, s, NH), 8.31 (2 H, d, JHH 16, CH=), 7.11-6.94 (10 H, 2 m, Ph), 6.39 (2 H, d, JHH 16, =CH), 4.4 and 4.1 (4 H, br, OCH,Ph), 4.27 (4 H, q, OCH,CH,), 4.1 and 3.2 (4 H, br, 2 bridge-CH,), 2.85 and 2.66 (4 H, m, CH,CH,), 2.33 (4 H, br, CH,CH,) and 1.22, 1.11 and 1.01 (18 H, 3 t, OCH,CH, and CH,CH,).2,5-Bis(5lsquo;-benzyloxycarbonyl-3lsquo;-ethyl-4lsquo;-methylpyrrol-2lsquo;-yl-methyl)-3,4-di(2-ethoxycarbonylvinyl)pyrrole 23 A mixture of compounds 15 (0.84 g, 2.06 mmol) and 21 (1 g, 4.12 mmol) in absolute ethanol (30 cm3) was heated under reflux in the presence of toluene-p-sulfonic acid (0.5 g) for 1.5 h. The solution was then concentrated and frozen to give the tripyrrane 23 as crystals which were filtered off (1.07 g, 67.5) (Found: C, 71.3; H, 6.7; N, 5.2. Calc. for C,,H,,O,N,: C, 71.41; H, 6.59; N, 5.43); dH(200 MHz, 2H,toluene) 11.44 (2 H, S, 2NH), 9.95 (1 H, S, NH), 8.33 (2 H, d, JHH 16, CH=), 7.2- 6.9(10 H, m, Ph), 6.43 (2H, d Jk1H 16,=CH),4.4and4.1 (4H, br, OCH,Ph), 4.28 (4 H, q, OCH,CH,), 4.I and 3.2 (4 H, br, bridge-CH,), 2.29 (10 H, br, CH,CH, and CH,) and 1.10 and 0.95 (1 2 H, 2 t, CH,CH, and OCH,CH,). 2,5-Bis(5rsquo;-benzyloxycarbonyl-4rsquo;-ethyl-3rsquo;-methylpyrrol-2rsquo;-yl-methy1)pyrrole 27 A mixture of the pyrrole 26 (1 g, 3.17 mmol) and the pyrrole (0.1 1 g, 1.58 mmol) in CH,Cl, (25 cm3) was stirred at room temperature in the presence of Montmorillonite K-10 clay (1 g). After 3 h, the clay was filtered off and the filtrate was evaporated. Recrystallization of the residue from hot absolute ethanol gave the tripyrrane 27(0.61 g, 64) (Found: C, 74.7; H, 6.7; N, 7.3. Calc. for C,,H,,N,O,: C, 74.87; H, 6.76; N, 7.28); dH(200 MHz, CDCI,) 10.85 (2 H, br, NH), 9.12 (1 H, br, NH), 7.23-7.06 (10 H, m, Ph), 5.21 (2 H, d, JHH 2.5, HD), 4.41 (4 H, s.OCH,Ph), 3.66 (4 H, s, bridge-CH,), 2.64 (4 H, q, OCH,CH,), 1.87 (6 H, s, CH,) and 0.99 (6 H, t, CH,CH,). Zinc 7,8-di(2-ethoxycarbonylethyl)-2,3,12,13-tetraethylpor-phyrinate (Zn30) Pd-C (10; 0.2 g) was added under argon to a solution of the tripyrrane 22 (0.325 g, 0.41 mmol) in distilled THF (25 cm3). Hydrogenation at room temperature was followed by measuring the hydrogen volume used. Removal of the catalyst by filtration through Celite and evaporation of the THF under reduced pressure gave the tripyrranedicarboxylic acid as a brown oil which was immediately dissolved in absolute ethanol (250 cm3). The pyrrole 7 (0.05 g, 1 equiv.) was then added to this solution followed by toluene-p-sulfonic acid (0.38 g, 5 equiv.) and hydrated zinc acetate Zn(OAc),-2H20 (0.27 g, 3 equiv.).This mixture was stirred at room temperature for 1 day, after which it was neutralized with triethylamine (1 cm3), and treated with DDQ (93 mg, 1 equiv.) for 1 h with stirring at 40 "C. After this, the mixture was evaporated and diluted with CH,CI,. The solution was washed with water several times to remove the oxidation reagent before it was dried (Na,SO,) and evaporated. The resulting crude product was chromatographed on a silica gel column with CH,Cl, as eluent to give pure zinc porphyrin Zn 30(0.015 g, 5.5) (Found: C, 65.6; H, 6.6; N, 7.6. Calc. for C,,H,,N,O, Zn: C, 66.53; H, 6.42; N, 8.17"/,);ii,(200 MHz, CDCI,) 9.94 and 9.85 (4 H, 2 s, 4 H, meso), 9.32 (2 H, s, 2H,), 4.33 (4 H, q, OCH,CH,), 4.25 (4 H, t, CH,CH,CO,), 3.96 (8 H, q, CH2CH,), 3.23 (4 H, t, CH,CH,CO,), 1.85 (6 H, t, CH,CH,) and 1.23 (1 2 H, t, CH,CH,); Amax/nm 401 (E 166 400), 531 (7340) and 570 (7750).7,8-Di(2-ethoxycarbonylethyl)-2,3,12,13-tetraethylporphyrin30 A solution of the tripyrrane 22 (1.17 g, 1.47 mmol) was hydrogenated following the procedure described above. The resulting brown oil was immediately dissolved in distilled CH,Cl, (900 cm3) to which the pyrrole 7 (0.18 g, 1 equiv.) was then added. After the solution had been acidified with trifluoroacetic acid (0.6 cm3), it was stirred at room temperature, under argon, in dark for 80 h.The reaction mixture was then neutralized with triethylamine (6 cm3) to oxidize the porphyrinogen and treated with DDQ (0.3 g, 1 equiv.), with stirring at 40 "C for 1 h. After work-up, the crude product was chromatographed on a silica gel column with CH,C12 as eluent to give, after evaporation of the solvent, the pure porphyrin 30 (0.56 g, 61.5) (Found: C, 73.1; H, 7.3; N, 8.9. Calc. for C,,H,,N,O,: C, 73.31; H, 7.39; N, 9.00);dH(2O0 MHqCDCI,) 10.18and 10.15(4H,2~,4Hmeso),9.38(2H,s, 2H,), 4.42 (4 H, t, CH,CH,CO,), 4.21 (12 H, m, CH,CH, and OCH,CH,), 3.28 (4 H, t, CH,CH,CO,), 1.93 (12 H, t, CH,- CH,), 1.19 (6 H, t, OCH,CH,) and -3.85 (2 H, s, NH); Amax/nm398 (E 207 600), 499 (12 720), 535 (10 140), 564 (7024) and 619 (1679). 12,13-Di(2-ethoxycarbonylethyl)-8,17-diethyl-2,7,1S-trimethyl-porphyrin 31 The conditions used for the preparation of the porphyrin 30were used for the reaction of the tripyrrane 29 (0.36 g, 0.47 mmol) with the pyrrole 8 (0.06 g, 1 equiv.).Chromatography of the product on a silica gel column with CH,Cl, as eluent gave the pure porphyrin 31 (0.12 g, 42.5) (Found: C, 71.5; H, 7.35; N, 8.8. Calc. for C,,H,,N,O,~CH,OH: C, 71.21; H, 7.55; N, 8.75);6,(200 MHz, CDCI,) 10.15 (2 H, s, 10-CH and 15-CH), 10.12 (1 H, S, 20-CH), 10.0 (1 H, S, 5-CH), 9.02 (1 H, S, 3-CH), 4.42 (4 H, t, CH,CH,CO,), 4.244. I 1 (8 H, m, OCH,CH, and CH,CH,), 3.71, 3.66 and 3.63 (9 H, 3 s, 2-CH,, 7-CH3, and 18-CH,), 3.27 (4 H, t, CH,CH,CO,), 1.87 (6 H, t, CH,CH,), 1.19 (6 H, t, OCH,CN,) and -3.84 (2 H, s, NH); Amax/nm 400 (E 192 600), 498 (1 3 600), 535 (1 0 400), 566 (7050) and 620 (3300).12,13-Di(2-ethoxycarbonylethyl)-2,3-di(2-ethoxycarbonyl-vinyl)-7,8,17,18-tetraethylporphyrin32 The conditions used for the preparation of the porphyrin 30 were used for the condensation of the tripyrrane 28 (0.1 g, 0.12 mmol) with the pyrrole 14(0.04 g, 1 equiv.). Chromatography of the product on a silica gel column with CH,CI,-Et,O (1 00 :3, v/v) as eluent gave the pure porphyrin 32 (0.05 g, 49) (Found: C, 69.7; H, 7.3; N, 6.8. Calc. for C,,H,,N,O,: C, 70.41; H, 7.09; N, 6.84);dH(2O0 MHz, CDCI,) 10.25and 10.06 (4 H, 2 S, 4 H meso),9.28 (2 H, d, JHH 16, CHKHCO,), 7.03 (2 H, d, JHH 16, CHSHCO,), 4.53 (4 H, 9, CN,CH,), 4.30 (4 H, t, CH,CH,C02), 3.25 (4 H, t, CH,CH,CO,), 1.92 (12 H, t, 4 OCH,CH,), 1.53 and 1.19 (12 H, 2 t, 4 CH,CH,) and -3.63 (2 H, s, NH); Amax/nm 427 (E 146 SOO), 523 (6700), 567 (23 600), 584 (20 200) and 64 1 (I 600). 7,8-Di(2-ethoxycarbonylvinyl)-3,12-diethy1-2,I3-dimethylpor-phyrin 34 The conditions used for the preparation of porphyrin 30 were used for the reaction of the tripyrrane 33 (0.082 g, 0.14 mmol) with the pyrrole 14 (0.045 g, 1 equiv.) except that the reaction time was 42 h.Chromatography of the product on a silica gel column with CH,CI,-Et,O (1 00 :5; v/v) as eluent gave the pure porphyrin 34 (0.03 g, 33.5) (Found: C, 72.3; H, 6.6; N, 8.8. Calc. for C,,H3,N,O,~O.5H,O: C, 72.1; H, 6.55; N, 9.34); 6,(200 MHz, CDCI,) 10.11 and 10.0 (4 H, 2 s, H nzeso), 9.28 (2 H, S, H,), 9.22 (2 H, d, JHH 16, CH=), 7.01 (2 H, d, JHH 16,=CH), 4.55 (4 H, q, OCH,CH,), 4.09 (4 H, q, CH,CH,), 3.63 (6 H, s, CH,), 1.84 (6 H, t, OCH,CH3), 1.55 (6 H, t, CH,CII,) and -4.17 (2 H, s, NH); Amax/nm 422 (E 134 600), 518 (5600) 563 (I 8 800), 588 (16 000) and 630 (1900).References 1 P. Rothemund, J Am. Chem. Soc., 1935,57,2010;P. Rothemundand A. R. Menotti, J. Am. Chem. Soc., 1941,63,267. 2 J. S. Lindsey, H. C. Hsu and H. C. Schreiman, Tetruhedron Lett., 1986,27,4969;J. S. Lindseyand R. Wagner, J. Org. Chem., 1989,54, 828. 3 N. Ono, H. Kawamura, M. Bougauchi and K. Maruyama, Telruhedron,1990,46, 7483. 4 Y. Kuroda, H. Murase, Y.Suzuki and H. Ogoshi, TetruhedronLett., 1989,30,241 I. 5 H.Fischer and H. Orth, in Die Chemie des Pyrroles, Johnson ReprintCorporation,New York, 1968, vol 11, part I. 6 E. J. Tarlton, S. F. MacDonald and E. Baltazzi, J. Am. Chem. Soc , 1960, 82, 4389; G. P. Arsenault, E. Bullock and S. F. Macnonald, J. Am. Chem. Soc., 1960,82,4384. 7 K M. Smith, in Porphyrinsand Metalloporphyrins, ed. K. M. Smith, Elsevier, Amsterdam, Oxford, New York, 1975. 8 J. A. P. Batista De Almeida, G. W. Kenner, J. Rimmer and K. M. Smith, Tetruhedron, 1976, 32, 1793; K. M. Smith and G. W. Craig, J. Org. Chem., 1983,48,4302. 9 T. P. Wijesekera and D. Dolphin, Synlett, 1990,235. 10 A. Boudif and M. Momenteau,J. Chem.Sot,.,Chern. Comrnun., 1994, 2096. I1 S. Cadamuro, L. Degani, R. Fochi, A.Gatti and L. Piscopo, J. Chem. Soc., Perkin Truns. I, 1993, 2939. 12 R. A. Jones and G. P. Bean, in The Chemistry uf' Pyrroles, ed. R. A. Jones and G. P. Bean, Academic Press, London, New York, San Francisco, 1977. 13 A. R. Battersby, Ch. J. Dutton and Ch. J. R. Fookes, J. Chern. Soc., Perkin Truns. 1, 1988, 1569. 14 K. Olsson and P.-A. Pernemalm, Actu Chem. Scund., 1979, 125. 15 G. G. Kleispehn,J. Am. Chem. Soc., 1955.77, 1546. 16 F. Bellamy, P. Martz and J. Streith, Heterocycles, 1975, 3, 395; F. Rellamy and J. Streith, J. Chem. Rex, 1979 (M), 101, 17 M. J. Broadhust and R. Grigg, J. Chem. Soc. C, 1971, 3681. 18 K. Berlin and E. Breitmaier, Angew. Chem., Int. Ed. Engl., 1994, 33, 219. 19 V. J. Rauer, D. L. J. Clive, D. Dolphin, J.B. Paine 111, F. L. Harris, M. M. King, J. Loder, S.-W. C. Wang and R. B. Woodward, J. Am. Chern. Soc , 1983, 105, 6429. 20 J. L. Sessler, M. Cyr and A. K. Burell, Tetruhedrun, 1992, 48, 9661. 21 J. L,. Sessler,A. Mozaffari and M. R. Johnson, Orgunic Synth., 1991, 70, 68. 22 H. H. Inhoffen, J. H. Furhrop, H. Voigt and H. Brockmann, Liebigs Ann. Chem., 1966, 695, 133; M. Momenteau, J. Mispelter, B. Loock and J. M. Lhoste, Cun. J. Chem., 1978,56, 2598. J. Chem. SOC.,Perkin Trans. I, 1996 1241 23 A. N. Sagredos, Liebigs Ann. Chem., 1966,700,29;C.-B. Wang and 28 M. Drsquo;Ambrosio, C. Debitus, 0. Ribes, B. Richer, B. Richer de C. K. Chang, Synthesis, 1979, 548. 24 A. H. Jackson, K. R. N. Rao, N. S. Ooi and E. Adelakun, Tetrahedron Lett., 1984,25,6049; A. H. Jackson, K. R. N. Rao and E. Smeaton, Tetrahedron Lett., 1989,30, 2673. 25 J. L. Sessler, M. R. Johnson and V. Lynch, J. Org. Chern., 1987, 52, 4394; M. J. Broadbust and R. Grigg, J. Chew. Soc. C, 1971, 3681. 26 M. Momenteau, J. Mispelter, B. Loock and J.-M. Lhoste, J. Chem. Soc., Perkin Truns I, 1985, 221. 27 F.-P. Montforts, Angew. Chem., hit. Ed. Engl., 1982, 21, 214; F.-P. Montforts and U. M. Schwartz, Angew. Cliem., Int. Ed. Engl., 1985,24, 775. Forges and F. Pietra, Helv. Chim. Ada, 1989,72, 1451. 29 P. You-Hin and A. I. Scott, Tetrahedron Lett., 1991,32,4231. 30 K. M. Smith, Porphyrins and Metalloporphyrins, Elsevier, Amsterdam, 1975,p. 23. Paper 51065421 Received 4th October 1995 Accepled 27th December 1995 1242 J. Cheni. SOC.,Perkin Trans. I, 1996