J. CHEM. SOC. PERKIN TRANS. I 1995 Some chemistry of 4,5-dichloro-l,2,3-dithiazolium chloride and its derivatives Thierry Bessont and Charles W. Rees Department of Chemistry, Imperial College of Science, Technology and Medicine, London S W7 2A K UK 4,5-Dichloro- 1,2,3-dithiazoliurn chloride 1 reacts with fluoroanilines (see Table 1) to give the imino- dithiazoles 5 in very high yield. Thermolysis of the latter gave the corresponding 2-cyanobenzothiazoles 6 together, in some cases, with the cyanoimidoyl chlorides 7.This reaction sequence provides modest yields of 2-cyanobenzothiazoles from the corresponding aniline, in two steps. Treatment of the iminodithiazoles with m-chloroperbenzoic acid in dichloromethane at or below room temperature opened the heterocyclic ring to give the N-arylcyanothioformamides(e.g.8 -lo), except for the p-nitrophenyl compound which gave p-nitrophenyl isothiocyanate 14 in high yield. 4,5-Dichloro- 1,2,3-dithiazolium chloride 1, which is readily prepared from chloroacetonitrile and disulfur dichloride, reacts rapidly with anilines in the presence of pyridine to give very stable, pale yellow to orange, N-arylimines 2. Previous work also showed that imino compounds 2cyclised when vigorously heated to give sulfur, hydrogen chloride and 2-cyanobenzothiazoles3.2An electron-releasing group (R = rn-OMe) favoured formation of the benzothiazole 3 whilst a strongly electron-withdrawing group (R = m-or p-NOz) reduced the yield of 3 dramatically, in favour of the cyano- imidoyl chloride 4, which became the major product.2 2 3 4 We have now explored further this new method for con- verting anilines into 2-cyanobenzothiazoles and cyanoimidoyl chlorides in two simple steps, with particular reference to fluoroanilines.The benzothiazoles 3 could, presumably, be formed by an electrocyclisation and fragmentation process, as shown in Scheme 1. The sulfur atom is presumably not extruded as such CI Scheme 1 but in some bimolecular process, possibly involving the nitrile sulfide. Imidoyl chloride formation involves the loss of both t Present address: Laboratoire de Gknie Proteique et Cellulaire, Chimie Organique et Biocatalyse, PBles des Sciences et Technologies, Universite de La Rochelle, Avenue Marillac, F-17042, La Rochelle Cedex 1, France.sulfur atoms and this could possibly occur by their direct loss as S2 to form the nitrilium chloride shown (Scheme 2) which collapses to the observed product. ci Scheme 2 Apart from the inherent interest of fluorinated derivatives of compounds 3 and 4, it was felt that fluoro substituents, being small and electron-withdrawing, would throw light on the factors controlling the alternative pathways of Schemes 1 and 2. The monofluoroanilines and 2,4- and 3,4-difluoroanilines all reacted cleanly with 4,5-dichloro- 1,2,3-dithiazolium chloride 1 (1 equiv.) in dichloromethane at room temperature for 2 h, followed by addition of pyridine (2 equiv.), to give the appro- priate iminodithiazole, 5a-e, in very high yield (Table 1). These products when heated neat at 250°C for 1 min gave black, messy reactions which were even more complex when con- ducted in a solvent.However all resulted in cyclisation to the corresponding 2-cyanobenzothiazole 6a-f, usually in modest yield, whilst three (5c, d, e) also gave some imidoyl chloride, 7. With 5e both possible benzothiazoles (6eand 6f) were formed together with a comparable amount of the imidoyl chloride 7e (Table 1). In general, the fluorines appear not to be sufficiently electron-withdrawing for the imidoyl chlorides to become dominant, and this simple reaction sequence still provides an acceptable route to fluorinated 2-cyanobenzothiazoles. m-Chloroperbenzoic acid reactions In view of the high temperature required for rearrangement of the iminodithiazoles 5 into benzothiazoles 6 and imidoyl chlorides 7, we decided to attempt S-oxidation of the dithiazole ring in the expectation that the less aromatic system so formed would decompose at a lower temperature.N-(4-Chloro-W- 1,2,3-dithiazol- 5-ylidene)-4-met hoxyaniline 82 was treated with m-chloroperbenzoic acid (1.1 equiv.) in dichloromethane at -20 "C and at room temperature; the Table 1 Prep ofthe iminodithiazoles S J. CHEM. soc. PERKIN TRANS. I 1995 Preparation aration and thermolysis Thermolysis Starting amine Product Yield of product () Products Yield of products () 2-Fluoroaniline Sa 98 6a:7a 50:O 3-Fluoroaniline 5b 99 6ba:7b 34:O CFluoroaniline 5c 92 :7c 34:10 2,4-Difluoroaniline 5d 90 6d:7d 11:2 3,4-Difluoroaniline 5e 91 6eb:6fc:7e 22: 3 :20 '5-Fluorobenzothiazole-2carbonitrile.5,6-Difluorobenzothiazole-2-carbonitrile.'6,7-Difluorobenzothiazole-2-carbonitrile. CI r CI 1 Jn 11 10 product isolated after chromatography proved to be N-(4-methoxypheny1)cyanothioformamide 10, in yields of 32 and 65 respectively.By analogy with the same oxidation of a similar iminodithiazole where the S,,,-oxide was isolated, we assume that the oxide 9 was formed but was readily hydrolysed on work-up to give the ring-opened product 10. Similar oxidation of 8, but with excess of m-chloroperbenzoic acid (3 equiv.) in refluxing dichloromethane gave the thioamide derivative 11 (72), presumably by oxidative hydration of the cyano group in 10.In a separate experiment, compound 10was shown to be converted into 11 (80) by treatment with m- chloroperbenzoic acid (2 equiv.) in refluxing dichloromethane.This efficient oxidative hydration of the cyano group of the cyanothioformamide 10,without oxidation of the thioamide group, is worthy of further investigation. The 2-fluoro- 5a and 4-fluoro-phenyl iminodithiazoles 5c were similarly treated with m-chloroperbenzoic acid to give the corresponding cyanothioformamides in 59 and 37 yields, respectively. It was also shown, though by TLC evidence only, that all of the cyanothioformamides made in this work could be reconverted into the starting iminodithiazoles by treatment with sulfur dichloride in dichloromethane at room temperature Cwn.(1)l. SClz ArNwc'IUArNH-CS-CN CI 13 14 Experimental Mps were determined using a Kofler hot-stage apparatus and are uncorrected. IR spectra were recorded on Perkin-Elmer 1710 instrument. 'H NMR spectra were recorded on a JEOL GSX 270 spectrometer. I3C NMR spectra were recorded on a Bruker WM 250 operating at 63 MHz. J values in Hz. Mass spectra were recorded on a AE MS12 or a VG micromass 7070B mass spectrometer; M refers to the isotopomer with the most abundant isotopes (35CI and 32S).Elemental .microanalyses were carried out in the Department of Chemistry, Imperial College by the Organic Micro-Analytical Laboratory. Column chromatography was on silica gel (C60).Light petroleum refers to the fraction bp 40-60 "C. N-(CChloro-5H-1,2,3-ditbiazol-5-ylidene)anilinederivatives: general procedure To a solution of the substituted aniline (2.33 rnmol) in di- chloromethane (1 0 cm3) was added 4,Sdichloro- 1,2,3-dithia- zolium chloride 1 (2.33 mmol). The mixture was stirred at room temperature for 2 h after which pyridine (4.66 mmol) was added to it to give a red solution. This was stirred for a further 2 h, filtered and the product isolated by flash column chroma- tography with light petroleumaiethyl ether (7 :3) as eluent. N-(4-Chloro-SH-1,2,3-dithiazol-5-ylidene)-2-fluoroaniline 5a. Treatment of 2-fluoroaniline (0.26 g, 2.33 mmol) with 1(0.485 g, 2.33 mmol) and pyridine (0.387 cm3, 4.66 mmol) in di- chloromethane (10 cm3), followed by column chromatography gave the title compound 5a (0.567 g, 98) as yellow needles, mp 69 "C (from light petroleum-dichloromethane) (Found: M+, 245.9536.C8H4ClFN2S2 requires M 245.9488); v,,,-(CCl,)/cm-' 1698, 1654, 1606, 1582, 1488, 1453, 1271, 1252, 1215, 1198 and 1164; SH(270 MHz, CDCl,) 7.18-7.23 (4 H, m); m/z (240 "C) 246 (M+, 38), 185 (M+ -S,, 32), 147 (M+ -S,, Cl, 1 l), 121 (M+ -S,-N=C-CI, 22) and 64 (S2+,100). 4-(1) N-(CChloro-SH-l,2,3-dithiazol-5-ylidene~~fluoroaniline5b.MCPBA 12a, b 9,b a, Ar = 2-fluorophenyl; b, Ar = 4-fluorophenyl Replacement of the methoxy group in 8 by a nitro group led to a very different, and unexpected, product on similar oxidation with m-chloroperbenzoic acid (1.1 equiv.) in dichloro- methane at room temperature. p-Nitrophenyl isothiocyanate 14 was formed very cleanly (90).Possibly the S-oxide 13was formed, as before (cf. ref. 3), followed rapidly by fragmentation as shown. Treatment of 3-fluoroaniline (0.26 g, 2.33 mmol) with 1 (0.485 g, 2.33 mmol) and pyridine (0.387 cm3, 4.66 mmol) in dichloro- methane (10 cm3), followed by column chromatography gave the title compound 5b (0.570 g, 99) as a yellow gum (Found: M+, 245.9528. C,H,ClFN,S, requires M 245.9488); v,,,-(CClJcm-' 1693,1663,1582,1544,1479,1448,1262 and 1166; SH(27O MHz, CDCl,) 6.88-7.05 (1 H, m) and 7.37-7.46 (3 H, m); m/~(240 "C) 246 (M+, 3373, 185 (M+ -S,, 31), 147 (M+ -S,, Cl, 9), 121 (M' -S,-N=C-CI, 17) and 64 (S,', 100).N-(4-Chlor0-5H-l,2,3-dithiazol-5-ylidene)fluoroaniline 5c. Treatment of 4-fluoroaniline (0.26 g, 2.33 mmol) with 1(0.485 g, 2.33 mmol) and pyridine (0.387 cm3, 4.66 mmol) in dichloro- J. CHEM. SOC. PERKIN TRANS. 1 1995 methane (10 cm3), followed by column chromatography gave the title compound5c (0.553 g, 92) as yellow needles, mp 53 "C (fromlight petroleum-dichloromethane) (Found: M ',245.9536. C,H,ClFN,S, requires kf 245.9488); v,,,(CC~,)/cm-' 1694, 1664, 1606, 1588,1498, 1464,1289,1232, 1210, 1161 and 1164; 6,(270MHz, CDCl,)7.1 1-7.25 (4H,m);m/z(220 "C)246(M+, 40), 185 (M+ -S2, 33), 147 (M' -S,, Cl, 15), 121 (M' -S,-N=C-Cl, 45) and 64 (S,', 100). N-(4-Chloro-SH-1,2,3-di thiazol-5-ylidene)-2,4difluoroaniline 5d. Treatment of 2,4-difluoroaniline (0.30 g, 2.33 mmol) with 1 (0.485 g, 2.33 mmol) and pyridine (0.387 cm', 4.66 mmol) in dichloromethane (1 0 cm3), followed by column chromatogra- phy gave the title compound5d (0.554 g, 90) as yellow needles, mp 92 "C (from light petroleum-dichloromethane) (Found: C, 36.3; H, 1.1; N, 10.5.C8H,C1F,N,S, requires C, 36.3; H, 1.1; N, 10.6); v,,,(CCI,)/cm-' 1591, 1552, 1506, 1265 and 1210; 6,(270 MHz, CDCl,) 6.93-7.01 (2 H, m) and 7.15-7.24 (1 H, m); m/z 264 (M', 24), 203 (M' -Cl, CN, 21), 171 (M' -Cl, CN, S, 38), 139 (M+ -Cl, CN, SJ, 27), 125 (CICNS,', 7) 113 (M' -Cl, CN, S,, 01, 24) and 64 (S,', 100). N(4-C hloro-5H- 1,2,3di thiazol-5-ylidene)-3,4difluoroaniline 5e. Treatment of 3,4-difluoroaniline (0.30 g, 2.33 mmol) with 1 (0.485 g, 2.33 mmol) and pyridine (0.387 cm3, 4.66 mmol), followed by column chromatography gave the title compound5e (0.530g, 91 )as yellow needles, mp 55 "C (fromlight petroleum- dichloromethane) (Found: C, 36.1; H, 1.0; N, 10.5.C,H,Cl- F,N,S, requiresc, 36.3; H, 1.1; N, 10.6); v,,,(CCl,)/cm-' 1591, 1552, 1506, 1425, 1294, 1265 and 1210; 6,(270 MHz, CDCl,) 6.9c7.30 (3 H, m); rn/z 264 (M+, 30),203 (M+ -Cl, CN, 20), 171 (M+ -Cl,CN, S,23), 139(M' -Cl,CN, SJ, 17), +125 (ClCNS, + , lo), 1 13 (M -Cl, CN, S,, 01, 34) and 64 (S, +,100). Benzothiazole-2-carbonitrilederivatives: general procedure N-(4-Chloro-SH-1,2,3-dithiazo1-5-ylidene)anilineswere heated under nitrogen at 250 "C for 1 min. The product was isolated by flash column chromatography.Light petroleum-diethyl ether eluted sulfur and then the following products. 4-Fluorobenzothiazole-2-carbonitrile6a. Thermolysis of 5a (0.1 g, 0.406 mmol) and purification by column chromatography with light petroleum-diethyl ether (6 :4) as eluent afforded the title compound 6a (0.036 g, 50) as pale yellow needles, mp 1 14 "C (from light petroleumdichloromethane) (Found: M+, 178.0008. C,H,FN,S requires M, 178.0001); ~,,,(CC~,)/crn-' 2235 (CN), 1624, 1599, 1562,1474, 1445, 1325, 1310, 1276 and 1253; 6,(270 MHz, CDCl,) 7.35 (1 H, ddd, J0.98, 7.99, 9.02), 7.62(1 H,dd,J4.64,8.15)and7.76(1H,d,J8.30);m/z(22O0C) 178 (M', 100)and 126 (M' -m=C-CN, 20). 5-Fluorobenzothiazole-2-carbonitrile6b.Thermolysis of 5b (0.1 g, 0.406 mmol) and purification by column chroma- tography with light petroleum-diethyl ether (6:4) as eluent afforded the title compound 6b (0.024 g, 34) as pale yellow needles, mp 1 10 "C (from light petroleum-dichloromethane) (Found: M', 178.0013. C,H,FN,S requires M, 178.0001); ~,,,(CC1~)/cm-' 2233 (CN), 1611, 1585, 1559, 1472, 1320, 1247 and 1204; 6,(270 MHz, CDCl,) 7.42 (1 H, dt, J 2.44, 8.55) and 7.82-7.97 (2 H, m); m/z (220°C) 178 (M', 100) and 126 (M' -N=C-CN,40). 6-Fluorobenzothiazole-2-carbonitrile6c. Thermolysis of 5c (0.1g, 0.406 mmol) and purification by column chromatography with light petroleum-diethyl ether (8 :2) as eluent afforded the title compound 6c (0.024 g, 34) as pale yellow needles, mp 112 "C (from light petroleumdichloromethane) (Found: M', 178.0008.C,H,FN,S requires M, 178.0001); v,,,(CCl,)/cm~' 2233 (CN), 1624,1599,1562,1473,1445,1412,1325,1310,1276 and 1253; 6,(270 MHz, CDCl,) 7.41 (1 H, dt, J2.69,8.89), 7.66 (1 H, dd, J 2.57, 7.68) and 8.20 (1 H, q, J 4.50); m/z (220 "C) 178 (M', 100) and 126 (M' -m=C-CN, 35) and N-chlorocyanomethylidene4fluoroaniline 7c (0.008 g, 10) as a colourless oil; v,,,,,(CCl,)/~m-~ 2241, 1578, 1510, 1430 and 1294; 6,(270 MHz, CDCl,) 7.12-7.18 (2 H, m) and 7.25-7.32 (2 H, m).4,6-Difluorobenzothiazole-Z-carbonitrile6d. Thermolysis of 5d (0.1 g, 0.406 mmol) followed by column chromatography with light petroleum-diethyl ether (8 :2) as eluent afforded the title compound 6d (0.012 g, 11) as pale yellow needles, mp 154 "C (from light petroleum-dichloromethane); vmax(CC14)/ cm-' 2238 (CN), 1580,1498, 1445,1422,1298 and 1266; 6,(270 MHz, CDCI,) 7.20 (1 H, dt, J2.32, 6.94) and 7.49 (1 H, dd, J 1.22, 7.34); m/z (24OOC) 196 (M+, 100) and 144 (M' -WS-CN, 26) and N-chlorocyanomethylidene-2,Cdifluoro-aniline 7d as a colourless oil (0.004 g, 2); v,,,(CCl,)/cm-' 2243, 1647, 1606, 1578, 1510, 1429, 1294, 1259 and 1210; m/z (220°C) 200 (M', 26), 165 (M' -C1, 77) and 113 (M' -PS-CN, Cl, 100).5,6-Difluorobenzothiazole-~rbo~~le6e.Thermol ysis of 5e (0.1 g, 0.406 mmol) and purification by column chromatography with light petroleum-diethyl ether (8 :2) as eluent afforded the title compound 6e (0.048 g, 22) as pale yellow needles, mp 124 "C (from light petroleum-dichloromethane) (Found: M ', 195.9929.C8H2F2N2S requires M, 195.9906); v,,,(CCl,)/cm-l 2237 (CN), 1570,1489,1454,1422,1299,1266 and 12 12; 6,(270 MHz, CDCl,) 7.35-7.81 (1 H, m) and 8.01-8.05 (1 H, m); m/z (220 "C) 196 (M+, 100) and 144 (M' -m=C-CN, 33), 6,7-difluorobenzothiazole-Zcarbonitrile6f (0.005 g, 3) as a pale yellow solid, mp 86 "C (from light petroleum-dichloromethane) (Found: M+, 195.9922. C,H,F,N,S requires M, 195.9906); v,,,(CCl,)/cm~' 2237 (CN), 1579, 1500, 1426, 1291 and 1266; 6,(270 MHz, CDCl,) 6.94-7.01 (1 H, m) and 7.18-7.27 (I H, m); m/z (22OOC) 196 (M', loo), 144 (M' -m=C-CN, 48), and N-chlorocyanomethylidene-3,4-difluoroaniline7e (0.045 g, 20) as a colourless oil; v,,,(CCl,)/cm-' 2243,1647,1606,1578, 1510, 1429, 1294, 1259 and 1213; 6,(270 MHz, CDCl,) 6.94- 7.02 (1 H, m), 7.13-7.27 (1 H, m) and 7.47-7.52 (1 H, m); m/z (220°C) 200 (M', 26), 165 (M' -Cl, 77) and 113 (M' -PS-CN, Cl, 100).N-(4-Methoxyphenyl)cyanothioforrnamide 10. To a cooled (0 "C) solution of the iminodithiazole 8 (0.1 g, 0.39 mmol) in dichloromethane (10 cm3)was added rn-chloroperbenzoic acid (0.075 g, 0.43 mmol). The mixture was stirred at 0 "C for 3 h then warmed to room temperature for 15 h. Purification by column chromatography with light petroleum4iethyl ether (7 :3) as eluent afforded the title compound 10 as an orange solid (0.06 g, 81), mp 112 "C (from light petroleum-dichloromethane) (Found: M+, 192.0378. C9H8N,0S requires M, 192.0357); v,,,(CCl,)/cm-' 2229 (CN), 1608, 15 10, 1462, 1441, 1427, 1305 and 1255; 6,(270 MHz, CDCl,) 3.85 (3 H, s, OCH,) 6.88-7.01 (2 H, m), 7.31 (1 H, t, J 7.40), 7.73 (1 H, d, J 7.40) and 9.40 (I H, s, NH); rn/z 192 (M', 21), 165 (M+ -CN, HI, loo), 150 (M' -CN, H, Me, 70) and 122 (M' -s--C-CN, 51).N-Carbamoylthiocarbonyl41nethoxyaniline11. To a solution of the iminodithiazole 8 (0.1 g, 0.39 mmol) in dichloromethane (1 0 cm3) was added m-chloroperbenzoic acid (0.2 g, 1.16 mmol). The mixture was stirred at reflux for 15 h after which puri- fication by column chromatography with light petroleum- diethyl ether (8:2) as eluent afforded the title compound 11 as a yellow solid (0.042 g, 72), mp 186 "C (from light petroleumdichloromethane) (Found: M , 2 10.048 1.C9H 1+ N,O,S requires M, 210.0462); ~,,,(CCl,)/cm 1623, 1601, 1588, 1517, 1446, 1395, 1343, 1312 and 1277; 6,(270 MHz, CDCl,) 3.95 (3 H, s, OCH,), 7.13 (2 H, d, J 9.04), 7.19 (1 H, s, NH), 8.21 (2 H, d, J 9.04) and 8.28 (2 H, s, NH,); m/z 210 (M' , 98), 166 (M' -CONHJ, loo), 135 (M+ -CONH,, OMe, 9) and 118 (M+ -CONH,, S, 4). N-(Nuorophenyl)cyanothioformamides: general procedure To a cooled (0 "C) solution of the iminodithiazoles 5a and 5c (0.1 g, 0.405 mmol) in dichloromethane (10 cm3)was added m-chloroperbenzoic acid (0.07 g, 0.405 mmol). The mixture was stirred at 0°C for 30 min then allowed to warm to room temperature over 15 h. Column chromatography with light petroleum-diethyl ether (6 :4) as eluent afforded the following compounds.N-(2-Fluorophenyl)cyanothioformamide 12a. An orange solid (0.043 g, 5973, mp 81 "C (from light petroleum-dichloro- methane) (Found: C, 53.0; H, 2.9; N, 15.5. C,H5FN2S requires C, 53.3; H, 2.8; N, 15.5); v,,,(CCl,)/cm-' 2306(CN), 1710,1599, 1521,1505,1487,1461,1422,1383,1266and 1110;6,(270MHZ, CDC1,) 7.18-7.45 (2 H, m), 7.67 (1 H, t, J 8.19), 8.50 (1 H, t, J 8.19) and 9.34 (1 H, s, NH); m/z (200 "C) 180 (M+, 6), 153 (M+ -CN, HI, 100) and 95 (M+ -HN-C(S)-CN, 31). N-(4FluorophenyI)cyanothioformamide12b. An orange solid (0.027 g, 3779, mp 97 "C (from light petroleum-dichloro- methane) (Found: C, 53.0; H, 2.9; N, 15.6. C,H5FN,S requires C, 53.3; H, 2.8; N, 15.5); v,,,(CCl,)/cm-' 2306 (CN), 1606,1510, 1422, 1386 and 1113; 6,(270 MHz, CDC1,) 7.1 1-7.21 (2 H, m), 7.31-7.41 (1 H, m), 7.84-7.99 (1 H, m) and 9.36 (1 H, s, NH); m/z (200 "C) 180 (M', 673,153 (M' -CN, HI, 100) and 95 (M' -HN-C(S)-CN), 65).4Nitrophenyl isothiocyanate 14 To a cooled (0 "C) solution of N-(4-chloro-5H-l,2,3-dithiazole-5-ylidene-4-nitroaniline (0.1 g, 0.37 mmol) in dichlorometh- ane (10 cm3) was added rn-chloroperbenzoic acid (0.069 g, 0.4 mmol). The mixture was stirred at 0 OC for 30 min then allowed to warm to room temperature over 15 h. Purification by column J. CHEM. SOC. PERKIN TRANS. 1 1995 chromatography with light petroleum4iethyl ether (6 :4) as eluent afforded the title compound 14 (0.064 g, 90) as an orange solid, mp 118 "C (from light petroleum-dichlorometh- ane) (lit.,5 mp 112-1 13 "C); v,,,(CCl,)/cm-' 161 8, 1596, 1559, 15 19,1422, 1342 and 1266; 6,(270 MHz, CDCl,) 8.07 (2 H, d, J 4.93) and 8.33 (2 H, d, J4.75); m/z 180 (M', 9473, 164 (M+ -0,24), 150 (M+ -NO, 27), 134 (M+ -NO,, 62), 107 (M+ -NCS, 01, 15), 90 (M' -NCS, O,, 60) and 76 (M' -NCS, NO,, 12). Acknowledgements We thank MDL Information Systems (UK) Ltd and the French Ministkre de la Recherche et de 1'Espace for financial support, the Wolfson Foundation for establishing the Wolfson Centre for Organic Chemistry in Medical Science, and Mr K. Emayan for assistance and helpful discussions. References 1 R. Appel, H. Janssen, M. Siray and F. Knoch, Chem. Ber., 1985,118, 1632. 2 R. F. English, PhD Thesis, University of London, 1989; C. W. Rees, J. Heterocycl. Chem., 1992,29, 639. 3 P. J. Dunn and C. W. Rees, J. Chem. SOC.,Perkin Trans. I, 1989,2489. 4 cf. J. E. Moore, US Pat., 4 059 590, 1977 (Chem. Abstr., 1978, 88, 50874). 5 P. Jacobson and J. Klein, Chem. Ber., 1893,26,2363. Paper 5/01 528F Received 13th March 1995 Accepted 20th March 1995
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