Preparation of Pyrroles from Pyroglutamic Acid Derivatives

References

• Fasseur , D. , Rigo , B. , Debacker , M. and Couturier , D. Tetrahedron Lett. , to be published
   Google Scholar
• We have observed that by heating 3a in MeOH, 3b was obtained, even when no acidic catalyst was added
   Google Scholar
• Shono , T. 1984 . Tetrahedron , 40 : 811 Horikawa, H., Iwasaki, T., Matsumoto, K. and Miyoshi, M., J. Org. Chem., 1978, 43, 335; Iwasaki, T., Horikawa, H. and Matsumoto, K., Bull. Chem. Soc. Jpn., 1979, 52, 826
   Web of Science ®Google Scholar
• Hubert , J. C. , Wijnberg , J. B. P. A. and Speckamp , W. N. 1975 . Tetrahedron , 31 : 1437 Shono, T., Matsumura, Y., Tsubata, K., Sugihara, Y., Yamame, S., Kanazawa, T., and Aoki, T., J. Am. Chem. Soc. 1982, 104, 6697
   Web of Science ®Google Scholar
• Hart , D. J. 1981 . J. Org. Chem. , 46 : 367
   Web of Science ®Google Scholar
• By analogy with N-acyliminium ions, the reactions 3 → 2 → 9 are thought to be reversible.7
   Google Scholar
• Speckamp , W. N. and Hiemstra , H. 1985 . Tetrahedron , 41 : 4367
   Web of Science ®Google Scholar
• The poorer results obtained by using formic acid instead of acetic acid, supports also this mechanism, because formyl anion is less basic than acetic anion
   Google Scholar
• Wang , P. C. 1985 . Heterocycles , 23 : 2237 Acetal 3b can react by a substitution reaction with acetic acid; acetal 3a can react by an etherification reaction with acetic anhydride. In both cases, acetic anhydride prevents the formation of water from the leaving group, and thus avoids the decomposition of 4a to 4b. For related MeOH eliminations by using AC2O, see, Wang, P. C., ibid., 1985, 23, 3041
   Google Scholar
• Speckamp , W. N. and De Boer , J. J. J. 1983 . Recl. Trav. Chim. Pays-Bas , 102 : 405 Nagasaka, T., Abe, M., Ozawa, N. and Kosugi, Y., Heterocycles, 1983, 20, 985
   Google Scholar
• Procedures and data:, 4b from 3a:, A mixture of 6a (20 g, 102 mmol), pyridine (13.6 ml), acetic anhydride (11.1 ml) and acetic acid was heated at reflux for 30 mn (100% NMR yield of 4a); Water (2.8 ml) was added and the reflux was continued for 5 hours. After treatment, the yield of 4b was 73%, bp 55° (0.05 mmHg). 1H NMR (60 MHz, CDCl3) d 3.60 (s, 3H), 3.66 (s, 2H), 5.95–6.20 (m, 2H), 6.62 (t, J = 2.3 Hz, 1 H)., 4a from 3b:, A mixture of 6b (20 g, 95 mmol), acetic acid (5.7 ml) and acetic anhydride (28.3ml), was heated at reflux for 2h30. Water and CH2Cl2 were added, the organic phase was washed with a saturated aqueous NaHCO3 solution, dried (Na2SO4) and distilled, bp 95° (0.1 mmHg), 71%., 1H NMR (60 MHz, CDCl3) d 3.62 (s, 3H), 3.76 (S, 3H), 4.81 (S, 1H), 5.95–6.15 (m, 1H), 6.15–6.30 (m, 1H), 6.60 (t, J = 2.2 Hz, 1H)., 4d: bp 135° (0.2 mmHg), 63% from 6a., 1H NMR (60 MHz, CDCl3) d 3.54 (s, 5H), 5.20–6.20 (b, 2H), 6.05–6.10 (m, 2H), 6.60 (t, J = 2.2 Hz), 1H
   Google Scholar