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Communication | Special issue | Vol 17, No. 1, 1982, pp.191-
Published online, 1st January, 1970
DOI: 10.3987/S-1982-01-0191
Acid-induced Cyclization of 3-Benzyl-3,4-dihydro-2-pyrazinones:synthesis of 1,2,3,4,-5,6-Hexahydro-1,5-imino-3-benzazocine Derivatives

Hideshi Kurihara and Hiroshi Mishima*

*Central Research Laboratories, Sankyo Co.,Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140 Japan


3,4-Dihydro-4-ethoxycarbonyl-2-pyrazinones (3), which can be prepared by cyclization of dipeptide aldehyde acetals (2) in the presence of a catalytic amount of proton acid, were shown to be useful intermediates for the preparation of complex heterocycles by acid-induced C-C bond formation. The acid-induced intramolecular cyclization of the intermediates (3) afforded regioselectively 1,5-ethoxycarbonylimino-3-methyl-1,2,5,6-tetrahydro-3-benzazocin-4(3H)-one (4) in quantitative yield. The structural characterization of the cyclization product (4) and its derivatives (6 and 7) was carried out mainly by the analysis of the NMR spectra.