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Preparation of New Nitrogen-Bridged Heterocycles. 29. Reinvestigation on the Dehydrogenation Reaction of 5,5a-Dihydropyrido[2,1- c ]thieno[3,2- e ][1,4]thiazine Derivatives

1992; Oxford University Press; Volume: 65; Issue: 5 Linguagem: Inglês

10.1246/bcsj.65.1244

1348-0634

Akikazu Kakehi, Suketaka Ito, Jun-ichi Hakui, Hiroaki Fukazawa,

Synthesis of heterocyclic compounds

Abstract Reactions of the title compounds with 2,3-dichloro-4,5-dicyano-p-benzoquinone were reinvestigated; it was found that the corresponding products were not the ring-contracted and rearranged thieno[2,3-b]indolizines, as described previously by us, but were ordinary dehydrogenated compounds, pyrido[2,1-c]thieno[3,2-e][1,4]thiazines. In contrast with pyrido[2,1-c]thieno[3,2-e][1,4]thiazine derivatives which have no substituent or only one methyl group on the pyridine ring, their 6,8-dimethyl compounds could be smoothly converted by keeping them at room temperature or heating their ethanolic solution to the corresponding desulfurized or rearranged 6,8-dimethylthieno[2,3-b]indolizine derivatives in moderately to good yields. The structures of these pyrido[2,1-c]thieno[3,2-e][1,4]thiazines and thieno[2,3-b]indolizines were assigned mainly based on elemental analyses, and spectral inspections; X-ray analyses for two compounds finally confirmed the former structure, pyrido[2,1-c]thieno[3,2-e][1,4]thiazine.