Synthesis of Quinobenzo-1,4-thiazines from Diquino-1,4-dithiin and 2,2’-Dichloro-3,3’-diquinolinyl Disulfide

Abstract

Synthesis of new type of tetracyclic azaphenothiazines, 6-, 8-, 9- and 10-substituted quinobenzo-1,4-thiazines (benzo[b]-1-azaphenothiazines) (5) and (10), has been worked out from diquino-1,4-dithiin (5,12-diaza-6,13-dithiapentacene) (2) as fusion reactions with aniline hydrochlorides (8)·HCl via the 1,4-dithiin ring opening and the 1,4-thiazine ring closure. The better results were obtained when 2,2'-dichloro-3,3'-diquinolinyl disulfide (9) reacted with anilines (8) in MEDG. Selected 6H-quinobenzo-1,4-thiazines (5a) (5c) and (5g) were transformed into 6-alkyl derivatives (10a-10n) by N-alkylation with alkyl halides. Homonuclear NOE experiment for the 6-methyl derivative (10a) confirmed the product structure as quino[3,2-b]benzo[1,4]thiazine.