Synthesis of new pentacyclic diquinothiazines

Abstract

Abstractmagnified imageReactions of 2,2′‐dichloro‐3,3′‐diquinolinyl sulfide 1 with ammonia derivatives and various primary alkylamines and arylamines proceeded as a thiazine ring closure to form linear annulated pentacyclic 6H‐diquinothiazine 2H and 6‐substituted derivatives 2 with alkyl, alkylaryl, aryl and heteroaryl substituents in moderate to good yields. Reaction with 2‐chloroethylamine did not stop at the formation of half‐mustard derivative 2k but ran to ethylenediquinothiazinium salt 11. 6H‐Diquinothiazine 2H was N‐alkylated and N‐arylated to give 6‐substituted derivatives 2. The crucial substrate 1 was obtained from other heteropentacenes 3 and 4 via 1,4‐dithiin ring opening and further transformations. X‐ray analysis of p‐nitrophenyldiquinothiazine 2i revealed unexpected planar thiazine ring.