Organic heterocyclothiazenes. Part 10. Reactions of the tetrathiatriazepinium cation with acetylideanions; new mesoionic thiones

Abstract

The reaction of tetrathiatriazepinium chloride (thiotrithiazyl chloride)(1) with phenylacetylene gives several products including the isomeric 1,3,2- and 1,2,3-dithiazole imines (3a) and (5). The salt (1) reacts much faster with phenylacetylide anions but again the reaction is complex and the products include S₄N₄, the imine (3a), and 5-phenyl-1,3,2-dithiazole-4-thione (7a), a new mesoionic thione. Analogous products are formed from other acetylides, together with the isomeric 4-t-butyl-1,2,3-dithiazole-5-thione (8) from t-butylacetylide. Mechanisms for the formation of (7)(Scheme 3) and (8) are proposed. 5-Phenyl-1,3,2-dithiazole-4-thione (7a) is converted into the 4-one (11) with lead tetraacetate, the sulphine (16) with m-chloroperbenzoic acid, and the phenylimine (17) with iodomethane followed by aniline. 5-Phenyl-1,3,2-thiazol-4-one (11) is very light sensitive and photoisomerises to 4phenyl-1,2,3-thiazole-5-one (12), probably via the bicyclic intermediate (13). Unlike the 1,3,2-imine (3a), the 1,2,3-imine (5) is oxidised by m-chloroperbenzoic acid in the dithiazole ring, to give (6), and this difference is rationalised in terms of electron delocalisation in the two systems.