Structures and reactivities of benzo-1,2,3-dithiazolium salts and their selenium analogs

A number of benzo-1,2,3-dithiazolium chlorides (I) and their selenium analogs — benzo-1,2,3-thiaselenazolium, benzo-2,1,3-thiaselenazolium, and benzo-1,2,3-diselenazolium salts — were synthesized. The electronic structures and reactivities of the I cation and salts I–IV are discussed on the basis of a quantum-chemical calculation of cation I and the PMR spectra of salts I–IV. Successive substitution of the sulfur atoms in the I cation by selenium atoms, particularly in the 2 position, substantially increases the degree of transfer of positive charge to the condensed benzene ring. The trend of the nucleophilic reactivities of 6-methoxy derivatives of salts I–IV in the reaction with aromatic amines is the same as the trend of the degree of localization of the positive charge in the 6 position.