Synthesis and properties of a novel cyclic sulfilimine, 2-methyl-2,4,1-benzodithiazin-2-ium-1-ide

A novel cyclic sulfilimine, 2-methyl-2,4,1-benzodithiazin-2-ium-1-ide ( 4 ) was synthesized by deprotonation of the corresponding azasulfonium salt ( 3 ) with base. The compound 4 was oxidized with potassium permanganate to afford the sulfoximine 5 , exclusively. On refluxing in several solvents, compound 4 underwent a ring contraction to afford benzothiazole ( 8 ) via the 1,2-imino shift. The reaction of 4 with a variety of electrophiles, such as dialkyl acetylenedicarboxylate, acylating agents, diphenylcyclopropenone, and phenyl isocyanate, afforded ringopened adducts. Synthetic approaches to cyclic disulfonium ylides are also described.