Syntheses and properties of novel cyclic sulfilimines, 2-azathiabenzene derivatives.

Novel cyclic sulfilimines (so-called azathiabenzenes), 2-methyl-1-aza-2-thianaphthalene (7) and 9-methyl-(14a) or 9-ethyl-10-aza-9-thiaphenanthrene (14b), were synthesized in high yields by deprotonation of the corresponding azasulfonium salts (6, 13a, 13b) with base. The ylidic properties of the azathiabenzenes were revealed by spectral and chemical evidence. The azathiabenzenes (14a, 14b) were easily oxidized with potassium permanganate to yield the corresponding azathiabenzene oxides (18a, 18b). Thermolysis of 14a in refluxing xylene afforded the ring-expanded product 7H-dibenzo [d, e] [1, 3] thiazepine (21), while 14b underwent β-elimination on refluxing in xylene to give 6H-dibenzo [c, e] [1, 2] thiazine (24). Reactions of the azathiabenzene derivatives with dimethyl acetylenedicarboxylate as an electrophile are also reported.