Chemistry of silyl thioketones. Part 3. Cycloaddition reactions with heterodienes (α-nitrosostyrene and ketene imines)

Abstract

Silylated heterocycles viz: 4H-1,5,2-oxathiazines (4a, b), 4H-3,1 -benzothiazines (8), (9), 5,6-dihydro-2H-thiopyrans (11a, b), were obtained in reactions of silyl thioketones (1a, b) with α-nitrosostyrene (2), dimethylketene N-p-tolylimine (3a), and methylvinylketene N-p-tolylimine (3b) respectively.

In the reaction of (1a, b) with (3b), in which a heterodiene and a homodiene system is present, a variation in the periselectivity is found with respect to diaryl thioketones. Desilylation of trimethylsilyl adducts was also investigated. In the case of (4a), desilylation affords α-aminostyryl benzoyl sulphide (5) whereas the adducts (9) and (11a) give, in good yield, the corresponding hydrogen-substituted heterocycles (10) and (12) respectively.