4H-1,4-THIAZINES AND 2H-1,4-THIAZINES FROM 2-(DIALKYLHYDRAZONO)THIOACETOPHENONES

2-(Dialkylhydrazono)thioacetophenones 1 react with N-phenylmaleimide and lead via [4 + 21 cycloaddition to 4-amino-3,4-dihydro-2H-1,4-thiazines 2 which are easily converted into 4H-1,4-thiazines 3. Reaction with 1,4-naphthoquinone leads directly to 4H-1,4-thiazines 4. Acetylenic dienophiles as methyl propiolate or dimethyl acetylenedicarboxylate authorize synthesis of 2-amino-2H-1,4-thiazines 5 after amino group transposition. Reaction with diethyl azodicarboxylate gives rise to new hydrazonothioacetophenones 6, rather unstable, which can undergo [4 + 2] cycloaddition with methyl acrylate leading to 3,4-dihydro-2H-1,4-thiazines 7.