SYNTHESIS OF 3,1-BENZOTHIAZINES FROM 2-ALKENYL- AND 2-ALKYNYLANILIDES AND LAWESSON REAGENT

Reaction of 2-vinylacetanilide with P4S10 gave 2-vinylthioacetanilide, whereas reaction of 2-vinylacetanilide with Lawesson reagent (LR) afforded 2,4-dimethyl-4H-3,1-benzothiazine in 62% yield. Reaction of 2-alkynylanilides with LR gave 4-exomethylene-4H-3,1-benzothiazines in good yields.