Synthesis, structure, and reactivity to nucleophiles of 3-benzylidene- and 3-ethylidene-2,3-dihydro-2-methyl-1,2-benzothiazin-4-one 1,1-dioxides

Abstract

A new approach to (Z)-3-benzylidene- and 3-ethylidene-2,3-dihydro-2-methyl-1,2-benzothiazin-4-one 1,1-dioxides (4) starting from the corresponding 3-acyl derivatives (1) is described. A hypothesis, based on ¹³C n.m.r. data, that products (4) may be considered as α,β-unsaturated carbonyl systems is confirmed experimentally by their chemical behaviour. Reaction with various nucleophiles such as hydrazine, sulphur ylides, and enamines leads to formation of polynuclear heterocyclic systems containing the 1,2-benzothiazine 1,1-dioxide skeleton.