Synthesis of a Series of 2,3-Disubstituted 4 H -1,4-Benzothiazines and X-ray Crystal Structure of Ethyl 7-Chloro-3-Methyl-4 H -1,4-Benzothiazine-2-Carboxylate

The reaction between 2-aminobenzenethiol and ethyl acetoacetate is studied under a variety of conditions, and a procedure for the exclusive synthesis of 1,4-benzothiazines by the neat reaction of substituted aminothiols with β-ketoesters and β-dicarbonyl compounds in 85–96% yield is described. With microwave heating, even when both the reactants are solid, yields are high, reaction times brief, and work-up easy. A facile reaction is also observed even in a solid-state reaction. The molecular structure of ethyl 7-chloro-3-methyl-4H-1,4-benzothiazine-2-carboxylate (4d) was determined by single-crystal X-ray diffraction.