Base-promoted cyclisation of hydrazonoyl chlorides bearing an alkynylsulphonyl group

Abstract

Treatment of the hydrazonoyl chlorides (1) and (3) with triethylamine in boiling benzene gives a pyrazolo[5,1-c][1,4]benzothiazine S,S-dioxide (12) arising from intramolecular cycloaddition of a nitrilimine intermediate, as well as 1,4-benzothiazine S,S-dioxides (15) and (16) due to intramolecular Michael-type addition of an aza-anion. The latter pathway is the exclusive one in acetonitrile at room temperature.