Synthesis of benzo[b][1,4]thiazines by hetero Diels-Alder reaction of o-iminothioquinones

The regioselective sulfenylation of N-sulfonylanilines with phthalimidesulfenyl chloride afforded the precursors of transient o-iminothioquinones obtained very easily under mild reaction conditions. These species are efficient electron-poor dienes able to react with several electron-rich alkenes to give, with complete control of the regiochemistry, benzo[b][1,4]thiazine cycloadducts