Synthesis of Benzothiazines via an Intramolecular Thioamide S-Michael Addition

Significance

A synthesis of 4H-3,1-benzothia­zines has been demonstrated through a simple three-step procedure that consists of sequential N-acylation and Mizoroki-Heck reaction of 2-iodoaniline. Reaction of the intermediate with Lawesson’s reagent leads to intramolecular cyclization of the resulting thioamide by an unusual intramolecular S-Michael addition. In the case of perfluoroalkyl derivative (R^¹ = C₃F₇, R^² = CO₂Et), the reaction was found to be very sluggish (high temperature, excess Lawesson’s reagent and three days of reaction time) and led to dithionated product [R^² = C(S)OEt] in low yield.