Reaction of Thiopivalophenones with Benzyne. Formation of 2H-Benzo[b]thietes

Reaction of thiopivalophenone with phenyl[2-(trimethylsilyl)phenyl]iodonium trifluoromethanesulfonate in the presence of tetrabutylammonium fluoride afforded the corresponding [2+2] cycloadduct, 2-tert-butyl-2-p-tolyl-2H-benzo[b]thiete, in 58% yield. On the other hand, reaction of thiopivalophenone with benzenediazonium 2-carboxylate gave 2-tert-butyl-2-p-tolyl-benzo[d][3,1]oxathiane-6-one in 82% yield. The difference in the reactivity might be owing to the leaving group ability.