Abstract: Treatment of oxazolium salts with phenylsilane/CsF generates 4-oxazolines 14 in situ. Provided that R,= H or alkoxy, ring opening to azomethine ylides 15 occurs spontaneously and [2+ 31 cycloadducts are obtained in the presence of acrylate, N- phenylmaleimide, propiolate, or dimethyl acetylenedicarboxylate (DMAD) dipolarophiles. If R,= alkyl or aryl, the initially formed 4-oxazoline resists ring opening, probably due to ...