Trimethylsilyl triflate promotes Ferrier−Petasis rearrangement of 4-(vinyloxy)-, 4-(propenyloxy)-, and 4-(isopropenyloxy)azetidin-2-ones to corresponding 4-(carbonylmethyl)azetidin-2-ones. The latter compounds may serve as attractive intermediates in the synthesis of carbapenem antibiotics. To illustrate the potential of this reaction, selected rearrangement products have been transformed into carbapenams