A new synthesis of acyclic,-acetals 3 and,-acetals 5 has been devised by way of a trimethylsilyl trifluoromethanesulfonate promoted formal 2, 3-bond fragmentation of 4- heteroatom substituted azetidinones 1 and 4, respectively. This reaction proceeds by nucleophilic attack of a nitrile group of the solvent on the c