An unprecedented cleavage of the β-lactam ring: a novel synthesis of acyclic N,O- and N,S-acetals

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Abstract
A new synthesis of acyclic N,O-acetals 3 and N,S-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 cation intermediate A. However, when there is a second nucleophile such as azidotrimethylsilane in the reaction system, no solvent attack occurs but, rather, the second nucleophile attacks the intermediate to form novel α-azido sulfides 6.