Staudinger reactions of unsymmetrical cyclic ketenes: a synthetically useful approach to spiro β-lactams and derivatives. Reaction mechanism and theoretical studies

Abstract

An efficient and operationally simple synthesis of tetrahydrofuran-derived spiro-β-lactams using the ketene–imine cycloaddition route is described. Also the preparation of spiro-N-sulfonyl-β-lactam derivatives, which are analogs of monobactams, is reported. As far as we know, this is the first time that an unsymmetrical cyclic ketene is used in a Staudinger-type reaction. The experimental evidence suggests the involvement of a ketene derived from the acyl chloride precursor in the reaction. High-level ab initio calculations have been performed in order to get insight into the electronic effects controlling the stereochemical outcome of the reactions.