Benzylic Newman-Kwart rearrangement of O-azidobenzyl thiocarbamates triggered by phosphines: pseudopericyclic [1,3] shifts via uncoupled concerted mechanisms

A series of O-(o- and p-azido)benzyl thiocarbamates smoothly rearranged in the course of Staudinger imination reactions with tertiary phosphines, giving rise to the respective S-(o- and p-phosphinimino)benzyl thiocarbamates as a result of an oxygen to sulfur migration of the functionalized benzyl group. By contrary, their m-azido isomers did not rearrange under similar conditions. Computational investigations using DFT methods revealed the uncoupled concerted mechanisms of these 1,3-benzyl shifts via polar transition states with pseudopericyclic orbital topologies, with the benzyl group migrating in the plane of the thiocarbamate fragment.