Mechanism of Z-Selective Allylic Functionalization via Thianthrenium Salts

A detailed mechanistic study of the Z-selective allylic functionalization via thianthrenium salts is presented. We have leveraged kinetic analysis and deuterium labeling to concretely determine each of the elementary steps involved and used computational methods to establish a high-resolution mechanistic model to rationalize the observed reactivity and selectivity. We find that the reaction proceeds via a rate- and stereodetermining allylic deprotonation of an alkenylthianthrenium species. The Z-configuration of the resultant allylic ylide is translated into the final Z-allylic amine product through a sequence of subsequent fast and irreversible steps: protonation to form a Z-allylic thianthrenium electrophile followed by regioselective substitution by the nucleophile. In the stereodetermining deprotonation step, computational studies have identified a series of stabilizing non-bonding interactions in the Z-alkene forming transition state that con-tribute to the observed stereoselectivity.