Studies on the Mechanism of Styrene Elimination from Sulfilimines: Hammett and Kinetic Isotope Effect Analysis and Computation

Abstract

N-Acylsulfenamides can be efficiently prepared by a one-pot synthetic sequence via S-functionalization of N-acyl S-phenethyl sulfenamides, utilizing diverse (hetero)aryl and alkenyl iodide and boronic acid inputs to give sulfilimines that then undergo concerted elimination of styrene. To probe the mechanism of styrene elimination from sulfilimines, a Hammett analysis was performed with substituents placed on both the S-aryl and S-phenethyl groups. Positive Hammett ρ values established a modest negative charge build up at both positions, with greater charge buildup at the phenethyl site. A primary isotope effect of 5.4 at the benzyl site was also determined through the synthesis of a deuterated sulfilimine and is consistent with significant C–H bond cleavage at the benzylic carbon in the transition state. Computation provides strong support for the proposed concerted elimination mechanism.