Z-Selective alpha-Arylation of alpha,beta-Unsaturated Nitriles via [3,3]-Sigmatropic Rearrangement

摘要

The Morita-Baylis-Hillman (MBH) reaction and [3, 3]-sigmatropic rearrangement are two paradigms in organic synthesis. We have merged the two types of reactions to achieve [3,3]-rearrangement of aryl sulfoxides with alpha,beta-unsaturated nitriles. The reaction was achieved by sequentially treating both coupling partners with electrophilic activator (Tf2O) and base, offering an effective approach to prepare synthetically versatile alpha-aryl alpha,beta-unsaturated nitriles with Z-selectivity through direct alpha-C-H arylation of unmodified alpha,beta-unsaturated nitriles. The control experiments and DFT calculations support a four-stage reaction sequence, including the assembly of Tf2O activated aryl sulfoxide with alpha,beta-unsaturated nitrile, MBH-like Lewis base addition, [3,3]-rearrangement, and E1cB-elimination. Among these stages, the Lewis base addition is diastereoselective and E1cB-elimination is cis-selective, which could account for the remarkable Z-selectivity of the reaction.