Z-Selective α-Arylation of α,β-Unsaturated Nitriles via [3,3]-Sigmatropic Rearrangement.

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 α,β-unsaturated nitriles. The reaction was achieved by sequentially treating both coupling partners with electrophilic activator (Tf2 O) and base, offering an effective approach to prepare synthetically versatile α-aryl α,β-unsaturated nitriles with Z-selectivity through direct α-C-H arylation of unmodified α,β-unsaturated nitriles. The control experiments and DFT calculations support a four-stage reaction sequence, including the assembly of Tf2 O activated aryl sulfoxide with α,β-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.