Stereodivergent <i>E</i>- and <i>Z</i>-selective Sulfonium [3,3]-Rearrangement Enabled by Brønsted Bases

The stereoselective synthesis of (<i>Z</i>/<i>E</i>)-α-aryl α,β-unsaturated carbonyl compounds remains a significant synthetic challenge. Recently, we demonstrated a novel <i>Z</i>-selective α-arylation of α,β-unsaturated nitriles via a Morita-Baylis-Hillman-type sulfonium [3,3]-rearrangement. In this study, we report that switching the base from K₂CO₃ to 4-methoxypyridine in the final elimination step reverses the stereochemistry of the products from <i>Z</i>- to <i>E</i>-geometry. Consequently, <i>E</i>/<i>Z</i>-divergent α-arylation of α,β-unsaturated nitriles was achieved through these sulfonium rearrangements. Additionally, mechanistic studies reveal that weak interactions such as hydrogen bonding, n-π or π-π interactions, and short-range steric repulsions play crucial roles in determining the stereochemistry of the reaction.