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

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The stereoselective synthesis of ( Z / E )-α-aryl α,β-unsaturated carbonyl compounds remains a significant synthetic challenge. Recently, we demonstrated a novel Z -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 K 2 CO 3 to 4-methoxypyridine in the final elimination step reverses the stereochemistry of the products from Z - to E -geometry. Consequently, E / Z -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.