Catalytic Asymmetric Vinylogous Conjugate Addition of Unsaturated Butyrolactones to α,β-Unsaturated Thioamides

Shibasaki et al. have reported the catalytic asymmetric vinylogous conjugate addition of unsaturated butyrolactones to α,β-unsaturated thioamides using soft Lewis acid/Brønsted base cooperative catalysts. According to their results, the reaction proceeds with high enantioselectivity by using [Cu(CH₃CN)₄]PF₆ as a soft Lewis acid, (R)-SEGPHOS as a ligand, and a tertiary amine as a Brønsted base, generating the conjugate adduct bearing consecutive tri- and tetrasubstituted stereogenic centers. This reaction can be conducted at room temperature through an operationally simple protocol. Then the thioamide functionality of the product can be transformed into various functional groups. Since butenolide units are found in a wide range of natural products and biologically active compounds, this reaction is expected to be a useful synthetic method for those compounds.