Intermolecular Michael Addition of S- and Se-nucleophiles

Addition of the thiophenolate anion to the / -carbon atom of the enone is the chirality-determining step it is, at the same time, rate-determining. The transition state is a ternary complex comprising the catalytic base in the protonated form, the thiophenolate anion, and the enone. The last is activated to nucleophilic attack by hydrogen-bonding to the catalysts / -hydroxy group. The chiral cinchona bases thus act as bifunctional catalysts. 

The cinchonidine-catalyzed addition of 4-tert-butylthiophenol reported by Wynberg and Hiemstra has also been used for kinetic resolution of racemic 5-methyl -2-cyclohexen-l-one At an enone/thiophenol ratio of 2 1, the remaining enone had an optical purity of 36% [54], A similar procedure was employed by Asaoka et al. for kinetic resolution of 5-trimethylsilyl-2-cyclohexen-l-one, affording 50% of the trans adduct (57% ee, enantiomerically pure after recrystallization) with 41% of the starting enone (59% ee) [55a]. 

Cyclic enones reacted with 4-fe/t-butyl thiophenol (% ee achieved)  

Thiophenols reacted with cyclohexenone in the presence of 2 mol-% of catalyst 68 [ yield (% ee) achieved]  

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