Conjugate Addition of Alkenylsulfides with α,β-Unsaturated Carbonyl Compounds. Remarkable n-π* Orbital Interaction for Control of Regio- and Stereochemistry

Abstract

A highly stereoselective conjugate addition reaction with α,β-unsaturated aldehydes was developed by using alkenylsulfide as a nucleophile. Under the influence of TiCl₃(O ⁱ Pr), (1S*,2S*)-1-butyl-2-[(1Z)-1-(methylthio)propenyl]-1-(triethylsiloxy)cyclopentane reacted with enals to give 11,12-dimethyl-10-(methylthio)-14-(triethylsiloxy)-9,13-tetradecadien-5-one derivatives in >99% anti selectivity. The high regio- and stereoselection can be explained by assuming the chair-like six-membered cyclic transition state involving the orbital interaction between the sulfur and a carbonyl carbon.