Diastereoselective Addition of n-Butyllithium to 2-Phenylpropanal: A Reassessment of the Solvent and Temperature Effects

摘要

The mechanism of asymmetric induction in reactions of α-chiral aldehydes and keiones has been a subject of continued speculation since Cram and Kopecky's seminal work. Among several factors that have been recognized to influence the Ti-facial diastereoselectivity. the role of the solvent has hitherto been underestimated. Recently we demonstrated that in nucleophilic addition reactions to O-protected (2S)-lactal and to its corresponding N-(trimethylsilyl)imine, the diastereoselection was highly dependent on the nature of the solvent and on the temperature. In these α-oxy substrates, chelation was often invoked to account for the stereochemical outcome of the reactions with organometallic reagents; thus, the diastereoselection was often discussed interms of a chelation versus a nonchelation mechanism.