Asymmetric Homoaldol Reaction by Enantioselective Lithiation of a Prochiral 2‐Butenyl Carbamate

Abstract

A second-order asymmetric conversion of the configurationally labile racemic lithium complex 2 initially formed from 1 enables the recovery of crystalline (R)-2.sparteine. This, and the transmetalation of (R)-2.sparteine (as solid) to the configurationally stable titanium derivative are decisive for the title reaction. (R)-2 is not only of interest as chiral homoenolate, but also as antiselective propanal enolate equivalent that adds with good reagent-controlled stereoselectivity; an example is the reaction leading to 3.