Abstract
The stereodivergent behavior of allenyl(cyano)- and allenyl(alkyl)- cuprates toward aldehydes, providing a selective preparation of both syn or anti homopropargylic alcohols, is described. This study, which combines both experimental and theoretical support, shows that the copper non-transferred "dummy ligand" controls the localization of the lithium cation with respect to the allenylcuprate moiety. As a consequence, Li+ acts as a Lewis acid activator but also controls the diastereoselectivity during the addition of allenylcuprates onto aldehydes. The combined high selectivity, efficiency and versatility of these cuprate compounds open the way to new one-pot synthetic procedures as illustrated by the combined Klein rearrangement / transmetallation methodology described herein.