Chiral Phosphoramide-Catalyzed Enantioselective Addition of Allylic Trichlorosilanes to Aldehydes. Preparative and Mechanistic Studies with Monodentate Phosphorus-Based Amides

The addition of allylic trichlorosilanes to benzaldehyde promoted by chiral phosphoramides to give the
enantioenriched homoallylic alcohol has been investigated. In a survey of Lewis bases as activators for
the addition of allyltrichlorosilane to benzaldehyde, phosphorus-based amides have been found to be the
most effective promoters. To achieve asymmetric induction, chiral phosphoric triamides derived from
chiral diamines have been developed and applied in the allylation reaction albeit with modest
enantioselectivities. The addition of 2-butenylsilanes was highly diastereoselective, suggesting a closed,
chairlike transition structure. A detailed mechanistic study has been carried out to probe into the origin
of activation. From a combination of nonlinear effects and kinetics studies, the reaction was found to
likely involve two phosphoramides in both the rate and stereochemistry determining steps. These studies
provided the background for the development of highly selective and reactive catalysts.