Axially Chiral N-Oxide Catalysts for the Allylation and Crotylation of Aromatic Aldehydes: Exploiting Nonlinear Effects

Abstract

A new family of IAN-type amine N-oxides is presented as catalysts for the allylation and crotylation of aromatic aldehydes with allyltrichlorosilanes. These reactions exhibit a remarkably positive nonlinear effect which enables the utilization of the catalysts in subenantiopure form. As enantiopure catalysts are not required under this regime, the synthesis of these N-oxides is straightforward through catalytic asymmetric synthesis, avoiding lengthy synthesis from the chiral pool or resolution of diastereoisomers. Studies of the corresponding crotylation with Z- and E-crotylsilanes suggest that the reaction proceeds through a chair-like transition state.