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

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A new family of IAN‐type amine N ‐oxides is presented as catalysts for the allylation and crotylation of aromatic aldehydes with allyltrichlorosilanes. These reaction exhibit a remarkably positive nonlinear effect which enables 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 lenghty 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.