Catalytic Asymmetric Formal Insertion of Aryldiazoalkanes into the C–H Bond of Aldehydes: Synthesis of Enantioenriched Acyclic α‑Tertiary Aryl Ketones

A novel, catalytic enantioselective route to synthesize a variety of α-tertiary aryl ketones via a boron Lewis acid promoted formal insertion of aryldiazoalkane into the C–H bond of both aromatic and aliphatic aldehydes is described. In the presence of chiral (S)-oxazaborolidinium ion catalyst 1, the reaction proceeded in good yields (up to 94%) with excellent enantioselectivities (up to 99% ee).