Chiral Primary Amine-Catalyzed Divergent Coupling of α‑Substituted Acrylaldehydes with α‑Diazoesters

We report, herein, aminocatalytic coupling of α-substituted acrylaldehydes with α-diazoesters, leading to chemoselective C–H insertion or cyclopropanation depending on α-substituents of diazoesters. A chiral primary–secondary diamine catalyst derived from l-tert-leucine enabled the efficient promotion of both C–H insertion and cyclopropanation pathways in good yields and high enantioselectivities at room temperature without any metal or a Lewis acid cocatalyst. Mechanistic studies uncovered an iminium ion-mediated 1,3-dipolar cycloaddition pathway, wherein the electronic nature of diazocarbons dictates the chemoselectivity in this aminocatalytic cycle.