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.