Enantioselective Conjugate Addition of Donor–Acceptor Hydrazones to α,β-Unsaturated Aldehydes through Formal Diaza–Ene Reaction: Access to 1,4-Dicarbonyl Compounds

Donor–acceptor monosubstituted hydrazones participate as suitable reagents able to undergo an enantioselective formal diaza–ene reaction with α,β-unsaturated aldehydes under chiral secondary amine catalysis. This constitutes a new approach for the enantioselective conjugate addition of hydrazones to enals under metal-free conditions and leads to the formation of γ-hydrazono carboxylic acids after oxidation/[1,3]-H shift. The methodology is also useful for the synthesis of enantioenriched β-substituted α-keto-1,5-diesters by using the hydrazone moiety as a masked carbonyl group.