Organocatalytic Activation of Donor-Acceptor Cyclopropanes: A Tandem (3 + 3)-Cycloaddition/Aryl Migration toward the Synthesis of Enantioenriched Tetrahydropyridazines.

An organocatalytic enantioselective (3 + 3)-cycloaddition reaction of racemic cyclopropane carbaldehydes and aryl hydrazones has been demonstrated for the first time. A wide range of enantioenriched tetrahydropyridazines with an exocyclic double bond were obtained with moderate to good yields and good to excellent enantiomeric excesses. Mechanistic investigations hinted toward a matched/mismatched kinetic resolution, and control experiments and DFT calculations unveiled that 1,3-aryl migration was concerted and intramolecular and proceeds via a four-membered transition state.