Employing secondary amines as covalently interacting Lewis basic organocatalysts allows for the activation of electron-deficient allenes (allenoates) for unprecedented formal (3+2+1)-cycloadditions with Michael acceptors and aromatic carbaldehydes. This strategy is proposed to proceed via nucleophilic addition of the catalyst to the allenoate's β-carbon first, followed by γ-addition to the Michael acceptor, a subsequent aldol-type step, and the final ring closure and catalyst liberation. Hereby, direct access to various highly functionalized spirocyclic cyclohexanone-derivatives (17 examples) in good to excellent yields (up to 98%) and a first proof-of-concept for an asymmetric variant (around 75:25 er) by using chiral secondary amine catalysts has been obtained as well.
Naderer et al. (Thu,) studied this question.