Enantioselective intermolecular all-carbon [4+2] annulation via N-heterocyclic carbene organocatalysis

The highly stereoselective intermolecular all-carbon [4+2] annulation between in situ generated acyclic dienolates and α,β-unsaturated acyl azoliums is disclosed. The identification of 2-acyloxy-3-butenones as suitable diene precursors is the key to the success of this transformation. The corresponding highly functionalized cyclohexene products, which are inaccessible from Diels–Alder reactions, were delivered with high levels of diastereo- and enantioselectivities. A series of further transformations based on the product showed the potential of this reaction.