Asymmetric [4+2] annulations to construct norcamphor scaffolds with 2-cyclopentenone via double amine-thiol catalysis.

An efficient double catalytic system, combining chiral amine and 2-mercaptobenzoic acid, is applied for α',β-regioselective [4+2] annulations of 2-cyclopentenone with a diversity of activated alkenes, constructing multifunctional chiral bicycle[2,2,1]heptane scaffolds in good to excellent yields and enantioselectivities. In comparison with the traditional cross-dienamine species between 2-cyclopentenone and chiral amine, the interrupted enamine intermediate containing a covalently linked thiol catalyst shows significantly improved reactivity.