Asymmetric β,γ′-regioselective [4 + 3] and [4 + 2] annulations of α-vinylenals via cascade iminium ion-dienamine catalysis

Abstract

Introduction of an α-vinyl group into enal substrates can prohibit the traditional [3 + 2] cycloaddition with N-2,2,2-trifluoroethyl isatin imines catalysed by a chiral secondary amine, but give β,γ′-regioselective [4 + 3] annulation products via cascade iminium ion-dienamine catalysis. A spectrum of CF₃-containing spirooxindoles incorporating an azepane motif were constructed with good to excellent enantioselectivities. In addition, asymmetric [4 + 2] annulations between α-vinylenals and α,α-dicyanoalkenes were disclosed through a similar catalytic strategy, generally affording complex tricyclic frameworks with outstanding enantioselectivities.