A nickel(ii)-catalyzed enantioselective all-carbon-based inverse-electron-demand Diels-Alder reaction of 2-pyrones with indenes

The Cephalotaxus norditerpenoids cephanolides A-D feature a densely functionalized hexahydrofluorenyl bridged-lactone scaffold. To concisely achieve these privileged structures, herein, an asymmetric inverse-electron-demand Diels-Alder (IEDDA) reaction of electron-deficient 2-pyrones with electronically unbiased indenes catalyzed by a chiral N,N '-dioxide/Ni(OTf)(2) complex has been disclosed. Based on this reaction, a variety of substituted hexahydrofluorenyl lactone scaffolds were obtained with good to excellent yields (up to 98% yield) and enantioselectivities (up to 93% ee) under mild conditions.