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.

中文翻译：

---

2-吡喃酮与茚的镍(II)催化对映选择性全碳基逆电子需求Diels-Alder反应

Cephalotaxus norditerpenoids cephanolides A-D 具有密集功能化的六氢芴基桥连内酯支架。为了简洁地实现这些特权结构，本文中，缺电子的 2-吡喃酮与电子无偏茚在手性N , N '-二氧化物/Ni(OTf) ₂催化下的不对称逆电子需求 Diels-Alder (IEDDA) 反应复杂的已被披露。基于该反应，在温和条件下获得了多种取代的六氢芴基内酯支架，其产率良好（高达 98%）和对映选择性（高达 93% ee）。