Enantioselective <i>anti</i>-Dihalogenation of Electron-Deficient Olefin: A Triplet Halo-Radical Pylon Intermediate
Dong Zhang, Maoping Pu, Zhenzhong Liu, Yuqiao Zhou, Zhendong Yang, Xiaohua Liu, Yun‐Dong Wu, Xiaoming Feng
Abstract
The textbook alkene halogenation reaction establishes straightforward access to vicinal dihaloalkanes. However, a robust catalytic method for dihalogenizing electron-deficient olefins in an enantioselective manner is still under development, and its mechanism remains controversial. Herein, we disclose efficient regio-, anti -diastereo-, and enantioselective dibromination, bromochlorination, and dichlorination reactions of enones catalyzed by a chiral N, N’ -dioxide/Yb(OTf) 3 complex. With the combination of electrophilic halogen and halide salts as halogenating agents, an array of homo- and heterodihalogenated derivatives is achieved in moderate to good enantioselectivities. Moreover, DFT calculations reveal that a novel triplet halo-radical pylon intermediate is probable in accounting for the exclusive regio- and anti -diastereoselectivity.