Iron‐Catalyzed Highly Enantioselective <i>cis</i>‐Dihydroxylation of Trisubstituted Alkenes with Aqueous H<sub>2</sub>O<sub>2</sub>
Jinhu Wei, Liangliang Wu, Hai‐Xu Wang, Xiting Zhang, Chun‐Wai Tse, Cong‐Ying Zhou, Jie‐Sheng Huang, Chi‐Ming Che
Abstract
Abstract Reliable methods for enantioselective cis ‐dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis ‐α‐[Fe II (2‐Me 2 ‐BQPN)(OTf) 2 ], which bears a tetradentate N 4 ligand (Me 2 ‐BQPN=( R , R )‐ N , N′ ‐dimethyl‐ N , N′ ‐bis(2‐methylquinolin‐8‐yl)‐1,2‐diphenylethane‐1,2‐diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron‐deficient alkenes were efficiently oxidized to chiral cis ‐diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H 2 O 2 ) as oxidant under mild conditions. Experimental studies (including 18 O‐labeling, ESI‐MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis ‐Fe V (O) 2 reaction intermediate as an active oxidant. This cis ‐[Fe II (chiral N 4 ligand)] 2+ /H 2 O 2 method could be a viable green alternative/complement to the existing OsO 4 ‐based methods for asymmetric alkene dihydroxylation reactions.