Iron‐Catalyzed Highly Enantioselective cis ‐Dihydroxylation of Trisubstituted Alkenes with Aqueous H 2 O 2

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.