Iron-Catalyzed Highly Enantioselective cis-Dihydroxylation of Trisubstituted Alkenes with Aqueous H O.

Reliable methods for enantioselective cis-dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis-α-[Fe (2-Me -BQPN)(OTf) ], which bears a tetradentate N ligand (Me -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 O ) as oxidant under mild conditions. Experimental studies (including 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 (O) reaction intermediate as an active oxidant. This cis-[Fe (chiral N ligand)] /H O method could be a viable green alternative/complement to the existing OsO -based methods for asymmetric alkene dihydroxylation reactions.