Site- and Enantioselective C-H Oxygenation Catalyzed by a Chiral Manganese Porphyrin Complex with a Remote Binding Site

A chiral manganese porphyrin complex with a two-point hydrogen-bonding site was prepared and probed in catalytic C-H oxygenation reactions of 3,4-dihydroquinolones. The desired oxygenation occurred with perfect site selectivity at the C4 methylene group and with high enantioselectivity in favor of the respective 4S-configured secondary alcohols (12 examples, 29-97% conversion, 19-68% yield, 87-99% ee). Mechanistic studies support the hypothesis that the reaction proceeds through a rate-and selectivity-determining attack of the reactive manganese oxo complex at the hydrogen-bound substrate and an oxygen transfer by a rebound mechanism.