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. At the active site: A chiral manganese porphyrin complex catalyzes the oxygenation of 3,4‐dihydroquinolones to the respective 4‐hydroxy compounds (12 examples, 87–99 % ee). The enantio‐ and site selectivity is enforced by hydrogen bonding to the catalyst; methylene groups at C3 or at C7 are not attacked.