Photochemical\nDeracemization of 4,7-Diaza-1-isoindolinones\nby Unidirectional Hydrogen Atom Shuttling

By coupling a photochemical\nand a thermal step, a single chiral\ncatalyst can establish a photostationary state in which the enantiopure\nform of a chiral compound is favored over its racemate. Following\nthis strategy, 3-substituted 4,7-diaza-1-isoindolones were successfully\nderacemized (74–98% yield, 86–99% <i>ee</i>) employing 2.5 mol % of a photocatalyst. Key to the success of the\nreaction is the fact that a chiral benzophenone recruits selectively\none enantiomer of the substrate for a photoinduced hydrogen atom transfer.\nA combination of computational and experimental studies suggests that\nthe hydrogen atom is shuttled via the oxygen atom of the catalyst\nto the 4-nitrogen atom of the substrate.