Photochemical Deracemization of 4,7-Diaza-1-isoindolinones by Unidirectional Hydrogen Atom Shuttling

By coupling a photochemical
and a thermal step, a single chiral
catalyst can establish a photostationary state in which the enantiopure
form of a chiral compound is favored over its racemate. Following
this strategy, 3-substituted 4,7-diaza-1-isoindolones were successfully
deracemized (74–98% yield, 86–99% ee) employing 2.5 mol % of a photocatalyst. Key to the success of the
reaction is the fact that a chiral benzophenone recruits selectively
one enantiomer of the substrate for a photoinduced hydrogen atom transfer.
A combination of computational and experimental studies suggests that
the hydrogen atom is shuttled via the oxygen atom of the catalyst
to the 4-nitrogen atom of the substrate.