Construction of axial chirality via asymmetric radical trapping by cobalt under visible light

Photoredox catalysis and organocatalysis represent two powerful fields of molecule activation that have found widespread application in the areas of inorganic and organic chemistry, respectively. We merged these two catalysis fields to solve problems in asymmetric chemical synthesis. Specifically, the enantioselective intermolecular alpha-alkylation of aldehydes has been accomplished using an interwoven activation pathway that combines both the photoredox catalyst Ru(bpy)3Cl2 (where bpy is 2,2'-bipyridine) and an imidazolidinone organocatalyst. This broadly applicable, yet previously elusive, alkylation reaction is now highly enantioselective and operationally trivial.

Chemists have long aspired to synthesize molecules the way that plants do-using sunlight to facilitate the construction of complex molecular architectures. Nevertheless, the use of visible light in photochemical synthesis is fundamentally challenging because organic molecules tend not to interact with the wavelengths of visible light that are most strongly emitted in the solar spectrum. Recent research has begun to leverage the ability of visible light-absorbing transition metal complexes to catalyze a broad range of synthetically valuable reactions. In this review, we highlight how an understanding of the mechanisms of photocatalytic activation available to these transition metal complexes, and of the general reactivity patterns of the intermediates accessible via visible light photocatalysis, has accelerated the development of this diverse suite of reactions.