Kinetic Resolution of Racemic Radicals in Asymmetric Photoredox Minisci Reactions with Azaarenes for Precise Construction of Two Non-adjacent Stereocenters.

Abstract

Despite the significant potential of photocatalysis as a robust synthetic tool, the high reactivity of radicals often presents challenges in achieving optimal chemoselectivity. In this study, we demonstrate that this inherent limitation can be strategically harnessed for asymmetric photoredox catalysis. By utilizing a chiral catalyst to facilitate kinetic resolution between the two enantiomers of racemic radical intermediates, one enantiomer selectively undergoes the desired transformation, while noncatalytic side reactions deplete the other enantiomer. Consequently, an attractive asymmetric photoredox three-component Minisci-type reaction involving bromides, racemic homoallylic tertiary alcohols or amines, and azaarenes has been developed. This approach enables efficient assembly of tertiary alcohols and amines onto the nonadjacent β-position of an azaarene-functionalized tertiary carbon stereogenic center with high levels of enantio- and diastereoselectivity. Therefore, this method not only allows for direct utilization of readily available racemic feedstocks that are challenging to convert into prochiral radicals via redox processes but also provides an efficient strategy for synthesizing complex molecules with multiple stereocenters.