Anti-Markovnikov Hydroamination of Vinylpyridines via a Novel Photocatalytic Strategy

In this paper, we report a novel photocatalytic strategy for hydroamination reactions under mild conditions of room temperature and air atmosphere, in which commercially available tribromomethylphenyl sulfone (TBMS) efficiently drives the highly selective anti-Markovnikov hydroamination of vinylpyridines with diverse aromatic amines under ultraviolet light irradiation. By optimizing the synthetic conditions, moderate to excellent yields were achieved along with good functional group tolerance, and the highest yield of the target product can reach 97%, while aliphatic amines, amines bearing strong electron-withdrawing groups (e.g., -NO2 and -CN), and sterically hindered ortho-substituted anilines are not compatible with this strategy. On this basis, via deuterium labeling studies and reference experiments, we proposed an aza-Michael-type free radical addition mechanism, which indicated that the activation of the N-H bond of the amines was the rate-determining step. This paper provides a new green and efficient synthetic protocol for hydroamination, which has potential application value in the synthesis of drugs and fine chemicals.