Manganese-Catalyzed Asymmetric Hydrogenation of 3H-Indoles

The asymmetric hydrogenation (AH) of 3H-indoles represents an ideal approach to the synthesis of useful chiral indoline scaffolds. However, very few catalytic systems based on precious metals have been developed to realize this challenging reaction. Herein, we report a Mn-catalyzed AH of 3H-indoles with excellent yields and enantioselectivities. The kinetic resolution of racemic 3H-indoles by AH was also achieved with high s-factors to construct quaternary stereocenters. Many acid-sensitive functional groups, which cannot be tolerated when using a state-of-the-art ruthenium catalyst, were compatible with manganese catalysis. This new process expands the scope of this transformation and highlights the uniqueness of earth-abundant metal catalysis. The reaction could proceed with catalyst loadings at the parts per million (ppm) level with an exceptional turnover number of 72350. This is the highest value yet reported for an earthabundant metal-catalyzed AH reaction.

Automated summary

This study presents a Mn-catalyzed asymmetric hydrogenation of 3H-indoles, achieving high yields and enantioselectivities. The use of manganese catalyst allows for the compatibility of acid-sensitive functional groups, expanding the scope of this transformation and highlighting the uniqueness of earth-abundant metal catalysis.