Kinetic Resolutions Enabled by N-Heterocyclic Carbene Catalysis

Background: Catalytic kinetic resolution continues to be one of the hottest research topics in the community of synthetic chemistry owing to the huge demand of optically pure substances. Besides enzyme and transition metal-catalyzed asymmetric transformations, last two decades have witnessed tremendous advances enabled by organocatalysis. In this context, N-heterocyclic carbene catalysis, which is featured by its unique umpolung strategy, wide substrate scope, and diversified activation modes, has been widely applied in a series of kinetic resolutions to access molecules with high diastereo- and enantioselectivities. Objective: The review focuses on recent progress in the area of N-heterocyclic carbene-catalyzed kinetic resolutions. Three types of resolution methods, i.e., classic kinetic resolution, dynamic kinetic resolution, and divergent reactions on racemic mixtures, will be the focus of discussion. Conclusion: It can be seen that the mostly studied resolution methods are still classical kinetic resolution and dynamic kinetic resolution, the method of divergent reactions on racemic mixtures remains underdeveloped. Nevertheless, we believe that there remains great potential in N-heterocyclic carbene-catalyzed divergent reactions and further investigation in this field will definitely prove its value. There is still huge space for this field to be further promoted, beacuse many intermediates, like conjugated acyl azoliums, allenoates, and radicals, have not been involved in kinetic resolutions. Further novel transformations through N-heterocyclic carbenecatalyzed resolution of racemates can be expected in the near future.