A Chiral Rhodium Carboxamidate Catalyst for Enantioselective C-H Amination

摘要

Catalytic intramolecular C-H amination has advanced as a general technology for chemical synthesis. The utility of the heterocyclic products fashioned from such processes validates efforts to identify chiral transition-metal complexes capable of effecting asymmetric insertion (Figure 1). On a more fundamental level, the challenges associated with the design of a catalytic system able to support a reactive oxidant that can discriminate between two hydrogen atoms on a prochiral methylene center are significant. Nonetheless, success of this type has been realized in enantioselective C-H insertion reactions of diazoalkane derivatives and in select instances involving intra- and intermolecular C-H amination. This report describes the development and performance of Rh_2(S-nap)_4, a valerolactam-derived dirhodium complex that affords some of the highest levels of asymmetric control to date in cyclization reactions of sulfamate esters. The strong preference of this catalyst for promoting allylic C-H bond insertion is also highlighted.