Enantioselective Dual-Catalysis: A Sequential Michael Addition/Asymmetric Transfer Hydrogenation of α-Nitrosulfone and Enones
Fengwei Chang, Shitong Wang, Zhitong Zhao, Lijian Wang, Tanyu Cheng, Guohua Liu
Abstract
Development of an efficient cocatalyst system to eliminate the intrinsic conflict of the cross-interactions in a pair of cocatalysts and to overcome the extrinsic conflict of the reaction conditions in an unmatched reaction environment has great significance in asymmetric dual catalysis. Herein, a compartmentalization method involving the integration of a cocatalyst system has been developed, which enables an efficient Michael addition/reduction enantioselective dual-catalysis process to be accomplished from a noncompatible system. In this process, the chiral squaramide species is encapsulated within the cavity of one hollow-shell-mesostructured silica support, whereas the chiral organoruthenium/diamine species is entrapped within the cavity of another water-soluble thermoresponsive polymer-coating hollow-shell-mesostructured silica support. This shielding feature together with the reversible on–off mode of the water-soluble thermoresponsive polymer not only controls the cross-interactions of dual species but also harmonizes the reaction conditions. As we envisioned, the one-pot sequential Michael addition of α-nitrosulfone and enones followed by asymmetric transfer hydrogenation provides various 1,4-distereocentered chiral δ-hydroxysulfones with enhanced yields and enantio/diastereoselectivities.