Synergetic activation of CO2 by the DBU-organocatalyst and amine substrates towards stable carbamate salts for synthesis of oxazolidinones

Abstract

The development of an efficient methodology to transform CO₂ into valuable chemicals has attracted increasing attention concerning the challenging issues of CO₂-utilization. Herein, an efficient approach for the preparation of oxazolidinones from CO₂, primary (aliphatic/aromatic) amines and 1,2-dichloroethane (or its derivatives) catalyzed by DBU organo-superbase was achieved with yields of 47–97% under mild conditions (80–100 °C, 12 h, 1.0 MPa CO₂). Control experiments demonstrated that the formation of an ion-pair carbamate salt intermediate IS-B derived from the reaction of CO₂, DBU (catalyst) and an amine (substrate) was the key step for this three-component reaction. The available DBU–amine–CO₂ adduct intermediate (like IS-B-2) with fair stability will evolve into the thermodynamically stable product oxazolidinones upon attack of 1,2-dichloroethane (or its derivatives), along with the regeneration of the DBU catalyst. Alternatively, the decomposition of the DBU–aryl amine–CO₂ adduct (like IS-B-1) with relatively poor stability also could result in the competitive substitution reaction of 1,2-dichloroethane (or its derivatives) with the aryl amine. This work provides insights into synergetic CO₂-activation by the DBU-catalyst and a nucleophilic amine-substrate via the formation of robust carbamate salt intermediates responsible for the final production of oxazolidinones.