Ga‐catalyzed temperature‐dependent oxazolidinone/piperazine synthesis from phenyl aziridines involving a divergent ligand‐assisted mechanism

Application of a binary Ga‐based catalyst system for the coupling of CO2 and aziridines to form oxazolidinones is presented. It has been possible to optimize the catalyst system for the selective formation of a single regioisomer, in excellent yield, under relatively mild reaction conditions. The optimized catalyst system has been successfully applied to a range of substituted aziridines derived from styrene oxide. It has been observed that aziridines bearing two aromatic substituents result in piperazine formation through an unexpected dimerization reaction. These piperazine products can be selectively formed in the absence of CO2 or are favored at lower reaction temperatures. A detailed DFT study into the reaction mechanism for the formation of both products has been carried out and an unusual ligand assistance in the case of oxazolidinone synthesis has been identified. More specifically, this ligand interaction promotes the initial ring‐opening of the aziridine and this work presents the first fully elucidated mechanism involving this intermediate.