Frustrated Lewis Pairs Catalyse the Solvent-Assisted Synthesis of Azoles from ortho-Substituted Anilines, CO2 and H2
Abstrakt
Synthesizing azoles from ortho-substituted anilines, CO2 and H2 has proved difficult due to the low nucleophilicity of anilines, which hinders their N-formylation, i. e., the first step of the reaction. This study demonstrates that R(3)SnX Lewis acids (LA), N-methylmorpholine (NMM) or DBU and polyethyleneimine (PEI) or N-formylmorpholine efficiently catalyse the synthesis of benzimidazole and other azoles from ortho-substituted anilines, CO2 and H2 by reductive coupling of CO2 to nucleophilic amine-based solvents, PEI or morpholine, followed by in-situ transfer of the formyl group to the appropriate ortho-substituted aniline.
Under these reaction conditions, spontaneous cyclization of the N-formylated intermediate yields the corresponding azole in up to 98 % yield.