Frustrated Lewis Pairs Catalyse the Solvent‐Assisted Synthesis of Azoles from ortho‐Substituted Anilines, CO2 and H2

Sn-based FLPs catalyse the synthesis of azoles by N-formylating aliphatic amines with CO₂ and H₂ followed by in situ formate transfer to ortho-substituted anilines and recycling of the aliphatic amine. This strategy eliminates issues with low reactivity of anilines in N-formylations with CO₂ and H₂ and allows simultaneous recycling of the transfer formylation reagent.

Abstract

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 R₃SnX 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.

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