2-Trifluoromethyl-Benzimidazolium Salt as a Dual-Function Reagent for Deoxytrifluoromethylation of Benzyl Alcohols

Abstract

Organofluorine compounds play a critical role in diverse fields such as medicinal chemistry, materials science, and agrochemicals. Due to their scarcity in nature, the construction of C–CF₃ bonds has emerged as one of the most actively pursued topics in synthetic chemistry. The direct deoxytrifluoromethylation of alcohols offers a highly attractive route to access valuable C(sp³)-CF₃ bonds, leveraging the ubiquity and ready availability of alcohols as feedstocks. Established strategies for such transformations typically require separate reagents for sequential deoxygenation of alcohol substrates and trifluoromethylation of activated intermediates. While dual-function reagents that combine activation and fluorination are well-established in deoxyfluorination chemistry, analogous reagents for deoxytrifluoromethylation have remained largely unexplored. In this study, we address this gap by introducing 2-trifluoromethyl-benzimidazolium salt as a novel dual-function reagent capable of promoting the deoxytrifluoromethylation of benzylic alcohols. This reagent uniquely integrates the ability to activate the alcohol substrate while simultaneously serving as a trifluoromethyl source in a single operational step. The transformation is facilitated by a synergistic system combining photoredox catalysis with a copper promotion. Under mild visible-light irradiation, the photoredox cycle initiates single-electron transfer processes, generating key benzylic radical intermediates from the activated alcohols. Concurrently, the copper species stabilizes the trifluoromethyl moiety and mediates the crucial C–CF₃ bond-forming cross-coupling step. This cooperative mechanism enables the efficient one-step conversion of benzylic alcohols into their trifluoromethylated analogues. The reaction demonstrates broad functional group tolerance, accommodating double bonds, aldehydes, ketones, nitro groups, halides, and other sensitive functionalities. Scalability was also confirmed through gram-scale synthesis. In summary, this work establishes the feasibility of a dual-function reagent for deoxytrifluoromethylation, expanding the toolbox for C–CF₃ bond formation. The developed methodology offers several advantages, including easy preparation and stability of the reagent, avoidance of substrate pre-functionalization, and excellent functional group compatibility. Furthermore, this study presents a less explored reagent system for copper-catalyzed or promoted trifluoromethylation of aliphatic substrates, opening avenues for further development in radical-mediated trifluoromethylation chemistry.

Keywords

Deoxytrifluoromethylation / Dual-function / Trifluoromethylation / Deoxygenation / Photoredox / Alcohol / Copper / 2-Trifluoromethyl-benzimidazolium salt

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2025 SIOC, CAS, Shanghai, & WILEY-VCH GmbH