para‐Selective Radical Trifluoromethylation of Benzamide Derivatives via Iminium Intermediates

摘要

Abstract The direct C?H trifluoromethylation of arenes via a radical pathway has attracted considerable attention recently. However, a major challenge of C?H trifluoromethylation is the lack of site‐selectivity on the phenyl ring especially para‐selectivity. Herein we show a new strategy for para‐selective C?H trifluoromethylation of benzamide derivatives using iminium activation. The reaction undergoes a radical‐type nucleophilic substitution instead of a radical‐type electrophilic substitution owing to iminium activation as a result of lowering the LUMO (lowest unoccupied molecular orbital). A wide range of substrates are compatible with this method giving almost exclusive para‐trifluoromethylated products.