A Modular Strategy for the Gram-Scale Synthesis of Tetraarylammonium Salts

Tetraarylammonium salts are a structurally unique yet synthetically challenging subclass of quaternary ammonium salts. Classical Menshutkin reactions are generally ineffective for their syntheses due to the diminished nucleophilicity of triarylamines and the low reactivity of aryl halides toward SN2 processes. Herein, we report a modular and scalable strategy for the synthesis of tetraarylammonium salts. Starting from readily accessible diarylamines, the target structures are obtained through a concise five-step sequence comprising Buchwald-Hartwig amination, halogen-lithium exchange/silylation, rhodium-catalyzed arylation, intramolecular cyclization, and protodesilylation. The optimized protocol enabled gram-scale isolation of tetraphenylammonium salt (1.2 g isolated). This work provides a practical platform for the scalable and flexible synthesis of tetraarylammonium salts, facilitating future studies of their properties and applications.