Straightforward formation of carbocations from tertiary carboxylic acids via CO release at room temperature

Abstract

We report an unprecedented mode of reactivity of carboxylic acids. A series of tertiary carboxylic acids, containing at least one phenyl α-substituent, undergo loss of carbon monoxide at room temperature (295 K), by a one pot reaction with 0.5–1 molar equivalents of WCl₆ in dichloromethane. A plausible mechanism for the Ph₃CCO₂H/WCl₆ reaction, leading to [CPh₃][WOCl₅] and Ph₃CCl, is proposed on the basis of DFT calculations. The analogous reactions involving CEt(Ph)₂CO₂H, CMe(Ph)₂CO₂H and CMe₂(Ph)CO₂H selectively afforded stable hydrocarbons (alkene or indene, depending on the case), apparently resulting from the rearrangement of elusive tertiary carbocations.