The reduction of triarylcarbenium ions by alcohols: simple hydride transfer or concerted breakdown of ortho-adducts ?

Abstract

Reduction of tris-(4-methoxyphenyl)methyl chloride (2) by refluxing methanol to tris-(4-methoxyphenyl)methane (3) is, as shown by ²H labelling, accompanied by exchange of methoxy-groups between solvent and substrate. This exchange reaction appears to be the first recognized example of an S_N2-Ar reaction of a triarylcarbenium ion and involves the intermediacy of the para-adduct (9a) which implies that in the course of the reduction of triarylcarbenium ions by n-nucleophiles, formation of the related type (1)ortho-adducts is possible as required by the Olah–Svoboda mechanism.