The reduction of triarylcarbenium ions by n-nucleophiles. The operation of the intramolecular version of the Olah–Svoboda mechanism in the reductive cyclization of the tris-(2,6-dimethoxyphenyl)carbenium ion

Abstract

Refluxing of tris-(2,6-dimethoxyphenyl)carbenium hydrogen dichloride (2b)·2H₂O with chloroform furnished 9-(2,6-dimethoxyphenyl)-1,8-dimethoxyxanthene (11). This cyclization process with concomitant hydride transfer to the central carbon atom is rationalized by assuming concerted breakdown of any of the intermediates (6), (7), and (9)(Scheme 3), i.e. the operation of the intramolecular version of the disputed Olah–Svoboda mechanism of hydride transfer to triarylcarbenium ions.