Lewis acid-catalysed reactions of aryl cyclopropyl ketones. Scope and mechanism
The effects of aryl substituents on the stannic chloride-catalysed cyclisation of aryl cyclopropyl ketones (1) to aryl tetralones (2) are consistent with the formation of a benzyl carbocation intermediate (8) or a cyclic oxonium ion intermediate (12). The secondary alcohols (3), occasionally formed as side-products, are derived from this intermediate. Tetralone formation by a concerted pathway is disproved.