Gas-phase synthesis of hydrodiphenylcyclopropenylium via nonclassical Favorskii rearrangement from alkali-cationized alpha,alpha'-dibromodibenzyl ketone.

The gas-phase synthesis of hydrodiphenylcyclopropenylium from alkali-cationized alpha,alpha'-dibromodibenzyl ketone (1) via nonclassical Lewis-acid-induced Favorskii rearrangement has been studied by electrospray ionization/tandem mass spectrometry (ESI-MS/MS) and theoretical methods, showing that cations [1-Br](+) by debromination from 1 and 1.M(+)(M = Li or Na) by alkali-metal cationization of 1 could convert into the protonated diphenylcyclopropenone 2.H(+) by collision-induced dissociation in the gas phase. A concerted mechanism for the Lewis-acid-induced Favorskii rearrangement from alkali-metal-cationized alpha,alpha'-dibromodibenzyl ketone was proposed and studied, based on mass spectrometric results and theoretical methods. Copyright 2010 John Wiley & Sons, Ltd.