Fluoride-promoted rearrangement of organo silicon compounds: a new synthesis of 2-(arylmethyl)aldehydes from 1-alkynes

A new approach to 2-(arylmethyl)aldehydes 4 based upon a 1,2-anionotropic rearrangement of an aryl group is presented. The synthetic sequence begins with a silylformylation reaction of terminal acetylenes 5 with aryl and heteroaryl silanes 6, followed by treatment of the products (Z)-1 with TBAF. The optimization of the experimental conditions of the fluoride-promoted step is described, together with the synthetic potentialities of the process. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety of beta-silylalkenals (Z)-1 and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can rearrange without any loss of configuration. Bromo-functionalized substrates undergo an intramolecular reaction that affords exclusively carbacyclobenzyl aldehydes, further enhancing the high synthetic value of this method.