Lewis Acid Catalyzed Cycloaddition of Methylenecyclopropanes with Salicylaldehydes

Lewis acid catalyzed cycloaddition of methylenecyclopropanes (MCPs) with o-quinonemethide analogues, derived from the corresponding salicylaldehydes and CH(OEt)3, produces the corresponding cycloadducts 3 in moderate to high yields at room temperature (20 °C). Moreover, the compounds 3 can be transformed to the indene derivatives 5 at high temperature. Plausible mechanisms have been proposed on the basis of control experiments.