Reversible alkylation of dimedone with aldehyde: A neglected way for maximizing selectivity of three-component reactions of dimedone and an aldehyde

Abstract

The selectivity of a three-component electrophilic reaction of an aldehyde with dimedone and another carbon-based nucleophile could be improved by a reversible alkylation procedure, which involves formation, breaking and regeneration of C-C bonds. In the presence of iron(III) chloride and triphenylphosphine, an analogous C-C bond breaking can be observed in the reaction of 2,3,4,9-tetrahydro-9-(2-hydroxy-4,4-dimethyl-6-oxo-1-cyclohexen-1- yl)-3,3-dimethyl-1H-xanthen-1-one, in which the fragment of dimedone was replaced by a carbon-based nucleophile. Inspired by this observation, some three-component reactions of salicyldehyde and dimedone were successfully developed by using iron(III) chloride and triphenylphosphine (PPh 3) as catalyst. PPh 3 plays the role of hydrogen bond acceptor, which confers a good flexibility of the substrate by weakening the intramolecular hydrogen bond, allowing thus an easy interaction of the substrate with iron(III) chloride catalyst. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.