Reversible Alkylation of Dimedone with Aldehyde: A Neglected Way for Maximizing Selectivity of Three‐Component Reactions of Dimedone and an Aldehyde

• DOI: 10.1002/adsc.201200299
• Publication Date: 2012-08-23T12:35:27Z
• Authors: Minghao Li; Yanlong Gu
• Keywords: 01 natural sciences; 0104 chemical sciences

AbstractThe 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 (PPh3) as catalyst. PPh3 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.