Ene-Carbonyl Reductive Coupling for the Synthesis of 3,3-Disubstituted Phthalide, 3-Hydroxyisoindolin-1-one and 3-Hydroxyoxindole Derivatives

An efficient method for the synthesis of three classes of heterocyclic derivatives such as 3,3-disubstituted phthalides, 3-hydroxyisoindolin-1-ones and 3-hydroxyoxindoles, is reported. In the presence of the simple reductive system, zinc (Zn)/ammonia (NH3) [or zinc-copper (Zn-Cu)/ammonia], a wide range of alkenes including acrylates, acrylonitrile, acrylamide and vinyl sulfoxide underwent reductive coupling with methyl 2-acylbenzoates and subsequent lactonization to provide 3,3-disubstituted phthalides in good to high yields at ambient temperature. In a similar manner, 3-hydroxyisoindolin-1-one and 3-hydroxyoxindole derivatives could also be easily prepared by direct reductive coupling of phthalimides and N-substituted isatins with activated alkenes, respectively. Application of this methodology towards the synthesis of 1-naphthol derivatives on a gram scale is also depicted. Furthermore, the intramolecular phthalimides-ene reductive coupling afforded the respective cyclization products with high diastereoselectivity.t