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DOI: 10.1039/A707946J (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1998, 535-540

Mechanism of hydrolysis of coumaran-2-ones

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David M. Heathcote, Gareth A. De Boos, John H. Atherton and Michael I. Page

Abstract

The hydrolysis of coumaran-2-one and 5-substituted 3-phenylcoumaran-2-ones is preceded by a pre-equilibrium involving the formation of an enolate anion at high pH. The pKa of 3-phenylcoumaran-2-one is 8.39 in water at 25 °C and the 3-phenyl substituent increases the carbon acidity by 104. However, despite this ready carbanion formation, the conventional addition–elimination mechanism for hydrolysis of 3-phenylcoumaran-2-ones is confirmed by a solvent kinetic isotope effect of 0.63 and a Brønsted β1g of –0.6. This is compatible with rate limiting formation of a tetrahedral intermediate.

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