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 pK a of 3-phenylcoumaran-2one is 8.39 in water at 25 ЊC and the 3-phenyl substituent increases the carbon acidity by 10 4 . 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 1g of ؊0.6. This is compatible with rate limiting formation of a tetrahedral intermediate.

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