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.
|Number of pages||6|
|Journal||Journal of the Chemical Society. Perkin Transactions 2|
|Publication status||Published - Mar 1998|