Kinetics and Mechanism of the Ivanov Reaction: Reaction of Aldehydes and Ketones with Phenylacetic Acit Magnesium Enediolate

Article abstract of DOI:10.1021/jo00214a030

Stopped-flow kinetics of the reaction between aldehydes or ketones and the magnesium enediolate of phenylacetic acid in THF are second order at enediolate concentrations <10^-3 M.At concentrations of 10^-3 - 3*10^-2 M, the formation of a bis(enediolate) requires a more complex kinetic equation.Second-order rate constans are reported for the reaction of the enediolate with a number of aldehydes and ketones at 25 deg C.Entropies of activation for cyclohexanone, benzaldehyde, 2-methylpropanal, and 2,2-dimethylpropanal are positive, and enthalpy-entropy compensation is observed.Ef fects of cycloalkanone ring size and benzaldehyde substituents are small and are ascribable to a transition state with a very small C-C bond order.A two-step mechanism is proposed, with preequilibrium formation of a coordination intermediate which, in some cases, is accompanied by a change in the magnesium coordination number.Effects of alkyl groups on aldehyde and ketone reactivity stem mainly from steric desolvation.