| The structures of a series of substituted lithium phenolates in solution in weakly polar aprotic solvents, such as ethers and tertiary amines, have been established by ;The mechanism of the degenerate transesterification of 3,5-dimethylphenyl esters with lithium 3,5-dimethylphenolate in weakly polar aprotic solvents was investigated as a model system for O-acylation of lithium enolates. The rates of transesterification were observed to be slower in more basic solvents and to have a first order dependence on the concentration of lithium phenolate. Esters containing a neighboring Lewis base exhibit enhanced relative rates of transesterification, when compared to their relative rates of base hydrolysis. This effect is attributed to a Complex Induced Proximity Effect and its magnitude is dependent upon the donicity of the neighboring Lewis base, as well as its proximity to the ester moiety. A reaction mechanism involving a pre-equilibrium of the ester coordinating to the lithium phenolate tetramer is proposed, and the implications of this mechanism to aldol chemistry are discussed. |
