Effect of solvent on aggregation and reactivity of two lithium enolates(1)

Studies with two lithium enolates show that aggregation varies from comparable to lower in dimethoxyethane (DME) compared to tetrahydrofuran (THF) but that aggregation is much higher in methyl tert-butyl ether (MTBE). Alkylation reactions, which occur dominantly with the enolate monomers, are exceptionally slow in MTBE, but even acylation reactions that can occur with aggregates are orders of magnitude slower in MTBE. These reactions apparently require additional solvation of the lithium cation, and MTBE is ineffective at such solvation.