Metalations in hydrocarbon solvents; media effects on n-BuLi reactivity

The relative basicities of solutions of n-BuLi in cyclohexane as a function of the addition of increasing increments of THF or TMEDA (designer media) have been assessed. As the chloro DMG is incapable of complexing to n-BuLi, it can neither affect the n-BuLi oligomeric equilibrium nor exhibit a DoM mechanistic component involving prior-coordination (CIPE). Accordingly, by measuring the rates of loss of chlorobenzene in the varied media as well as by certain 7Li NMR studies, a gradual, controlled increase in the basicity of n-BuLi in cyclohexane with increasing increments of THF or TMEDA was observed. Relationships of the basicity in the varied media to the three oligomeric forms of n-BuLi are proposed.