Metalation of toluene

Toluene itself can be lithiated by w-BuLi-TMEDA at or above room temperature, and deprotonation occurs almost exclusively at the methyl group—about 10% ring metallation (mainly in the meta position) is observed with w-BuLi-TMEDA (Scheme 188) . At lower temperatures deprotonation is very slow , and the best conditions for achieving the metallation of toluene are the Lochmann-Schlosser superbases (see Section VI) °. 

Several investigations have been directed at the metalation of substituted ferrocenes (60, 106). Rinehart and coworkers have recently found that 1,1 -dimethylferrocene is metalated in the ring and not at the methyl group, in contrast to the metalation of toluene. 

Step 2, chain initiation, involves the metalation of toluene by an organosodium compound. Since the action of sodium on the reactants does not produce organosodium compounds, a "promoter is added to accomplish it. o-Chloro-toluene and anthracene were found to be effective pronibters since they readily react with sodium to form benzylsodium and disodium anthracene (6), respectively. The promoters also facilitate the dispersion of sodium into a very fine black powder which can form additional organosodium compounds as the reactions progress. 

The preparation of benzyllithium from benzyl halides and alkyllithiums is not feasible because the benzyllithium initially formed reacts with the starting benzyl halides, producing 1,2-diphenylethane. Metalation of toluene with n-BuLi in the presence of TMEDA at 30 °C results in a 92 8 ratio of benzyllithium and ring metalated products. Metalation of toluene with n-BuLi in the presence of potassium rert-butoxide, and treatment of the resultant organopotassium compound with lithium bromide, affords pure benzyllithium in 89% yield. Alternatively, benzyllithiums are accessible by cleavage of alkyl benzyl ethers with lithium metal. " ... 

Metallation of Toluene with BuLi t-BuOK in Hexane... 

Studying these reactions in solution by quenching with electrophilic iodine revealed that while the weta-metalated product was the major product (73%), a small amount of ortho-metalation (6%) and para-metalation (21%) had also occurred [62]. The wefa-metalation of toluene can also be accomplished using the heteroleptic sodium magnesiate TMEDA-Na(TMP)(nBu)Mg(TMP) (Fig. 16) [63]. This base operates synergically via overall alkyl basicity to yield a discrete molecular framework containing a bridging molecule of toluene, metalated at the meta position [64]. 

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