Trimers chiral lithium amides

In summary, chelating chiral lithium amides exist in either of four major structural motifs or mixtures of them (Scheme 3). Non-coordinating solvents generally favor cyclic trimers, A. Ladder tetramers are favored for pyrrolidide amides in the absence of coordinating solvents. 

NMR studies of the chiral lithium amide Li-10 showed that in the absence of coordinating solvents, e.g. in hexane or toluene, mixed trimers (Li-10)2/n-BuLi dominate, both... 

The rate constant for the exchange of lithiums within the trimer (Li-10)2/w-BuLi is reported to be 0.8 s-1 at — 33 °C, corresponding to an exchange barrier AG 24o of 14.7 kcalmol-1. The rate of lithium-lithium exchange is suggested to be faster within mixed complexes of the chiral lithium amides with n-BuLi than within the homoaggregates49. 

Li-C couplings have been collected for a series of lithium reagents by Reich and co-workers, who studied their chelation and aggregation with potential 5-, 6-, and 7-ring chelating ether and amine ortho substituents. The couplings have been also applied by Hilmersson and Malmros in their studies on mixed dimer and mixed trimer complexes of -BuLi and a chiral hthium amide. 

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