Solvent effects control the regioselectivity with which tert-butyllithium deprotonates 2-ethyl-N,N-diisopropyl-1-benzamide. From THF an ortho-lithiated dimer is isolated but from N,N,N′,N′′,N′′pentamethyldiethylenetriamine (pmdeta) a laterally lithiated monomer is obtained (see scheme). Density functional theory (DFT) calculations point to the importance of Lewis base solvation and aggregation state in determining the chemoselectivity.
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Armstrong et al. (2004) studied this question.