Solution structures and reactivities of the mixed aggregates derived from n-butyllithium and vicinal amino alkoxides

Low-temperature Li-6, C-13, and N-15 NMR spectroscopies reveal that mixtures of n-BuLi and (1R,2S)-R'2NCH(R)CH(Ph)OLi (R*OLi; R = Ph or Me; R'N-2 = pyrrolidino or Me2N) in THF/pentane afford a (nBuLi)(3)(R*OLi) (3: 1) mixed tetramer and a C-2-symmetric (n-BuLi)(2)(R*OLi)(2) (2:2) mixed tetramer depending on the proportions of the reactants. The corresponding (n-BuLi)(R*OLi)(3) (1:3) mixed tetramer is not observed. R*OLi-mediated additions of n-BuLi to benzaldehyde proceed with up to 21:1 enantiomeric ratios that depend on the n-BuLi/R*OLi stoichiometries. The enantioselectivities are considered in light of a previously posited mechanism involving reaction via the C-2-symmetric 2:2 mixed tetramer.