Formation of Heterodimer Complexes between Analogous Chiral Lithium Amides:  NMR Spectroscopic and Computational Studies

Mixing two analogous lithium amide salts from methyl(1-phenyl-2-(pyrrolidin-1-yl)ethyl)[15N]amine (1) and (2-methoxy-1-phenylethyl)methylamine (2) in a 1:1 ratio in diethyl ether resulted in a formation of five different dimer complexes, three homodimers and two heterodimers. Computational studies of the relative stabilities of the different dimers were found to be in concordance with relative concentrations observed by NMR spectroscopy. The desymmetrization of cyclohexene oxide using the mixture of Li-1 and Li-2 indicated that the heterodimer exhibited a higher asymmetric induction than either lithium amide by itself according to the “superbases” and the alkyllithium/lithium alkoxide mixtures.