CHIRAL ORGANOLITHIUM COMPLEXES - THE STRUCTURE OF BETA-LITHIATED BETA-PHENYLCARBOXAMIDES AND THE MECHANISM OF ASYMMETRIC SUBSTITUTION IN THE PRESENCE OF (-)-SPARTEINE

Investigation of the structure and reactivity of beta-lithiated beta-p henylcarboxamides is reported. NMR spectroscopic investigations of bet a-lithiated amides 15 and 24 establish that the benzylic lithium is co mplexed by the nitrogen of the amide. The beta-lithiated N-methyl amid e 15 forms a complex with (-)-sparteine (4) which undergoes electrophi lic substitution to provide enantioenriched products. The beta-lithiat ed N-isopropyl amide 24 does not form a complex with 4, so there is no asymmetric induction. The enantioselectivity of the reaction is shown to arise by the pathway of asymmetric substitution in which asymmetry is induced in a postdeprotonation step. Asymmetric induction in this lithiation-substitution sequence is suggested to occur via a dynamic t hermodynamic resolution.