A MECHANISTIC AND STRUCTURAL INVESTIGATION OF THE (-)-SPARTEINE MEDIATED ASYMMETRIC BENZYLIC LITHIATION SUBSTITUTION-REACTIONS OF N-BOC-N-(P-METHOXYPHENYL)BENZYLAMINE

Mechanistic and structural studies show the high enantioenrichments in the products from lithiation-substitutions of N-Boc-N-(p-methoxypheny l)benzylamine (1) by n-BuLi/(-)-sparteine (6) arise from an enantiosel ective deprotonation of 1 to provide configurationally stable(R)-2/6. NMR spectroscopy establishes that C-13, Li-6 labeled (R)-2/6 and (S)-2 /6 are monomeric with lithium complexed to the benzylic position, the carbonyl of the Boc group and (-)-sparteine. Deprotonations of the ter tiary protons in (R)- and -N-Boc-N-(p-methoxyphenyl)-alpha-methylbenzy lamine ((R)-8 and (S)-8) with n-BuLi/TMEDA provide (R)-9/TMEDA and (S) -9/TMEDA, respectively, with high enantioenrichments. Absolute configu rations assigned to (R)-2 and (R)-1-d(1) allow analysis of the electro phile dependent stereochemistry of the reactions of these configuratio nally stable organolithium intermediates.