Sparteine-mediated a-lithiation of N-BOC-N-methylbenzylamine: Rapid racemization and subsequent deracemization

Upon a-lithiation of N-BOC-N-methylbenzylamine (tert-Bu N-benzyl-N-methylcarbamate) with sec-BuLi in the presence of (-)-sparteine, the pro-(S) proton is preferentially abstracted (kinetic resoln. of the racemic a-deuterated deriv. up to 88% enantiomeric excess). The enantiomerically enriched organometallic intermediate thus generated instantaneously racemizes. Enantioselectivity, however, is restored in the course of 15-45 min., apparently due to adduct formation between the (S)-aminobenzyllithium species and sparteine. Subsequent reaction with typical electrophiles (CO2, CS2, MeI, Me2SO4, w-deuteriophenylacetylene) occurs with retention (51-90% enantiomeric excess), in hexane or Et2O, and with inversion (68-85%), in THF. [on SciFinder (R)]


Published in:
Journal of the American Chemical Society, 117, 49, 12342-3
Year:
1995
Keywords:
Note:
CAN 124:145553 25-18 Benzene, Its Derivatives, and Condensed Benzenoid Compounds Institut de Chimie organique,Universite Lausanne,Lausanne-Dorigny,Switz. Journal 0002-7863 written in English. 74-88-4 (Methyl iodide); 75-15-0 (Carbon disulfide); 77-78-1 (Dimethyl sulfate); 90-39-1 ((-)-Sparteine); 124-38-9 (Carbon dioxide); 2032-35-1 (2,2-Diethoxyethyl bromide); 3240-11-7; 81616-14-0; 173278-21-2 Role: RCT (Reactant), RACT (Reactant or reagent) (rapid racemization and subsequent deracemization in the sparteine-mediated lithiation of protected methylbenzylamine); 173278-23-4P; 173278-25-6P; 173278-27-8P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (rapid racemization and subsequent deracemization in the sparteine-mediated lithiation of protected methylbenzylamine); 30925-11-2P; 30925-12-3P; 173278-22-3P; 173278-24-5P; 173278-26-7P; 173278-28-9P; 173278-29-0P; 173278-30-3P Role: SPN (Synthetic preparation), PREP (Preparation) (rapid racemization and subsequent deracemization in the sparteine-mediated lithiation of protected methylbenzylamine)
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