Analysis of an asymmetric addition with a 2:1 mixed lithium amide/n-butyllithium aggregate.
A 2:1 lithium amide/ n-butyllithium aggregate 1 is investigated as an asymmetric addition template in hydrocarbon solvents. Several different chiral lithium amides were synthesized from l-valine and tested in the asymmetric addition of n-BuLi to various aldehydes. Enantiomeric excesses up to 83% were obtained in the case of the addition of n-BuLi to pivaldehyde at -116 degrees C in pentane. (1)H and (13)C INEPT DOSY were utilized to characterize a new trimeric complex 12 between 2 equiv of lithium amide and 1 equiv of lithium alkoxide. This mixed aggregate strongly indicates the possibility of product-induced chirality inhibition that is detrimental to the enantioselectivity of asymmetric addition reaction.
Liu
Jia
J
Department of Chemistry, Brown University, Providence, RI 02912, USA.
Li
Deyu
D
Sun
Chengzao
C
Williard
Paul G
PG
D000577:Amides / Q000737:chemistry*; D008024:Ligands; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism
D000577:Amides; D008024:Ligands; D009942:Organometallic Compounds; C434823:n-butyllithium; D008094:Lithium