Characterization of a chiral enolate aggregate and observation of 6Li-1H scalar coupling.
A chiral enolate aggregate 1 containing a lithium enolate and a chiral lithium amide was systematically investigated by various NMR techniques. (1)H and (13)C DOSY at 25 and -78 degrees C provide its solution structure, aggregation number, and formula weight. Multiple 2D (6)Li NMR techniques, such as (6)Li-(6)Li EXSY, (6)Li-(1)H HOESY, were utilized to investigate its stereochemical structure. The configuration of the enolate in complex 1 was confirmed by (6)Li-(1)H HOESY and trapping with TMS-Cl. A unique (6)Li-(1)H coupling through the Li-N-C-H network was observed. This scalar coupling was corroborated by (6)Li-(1)H HMQC, deuterium labeling experiments, and selective (1)H decoupling (6)Li NMR. The stereostructure of 1 provides a model for the origin of enantioselectivity of chiral lithium amide-induced enolate addition reactions.
Li
Deyu
D
Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
Sun
Chengzao
C
Williard
Paul G
PG
D000577:Amides / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D018020:Lithium Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*
D000577:Amides; D018020:Lithium Compounds; D006859:Hydrogen