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Titolo:
Rational design of chiral lithium amides for asymmetric alkylation reactions - NMR spectroscopic studies of mixed lithium amide/alkyllithium complexes
Autore:
Arvidsson, PI; Hilmersson, G; Davidsson, O;
Indirizzi:
Univ Gothenburg, Dept Chem, SE-41296 Gothenburg, Sweden Univ Gothenburg Gothenburg Sweden SE-41296 , SE-41296 Gothenburg, Sweden
Titolo Testata:
CHEMISTRY-A EUROPEAN JOURNAL
fascicolo: 8, volume: 5, anno: 1999,
pagine: 2348 - 2355
SICI:
0947-6539(199906)5:8<2348:RDOCLA>2.0.ZU;2-B
Fonte:
ISI
Lingua:
ENG
Soggetto:
ENANTIOSELECTIVE ADDITION; N-BUTYLLITHIUM; ORGANOMETALLIC REAGENTS; AROMATIC-ALDEHYDES; CARBONYL-COMPOUNDS; LIGAND STRUCTURE; TERT-BUTOXIDE; DEPROTONATION; (-)-SPARTEINE; SUBSTITUTION;
Keywords:
alkylations; asymmetric synthesis; chiral lithium amides; mixed complexes; NMR spectroscopy;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
75
Recensione:
Indirizzi per estratti:
Indirizzo: Davidsson, O Univ Gothenburg, Dept Chem, SE-41296 Gothenburg, Sweden Univ Gothenburg Gothenburg Sweden SE-41296 thenburg, Sweden
Citazione:
P.I. Arvidsson et al., "Rational design of chiral lithium amides for asymmetric alkylation reactions - NMR spectroscopic studies of mixed lithium amide/alkyllithium complexes", CHEM-EUR J, 5(8), 1999, pp. 2348-2355

Abstract

Treatment of solutions of chiral lithium amides, containing internally coordinating groups, in diethyl ether (DEE) with alkyllithiums results in the formation of chiral lithium amide/alkyl-lithium mixed dimers. We report theuse of eight different chiral lithium amides/n-butyllithium mixed dimers in the asymmetric alkylation of benzaldehyde in DEE solution at -116 degreesC. The addition product, (S)-1-phenyl-1-pentanol, was formed with enantiomeric excesses (ee's) ranging from 0 to 82%. In DEE/dimethoxy methane solvent mixtures the stereoselectivity was improved and gave the product in 91% ee. Comparison of the ligand structures revealed that only one chiral centerwas necessary to obtain high enantioselectivity. Replacement of the internally coordinating methoxy group with a pyrrolidine group lowered the ee from 82% to 24%, Low-temperature Li-6 NMR studies of mixtures of these reagents in DEE revealed large differences in the concentration of the reactive mixed dimers formed. Full complexation of nBuLi to the chiral lithium amides is not necessary in order to obtain high enantioselectivity, as the result of an increased reactivity of the complexed nBuLi.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 26/01/20 alle ore 16:01:00