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Titolo:
Enantioselective deprotonation of alkyl carbamates by means of (R,R)-1,2-Bis(N,N-dimethylamino)cyclohexane/sec-butyllithium - Theory and experiment
Autore:
Wurthwein, EU; Behrens, K; Hoppe, D;
Indirizzi:
Univ Munster, Inst Organ Chem, D-48149 Munster, Germany Univ Munster Munster Germany D-48149 rgan Chem, D-48149 Munster, Germany
Titolo Testata:
CHEMISTRY-A EUROPEAN JOURNAL
fascicolo: 12, volume: 5, anno: 1999,
pagine: 3459 - 3463
SICI:
0947-6539(199912)5:12<3459:EDOACB>2.0.ZU;2-S
Fonte:
ISI
Lingua:
ENG
Soggetto:
LITHIATION; COMPLEX;
Keywords:
chiral diamines; lithiation; quantum-chemical calculations; (-)-sparteine; transition states;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
25
Recensione:
Indirizzi per estratti:
Indirizzo: Wurthwein, EU Univ Munster, Inst Organ Chem, Corrensstr 40, D-48149 Munster, Germany Univ Munster Corrensstr 40 Munster Germany D-48149 Germany
Citazione:
E.U. Wurthwein et al., "Enantioselective deprotonation of alkyl carbamates by means of (R,R)-1,2-Bis(N,N-dimethylamino)cyclohexane/sec-butyllithium - Theory and experiment", CHEM-EUR J, 5(12), 1999, pp. 3459-3463

Abstract

The O-ethyl-, O-isobutyl-, and O-neopentyl carbamates la-e were subjected to the conditions of chiral diamine-assisted deprotonation, The efficiencies were compared for (-)-sparteine (7), title compound 8 and (-)-alpha-isosparteine (9). The degree of enantiotopos-differentiation in the deprotonation step was concluded from the enantiomeric ratio in the carboxylation products 6/ent-6, The deprotonation of carbamates la and Ib by sec-butyl-lithium/7 proceeds with very good selectivity (> 95 % ee in favor for the pro-S-H), but is not successful with 1c. (-)-alpha-Isosparteine (9) does not support the deprotonation of alkyl carbamates at all, The medium efficiency of diamine 8 is enhanced by increasing bulk in the beta-position (1a>1b>1c). Quantum-chemical calculations (PM3, ab initio methods) on several models for the competing diastereomorphic transition states of the deprotonation under the influence of 8 reflect well the sense and the magnitude of the observedchiral induction and, in addition, give the first insight in the effects which determine the stereochemical outcome of these reactions.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 24/01/20 alle ore 12:20:56