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Titolo:
HOMOLYTIC REACTIONS OF LIGATED BORANES .16. ENANTIOSELECTIVE HYDROGEN-ATOM ABSTRACTION BY CHIRAL AMINE BORYL RADICALS - CATALYTIC KINETIC RESOLUTION OF ESTERS AND OF CAMPHOR
Autore:
MOK PLH; ROBERTS BP; MCKETTY PT;
Indirizzi:
UNIV LONDON UNIV COLL,DEPT CHEM,CHRISTOPHER INGOLD LABS,20 GORDON ST LONDON WC1H 0AJ ENGLAND UNIV LONDON UNIV COLL,DEPT CHEM,CHRISTOPHER INGOLD LABS,20 GORDON ST LONDON WC1H 0AJ ENGLAND
Titolo Testata:
Perkin transactions. 2
fascicolo: 4, , anno: 1993,
pagine: 665 - 674
SICI:
0300-9580(1993):4<665:HROLB.>2.0.ZU;2-O
Fonte:
ISI
Lingua:
ENG
Soggetto:
ASYMMETRIC REDUCTION; SELECTIVE REDUCTIONS; STERIC REQUIREMENTS; ADDITION-COMPOUNDS; PROCHIRAL KETONES; TRANSITION-STATE; REAGENTS; MONOISOPINOCAMPHEYLBORANE; TRIETHYLSILANE; HYDROBORATION;
Tipo documento:
Article
Natura:
Periodico
Citazioni:
65
Recensione:
Indirizzi per estratti:
Citazione:
P.L.H. Mok et al., "HOMOLYTIC REACTIONS OF LIGATED BORANES .16. ENANTIOSELECTIVE HYDROGEN-ATOM ABSTRACTION BY CHIRAL AMINE BORYL RADICALS - CATALYTIC KINETIC RESOLUTION OF ESTERS AND OF CAMPHOR", Perkin transactions. 2, (4), 1993, pp. 665-674

Abstract

UV irradiation of an oxirane solution containing di-tert-butyl peroxide, an amine-alkylborane complex (in which the B-alkyl group is optically active) and a racemic ester or camphor as substrate, gives rise initially to the tert-butoxyl radical which rapidly abstracts hydrogen from the complex to form an optically active amine-boryl radical. The amine-boryl radical then abstracts hydrogen enantioselectively from a C-H group alpha to the carbonyl group in the substrate to regenerate the amine-alkylborane. This abstraction reaction has been used to bring about catalytic kinetic resolution of the substrate, using the bis(isopinocampheylborane) complex of N,N,N',N'-tetramethylethylenediamine and some of its derivatives as catalysts. After partial consumption of the substrate, the amount remaining and its enantiomeric excess (ee) have been used to derive enantioselectivity constants for hydrogen-atom abstraction. Enantioselectivity varies considerably with the structureof the substrate. The highest selectivity was observed for hydrogen abstraction from dimethyl 2,2-dimethyl-1,3-dioxolane-trans-4,5-dicarboxylate when after 75% consumption of initially-racemic ester at -90-degrees-C, the residual substrate showed an ee of 97%. A transition-statemodel is proposed to account for the observed enantioselectivities.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 28/09/20 alle ore 05:00:33