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Titolo:
PLATINUM-CATALYZED AND ACID-CATALYZED ENYNE METATHESIS REACTIONS - MECHANISTIC STUDIES AND APPLICATIONS TO THE SYNTHESES OF STREPTORUBIN-B AND METACYCLOPRODIGIOSIN
Autore:
FURSTNER A; SZILLAT H; GABOR B; MYNOTT R;
Indirizzi:
MAX PLANCK INST KOHLENFORSCH D-45470 MULHEIM GERMANY
Titolo Testata:
Journal of the American Chemical Society
fascicolo: 33, volume: 120, anno: 1998,
pagine: 8305 - 8314
SICI:
0002-7863(1998)120:33<8305:PAAEMR>2.0.ZU;2-5
Fonte:
ISI
Lingua:
ENG
Soggetto:
RING-CLOSING METATHESIS; LOW-VALENT TITANIUM; PRODIGIOSIN 25-C; CONJUGATE REDUCTION; MURINE SPLENOCYTES; OLEFIN METATHESIS; H+-ATPASE; T-CELLS; DEOXYGENATION; ROUTE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
86
Recensione:
Indirizzi per estratti:
Citazione:
A. Furstner et al., "PLATINUM-CATALYZED AND ACID-CATALYZED ENYNE METATHESIS REACTIONS - MECHANISTIC STUDIES AND APPLICATIONS TO THE SYNTHESES OF STREPTORUBIN-B AND METACYCLOPRODIGIOSIN", Journal of the American Chemical Society, 120(33), 1998, pp. 8305-8314

Abstract

Formal total syntheses of the antibiotics metacycloprodigiosin (2) and streptorubin B (3) are described, which are known to exhibit promising immunomodulating properties. The key step en route:to their meta-bridged pyrrole core structures 5 and 7, respectively, consists of a metathesis reaction of electron-deficient enynes catalyzed by either platinum halides, hard Lewis acids, or HBF4. This transformation expands the pre-existing cycloalkene of the substrates by two C atoms, forges the bicyclic pyrrolophane structure of the targets, and simultaneously forms a bridgehead alkene function. The products of this skeletal rearrangement are converted into the targets by a sequence comprising (i) a stepwise reduction of their enone entity to the corresponding saturated alcohols and (ii) an aromatization of the N-tosylated dihydropyrroles 20 and 34 thus obtained via elimination of potassium sulfinate on exposure to KAPA (potassium 3-aminopropylamide). A careful analysis ofthe minor byproducts formed in the enyne metathesis reactions allows a mechanistic rationale to be proposed for this operationally trivial yet highly attractive transformation which involves ''nonclassical'' cycloprbpylmethyl-homoallyl-cyclobutyl cations as key intermediates. This cationic pathway is distinctly different from mechanistic interpretations of other enyne metathesis reactions previously reported in the literature.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 02/04/20 alle ore 22:17:53