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Titolo:
STEREOCHEMICAL AND MECHANISTIC STUDIES ON CONJUGATE ADDITION OF ORGANOCUPRATES TO ACYCLIC ENONES AND ENOATES - SIMPLE RULE FOR DIASTEREOFACIAL SELECTIVITY
Autore:
YAMAMOTO K; OGURA H; JUKUTA J; INOUE H; HAMADA K; SUGIYAMA Y; YAMADA S;
Indirizzi:
TOKYO MED & DENT UNIV,INST MED & DENT ENGN,CHIYODA KU,2-3-10 SURUGADAI KANDA TOKYO 101 JAPAN TOKYO MED & DENT UNIV,INST MED & DENT ENGN,CHIYODA KU TOKYO 101 JAPAN
Titolo Testata:
Journal of organic chemistry
fascicolo: 13, volume: 63, anno: 1998,
pagine: 4449 - 4458
SICI:
0022-3263(1998)63:13<4449:SAMSOC>2.0.ZU;2-3
Fonte:
ISI
Lingua:
ENG
Soggetto:
ELECTRON-TRANSFER PROCESS; SIDE-CHAIN CONFORMATION; DOUBLE-BOND GEOMETRY; ORGANOCOPPER REAGENTS; LITHIUM DIMETHYLCUPRATE; ASYMMETRIC INDUCTION; HIGHER-ORDER; GAMMA-ALKOXY-ALPHA,BETA-UNSATURATED ESTERS; 1-ALPHA,25-DIHYDROXYVITAMIN D-3; SUBSTITUTION-REACTIONS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
82
Recensione:
Indirizzi per estratti:
Citazione:
K. Yamamoto et al., "STEREOCHEMICAL AND MECHANISTIC STUDIES ON CONJUGATE ADDITION OF ORGANOCUPRATES TO ACYCLIC ENONES AND ENOATES - SIMPLE RULE FOR DIASTEREOFACIAL SELECTIVITY", Journal of organic chemistry, 63(13), 1998, pp. 4449-4458

Abstract

Systematic studies of organocuprate conjugate additions to three pairs of gamma-epimeric and geometrically isomeric gamma-chiral acyclic enones (1a, 2a; 1b, 2b; and 3, 4) and two pairs of gamma-chiral acyclic enoates (5, 6 and 7, 8) allowed us to generalize diastereofacial selectivity of these reactions. The diastereoselectivity depended on the double-bond geometry, the configuration at the gamma-position, and the reaction conditions. In reactions without activating additives, cuprateadded to the si-face of the geometrically isomeric pair of E- and Z-enones (1a and 2a) with high diastereoselectivity (98%), while their epimers at the gamma-position (3 and 4) yielded re-facial adduct preferentially (86-97%). Addition of TMSC1 and HMPA together not only accelerated the addition reaction but also completely changed the pattern of pi-facial selectivity. In reactions containing those additives, cuprates added to isomeric E- and Z-enones with reverse facial selectivity: E-enone la gave the si-facial adduct exclusively, whereas isomeric Z-enone 2a yielded the re-facial adduct with high selectivity(97%). Theirgamma-epimers gave opposite results; namely, the E-isomer 3 reacted with re-facial selectivity (97%), while the Z-isomer 4 reacted with si-facial selectivity (75%).;Under conditions where both TMSC1 and HMPA were present, even the enoates (5-8) reacted efficiently with similarlyreverse and high facial selectivity. On the basis of these results, we postulate a general and clear-cut rule to predict diastereofacial selectivity of cuprate conjugate additions in which a possibility of Z-Eisomerization of starting enones is taken into account as a crucial determinant.

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Documento generato il 26/09/20 alle ore 04:39:48