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Volumn 63, Issue 20, 1998, Pages 7037-7052

Camphor-derived, chelating auxiliaries for the highly diastereoselective intermolecular Pauson-Khand reaction: Experimental and computational studies

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EID: 0001263521     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo9809985     Document Type: Article
Times cited : (93)

References (136)
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    • note
    • Preliminary studies performed with the dicobalt hexacarbonyl complexes of the alkoxyacetylenes derived from frans-2-phenylthiocyclohexanol and trans-2-(tert-butylthio)cyclohexanol did not provide any evidence of chelation (see the following text in the paper).
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    • Parallel behavior has been observed by Krafft and co-workers in the dicobalt hexacarbonyl complex of a bis-homopropargylic thioether (see ref 8e).
    • Parallel behavior has been observed by Krafft and co-workers in the dicobalt hexacarbonyl complex of a bis-homopropargylic thioether (see ref 8e).
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    • According to PM3 calculations, the electron density at sulfur in alcohols 1-3 varies in the order 2 > 1 > 3.
    • According to PM3 calculations, the electron density at sulfur in alcohols 1-3 varies in the order 2 > 1 > 3.
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    • For some non-Pauson-Khand enantioselective cycloaddition routes leading to five-membered rings, see: (a) Greene, A. E.; Charbonnier, F. Tetrahedron Lett. 1985,26, 5525-5528.
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    • note
    • Given the existence otE/Z isomers in 25, which could influence the value of the optical rotation (cf. ref 34), a commercial sample of enantiomerically pure (fl)-(+)-3-methylcyclopentanone (Aldrich, no. M3.970-9) was converted to the semicarbazone under exactly the same experimental conditions. This semicarbazone was subsequently used as a reference.
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    • note
    • The formation of these cobaltacycles has the stereoelectronic requirement of eclipsing C=C and Co-C(H) bonds. A similar set of regioisomeric cobaltacyles leading to the never detected β-alkoxysubstituted cyclopentenones would form via eclipsing of the C=C and the Co-C(OR*) bonds.
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    • SPARTAN, version 4.1.1, Wavefunction, Inc., 18401 Von Karman Ave., Suite 370, Irvine, CA, 92612.
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    • note
    • 2 cluster, both the Co-Co and the C-Co distances are accurately reproduced, while the C-C distance is somewhat overestimated. If desired, this parameter can be fixed to the mean crystallographic value of 1.336 Å without introduction of distortion in the overall structure. With respect to coordinatively unsaturated cobalt species, PM3(tm) shows an exaggerated tendency (with respect to higher level DFT methods) to saturate cobalt either through bridging carbonyls or through agostic interactions with hydrogen atoms. Structures presenting these characteristics should be treated carefully until confirmation of these effects by means of independent DFT optimization.
  • 126
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    • bridge, performed at the same DFT level used for energy calculations in the present study, showed that the bridged structure is a stationary point at that level of theory.
    • bridge, performed at the same DFT level used for energy calculations in the present study, showed that the bridged structure is a stationary point at that level of theory.
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    • note
    • Note, however, that this or a similar mechanism could be involved in a hypothetical equilibration of lOb when generated at room temperature by NMO oxidation of lOa in the absence of any olefin. Under these reaction conditions (presence of olefin), if diastereoselectivity depends on cobalt-specificity of the chelating arm/olefin substitution process, its level will be determined by the relative rates of Pauson-Khand reaction and epimerization. This is in agreement with the fact that the more reactive olefins provide the higher diastercomeric ratios of ketone products.
  • 128
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    • -1.
    • -1.
  • 129
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    • Phosphine-substituted dicobalt pentacarbonyl complexes of alkynes are less reactive toward alkenes than the parent hexacarbonyl complexes. See, for instance, ref 6e and: Bradley, D. H.; Khan, M. A.; Nicholas, K. M. Organometallics 1992, 11, 2598-2607.
    • (1992) Organometallics , vol.11 , pp. 2598-2607
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    • For a similar suggestion on solvent stabilization of (otherwise) unsaturated intermediates in ligand-exchange reactions taking place by a dissociative mechanism, see: Cowey, W. D.; Brown, T. L. Inorg. Chem. 1973,12, 2820-2825.
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    • -1) should be similar to the activation enthalpy of the substitution process.
    • -1) should be similar to the activation enthalpy of the substitution process.
  • 134
    • 85034200064 scopus 로고    scopus 로고
    • note
    • 3) δ 0.88 (s, 3H), 0.98 (s, 3H), 1.10-1.90 (m, 7H), 2.08 (s, 3H), 2.45-2-75 (AB, J = 11 Hz, 2H), 3.69 (s, 3H), 4.12 (m, 1H), 5.20, 7.60 (AB, J = 12 Hz, 2H) ppm.
  • 135
    • 85034186366 scopus 로고    scopus 로고
    • Extended reduction times may result in overreduction of 22. In this case, the corresponding alcohol can be rcoxidized with PCC.
    • Extended reduction times may result in overreduction of 22. In this case, the corresponding alcohol can be rcoxidized with PCC.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.