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Volumn 120, Issue 13, 1998, Pages 3220-3226

Cyclizations of 3-chlorocarbanions to cyclopropanes: 'Strain-free' transition states for forming highly strained rings

Author keywords

[No Author keywords available]

Indexed keywords

CYCLOPROPANE DERIVATIVE;

EID: 0032495782     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja974068z     Document Type: Article
Times cited : (20)

References (48)
  • 10
    • 2642663050 scopus 로고    scopus 로고
    • note
    • N2 reactions has been well documented; however, their early appearance on the reaction coordinate may not have been appreciated.
  • 11
    • 2642627241 scopus 로고    scopus 로고
    • note
    • The destabilization results from a 1,3 repulsive interaction (nucelophile/α-carbon) in the cyclization substrate. Wiberg and Bauld have discussed this type of interaction and the resulting destabilization previously. We will present a detailed analysis soon.
  • 19
    • 0003450764 scopus 로고    scopus 로고
    • Mallard, W. G., Linstrom, P. J., Eds.; National Institute of Standards and Technology Gaithersburg, MD
    • Afeefy, H. Y.; Liebman, J. F.; Stein, S. E. In NIST Standard Reference Database Number 69; Mallard, W. G., Linstrom, P. J., Eds.; National Institute of Standards and Technology (http://webbook.nist.gov): Gaithersburg, MD, 1997.
    • (1997) NIST Standard Reference Database Number 69
    • Afeefy, H.Y.1    Liebman, J.F.2    Stein, S.E.3
  • 20
    • 0003450764 scopus 로고    scopus 로고
    • Mallard, W. G., Linstrom, P. J., Eds.; National Institute of Standards and Technology (http://webbook.nist.gov): Gaithersburg, MD
    • Bartmess, J. E. In NIST Standard Reference Database Number 69; Mallard, W. G., Linstrom, P. J., Eds.; National Institute of Standards and Technology (http://webbook.nist.gov): Gaithersburg, MD, 1997.
    • (1997) NIST Standard Reference Database Number 69
    • Bartmess, J.E.1
  • 21
    • 2642695281 scopus 로고    scopus 로고
    • note
    • In fact, we started with a geometry where the carbanion interacted most strongly with the methyl chloride but it relaxed to IVid.
  • 22
    • 2642630288 scopus 로고    scopus 로고
    • note
    • In each case, it is assumed that the strain in the substituted system is similar to the parent (cyclopropane). Available thermochemistry indicates that this will introduce only a small error; see ref 19.
  • 23
    • 2642623165 scopus 로고    scopus 로고
    • note
    • - → IVr. For these calculations, the separated reactants are used as the ground state in each case, but the ring-opening transition state is favored by more than the entire ring strain of Ip. As a result, a factor other than ring strain must be at work.
  • 24
    • 2642604804 scopus 로고    scopus 로고
    • note
    • - was investigated, and similar barriers were found for the formation of 1,2-butadiene and 1-butyne.
  • 25
    • 2642690237 scopus 로고    scopus 로고
    • note
    • Examples have been reported where cyclizations to three-membered rings have large entropic advantages (>20 eu); however, these are undoubtedly the result of solvation effects.
  • 26
    • 2642596664 scopus 로고    scopus 로고
    • note
    • N2 reaction; however, the proximity effect is still significant (it can provide nearly 50% of the free-energy advantage).
  • 27
    • 2642657898 scopus 로고    scopus 로고
    • note
    • The difference is not the result of additional angle strain in the cyclization transition state. The O-C-C angle is about the same as the C-C-C angles in the carbanion systems. In fact it is wider than the C-C-C angle in the enolate system.
  • 32
    • 2642655883 scopus 로고    scopus 로고
    • note
    • We have shown that four-and five-membered rings do not benefit from the proximity effect. See ref 1.
  • 46
    • 2642593604 scopus 로고    scopus 로고
    • note
    • In fact, it is difficult to find exceptions. One exception involves systems where an aniline nitrogen is the nucleophile - a higher rate constant for forming a three-membered ring is observed. However, delocalization is possible, and therefore, it is not surprising that they do not behave like simple amines. See ref 29.
  • 47
    • 2642653807 scopus 로고    scopus 로고
    • note
    • All the cyclizations to three-membered rings have an entropy advantage. It is the shift in preference from five-membered rings to three-membered rings that involves the proximity effect.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.