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Volumn 69, Issue 6, 2004, Pages 2056-2069

Alkanethioimidoyl Radicals: Evaluation of β-Scission Rates and of Cyclization onto S-Alkenyl Substituents

Author keywords

[No Author keywords available]

Indexed keywords

CONFORMATIONS; ELECTRON SPIN RESONANCE SPECTROSCOPY; PROBABILITY DENSITY FUNCTION; RATE CONSTANTS; ROTATION; SUBSTITUTION REACTIONS;

EID: 1642329299     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo0353637     Document Type: Article
Times cited : (26)

References (62)
  • 6
    • 0002002167 scopus 로고    scopus 로고
    • Renaud, P., Sibi, M. P., Eds., Wiley-VCH: Weinheim, Germany, Chapt. 1.3.1
    • For a review on radical addition to isonitriles, see Nanni, D. In Radicals in Organic Synthesis, Renaud, P., Sibi, M. P., Eds., Wiley-VCH: Weinheim, Germany, 2001; Vol. 2, Chapt. 1.3.1, pp 44-61.
    • (2001) Radicals in Organic Synthesis , vol.2 , pp. 44-61
    • Nanni, D.1
  • 19
    • 0009922754 scopus 로고    scopus 로고
    • Recent theoretical work has suggested that the bent σ-structure is essentially independent of the electronic nature of the α-substituent: Guerra, M. J. Phys. Chem. 1996, 100, 19350.
    • (1996) J. Phys. Chem. , vol.100 , pp. 19350
    • Guerra, M.1
  • 22
    • 1642306816 scopus 로고    scopus 로고
    • note
    • Note, however, that Blum and Roberts observed C-N β-scission of t-BuN=C·OMe to afford the EPR spectrum of t-Bu· radicals at higher temperatures.
  • 23
    • 1642308414 scopus 로고    scopus 로고
    • note
    • An experiment with n-propane as solvent showed no interpretable spectra in the range 110-150 K.
  • 34
    • 0025277178 scopus 로고
    • For some representative papers on alkoxycarbonyl radicals, see (with references therein) (a) Forbes, J. E.; Zard, S. Z. J. Am. Chem. Soc. 1990, 112, 2034.
    • (1990) J. Am. Chem. Soc. , vol.112 , pp. 2034
    • Forbes, J.E.1    Zard, S.Z.2
  • 42
    • 1642349114 scopus 로고    scopus 로고
    • note
    • H2 process of alkyl radicals onto the dichalcogenide was also supported by the presence of dibutenyl sulfide among the reaction products of disulfide 5i with isonitrile 4C (see the section on cyclization). Although this product could also form by coupling of butenyls with sulfanyl radicals, it is likely that the major formation pathway is actually intermolecular attack of the butenyl radicals onto the starting disulfide.
  • 49
  • 50
    • 1642326401 scopus 로고    scopus 로고
    • note
    • 2) values were in the range 0.7530-0.7650 before annihilation and 0.7500 after annihilation of higher multiplicity spin states. The transition states for β-fragmentations (or cyclization) were optimized by performing a progressive elongation of the bond involved in the scission (or ring closure) and optimizing each single step (relaxed scan) with a small basis set (UB3LYP/6-31G). Eventually, the energy maximum was optimized with the usual basis set [6-31+G(2d,p)]. All the transition states were characterized by a unique imaginary frequency corresponding to the desired bond scission (see Supporting Information). Isotropic EPR hfs were derived from the computed Fermi contact integrals and were taken directly from the Gaussian output file.
  • 53
    • 1642282438 scopus 로고    scopus 로고
    • note
    • Analogous differences were found by replacing the c-hexyl group with other secondary chains.
  • 54
    • 1642321576 scopus 로고    scopus 로고
    • note
    • The activation energies reported in Table 4 are properly related to the favored non-W (TS-X-like) transition states.
  • 55
    • 0344293778 scopus 로고
    • Thyagarajan, B. S., Ed.; Wiley: New York
    • Computations on the cis-cyclized radical 11C (see Supporting Information, page S32, right figure) indicated it is more stable by as much as 7.4 kcal/mol than the trans isomer and its computed hfs are in much better agreement with the experimental ones. Calculations therefore suggest that the cyclized radical observed by EPR could be cis- and not trans-11C. All the thioimidoyl radicals are more stable in their trans configurations, and the C=N double bonds are not directly involved in the ring closures. Hence, the formation of the cis-cyclized radical implies a trans-cis equilibration of the starting thioimidoyls, followed by thermodynamically controlled 5-exo cyclizations. This explanation is also favored by the relatively high activation barrier for reopening of cis-11C (19.7 kcal/mol compared to 12.7 kcal/mol for reopening of trans-11C). Trans-cis isomerization of thioimidoyls can be in principle a viable process, since they are isoelectronic with vinyl radicals, which in turn are well-known to undergo fast E/Z equilibration [see for instance (a) Singer, L. A. Selective Organic Transformations; Thyagarajan, B. S., Ed.; Wiley: New York, 1972; Vol. 11, p 239.
    • (1972) Selective Organic Transformations , vol.11 , pp. 239
    • Singer, L.A.1


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.