Pericyclic reactions of cyclobutyne: An exception to orbital symmetry considerations

Tetrahedron

Volumn 52, Issue 7, 1996, Pages 2279-2290

  Gilbert, John C ^a   Kirschner, Steven ^a,b  

^a UNIVERSITY OF TEXAS AT AUSTIN   (United States)

^b AUSTIN COMMUNITY COLLEGE   (United States)

Author keywords

AM1 reaction path; cyclobutyne; orbital isomerism; orbital symmetry; pericyclic reactions

Indexed keywords

ALKYNE DERIVATIVE; CYCLOALKANE DERIVATIVE;

ARTICLE; COMPUTER SIMULATION; DRUG STRUCTURE; MOLECULAR DYNAMICS; PRIORITY JOURNAL; THERMODYNAMICS;

EID: 0030063158     PISSN: 00404020     EISSN: None     Source Type: Journal    
DOI: 10.1016/0040-4020(95)01061-0     Document Type: Article

References (42)

1. The University of Texas at Austin
2. Austin Community College
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12. A preliminary report (Baumgart, K. D.; Szeimies, G. Tetrahedron Lett. 1984, 25, 737-740) has appeared claiming the intermediacy of bicyclo[3.2.0]hept-6-yne, but full details have not been published.
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19. 10 Our own work suggests that this definition is too restrictive with respect to the relationship of the orbitals that cross.
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27. 12 A classical cycloalkyne therefore undergoes cycloaddition reactions in a conventional manner, with [2+2] cycloadditions thermally forbidden and [2+4] cycloadditions thermally allowed. A non-classical alkyne would then be a species that, relative to its classical analog, would have a transposition of an occupied and an unoccupied molecular orbital, with the appropriate change in electronic occupation. Such a molecule would be classified as an orbital isomer and would react via a mechanistic motif opposite to that of the classical species, yielding thermally allowed [2+2] and thermally forbidden [2+4] cycloaddition, respectively.
28. Dewar, M. J. S.; Kirschner, S. J. Am. Chem. Soc. 1971, 93, 4290-4291.
29. 20
30. Kirscher, S. unpublished results.
31. Dewar, M. J. S.; Kirschner, S. J. Am. Chem. Soc. 1971, 93, 4292-4294.
32. The authors thank Prof. Roald Hoffmann for helpful discussions that led to this approach.
33. (a) Longuet-Higgins, H. C.; Abrahamson, E. W. J. Am. Chem. Soc. 1965, 87, 2045-2046;
34. (b) Woodward, R. B.; Hoffmann, R. J. Am. Chem. Soc. 1965, 87, 2046-2048.
35. These eigenvectors are available upon request from the authors.
36. 10
37. 23 cyclobutyne, but it is not.
38. Possible rationales for the relatively favorable kinetics of the stepwise pathway may be derived from the orthogonal relationship between the methylene groups at C(2) and C(1) of 10a, which minimizes torsional strain, and from the overlap of the p-orbital on C(2) with the π-bond of the cyclobutene ring.
39. 31 It is in this context that we rationalize the seemingly large magnitude of the computed activation barrier.
40. Dewar, M. J. S.; Kirschner, S.; Kollmar, H. W.; Wade, L. E. J. Am. Chem. Soc. 1974, 96, 5242-5244.
41. (a) Dewar, M. J. S.; Kirschner, S. J. Am. Chem. Soc. 1974, 96, 5246-5247;
42. (b) Doubleday, C. Jr. J. Am. Chem. Soc. 1993, 115, 11968-11983.