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DOI: 10.1039/A805319G (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1999, 333-340

The gas phase 1,2-Wittig rearrangement is an anion reaction. A joint experimental and theoretical study

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John C. Sheldon, Mark S. Taylor, John H. Bowie, Suresh Dua, C. S. Brian Chia and Peter C. H. Eichinger

Abstract

The migratory aptitudes of alkyl groups in the gas phase 1,2-Wittig rearrangement have been determined experimentally as follows. An anion Ph––C(OR1)(OR2), on collisional activation, competitively rearranges to the two 1,2-Wittig ions PhC(R1)(OR2)(O–) and PhC(R2)(OR1)(O–) [R1 and R2 = alkyl and R1 < R2]. These two ions respectively eliminate R2OH and R1OH. The smaller alkanol is eliminated preferentially, indicating that R2 (the larger alkyl group) is migrating preferentially (observed tert-Bu > iso-Pr > Et > Me): a trend generally taken to indicate a radical reaction. However, a Hammett investigation of the relative losses of MeOH from R–C6H4––C(OMe)2 shows this loss decreases markedly as R becomes more electron withdrawing, an observation not consistent with a radical reaction. Ab initio calculations [at the CISD/6-311++G**//RHF (and UHF)/6-311++G** levels of theory] have been used to construct potential surface maps for the model 1,2-Wittig systems –CH2OMe→ EtO–, and –CH2OEt→PrO–. Each of these exothermic reactions involves migration of an alkyl anion. There are no discrete intermediates in the reaction pathways. There is no indication of a radical pathway for either rearrangement. It is proposed that the gas phase 1,2-Wittig rearrangement involves an anionic migration, and that it is not the barrier to the early saddle point but the Arrhenius A factor (or the frequency factor of the QET), which controls the rate of the rearrangement. Weak H-bonding between the alkyl anion and the oxygen of the neutral carbonyl species acts as a pivot in holding the molecular complex together during the migration process. This electrostatic interaction increases with an increase in the number of hydrogens able to H-bond to oxygen and with the number of equivalent ways this H-bonding can occur. The relative migratory aptitude of alkyl anions bound within these molecular complexes is tert-Bu– > iso-Pr– > Et– [double greater-than, compressed] Me–, an order quite different from the migratory aptitudes of anions expected from thermodynamic considerations. This conclusion indicates that great care must be exercised in utilising thermodynamically derived migratory aptitudes to explain the course of a kinetically controlled reaction in the gas phase.

References

  1. W. Schlenk and E. Bergmann, Justin Liebigs Ann. Chem., 1928, 464, 22 Search PubMed; G. Wittig and L. Lohmann, Justin Liebigs Ann. Chem., 1942, 550, 260 Search PubMed; G. Wittig, Angew. Chem., 1954, 66, 10 CAS; H. E. Zimmerman, in Molecular Rearrangements, ed. P. DeMayo, Interscience, Vol. 1, p. 345, 1963 Search PubMed; J. E. Baldwin, J. DeBernardis and J. E. Patrick, Tetrahedron Lett., 1970, 353 Search PubMed.
  2. C. R. Hauser and S. W. Kantor, J. Am. Chem. Soc., 1951, 73, 1437 CrossRef CAS; J. Cast, T. S. Stevens and J. Holmes, J. Chem. Soc., 1960, 3521 RSC.
  3. P. T. Lansbury, V. A. Pattison, J. D. Sidler and J. B. Bierber, J. Am. Chem. Soc., 1966, 88, 78 CrossRef CAS; H. Schafer, U. Schöllkopf and D. Walter, Tetrahedron Lett., 1968, 2809 CrossRef; T. Weiske and H. Schwarz, Tetrahedron, 1986, 42, 6245 CrossRef CAS and references cited therein.
  4. U. Schöllkopf, Angew. Chem., Int. Ed. Engl., 1970, 9, 763 CrossRef.
  5. J. F. Garst and C. D. Smith, J. Am. Chem. Soc., 1976, 98, 1526 CrossRef CAS.
  6. R. A. W. Johnstone and T. S. Stevens, J. Chem. Soc., 1960, 3340 RSC; J. J. Eisch, S. K. Dua and C. A. Kovacs, J. Org. Chem., 1987, 52, 4437 CrossRef CAS and references cited therein.
  7. P. C. H. Eichinger, J. H. Bowie and T. Blumenthal, J. Org. Chem., 1986, 51, 5078 CrossRef.
  8. P. C. H. Eichinger and J. H. Bowie, J. Chem. Soc., Perkin Trans. 2, 1987, 1499 RSC; P. C. H. Eichinger and J. H. Bowie, J. Chem. Soc., Perkin Trans. 2, 1988, 497 RSC; P. C. H. Eichinger and J. H. Bowie, J. Chem. Soc., Perkin Trans. 2, 1990, 1763 RSC.
  9. P. Antoniotti and G. Tonachini, J. Org. Chem., 1993, 58, 3622 CrossRef CAS.
  10. Y.-D. Wu, K. N. Houk and J. A. Marshall, J. Org. Chem., 1990, 55, 1421 CrossRef CAS.
  11. M. R. Ahmad, G. D. Dahlke and S. R. Kass, J. Am. Chem. Soc., 1996, 118, 1398 CrossRef.
  12. G. B. Ellison and P. C. Engelking, J. Chem. Phys., 1978, 69, 1826 CrossRef.
  13. C. H. DePuy, V. M. Bierbaum and R. Damrauer, J. Am. Chem. Soc., 1984, 106, 4051 CrossRef CAS.
  14. J. Fossey, D. Lefort and J. Sorba, Free Radicals in Organic Chemistry, Wiley, New York, 1995, pp. 31–38 Search PubMed.
  15. S. W. Benson, Thermochemical Kinetics, Wiley, New York, London and Sydney, 1968 Search PubMed.
  16. NIST Standard Reference Database - March 1998. Electron Affinities.
  17. F. Ruff and I. G. Csizmadia, Organic Reactions, Equilibria, Kinetics and Mechanism, Elsevier, Amsterdam, 1994, pp. 161–210 Search PubMed.
  18. K. Levsen, Fundamental Aspects of Organic Mass Spectrometry, Verlag Chemie, Weinheim and New York, 1978, p. 119 Search PubMed.
  19. C. H. DePuy, V. M. Bierbaum and R. Damrauer, J. Am. Chem. Soc., 1984, 106, 4051 CrossRef CAS.
  20. D. E. Applequist and D. F. O'Brien, J. Am. Chem. Soc., 1963, 85, 743 CrossRef CAS; R. E. Dessy, W. Kitching, T. Psarras, R. Salinger, A. Chen and T. Chivers, J. Am. Chem. Soc., 1966, 88, 460 CrossRef CAS; A. I. Shatenshtein, Adv. Phys. Org. Chem., 1963, 1, 156.
  21. G. B. Ellison, P. C. Engelking and W. C. Lineberger, J. Am. Chem. Soc., 1978, 100, 2556 CrossRef CAS; C. H. DePuy, V. M. Bierbaum and R. Damrauer, J. Am. Chem. Soc., 1984, 106, 4051 CrossRef CAS; see also S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes, R. D. Levin and W. G. Mallard, Gas Phase Ion and Neutral Thermochemistry, J. Phys. Chem. Ref. Data 17, 1988, Suppl. 1 (the computer version was used) Search PubMed.
  22. G. W. Castellan, Physical Chemistry, Addison-Wesley Publ. Co., Amsterdam, 1983, 3rd edn., pp. 813, 858 Search PubMed.
  23. S. Okada, Y. Abe, S. Tanaguchi and S. Yamabe, J. Am. Chem. Soc., 1987, 109, 295 CrossRef CAS.
  24. For discussions of reaction path degeneracy see: P. J. Robinson and K. A. Holbrook, Unimolecular Reactions, Wiley Interscience, New York, 1972, pp. 80–85 Search PubMed; R. G. Gilbert and S. C. Smith, Theory of Unimolecular and Recombination Reactions, Blackwell Scientific Publications, Oxford, UK, 1990, pp. 87–98 Search PubMed.
  25. V. G. Instruments, Wythenshawe, Manchester, UK, Model ZAB 2HF.
  26. M. B. Stringer, J. H. Bowie and J. L. Holmes, J. Am. Chem. Soc., 1986, 108, 3888 CrossRef CAS.
  27. J. H. Bowie and T. Blumenthal, J. Am. Chem. Soc., 1975, 97, 2959 CrossRef CAS; J. E. Szulejko, J. H. Bowie, I. Howe and J. H. Beynon, Int. J. Mass Spectrom. Ion Phys., 1980, 13, 76.
  28. J. N. Frescos, G. W. Morrow and J. S. Swenton, J. Org. Chem., 1985, 6, 805 CrossRef.
  29. T. Sigeru, I. Tsutoma, T. Sadahito, H. Hirofimi, K. Hideki and U. Kenji, Bull. Chem. Soc. Jpn., 1987, 60, 2173 CAS.
  30. I. Fleming, J. Iqbal and E. P. Krebs, Tetrahedron, 1983, 39, 841 CrossRef CAS.
  31. J. Klein and E. D. Bergmann, J. Am. Chem. Soc., 1957, 79, 3452 CrossRef CAS.
  32. M. J. Frisch, G. W. Trucks, M. Head-Gordon, P. M. W. Gill, M. W. Wong, J. B. Foresman, B. J. Johnson, H. B. Schlegel, M. A. Robb, E. S. Replogle, R. Gomperts, J. L. Andres, K. Raghavachari, J. S. Binkley, C. Gonzalez, R. L. Martin, D. J. Fox, D. J. Defrees, J. Baker, J. J. P. Stewart and J. A. Pople, GAUSSIAN92, Revision G3, Gaussian Inc., Pittsburgh, PA, 1992.
  33. M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Latham, V. G. Zakrewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. V. Ayala, W. Chem, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fow, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzales and J. A. Pople, GAUSSIAN94, Revision C3, Gaussian Inc., Pittsburgh, PA, 1995.
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