13C and 2H kinetic isotope effects and the mechanism of Lewis acid- catalyzed ene reactions of formaldehyde

Journal of Organic Chemistry

Volumn 65, Issue 3, 2000, Pages 895-899

  Singleton, Daniel A ^a   Hang, Chao ^a  

^a TEXAS A AND M UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CARBON 13; DEUTERIUM; FORMALDEHYDE; ACID; CARBON;

ARTICLE; CATALYSIS; CATALYST; CHEMICAL REACTION; CHEMICAL STRUCTURE; CHIRALITY; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; PROTON TRANSPORT; CHEMISTRY; KINETICS;

ACIDS; CARBON ISOTOPES; DEUTERIUM; FORMALDEHYDE; KINETICS; MAGNETIC RESONANCE SPECTROSCOPY;

EID: 0033625461     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo9917590     Document Type: Article

References (31)

1. Snider, B. B. Acc. Chem. Res. 1980, 13, 426.
2. 2; Frimer, A. A., Ed.; CRC Press: Boca Raton, FL, 1985; pp 68-87.
3. Seymour, C. A.; Greene, F. D. J. Org. Chem. 1982, 47, 5227.
4. Stephenson, L. M.; Speth, D. R. J. Org. Chem. 1979, 44, 4683-9.
5. Cheng, C.-C.; Seymour, C. A.; Petti, M. A.; Greene, F. D.; Blount, J. F. J. Org. Chem. 1984, 49, 2910.
6. Salomon, M. F.; Pardo, S. N. Salomon, R. G. J. Am. Chem. Soc. 1980, 102, 2473.
7. + for solvolysis of 1-arylcyclpentyl p-nitrobenzoates is -3.82. See: Brown, H. C.; Ravindranathan, M.; Peters, E. N.; Rao, C. G.; Rho, M. M. J. Am. Chem. Soc. 1977, 99, 5373.
8. Kwart, H.; Brechbiel, M. J. Org. Chem. 1982, 47, 5409.
9. Snider, B. B.; Rodini, D. J.; Kirk, T. C.; Cordova, R. J. Am. Chem. Soc. 1982, 104, 555.
10. Mehführer, M.; Thirring, K.; Berner, H. J. Org. Chem. 1997, 62, 4078.
11. Jenner, G.; Papadopoulos, M. Tetrahedron Lett. 1996, 37, 1417. Jenner, G. New J. Chem. 1997, 21, 1085.
12. Jenner, G.; Papadopoulos, M. Tetrahedron Lett. 1996, 37, 1417. Jenner, G. New J. Chem. 1997, 21, 1085.
13. Laszlo, P.; Testonhenry, M. J. Phys. Org. Chem. 1991, 4, 605.
14. Stephenson, L. M.; Orfanopoulos, M. J. Org. Chem. 1981, 46, 2200.
15. Grdina, B.; Orfanopoulos, M.; Stephenson, L. M. J. Am. Chem. Soc. 1979 101, 3111-2.
16. Snider, B. B.; Ron, E. J. Am. Chem. Soc. 1985, 107, 8160.
17. Singleton, D. A.; Thomas, A. A. J. Am. Chem. Soc. 1995, 117, 9357.
18. The experimental isotope effects here are relative to those in the C4 methyl group, though it is dubious whether the deuterium KIE for the C4 methyl group is negligible. To aid in comparison with experiment, the theoretical isotope effects in Figure 2 are also made relative to the C4 methyl group. The predicted absolute deuterium isotope effect at C4 is 0.957.
19. Snider, B. B.; Rodini, D. J.; Kirk, T. C.; Cordova, R. J. Am. Chem. Soc. 1982, 104, 555.
20. Mazzocchi, H. P.; Klinger, L. J. Am. Chem. Soc. 1984, 106, 7567.
21. D = 1.44-1.55. This is only slightly larger than the KIE previously observed (1.1 ± 0.15, see ref 15), but is only moderately smaller than the intramolecular isotope effects observed in this reaction. This hinders any clear interpretation of the isotope effects in this reaction.
22. The intermolecular and intramolecular isotope effects need not be identical due to differing contributions from secondary effects.
23. 13C KIEs of ≈ 1.026 and 1.036, respectively. (Keating, A. E.; Merrigan, S. R.; Singleton, D. A.; Houk, K. N. J. Am. Chem. Soc. 1999, 121, 3933, and Singleton, D. A.; Hang, C. J. Am. Chem. Soc. 1999, 121, 11885.) Unfortunately, better models are currently lacking.
24. 13C KIEs of ≈ 1.026 and 1.036, respectively. (Keating, A. E.; Merrigan, S. R.; Singleton, D. A.; Houk, K. N. J. Am. Chem. Soc. 1999, 121, 3933, and Singleton, D. A.; Hang, C. J. Am. Chem. Soc. 1999, 121, 11885.) Unfortunately, better models are currently lacking.
25. (a) Bigeleisen, J.; Mayer, M. G. J. Chem. Phys. 1947, 15, 261.
26. (b) Wolfsberg, M. Acc. Chem. Res. 1972, 5, 225.
27. (c) The calculations used the program QUIVER (Saunders, M.; Laidig, K. E.; Wolfsberg, M. J. Am. Chem. Soc. 1989, 111, 8989) with Becke3LYP frequencies scaled by 0.9614. (Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.).
28. (c) The calculations used the program QUIVER (Saunders, M.; Laidig, K. E.; Wolfsberg, M. J. Am. Chem. Soc. 1989, 111, 8989) with Becke3LYP frequencies scaled by 0.9614. (Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.).
29. Lewis acid-catalyzed ene reactions that could involve rearrangeable carbocations sometime show rearrangement and sometimes not. See: Benner, J. P.; Gill, G. B.; Parrott, S. J.; Wallace, B. J. Chem. Soc., Perkin Trans. 1 1984, 291.
30. This is exactly the idea in the explanation of the results with 1 proposed by Snider and Ron (See ref 15). However, an inconsistency arises upon consideration of the three-membered ring intermediate that was proposed. With tetramethylethylene, such an intermediate was concluded to be configurationally fluxional to explain the significant isotope effects with 3-5. Such fluxional character in the intermediate with 1 would allow the intermediate to freely choose between a labeled methylene group and an equally reactive unlabeled methyl group, and the observation of an isotope effect would be expected. The absence of an isotope effect on the product distribution with 1 requires that the product regiochemistry be predecided in the first step of a step wise process.
31. In a related reaction, the Lewis acid-promoted cyclization of 5-hexenyl acetals, identical intermolecular and intramolecular isotope effects of 1.65 were observed. (See: Blumenkopf, T. A.; Look, G. C.; Overman, L. E. J. Am. Chem. Soc. 1990, 112, 4399.) These results were interpreted in terms of a concerted reaction, but are also consistent with a stepwise process with the second step being rate limiting, as in the mechanism here.