Stereochemical reversal of nucleophilic substitution reactions depending upon substituent: Reactions of heteroatom-substituted six-membered-ring oxocarbenium ions through pseudoaxial conformers

Journal of the American Chemical Society

Volumn 122, Issue 1, 2000, Pages 168-169

  Romero, Jan Antoinette C ^a   Tabacco, Sarah A ^a   Woerpel, K A ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ACETAL; CARBENE; ION;

ARTICLE; CHEMICAL MODIFICATION; CHEMICAL REACTION; CONFORMATION; MOLECULAR DYNAMICS; STEREOCHEMISTRY;

EID: 0034639452     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja993366o     Document Type: Article

References (28)

1. Eliel, E. L.; Wilen, S. H.; Mander, L. N. Stereochemistry of Organic Compounds; Wiley: New York, 1994; pp 686-740.
2. The numbering used in this paper considers the carbocationic carbon as C-1.
3. Woods, R. J.; Andrews, C. W.; Bowen, J. P. J. Am. Chem. Soc. 1992, 114, 859-854.
4. Other calculations (HF/6-31G*) indicate that oxocarbenium ion 2 (R = Me) is favored over 1 by 4.1 kcal/mol: Miljkovic, M.; Yeagley, D.; Deslongchamps, P.; Dory, Y. L. J. Org. Chem. 1997, 62, 7597-7604.
5. Dudley, T. J.; Smoliakova, I. P.; Hoffmann, M. R. J. Org. Chem. 1999, 64, 1247-1253.
6. Winkler, D. A.; Holan, G. J. Med. Chem. 1989, 32, 2084-2089.
7. Blériot, Y.; Genre-Grandpierre, A.; Imberty, A.; Tellier, C. J. Carbohydr. Chem. 1996, 15, 985-1000.
8. This counter-intuitive conformational preference has been invoked to explain stereoselective reactions of acetoxy-substituted vinyloxocarbenium ions: Hosokawa, S.; Kirschbaum, B.; Isobe, M. Tetrahedron Lett. 1998, 39, 1917-1920.
9. Roush has proposed pseudoaxially substituted oxocarbenium ions as reactive intermediates in highly stereoselective glycosidation reactions: Roush, W. R.; Sebesta, D. P.; James, R. A. Tetrahedron 1997, 53, 8837-8852.
10. Acetals with alkyl substituents al C-5 undergo nucleophilic substitution with high anti selectivity. See, for example: Brown, D. S.; Ley, S. V.; Bruno, M. Heterocycles 1989, 28, 773-777.
11. Stevens, R. V.; Lee, A. W. M. J. Am. Chem. Soc. 1979, 101, 7032-7035.
12. Deslongchamps, P. Stereoelectronic Effects in Organic Chemistry; Pergamon: New York, 1983; pp 209-221.
13. Postema, M. H. D. C-Glycoside Synthesis; CRC Press: Boca Raton, FL, 1995.
14. Levy, D. E.; Tang, C. The Chemistry of C-Glycosides: Pergamon: Tarrytown. NY, 1995; Vol. 13.
15. Reactions of acetals with carbon nucleophiles have been shown to proceed via carbocation intermediates. See, for example: (a) Sammakia, T.; Smith, R. S. J. Am. Chem. Soc. 1994, 116, 7915-7916. (b) Matsutani, H.; Ichikawa, S.; Yaruva, J.; Kusumoto, T.; Hiyama, T. J. Am. Chem. Soc. 1997, 119, 4541-4542. Other reactions of acetals do not appear to involve free cations. See, for example: (c) Denmark, S. E.; Almstead, N. G. J. Am. Chem. Soc. 1991, 113, 8089-8110.
16. Reactions of acetals with carbon nucleophiles have been shown to proceed via carbocation intermediates. See, for example: (a) Sammakia, T.; Smith, R. S. J. Am. Chem. Soc. 1994, 116, 7915-7916. (b) Matsutani, H.; Ichikawa, S.; Yaruva, J.; Kusumoto, T.; Hiyama, T. J. Am. Chem. Soc. 1997, 119, 4541-4542. Other reactions of acetals do not appear to involve free cations. See, for example: (c) Denmark, S. E.; Almstead, N. G. J. Am. Chem. Soc. 1991, 113, 8089-8110.
17. Reactions of acetals with carbon nucleophiles have been shown to proceed via carbocation intermediates. See, for example: (a) Sammakia, T.; Smith, R. S. J. Am. Chem. Soc. 1994, 116, 7915-7916. (b) Matsutani, H.; Ichikawa, S.; Yaruva, J.; Kusumoto, T.; Hiyama, T. J. Am. Chem. Soc. 1997, 119, 4541-4542. Other reactions of acetals do not appear to involve free cations. See, for example: (c) Denmark, S. E.; Almstead, N. G. J. Am. Chem. Soc. 1991, 113, 8089-8110.
18. 1H NMR coupling constant data and NOE measurements. The yields are reported for purified products.
19. 4).
20. Except for 13a (which is prepared as only the cis isomer), mixtures of anomeric acetates were employed. For the acetate 18 (eq 8), the two anomers of starting material are separable. Control experiments indicate that both anomers give the same product with the same degree of selectivity.
21. Ichikawa, Y.-i.; Kubota, H.; Fujita, K.; Okauchi, T.; Narasaka, K. Bull. Chem. Soc. Jpn. 1989, 62, 845-852.
22. This selectivity is reminiscent of chelation-controlled additions to β-alkoxy aldehydes. See, for example: Chen, K.; Goetz, E. H.; Prasad, K.; Repic, O.; Shapiro, M. J. Tetrahedron Lett. 1987, 28, 155-158.
23. Calculations (B3LYP/6-31G*//HF/6-31G*) indicate that the methoxy-substituted cation prefers the pseudoaxial conformer by 2.8 kcal/mol, and the methyl-substituted cation favors the pseudoequatorial conformer by 1.4 kcal/ mol.
24. Schmitt, A.; Reissig, H.-U. Synlett 1990, 40-42.
25. 2 resulted in lower selectivity (66:34, 85% yield). Using TMSOTf as the Lewis acid with the corresponding methyl acetal results in no stereoselectivity: Nicolaou, K. C.; McGarry, D. G.; Somers, P. K.; Kim, B.-H.; Ogilvie, W. W.; Yiannikouros, G.; Prasad, C. V. C.; Veale, C. A.; Hark, R. R. J. Am. Chem. Soc. 1990, 112, 6263-6276.
26. Calculations (B3LYP/6-31G*//HF/6-31G*) show that conformer 16 is favored by only 0.5 kcal/mol when X = Me, but is preferred by 1.6 kcal/ mol for X = OMe.
27. Ab initio calculations (HF/3-21G*) show that the pseudoaxial oxo-carbenium 7 (X = Cl) is favored over the pseudoequatorial cation 6 by 2.5 kcal/mol.
28. Herdeis, C.; Engel, W. Tetrahedron: Asymmetry 1991, 2, 945-948.