Conformational fixation of enolates by intramolecular metal...Fluorine interaction

Organic Letters

Volumn 1, Issue 6, 1999, Pages 905-908

  Yamazaki, Takashi ^a   Ando, Makoto ^a   Kitazume, Tomoya ^a   Kubota, Toshio ^b   Omura, Masao ^b  

^a TOKYO INSTITUTE OF TECHNOLOGY   (Japan)

^b IBARAKI UNIVERSITY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000184660     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol990821c     Document Type: Article

References (35)

1. (1)(a) Evans, D. A. In Asymmetric Synthesis: Morrison, J. D., Ed.; Academic Press: New York, 1984; Vol. 3, p 1.
2. (b) Chiral Auxiliaries and Ligands in Asymmetric Synthesis; Seyden-Penne, J., Ed.; John Wiley & Sons; New York, 1995; p 157.
3. 2N substrates: (a) Panek, J. S.; Masse, C. E. J. Org. Chem. 1998, 63, 2382.
4. (b) Blaser, D.; Ko, S.-Y.; Seebach, D. J. Org. Chem. 1991, 56, 6230.
5. (c) Tabcheh, M.; El Achqar, A.; Pappalardo, L.; Roumestant, M.-L.; Viallefont, P. Tetrahedron 1991, 47, 4611.
6. (d) Chaari, M.; Jenhi, A.; Lavergne, J.-P.; Viallefont, P. Tetrahedron 1991, 47, 4619.
7. (e) McIntosh, J. M.; Leavitt, R. K.; Mishra, P.; Cassidy, K. C.; Drake, J. E.; Chadha, R. J. Org. Chem. 1988, 53, 1947.
8. α-R*O substrates: (a) Fujita, M.: Laińe, D. Ley, S. V. J. Chem. Soc., Perkin Trans. 1 1999, 1647.
9. (b) d'Angelo, J.; Pagès, O.; Maddaluno, J.; Sumas, F.; Revial, G. Tetrahedron Lett. 1983, 24, 3951. See also Touzin, A. M. Tetrahedron Lett. 1975, 1477.
10. (b) d'Angelo, J.; Pagès, O.; Maddaluno, J.; Sumas, F.; Revial, G. Tetrahedron Lett. 1983, 24, 3951. See also Touzin, A. M. Tetrahedron Lett. 1975, 1477.
11. (a) Ooi, T.; Kagoshima, N.; Uraguchi, D.; Maruoka, K. Tetrahedron Lett. 1998, 39, 7105.
12. (b) Ooi, T.; Kagoshima, N.; Maruoka, K. J. Am. Chem. Soc. 1997, 119, 5754.
13. (c) Ooi, T.; Kondo, Y.; Miura, T.; Maruoka, K. Tetrahedron Lett. 1997, 38, 3951.
14. (a) Yamazaki, T.; Kitazume, T. In Enantiocontrolled Synthesis of Fluoro-Organic Compounds: Stereochemical Challenges and Biomedicinal Targets; Soloshonok, V. A., Ed.; John Wiley & Sons: New York, 1999; Chapter 19.
15. (b) Murphy, E. F.; Murugavel, R.; Roesky, H. W. Chem. Rev. 1997, 97, 7, 3425.
16. (c) Plenio, H. Chem. Rev. 1997, 97, 3363.
17. Although such interaction has been computationally expected, very little experimental evidence has been reported on the metal...fluorine interaction. See ref 4 for details.
18. (a) Weseloh, G.; Wolf, C.; König, W. A. Chirality 1996, 8, 441.
19. (b) Bott, G.; Field, L. D.; Sternhell, S. J. Am. Chem. Soc. 1980, 102, 5618. See also: Nagai, T.; Nishioka, G.; Koyama, M.; Ando, A.; Miki, T.; Kumadaki, I. Chem. Pharm. Bull. 1991, 39, 233.
20. (b) Bott, G.; Field, L. D.; Sternhell, S. J. Am. Chem. Soc. 1980, 102, 5618. See also: Nagai, T.; Nishioka, G.; Koyama, M.; Ando, A.; Miki, T.; Kumadaki, I. Chem. Pharm. Bull. 1991, 39, 233.
21. KHMDS was used after evaporation of the original solvent, toluene, under reduced pressure.
22. All new products showed satisfactory spectral as well as analytical data.
23. 3: C, 64.77; H, 5.43. Found: C, 64.40; H, 5.20.
24. For Es value, see: Taft, R. W., Jr. In Steric Effects in Organic Chemistry; Newman, M. S., Ed.; John Wiley & Sons: New York, 1956; p 556. For the revised Es value, Es', see: MacPhee, J. A.; Panaye, A.; Dubois, J.-E. Tetrahedron 1978, 34, 3553.
25. For Es value, see: Taft, R. W., Jr. In Steric Effects in Organic Chemistry; Newman, M. S., Ed.; John Wiley & Sons: New York, 1956; p 556. For the revised Es value, Es', see: MacPhee, J. A.; Panaye, A.; Dubois, J.-E. Tetrahedron 1978, 34, 3553.
26. 2: C, 64.95; H, 5.74; N, 3.99. Found: C, 64.95; H, 5.35; N, 3.92.
27. w = 0.042, GOF = 1.44.
28. Matthews, B. R.; Jackson, W. R.; Jacobs, H. A.; Watson, K. G. Aust. J. Chem. 1990, 43, 1195.
29. 19F NMR δ 82.20 (s).
30. In this text, E,Z nomenclature for enolates refers to the relative relationship between OR moieties at the 2 position and OM (M: metal) groups.
31. Since Kanemasa and co-workers reported that methyl 2-(1,1-dimethylethoxy)acetate yielded the ketene silyl acetal in favor of the Z isomer (E/Z = 17/83), our ketene silyl acetal from 1a, obtained as a single stereoisomer, was believed to have the same stereoisomeric preference. See: Kanemasa, S.; Nomura, M.; Wada, E. Chem. Lett. 1991, 1735.
32. Because of computational limitation, we have considered the lithium enolate from Ia with substitution of an ester methoxy group for hydrogen. This metal change from potassium (actual species) to lithium might be valid as long as this model is employed for the explanation of the diastereofacial selectivity because of their same propensity in the enolate π-facial selection despite poor yield (see entries 1 and 4 in Table 1). All structures were fully optimized with the ab initio software Mulliken implemented in CAChe Worksystem (SONY/Tektronix Corporation) on an IBM RS-6000-3CT workstation at the asdfsadfasMB3LYP/3-21G level of theory.
33. Since the van der Waals radius of fluorine is 0.05 Å smaller than that of oxygen, interaction of lithium with fluorine would be roughly estimated to be as strong as that with oxygen.
34. As shown in Table 1, when HMPA was added, the DS values were slightly decreased with the same sense of diastereofacial preference. Computation of the "naked" enolate was also performed to determine that the auxiliary of the most stable conformer covered the si face, but the opposite face was shielded by the second most stable isomer, 2.76 kcal/ mol higher in energy. These results led to the anticipation that the alkylation would preferentially occur from the re face even in the presence of HMPA. Details will be published elsewhere.
35. O'Hagan, D.; Zaidi, N. A. J. Chem. Soc., Perkin Trans. 1 1992, 947.