Alkali enolates of unsymmetrical ketones from silyl enol ethers. Highly regioselective aldol reactions dependent on the nature of the cation

Journal of Organic Chemistry

Volumn 61, Issue 6, 1996, Pages 2232-2235

  Duhamel, Pierre ^a   Cahard, Dominique ^a   Quesne, Yannick ^a   Poirier, Jean Marie ^a  

^a UNIVERSITÉ DE ROUEN   (France)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001079096     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo951429p     Document Type: Article

References (22)

1. House, H. O.; Czuba, L. J.; Gall, M.; Olmstead, H. D. J. Org. Chem. 1969, 34, 2324.
2. J. Org. Chem. 1971, 36, 2361.
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4. (b) Stork, G.; Hurdlick, P. F. J. Am. Chem. Soc. 1968, 90, 4464.
5. (a) Nakamura, E.; Shimizu, M.; Kuwajima, I.; Sakata, J.; Yokoyama, K.; Noyori, R.; J. Org. Chem. 1983, 48, 932.
6. (b) Nakamura, E.; Yamago, S. Machii, D.; Kuwajima, I. Tetrahedron Lett., 1988 29, 2207.
7. (c) Yamago, S. Machii, D.; Nakamura, E. J. Org. Chem. 1991, 56, 2098 and references cited therein.
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9. (a) Noyori, R.; Nishida, I.; Sakata, J. Tetrahedron Lett. 1980, 21, 2085.
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12. Gingras, M. Tetrahedron Lett. 1993, 32, 7381.
13. Duhamel, P.; Cahard, D.; Poirier, J. M. J. Chem. Soc. Perkin Trans. 1 1993, 2509 .
14. The classical preparation methods from carbonyl compounds and metal hydride lead to enolates contaminated by aldolates even when starting from ketones.
15. Cazeau, P.; Duboudin, F.; Moulines, F.; Babot, O.; Dunogues, J. Tetrahedron, 1983, 43, 2075. In such a procedure the silyl enol ethers 1a,b were accompanied, respectively, by 10% and 5% of their regioisomer 2a,b.
16. 10
17. Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1969, 34, 2923.
18. The aldol reaction product 9a was accompanied by 4 to 5% of its regioisomer 10a due to the presence of the silyl enol ether 2a in the starting material.
19. The enol acetate 5a was accompanied by 10% of its regioisomer 8a. Ratio 5a:8a = 9:1 identical to the ratio of the starting silyl enol ethers 1a:2a.
20. Bis-hydroxyalkylation product i (2-4%) was also present and easily separated by flash chromatography. Compound i is a mixture of several diastereoisomers (ratio not determined). (Chemical Equation Presented)
21. 3. No vinylic proton could be observed during the experiment.
22. Aldol 9a was treated with KH at -20°C for 1.25 h and then stirred at -78°C for 2 h. Dehydration product and benzaldehyde were also detected.