Excellent Aldehyde and Ketone Selectivity in Chromium(II)-Mediated Reformatsky Reactions

Synlett

Volumn 1997, Issue 6, 1997, Pages 731-733

  Wessjohann, Ludger ^a   Wild, Harry ^a  

^a UNIVERSITY OF MUNICH   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001100485     PISSN: 09365214     EISSN: None     Source Type: Journal    
DOI: 10.1055/s-1997-3239     Document Type: Article

References (20)

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6. Wessjohann, L.; Wild, H. Synthesis 1997, 512.
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9. Wessjohann, L. A.; Gabriel, T. J. Org. Chem. 1997, accepted.
10. Kauffmann, T.; Möller, T.; Wilde, H.-W. Chem. Ber. 1994, 127, 2277.
11. Typical procedure: 2.3 equivalents ot chromium dichloride (99.9% Strem Chemicals) and 5 to 20 mol% lithium iodide are suspended in the respective solvent under argon. After stirring at room temperature the carbonyl compound/s (1.05 - 4 equivalents) is/are added, followed by one equivalent of the halide. After stirring for 0.5 - 5 h, the suspension (or solution, if DMF is the solvent) is quenched with brine. The resulting mixture is extracted three times with ether/pentane (4:1) and the combined organic layers are washed successively with satd. ammonium chloride solution and brine (in addition twice with water, if DMF was the solvent), dried with magnesium sulfate and the solvents and excess aldehyde and ketone are evaporated in vacuo. Sometimes, especially with THF as solvent, the crude products contain traces of lipophilic complexed paramagnetic chromium(III), often coloured green. In this case, the material is filtered through silica gel. Usually the products are NMR-spectroscopically pure. If not, further purification can be achieved by column chromatography on silica gel. Competition experiments were run analogously with methyl ketone / ketone or aldehyde / ketone mixtures with a tenfold excess of the ketone as specified in the table. Preparation of chromium enolates by transmetalation e. g. of lithium enolates is possible but not very practical or at least as difficult as the first attempts reported for titanium enolates. 10,13
12. Buse, C. T.; Heathcock, C. H. Tetrahedron Lett. 1978, 1685.
13. Reetz, M. T. Organotitanium Reagents in Organic Synthesis: Springer-Verlag: Berlin, 1985; pp. 75.
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16. Kauffmann, T. in Organometallics in Organic Synthesis 2; Werner, H.; Erker, G. Eds.; Springer-Verlag: Berlin, 1989; pp. 162.
17. Rathke, M. W.; Weipert, P. in Comprehensive Organic Synthesis, Vol. 2; Trost, B. M.; Fleming, I. Eds.; Pergamon Press: Oxford, 1991; p 277.
18. 3): δ = syn: 13.9, 22.5, 22.9, 25.5, 32.2, 39.0, 51.9, 58.9, 72.9, 119.8, 132.5, 174.2; anti; 14.0, 22.6, 23.3, 23.6, 41.4, 51.9, 59.0, 73.3, 119.9, 132.7, 174.3. IR, MS and elemental analysis are also in accordance with the theory. Compounds 6 - 11 are known. 6,9
19. Moursounidis, J.; Wege, D. Aust. J. Chem. 1983, 36, 2473.
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