Catalytic enantioselective allylboration of ketones

Journal of the American Chemical Society

Volumn 126, Issue 29, 2004, Pages 8910-8911

  Wada, Reiko ^a   Oisaki, Kounosuke ^a   Kanai, Motomu ^a,b   Shibasaki, Masakatsu ^a  

^a UNIVERSITY OF TOKYO   (Japan)

^b JAPAN SCIENCE AND TECHNOLOGY AGENCY   (Japan)

Author keywords

[No Author keywords available]

Indexed keywords

COPPER CHLORIDE; KETONE DERIVATIVE; SILICATE; TETRABUTYLAMMONIUM DIFLUOROTRIPHENYLSILICATE; UNCLASSIFIED DRUG;

ALLYLATION; ARTICLE; CATALYSIS; CHEMICAL BOND; CHEMICAL MODIFICATION; CHEMICAL REACTION; CHIRALITY; ENANTIOSELECTIVITY; ENVIRONMENTAL TEMPERATURE; HIGH PERFORMANCE LIQUID CHROMATOGRAPHY; NUCLEAR MAGNETIC RESONANCE; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 3242808098     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja047200l     Document Type: Article

References (32)

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18. For the use of allylboronates in allylation of activated ketones in the absence of catalyst, see: (f) Pace, R. D.; Kabalka, G. W. J. Org. Chem. 1995, 60, 4838.
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20. Gulliner, D. J.; Levason, W.; Webster, M. Inorg. Chim. Acta 1981, 52, 153. Generation of CuF was observed on 19F NMR via the reaction of CuCl with TBAT, and CuF is the actual catalyst in our catalytic allylation using allyltrimethoxysilane. See ref 5.
21. See Supporting Information (SI) for details. No reaction proceeded in the absence of catalyst.
22. Brief conclusions of the preliminary optimization: (a) No enantioselectivity was observed using chiral diamines or monophosphines as a ligand for Cu.
23. 3· 2EtOH produced a less active or less enantioselective catalyst.
24. (c) As a solvent, DMF is superior to THF in terms of enantioselectivity.
25. 2O and 4 in MeOH was refluxed for 2 h to generate CuF-4 complex, which was suggested by ESI-MS measurement.
26. Shibasaki, M.; Kanai, M.; Funabashi, K. Chem. Commun. 2002, 1989.
27. A dynamic ligand exchange between silicon and copper atoms is the key for the high reactivity of the previous CuF-catalyzed allylsilylation. See ref 5. For a review of the coordinating nature of lanthanide metals, see: Parker, D.; Dickins, R. S.; Puschmann, H.; Crossland, C.; Howard, J. A. K. Chem. Rev. 2002, 102, 1977.
28. Other lanthanide isopropoxides gave less satisfactory results.
29. Even reliable stereoselective allylation methods using chiral allylborane or allylboronate gave only moderate results when applied to ketones: Barton's allyldiisopinocampheylborane and Roush's tartrate ester-modified allylboronate gave 3a in 41% yield with 2% ee (0 °C for 2 h) and 16% yield with 41% ee (-40 °C for 24 h), respectively.
30. Allylcoppers generated via the reaction of CuX + allyllithium or allyl Grignard reagent are known to give a mixture of 1,2- and 1,4-adducts to enones. See: Lipshutz, B. H.; Ellsworth, E.; Dimock, S. H.; Smith, R. A. J. J. Am. Chem. Soc. 1990, 112, 4404.
31. 3·2EtOH, 2a, and acetophenone was 1.4, 1, and 0, respectively.
32. One possible scenario is the activation of CuF through lanthanum alkoxyfluorocuprate formation.