Chlorodicyclohexylborane-mediated aldol additions of α,α′-dioxygenated ketones

Organic Letters

Volumn 3, Issue 6, 2001, Pages 901-903

  Murga, Juan ^a   Falomir, Eva ^a   Carda, Miguel ^a   González, Florenci ^a   Marco, J Alberto ^b  

^a UNIVERSITAT JAUME I   (Spain)

^b UNIVERSITY OF VALENCIA   (Spain)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001349560     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol015542f     Document Type: Article

References (26)

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10. Carda, M.; Murga, J.; Falomir, E.; González, F.; Marco, J. A. Tetrahedron 2000, 56, 677-683.
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15. 13C NMR of the crude aldolization mixture, prior to chromatography. For ketones 3, 5, 6a-c, and 10, no minor aldols were detected by NMR. At the signal/noise ratio of the measured spectra, this means more than 95% of the major isomer.
16. Throughout the manuscript, we will use the abbreviated expression "regioisomeric aldols" with the actual meaning of "aldols formed through regioisomeric enolates." Predictions of regioselectivity in the enolization of nonsymmetrical α-oxygenated ketones constitute a difficult issue: Paquette, L. A.; O'Neil, S. V.; Guillo, N.; Zeng, Q.; Young, D. G. Synlett 1999, 1857-1866.
17. Paterson, I.; Channon, J. A. Tetrahedron Lett. 1992, 33, 797-800.
18. 13C NMR chemical shift values of the acetonide methyl groups. See: Rychnovsky, S. D.; Rogers, B. N.; Richardson, T. I. Acc. Chem. Res. 1998, 31, 9-17.
19. Complete experimental procedures, including the preparation of all new model ketones described in this paper and physical data thereof, will be described in a future paper.
20. Aldol reactions with dihydroxyacetone derivatives have recently been reported: (a) Majewski, M.; Nowak, P. J. Org. Chem. 2000, 65, 5152-5160.
21. (b) Kim, K. S.; Hong, S. D. Tetrahedron Lett. 2000, 41, 5909-5913.
22. Galobardes, M.; Gascón, M.; Mena, M.; Romea, P.; Urpí, F.; Vilarrasa, J. Org. Lett. 2000, 2599-2602.
23. 2 are used as Lewis acids: Evans, D. A.; Allison, B. D.; Yang, M. G. Tetrahedron Lett. 1999, 40, 4457-4460. However, while the steric crowding in the assumed six-membered chelates containing relatively long O-Sn or O-Al bonds might be possibly tolerable, this may not be true for the presently discussed five-membered chelate, which contains the shorter O-B bonds.
24. 2 are used as Lewis acids: Evans, D. A.; Allison, B. D.; Yang, M. G. Tetrahedron Lett. 1999, 40, 4457-4460. However, while the steric crowding in the assumed six-membered chelates containing relatively long O-Sn or O-Al bonds might be possibly tolerable, this may not be true for the presently discussed five-membered chelate, which contains the shorter O-B bonds.
25. Murga, J.; Carda, M.; Falomir, E.; Marco, J. A., submitted for publication.
26. α are sterically shielded to a very similar degree by the bulky silyl group. This preliminary result led us to conceive the qualitative proposal depicted in Scheme 6.