C O M M U N I C A T I O N S
(4) (a) Evans, D. A.; Burgey, C. S.; Kozlowski, M. C.; Tregay, S. W. J. Am.
Chem. Soc. 1999, 121, 686. (b) Evans, D. A.; Johnson, J. Acc. Chem.
Res. 2000, 33, 325.
In conclusion we have taken the first steps toward the realization
of catalytic enantioselective aldol additions to ketones in the use
of ester trichlorosilyl enolates and have demonstrated the potential
of chiral bis N-oxide catalysts. Mechanistic and preparative
investigations of this newly designed class of Lewis basic catalysts
are in progress.
(5) For a discussion of this problem in general, see: (a) Heathcock, C. H. In
ComprehesiVe Organic Synthesis: Additions to C-X π-Bonds Part 2;
Heathcock, C. H., Ed.; Pergamon Press: Oxford, 1991; Chapter 1.5.
(6) Organometallic additions: (a) Dosa, P. I.; Fu, G. C. J. Am. Chem. Soc.
1998, 120, 445. (b) Ramo´n, D. J.; Yus, M. Tetrahedron 1998, 54, 5651.
(c) Casolari, S.; D’Addario, D.; Tagliavini, E. Org. Lett. 1999, 1, 1061.
(d) Weber, B.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1992, 31, 84.
Cyanosilylation: (e) Hamashima, Y.; Kanai, M.; Shibasaki, M. J. Am.
Chem. Soc. 2000, 122, 7412. (f) Hamashima, Y.; Kanai, M.; Shibasaki,
M. Tetrahedron Lett. 2001, 42, 691. (g) Tian, S.-K.; Deng, L. J. Am.
Chem. Soc. 2001, 123, 6195.
Acknowledgment. We are grateful to the National Science
Foundation for generous financial support (NSF CHE 9803124 and
0105205). Y.F. also thanks the Boehringer Ingelheim Pharmaceuti-
cal Company for a graduate fellowship.
(7) Denmark, S. E.; Winter, S. B. D.; Su, X.; Wong, K.-T. J. Am. Chem.
Soc. 1996, 118, 7404.
(8) Denmark, S. E.; Stavenger, R. A. Acc. Chem. Res. 2000, 33, 432.
(9) Bassindale, A. R.; Stout, T. Tetrahedron Lett. 1985, 26, 3403.
(10) Conversion (1 and acetophenone, 0.2 M, CHCl3) after 3 h with 1.0 equiv
of promoter: Ph3P, 21%; DMF, 26%; pyridine, 35%; DMPU, 27%;
DMSO, 26%.
(11) N-Oxides have been employed previously to promote the reactions of
other chlorosilane reagents; see: (a) Nakajima, M.; Saito, M.; Shiro, M.;
Hashimoto, S. J. Am. Chem. Soc. 1998, 120, 6419. (b) Tao, B.; Lo, M.-
C.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 353.
(12) (a) Chen, C.; Tagami, K.; Kishi, Y. J. Org. Chem. 1995, 60, 5386. (b)
Malkov, A. V.; Bella, M.; Langer, C. V.; Kocˇovsky´, P. Org. Lett. 2000,
2, 3047.
(13) Denmark, S. E.; Pham, S. M. HelV. Chim. Acta 2000, 83, 1846.
(14) (a) Denmark, S. E.; Ghosh, S. K. Angew. Chem., Int. Ed. 2001, 40, 4759.
(b) Denmark, S. E.; Fu, J. J. Am. Chem. Soc. 2000, 122, 12021. (c)
Denmark, S. E.; Fu, J. J. Am. Chem. Soc. 2001, 123, 9488.
(15) Kostuki, H.; Sakai, H.; Jun, J.-G.; Shiro, M. Heterocycles 2000, 52,
661.
Supporting Information Available: Procedures for the preparation
and full characterization of catalysts 7 and 8; aldolization products along
with representative procedures for the addition reactions and correlation
of absolute configuration of 3a and 3c (PDF). This material is available
References
(1) For recent authoritative reviews, see: (a) Nelson, S. G. Tetrahedron:
Asymmetry 1998, 9, 357-389. (b) Carreira, E. M. In ComprehensiVe
Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.;
Springer-Verlag: Heidelberg, 1999; Vol. III, Chapter 29.1. (c) Carreira,
E. M. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-VCH:
Weinheim, 2000; Chapter 8. (d) Carreira, E. M. In Catalytic Asymmetric
Synthesis; 2nd ed.; Ojima, I., Ed.; Wiley-VCH: Weinheim, 2000; Chapter
8B2.
(2) For reactions of chirally modified ester enolates, see: (a) Mioskowski,
C.; Solladie, G. Tetrahedron 1980, 36, 227. (b) d’Angelo, J.; Page`s, O.;
Maddaluno, J.; Dumas, F.; Revial, G. Tetrahedron Lett. 1983, 24, 5869.
(c) Basaviaih, D.; Bharathi, T. K. Tetrahedron Lett. 1991, 32, 3417. (d)
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Y.; Kojima, S.; Ohkata, K. J. Chem. Soc., Perkin Trans. 1 1998, 689.
(3) For reactions of ester enolates with chiral additives, see: (a) Guette´, M.;
Capillon, J.; Guette´, J.-P. Tetrahedron 1973, 29, 3659. (b) Soai, K.; Oshio,
A.; Saito, T. J. Chem. Soc., Chem. Commun. 1993, 811. (c) Andre´s, J.
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(16) Bolm, C.; Ewald, M.; Felder, M.; Schlingloff, G. Chem. Ber. 1992, 125,
1169.
(17) These ligands were prepared in a relatively short sequence; see Supporting
Information for full details and characterization.
(18) The configuration of these ligands was assured by X-ray crystallographic
analysis of a complex with silicon tetrachloride. The details of this structure
will be described in a full account.
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