LETTER
Ligands for the Aluminum-Catalyzed Asymmetric Baeyer–Villiger Reaction
1621
original BINOL-based system the catalyst loading for
achieving full ketone conversion could significanly be re-
duced from 50 mol% to only 20 mol% of catalyst. Our
current efforts are directed towards further catalyst opti-
mizations.
(7) Zhang, Y.; Yeung, S.-M.; Wu, H.; Heller, D. P.; Wu, C.;
Wulff, W. D. Org. Lett. 2003, 5, 1813.
(
(
8) (a) Loncaric, C.; Wulff, W. D. Org. Lett. 2001, 3, 3675.
(
b) Antilla, J. C.; Wulff, W. D. Angew. Chem. Int. Ed. 2000,
39, 4518. (c) Antilla, J. C.; Wulff, W. D. J. Am. Chem. Soc.
1999, 121, 5099.
9) Xue, S.; Yu, S.; Deng, Y.-H.; Wulff, W. D. Angew. Chem.
Int. Ed. 2001, 40, 2271.
Acknowledgment
(
(
10) After 72 h at –40 °C the reaction was quenched to give the
lactone with 84% ee in 40% yield.
11) Experimental Procedure for the Al-Catalyzed
Asymmetric Baeyer–Villiger Reaction.
The Deutsche Forschungsgemeinschaft within the Graduierten-
kolleg 440 and the Fonds der Chemischen Industrie are gratefully
acknowledged for financial support. This work was also supported
by the National Institutes of Health Grant GM 63019.
To a solution of (R)-VANOL (26.4 mg, 0.06 mmol) in
toluene (2.5 mL) was added dropwise Me AlCl (0.06 mmol,
2
60 mL, 1 M solution in hexanes) at r.t. The mixture was
References
stirred for 30 min and then cooled at –30 °C. After 15 min at
this temperature, a solution of the ketone (0.3 mmol) in
toluene (0.5 mL) was added. Stirring was continued for 15
min, cumene hydroperoxide (technical grade 80%, 1.2
equiv, 75 mL) was then added in one portion. Subsequently,
the reaction mixture was stirred at –30 °C until full
(
1) (a) Krow, G. R. Org. React. 1993, 43, 251. (b) Krow, G. R.
In Comprehensive Organic Chemistry, Vol. 7; Trost, B. M.,
Ed.; Pergamon Press: Oxford, 1991, 671. (c) Renz, M.;
Meunier, B. Eur. J. Org. Chem. 1999, 737.
(
2) (a) Bolm, C.; Beckmann, O.; Luong, T. K. K. In Transition
Metals for Organic Synthesis, Vol. 2; Beller, M.; Bolm, C.,
Eds.; Wiley-VCH: Weinheim, 1998, 213. (b) Bolm, C. In
Advances in Catalytic Processes, Vol. 2; Doyle, P. M., Ed.;
JAI Press: Greenwich, 1997, 43. (c) Strukul, G. Angew.
Chem. Int. Ed. 1998, 37, 1199.
conversion of the ketone (as monitored by GC). The solvent
was then evaporated, and the crude product absorbed onto
silica gel. Extraction with Et O afforded the crude product,
2
which was analyzed by GC or HPLC using chiral columns
(
for details of the enantiomeric ratio determinations and
assignments of absolute configurations, see ref. 4 and
references therein).
(
3) Reviews: (a) Bolm, C.; Luong, T. K. K.; Beckmann, O. In
Asymmetric Oxidation Reactions; Katsuki, T., Ed.; Oxford
University Press: New York, 2001, 147. (b) Bolm, C. In
Peroxide Chemistry; Adam, W., Ed.; Wiley-VCH:
Weinheim, 2000, 494. (c) Bolm, C.; Beckmann, O. In
Comprehensive Asymmetric Catalysis, Vol. 2; Jacobsen, E.
N.; Pfaltz, A.; Yamamoto, H., Eds.; Springer-Verlag:
Stuttgart, 1999, 803. (d) Bolm, C. Med. Res. Rev. 1999, 19,
(
(
12) Slightly better results can be obtained for benzyl-substituted
substrates when 50 mol% of the BINOL/Me AlCl catalyst
2
system are applied (comp. ref. 4a). Thus, conversions of 6c
and 6d give lactones with 73% and 58% ee, respectively.
13) For other recent examples of metal-catalyzed asymmetric
Baeyer–Villiger reactions focusing on the conversions of
cyclobutanones, see: (a) Uchida, T.; Katsuki, T.; Ito, K.;
Akashi, S.; Ishii, A.; Kuroda, T. Helv. Chim. Acta 2002, 85,
3
48.
4) (a) Bolm, C.; Beckmann, O.; Palazzi, C. Can. J. Chem. 2001,
9, 1593. (b) Bolm, C.; Beckmann, O.; Kühn, T.; Palazzi,
(
3078. (b) Ito, K.; Ishii, A.; Kuroda, T.; Katsuki, T. Synlett
7
2003, 643; and references therein.
C.; Adam, W.; Rao, P. B.; Saha-Möller, C. R. Tetrahedron:
Asymmetry 2001, 12, 2441.
(
14) To the best of our knowledge there is only a single report
with a higher ee. Katsuki et al. found a zirconium catalyst
bearing a complex salen ligand to give 87% ee in the
conversion of 4 to 5. See: Watanabe, A.; Uchida, T.; Ito, K.;
Katsuki, T. Tetrahedron Lett. 2002, 43, 4481.
(5) Chen, Y.; Yekta, S.; Yudin, A. K. Chem. Rev. 2003, 103,
3
155.
6) Bao, J.; Wulff, W. D.; Rheingold, J. J. Am. Chem. Soc. 1993,
15, 3814.
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Synlett 2004, No. 9, 1619–1621 © Thieme Stuttgart · New York