Q.-H. Fan et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1867–1871
Table 5. The asymmetric addition of diethylzinc to benzaldehyde
catalyzed by (R)-BINOL and dendritic BINOL ligands in the absence
1871
References and Notes
of Ti(Oi-Pr)4
a
1. Lin, G. Q.; Li, Y. M.; Chan, A. S. C. Principles and Appli-
cations of Asymmetric Synthesis; Wiley-Interscience: New
York, 2001.
Entry
Ligand
Conv.
(%)b
ee
(%)b
2. De Vos, D. E., Vankelecom, I. F. J., Jacobs, P. A., Eds.
Chiral Catalyst Immobilization and Recycling Wiley-VCH:
Weinheim, 2000.
1
2
3
4
(R)-BINOL
(R)-15a
(R)-15b
19.04.6
97.5
77.7
61.9
49.5
48.6
3. Insoluble polymer-supported chiral catalysts with positive
support effect reported recently by others, see (a) Annis, D. A.;
Jacobsen, E. N. J. Am. Chem. Soc. 1999, 121, 4147. (b) Hu, J.;
Zhao, G.; Yang, G.; Ding, Z. J. Org. Chem. 2001, 66, 303.
4. (a) Yang, X. W.; Sheng, J. H.; Da, C. S.; Wang, H. S.; Su, W.;
Wang, R.; Chan, A. S. C. J. Org. Chem. 2000, 65, 295. (b) Yang,
X. W.; Su, W.; Liu, D. X.; Wang, H. S.; Shen, J. H.; Da, C. S.;
Wang, R.; Chan, A. S. C. Tetrahedron 2000, 56, 3511.
5. (a) Zhang, F. Y.; Yip, C. W.; Cao, R.; Chan, A. S. C. Tet-
rahedron: Asymmetry 1997, 8, 585. (b) Zhang, F. Y.; Chan,
A. S. C. Tetrahedron: Asymmetry 1997, 8, 3651.
6. Soluble polymer-supported chiral catalysts with positive
support effect reported recently by others, see: Yu, H. B.;
Zheng, X. F.; Lin, Z. M.; Hu, Q. S.; Huang, W. S.; Pu, L.
J. Org. Chem. 1999, 64, 8149.
7. (a) Fan, Q. H.; Ren, C. Y.; Yeung, C. H.; Hu, W. H.; Chan,
A. S. C. J. Am. Chem. Soc.1999, 121, 7407. (b) Chan, A. S. C.;
Fan, Q. H. US Patent 5,990,318 Chem. Abstr. 1999, 132, 12597.
8. (a) Fan, Q. H.; Deng, G. J.; Chen, X. M.; Xie, W. C.; Jiang,
D. Z.; Liu, D. S.; Chan, A. S. C. J. Mol. Cat. A: Chem. 2000,
159, 37. (b) Fan, Q. H.; Deng, G. J.; Lin, C. C.; Chan, A. S. C.
Tetrahedron: Asymmetry 2001, 12, 1241.
(R)-15c
79.8
aBenzaldehyde/ligand/ZnEt2=1.0:0.2:3 (molar ratio), reaction temp-
erature=0 ꢀC; solvent=toluene; reaction time=7 h.
bDetermined by chiral GLC analyses. The absolute configuration of
product is in R-form.
3,30-dihydroxymethyl-binaphthol and Fre
´
chet’s type
polyether dendritic benzyl bromide followed by depro-
tection of MOM groups by TsOH.15 The proximity of
the dendritic wedges to the catalytic center also pro-
vided some different catalytic properties from BINOL in
the enantioselective diethylzinc addition to benzalde-
hyde. In the absence of Ti(OiPr)4, the dendritic chiral
BINOL ligands showed much higher catalytic activity
and enantioselectivity than BINOL (Table 5).
Several polymer-supported chiral catalysts based on the
use of insoluble polymer, soluble polymer or dendrimer
as supports have been prepared and tested for asym-
metric catalysis. Higher catalytic activity/enantio-
selectivity than the corresponding monomeric
homogeneous catalysts have been achieved through the
rational design and adjustment of the polymer supports.
The combined advantages of catalysis in homogeneous
phase and facile separation by precipitation or ultra-
filtration may open up a new area for active research
and attractive commercial application.
9. Wan, K. T.; Davis, M. E. J. Catal. 1994, 148, 1.
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A. S. C. Tetrahedron Lett. 2001, 42, 9047.
11. Dendrimer chiral catalysts with positive dendrimer effect
reported recently by others, see: (a) Hu, Q. S.; Pugh, V.; Sabat,
M.; Pu, L. J. Org. Chem. 1999, 64, 7528. (b) Breinbauer, R.;
Jacobsen, E. N. Angew. Chem., Int. Ed. 2000, 39, 3604. (c)
Chen, Y. C.; Wu, T. F.; Deng, J. G.; Liu, H.; Jiang, Y. Z.;
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12. Knapen, J. W. J.; van der Made, A. W.; de Wilde, J. C.;
van Leeuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van
Koten, G. Nature 1994, 372, 659.
13. (a) Oosterom, G. E.; Reek, J. N. H.; Kamer, P. C. J.; van
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(b) Astruc, D.; Chardac, F. Chem. Rev. 2001, 101, 2991.
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Acknowledgements
We thank the Hong Kong Polytechnic University ASD
fund and the Hong Kong Research Grants Councils
Central Allocation Fund (Project ERB 03) for financial
support of this study.
15. Fan, Q. H.; Liu, G. H.; Chen, X. M.; Deng, G. J.; Chan,
A. S. C. Tetrahedron: Asymmetry 2001, 12, 1559.