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Table 4 Recyclability of proline immobilized on gld nanoparticles via cysteinea
References
1 C. Palomo, M. Oiarbide and J. M. Garcia, Chem.–Eur. J.,
2002, 8, 36.
2 G. Marciniak, A. Delgado, J. Velly, G. Leclerc, N. Decker and
J. Schwartz, J. Med. Chem., 1989, 32, 1402.
3 D. Enders, S. Muller and A. S. Demir, Tetrahedron Lett.,
1988, 29, 6437.
Entry
Run
Yield (%)
Time (h)b
1
2
3
4
5
1st
96
95
96
96
96
3
3
3
3
3
2nd
3rd
4th
5th
4 M. A.Y. Yamada and M. Shibasaki, Tetrahedron Lett., 1998,
39, 5561.
a
Reaction conditions: 4-nitrobenzaldehyde (4 mmol), acetone (20
b
mmol), catalyst (5 mg), PEG-400 (5 mL). Isolated yields.
5 B. M. Trost and H. Ito, J. Am. Chem. Soc., 2000, 122, 12003.
6 A. Bogevig, N. Kumaragurubaran and K. A. Jorgensen,
Chem. Commun., 2002, 620.
7 A. B. Northrup and D. W. C. MacMillan, J. Am. Chem. Soc.,
2002, 124, 6798.
8 B. List, R. A. Lerner and C. F. Barbas, J. Am. Chem. Soc.,
2000, 122, 2395.
9 A. Cordova, W. Notz and C. F. Barbas, J. Org. Chem., 2002,
67, 301.
10 A. Cordova, Tetrahedron Lett., 2004, 45, 3949.
11 P. Kotrusz, I. Kmentova, B. Gotov, S. Toma and
E. Solcaniova, Chem. Commun., 2002, 2510.
12 Y.-Y. Peng, Q. P. Ding, Z. Li, P. G. Wang and J.-P. Cheng,
Tetrahedron Lett., 2003, 44, 3871.
Conclusions
L-Proline–cysteine conjugate on functionalized Au nanoparti-
cles has been shown to serve as an efficient, recyclable, clean
catalyst for catalyzing asymmetric aldol reaction in recyclable
PEG-400 media. The catalyst can be reused multiple times with
negligible loss in activity The presented methodology
addresses environmental concerns and encompasses the
principles of green chemistry.
13 T. Darbre and M. Machuqueiro, Chem. Commun., 2003,
1090.
14 P. I. Dalko and L. Moisan, Angew. Chem., Int. Ed., 2001, 40,
3726.
Experimental
In a 50 mL round-bottomed flask, L-proline–cysteine con-
jugated Au nanoparticles (5 mg) in 5 mL PEG solution was
taken and stirred for 5 min at room temperature (25 uC) in the
presence of 20 mmol of anhydrous acetone. After stirring for 5
min, 4 mmol aldehyde was added and the reaction mixture
was allowed to stir for appropriate times as mentioned in
Table 3. The progress of the reaction was monitored by TLC
(thin-layer chromatography) and after completion the mixture
was centrifuged at 10 000 rpm for 10 min. This provides the
catalytic nanoparticle system as a solid pellet at the bottom of
the centrifuge tube. The nanoparticles were washed with
acetone and subsequently washed four times with water to
ensure the complete removal of any residual material. The
particles were then re-dispersed in acetone for further catalytic
cycles. 15 mL anhydrous ether was added to dilute the reaction
mixture (obtained from the upper layer of the centrifuge tube)
and stirred for 5–10 min so as to separate out the ether layer.
This process was repeated three times to obtain the products
in ether. The solvent was removed by rotary evaporator under
reduced pressure.
15 B. List, Synlett, 2001, 1675.
16 B. Alcaide and P. Almendros, Eur. J. Org. Chem., 2002, 1595.
17 E. R. Jarvo and S. J. Miller, Tetrahedron, 2002, 58, 2481.
18 R. O. Duthaler, Angew. Chem., Int. Ed., 2003, 42, 975.
19 A. De and R. D. DiMarchi, Peptide Science, 2010, 94(4), 448.
20 A. De and R. D. DiMarchi, Int. J. Pept. Res. and Therapeutics,
2008, 14, 255.
21 A. Kumar, M. Dewan, A. Saxena, A. De and S. Mozumdar,
Catal. Commun., 2010, 11, 679.
22 M. Dewan, A. Kumar, A. Saxena, A. De and S. Mozumdar,
Tetrahedron. Lett., 2010, 51, 6108.
23 A. Kumar, S. Aerry, A. Saxena, A. De and S. Mozumdar,
Green Chemistry, 2012, 14, 1298.
24 M. Dewan, A. Kumar, A. Saxena, A. De and S. Mozumdar,
PloS One, 2012, 7(1), e29131.
25 M. Dewan, A. Kumar, A. Saxena, A. De and S. Mozumdar,
PloS One, 2012, 7(8), e43078.
26 A. Kumar, S. Kumar, A. Saxena, A. De and S. Mozumdar,
Catal. Commun., 2008, 9, 778.
27 A. Kumar, S. Kumar, A. Saxena, A. De and S. Mozumdar,
Catal. Lett., 2008, 122, 98.
28 A. Kumar, M. Dewan, A. Saxena, A. De and S. Mozumdar,
Tetrahedron. Lett., 2011, 52, 4835.
29 A. Kumar, P. Singh, A. Saxena, A. De and S. Mozumdar,
Catal. Commun., 2008, 10, 17.
Acknowledgements
S.M. and A.K. acknowledge the financial support from the
Department of Science & Technology (DST) and Council of
Scientific Industrial Research (CSIR), Government of India,
respectively.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 603–607 | 607