A Mild, Highly Efficient Addition of Alkynes to Aldehydes
ether (3ꢂ3 mL). The extraction was then dried with anhy-
drous sodium sulfate and concentrated by rotary evapora-
tion. The residue was purified by flash column (10:1 hexanes
and EtOAc) to give 3a; yield: 97%.
In summary, titanium dioxide-supported silver
nanoparticles (Ag/TiO2) were utilized as a highly ef-
fective and recyclable catalyst for the coupling of al-
dehydes and terminal alkynes in the presence of cata-
lytic amounts of PPh3 in water. In the reaction, signifi-
cant support and ligand effects were observed. This
result has provided a new approach to develop novel
catalytic reactions by coinage metal nanoparticles.
The detailed mechanism, the effect of particle size
and supports as well as the scope of the reaction are
currently under further investigations.
Acknowledgements
We are grateful to the financial support from Natural Science
Foundation of Jiangsu Province (BK2008386 to XY), NUAA
Research Funding (No. 2010169 to XY), National Natural
Science Foundation of China (20602018 to XY) and Jiangsu
Innovation
Program
for
Graduate
Education
(CXZZ11 0207 to MY).
Experimental Section
All experiments were carried out in air. Flash column chro-
matography was performed over silica gel 200–300 mesh.
1H NMR and 13C NMR spectra were acquired at 300 MHz
and 75 MHz, respectively, and referenced to the internal sol-
vent signals. HR-MS were obtained from Shanghai Institute
of Organic Chemistry, CAS.
References
[1] a) X. Zhang, W. T. Teo, P. W. H. Chan, Org. Lett. 2009,
11, 4990–4993; b) A. Aponick, C. Y. Li, J. Malinge,
E. F. Marques, Org. Lett. 2009, 11, 4624–4627; c) E. M.
Bunnelle, C. R. Smith, S. K. Lee, R. Sarpong, Tetrahe-
dron 2008, 64, 7008–7014; d) J. P. Sonye, K. Koide, J.
Org. Chem. 2006, 71, 6254–6257; e) S. Chen, J. Wang, J.
Org. Chem. 2007, 72, 4993–4996; f) V. Cadierno, S. E.
Garcꢃa-Garrido, J. Gimeno, Adv. Synth. Catal. 2006,
348, 101–110; g) B. M. Trost, R. C. Livingston, J. Am.
Chem. Soc. 2008, 130, 11970–11978; h) J. P. Sonye, K.
Koide, J. Org. Chem. 2007, 72, 1846–1848; i) W. Huang,
Q. Shen, J. Wang, X. Zhou, J. Org. Chem. 2008, 73,
1586–1589; j) X. Pu, J. M. Ready, J. Am. Chem. Soc.
2008, 130, 10874–10875; k) C. Zhang, X. Zhang, F.
Qing, Tetrahedron Lett. 2008, 49, 3927–3930; l) R. W.
Bates, S. Sridhar, J. Org. Chem. 2008, 73, 8104–8105.
[2] N. K. Anand, E. M. Carreira, J. Am. Chem. Soc. 2001,
123, 9687–9688.
[3] a) R. Takita, K. Yakura, T. Ohshima, M. Shibasaki, J.
Am. Chem. Soc. 2005, 127, 13760–13761; b) R. Takita,
Y. Fukuta, R. Tsuji, T. Ohshima, M. Shibasaki, Org.
Lett. 2005, 7, 1363–1366.
[4] C. Wei, C.-J. Li, Green Chem. 2002, 4, 39–41.
[5] X. Yao, C.-J. Li, Org. Lett. 2005, 7, 4395–4398.
[6] For a review, see: a) R. J. White, R. Luque, V. L. Bu-
darin, J. H. Clark, D. J. Macquarrie, Chem. Soc. Rev.
2009, 38, 481–494; b) G. A. Somorjai, J. Y. Park,
Angew. Chem. 2008, 120, 9352–9368; Angew. Chem.
Int. Ed. 2008, 47, 9212–9228; c) Y. Gu, G. Li, Adv.
Synth. Catal. 2009, 351, 817–847; d) N. R. Shiju, V. V.
Guliants, Appl. Catal. A 2009, 356, 1–17.
Synthesis of Silver Nanoparticles (Ag NPs) Catalyst
In a 100-mL round-bottom flask equipped with a stir bar
and fitted with a rubber septum placed in a preheated oil
bath at 608C, trisodium citrate dehydrate (Na3Cit·2H2O,
0.1M, 5 mL) and polyvinylpyrrolidone (PVP, average MW:
40,000, 100 mg) were added. After stirring at 608C for
15 min, aqueous silver nitrate solution (0.01M, 25 mL) was
added by dropwise over a period of 15 min, and stirred vigo-
rously for 5 h in order to ensure the reduction was finished
completely. The solution turned to blue-black color which is
the characteristic color of silver nanoparticles. The silver
nanoparticles were separated by centrifugation, and then
the precipitate was washed with distilled water (3ꢂ10 mL),
ethanol (3ꢂ5 mL) and ether (3ꢂ5 mL) successively. The res-
idue was then dried in vacuum at 408C overnight.
Synthesis of Metal Oxide (MO)-Supported Silver
Nanoparticle Catalyst
The preparation of Ag/Al2O3, Ag/SiO2, Ag/CeO2, Ag/TiO2
followed the procedure described in ref.[10b] Ag/MOx-10
(Ag=10 wt%, MOx =Al2O3, SiO2, CeO2, TiO2) catalysts
were prepared by impregnating the support with an aqueous
solution of silver nitrate followed by evaporation to dryness
at 808C. Before each catalytic or spectroscopic experiment,
the precursor was calcined in air at 6008C for 1 h, followed
by reduction in H2 at 3008C for 10 min. The material was
cooled to room temperature under an H2 atmosphere.
[7] a) D. Raut, K. Wankhede, V. Vaidye, S. Bhilare, N. Dar-
watkar, A. Deorukhkar, G. Trivedi, M. Salunkhe, Catal.
Commun. 2009, 10, 1240–1243; b) F. Alonso, Y. Moglie,
G. Radivoy, M. Yus, Eur. J. Org. Chem. 2010, 10, 1875–
1884; c) H. Sharghi, R. Khalifeh, M. M. Doroodmand,
Adv. Synth. Catal. 2009, 351, 207–218; d) A. K. Verma,
R. Kumar, C. Preeti, A. Saxena, R. Shankar, S. Mo-
zumdar, R. Chandra, Tetrahedron Lett. 2005, 46, 5229–
5232; e) B. C. Ranu, A. Saha, R. Jana, Adv. Synth.
Catal. 2007, 349, 2690–2696; f) M. Kidwai, V. Bansal,
A. Saxena, S. Aerry, S. Mozumdar, Tetrahedron Lett.
2006, 47, 8049–8053.
General Procedure for Coupling of Alkyne and
Aldehyde (Table 3, entry 1)
2-Bromobenzylaldehyde (1a, 117 mL, 1 mmol), phenyacety-
lene (2a, 313 mL. 3 mmol), Ag/TiO2-10 (54.0 mg, 0.05 mmol,
5 mol%), PPh3 (26.2 mg, 0.1 mmol, 10 mol%), Et3N (54 mL,
0.4 mmol, 40 mol%), and 3 mL of distilled water were
added into a 15 mL Schlenk tube in atmosphere, and then,
were stirred at 608C for 12 h. The mixture was extracted by
Adv. Synth. Catal. 2012, 354, 71 – 76
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
75