3
3.
4.
Yadav, J. S.; Reddy, G. S.; Reddy, M. M.; Meshram, H. M.
Tetrahedron Lett. 1998, 39, 3259-3262.
reaction between DMF and methyl acetoacetate, the catalyst was
recovered using an external magnet, washed with H2O and
ethanol and oven-dried at 80 °C overnight. A new second
reaction was then performed with fresh solvent and reactants
under identical conditions. Using this approach, our catalyst
could be reused at least five times without any further treatment,
while no appreciable loss in the catalytic activity was observed
(Figure 1). A hot filtration test was conducted to demonstrate the
heterogeneous nature of the catalyst. For this purpose, the
catalyst and the solvent were allowed to stir under the reaction
conditions. After four hours the catalyst was removed from the
reaction vessel using an external magnet and then the vessel was
charged with acetoacetate and TBHP. The reaction progress was
followed by TLC, which after four hours, showed no formation
of product. This indicates that the CuO nanoparticles are stable
on CNTs and do not leach.
Angeles, E.; Santillan, A.; Martinez, I.; Ramirez, A.; Moreno, E.;
Salmon, M.; Martinez, R. Synth. Commun. 1994, 24, 2441-2447.
Kocovsky, P. Tetrahedron Lett. 1986, 27, 5521-5524.
5.
6.
(a) Ragaini, F.; Cenini S. Organometallics 1994, 13, 1178-1189;
(b) Paul, F.; Fischer, J.; Ochsenbein, P.; Osborn, J. A.
Organometallics 1998, 17, 2199-2206, and references cited
therein; (c) Cenini, S.; Crotti, C.; Pizzoti, M.; Porta, F. J. Org.
Chem. 1988, 53, 1243-1250; (d) Shi, F.; Deng, Y. Chem.
Commun. 2001, 443-444; (e) Leung,T. W.; Dombek, B. D. J.
Chem. Soc. Chem. Commun. 1992, 205-206; (f) Alper, H.;
Hartstock, F. W. J. Chem. Soc., Chem. Commun. 1985, 1141-
1142; (g) Fukuoka, S.; Chono, M.; Kohno, M. J. Chem. Soc.,
Chem. Commun. 1984, 399-400.
7.
8.
9.
Kianmehr, E.; Baghersad M. H. Adv. Synth. Catal. 2011, 353,
2599-2603.
Kumar, G. S.; Maheswari, C.U.; Kumar, R. A.; Kantam, M. L.;
Reddy, K. R. Angew. Chem. Int. Ed. 2011, 50, 11748 -11751.
(a) Gagan, C.; Dashan, W.; Howard, A. Chem. Commun. 2007,
4809-4811; (b) Dalaigh, C. O.; Corr, S. A.; Gun’ko, Y.; Connon,
S. J. Angew. Chem. 2007, 119, 4407-4410; Angew. Chem. Int. Ed.
2007, 46, 4329-4332; (c) Shin, J.; Kim, H.; Lee, I. S. Chem.
Commun. 2008, 5553-5555; (d) Polshettiwar, V.; Baruwati, B.;
Varma, R. S. Chem. Commun. 2009, 1837-1839; (e) Raed, A.-R.;
Howard, A.; Dashan, W.; Michael, L. P. J. Am. Chem. Soc. 2006,
128, 5279-5282; (f) Cano, R.; Yus, M.; Ramon, D. J. ACS Catal.
2012, 2, 1070-1078; (g) Riente, P.; Yadav, J.; Pericas, M. A. Org.
Lett. 2012, 14, 3668-3671; (h) Costa, V. V.; Jacinto, M. J.; Rossi,
L. M.; Landers, R.; Gusevskaya, E. V. J. Catal. 2011, 282, 209-
214; (i) Wang, J.; Xu, B.; Sun, H.; Song, G. Tetrahedron Lett.
2013, 54, 238-241; (j) Rattanaburi, P.; Khumraksa, B.;
Pattarawarapan, M. Tetrahedron Lett. 2012, 53, 2689-2693.
10. Saberi, D.; Sheykhan, M.; Niknam, Kh.; Heydari, A. Catal. Sci.
Technol. DOI: 10.1039/C3CY00082F
11. (a) Sheykhan, M.; Ma’mani, L.; Ebrahimi A.; Heydari, A. J. Mol.
Cat. A: Chem. 2011, 335, 253-261; (b) Ma’mani, L.; Sheykhan
M.; Heydari, A. Appl. Catal. A: Gen. 2011, 395, 34-38; (c)
Ma’mani, L.; Heydari, A.; Sheykhan, M. Appl. Catal. A: Gen.
2010, 384, 122-127.
12. General procedure: TBHP (70 wt% in H2O) was added dropwise
to a mixture of the 1,3-dicarbonyl compound (1 mmol), catalyst
(20 mg, 3.7 mol%) and N,N-dialkylformamide (2 mL). The
reaction temperature was increased to 80 °C and the mixture was
stirred for 4 h. After cooling to RT, the mixture was extracted with
EtOAc (3x10 mL) and dried over anhydrous Na2SO4. Removal of
the solvent under vacuum afforded the crude product, which was
purified by column chromatography to afford the desired product.
For the oxidative esterification reactions, a slightly modified
procedure was employed, which utilized DMSO as the solvent and
the reaction time was increased to 10 h, giving rise to the
formation of products (2a-f)
13. (Z)-allyl 3-((dimethylcarbamoyl)oxy)hex-2-enoate (Table 2, 1f)
Isolated yield = 70%; yellow oil; IR cm-1: 750, 1035, 1145, 1211,
1271, 1320, 1382, 1669, 1727; 1H NMR (250 MHz, CDCl3) δ 2.06
(s, 3H, CH3), 2.97 (s, 3H, CH3N), 3.02 (s, 3H, CH3N), 4.57 (dd,
2H, 3J = 5.5 Hz, 4J = 1.3 Hz, CH2O), 5.18-5.34 (m, 2H, CH2=CH),
5.58 (s, 1H, CHCO2), 5.82-5.97 (m, 1H, CH2=CH). 13C NMR
(62.9 MHz, CDCl3) δ 22.20, 36.60, 64.62, 107.62, 118.03, 132.31,
153.01, 161.33, 163.66; MS (EI, 70 ev): m/z (%) = 213 (M+, 8),
156 (64), 72 (100). Anal. Calcd for C10H15NO4 (213.23): C, 56.33;
H, 7.09; N, 6.57. Found: C, 56.25; H, 7.16; N, 6.47.
Figure 1: Recycling of the catalyst in the C-O coupling reaction of
compound 1a carried out for 4 h.
In summary, we have introduced an efficient strategy for the
C-O cross-coupling of 1,3-dicarbonyl compounds with
formamides to form enol carbamates, as well as oxidative
coupling of 2-hydroxyacetophenone with aromatic aldehydes,
using nano-CuO supported on magnetic CNTs as a heterogenous
and magnetically separable catalyst. Its advantages include a
straightforward preparation, facile separation from the reaction
medium and recyclability up to five times.
Acknowledgments
We are thankful to Tarbiat Modares University for partial
support of this work
References and notes
2-Acetylphenyl 4-methoxybenzoate (Table 2, 2c) Isolated yield =
82%; white solid; mp: 94-96 °C; IR cm-1: 610, 762, 963, 1069,
1364, 1481, 1683, 1724, 2965; 1H NMR (400 MHz, CDCl3) δ 2.47
(s, 3H, CH3C=O), 3.84 (s, 3H, OCH3), 6.94 (d, 2H, J = 9.2 Hz, CH
of Ar), 7.16 (dd, 1H, 3J = 8.0, 4J = 0.8 Hz, CH of Ar), 7.29 (td, 1H,
3J = 7.2 Hz, 4J = 1.2 Hz, CH of Ar), 7.51(td, 1H, 3J = 8.0 Hz, 4J =
1.
(a) Hartley, D.; Kidd, H. in: The Agrochemicals Handbook,
Royal Society of Chemistry, Cambridge, 1991; (b) Nasr, M.;
Paull, K. D.; Narayanan, V. L.; J. Pharm. Sci. 1985, 74, 831-836;
(c) Adams, P.; Baron, F. A. Chem. Rev. 1965, 65, 567-602; (d)
Tai-The W.; Huang, J.; Arrington, N. D.; Dill, G. M. J. Agric.
Food Chem. 1987, 35, 817-823; (e) Vauthey, I.; Valot, F.; Gozzi,
C.; Fache, F.; Lemaire, M. Tetrahedron Lett. 2000, 41, 6347-
6350; (f) Angeles, E.; Martinez, P.; Keller, J.; Martinez, R.;
Rubio, M.; Ramirez, G.; Castillo, R.; Lopez-Castanares, R.;
Jimenez, E. J. Mol. Struct. 2000, 504, 141-170.
(a) Green, T. W.; Wuts, P. G. M. in: Protecting Groups in Organic
Synthesis, 2nd edn., Wiley, New York, 1999; (b) Caroino, L. A.
Acc. Chem. Res. 1973, 6, 191-198; (c) Xiuo, X. Yi.; Ngu, K.;
Choa, C.; Patel, D. V. J. Org. Chem. 1997, 62, 6968-6973.
3
4
2.0 Hz, CH of Ar), 7.79(dd, 1H, J = 7.6 Hz, J = 1.6 Hz, CH of
Ar), 8.10 (d, 2H, 3J = 8.8 Hz, CH of Ar). 13C NMR (100 MHz,
CDCl3) δ 29.99, 55.58, 114.03, 121.49, 123.99, 126.07, 130.18,
131.52, 132.50, 133.35, 164.14, 190.75; MS (EI, 70 ev): m/z (%)
= 270 (M+, 5), 135 (100), 107 (25). Anal. Calcd for C16H14O4
(270.28): C, 71.10; H, 5.22. Found: C, 71.02; H, 5.15.
2.