J IRAN CHEM SOC (2017) 14:737–742
741
and short times, but for the phenols possessing the steric
effect or electron deficient phenols, the condensation reac-
tions need long times, even in low yields.
Conclusion
In conclusion, it has been demonstrated that SnCl4 can effi-
ciently catalyze the Pechmann condensation of resorcinol
with ethyl acetoacetate at 60 °C within 6 h, not at room
temperature. A methodology has been developed for the
synthesis of coumarin and its derivatives by using SnCl4
grafted on silica gel catalysts under solvent-free hetero-
geneous catalytic conditions. The reaction temperature is
a major factor for the Pechmann condensation catalyzed
by SnCl4 grafted on silica gel. The reaction times were
found to significantly shorten with increasing reaction tem-
perature from 60 to 120 °C. SnCl4 grafted on silica gel is
inexpensive, easy to prepare and handle, and represents
effective catalytic activity for the condensation of various
phenols with β-ketoesters. Short reaction time, high yield,
simplicity of operation, easy workup, and environmentally
benign are advantages of this method.
Experimental section
General
Silica gel was purchased from the Branch of Qingdao Hai-
yang Chemical Plant Co. SnCl4·5H2O, SnCl4, SbF3, and
SbCl3 were purchased from Sinopharm Chemical Rea-
gent Co. Ltd, China, and other chemicals were provided
by Energy Chemical Co. Ltd, China. Melting points were
1
recorded on an electrothermal melting point apparatus. H
NMR spectra were recorded with a Bruker spectrometer
at 400 MHz using TMS as internal standard. Mass spec-
tra analyses were performed on mass spectrometer Esquire
6000, Bruker. Reactions were monitored by thin layer chro-
matography (TLC) on 0.2-mm silica gel F-254 plates. All
the products are known compounds and are characterized
by comparing their 1H NMR, MS, and melting points with
those reported in the literature.
Supporting information
1
Full experimental details, H NMR data, and MS spectra
for this article can be accessed on the publisher’s website.
SnCl4 grafted on silica gel
Acknowledgements This work was supported by the National
Natural Science Foundation of China (Grant Nos. 81272448 and
81373368) and Innovation Project Plan Program of Shaanxi Province
(Grant No. 2011KTCL03-16).
The starting silica gel before use was dehydrated at 300 °C
for 3 h. A solution of 10 g of anhydrous SnCl4 in 30 mL
ethanol was added dropwise to 10 g of silica gel. The
resulting suspension was stirred overnight under reflux
conditions, then filtered, exhaustively washed with ethanol,
and dried under vacuum. The loading amount of Sn on 1 g
of silica gel grafted SnCl4 was determined by the addition
of hot water and separation of the obtained Sn(OH)4 as a
floating solid.
References
1. R.O’. Kennedy, R.D. Thornes, Coumarins: Biology, Applications
and Mode of Action (Wiley, Chichester, 1997)
2. L.A. Singer, N.P. Kong, J. Am. Chem. Soc. 88, 5213 (1966)
3. M. Zahradnik, The Production and Application of Fluorescent
Brightening Agents (Wiley, New York, 1992)
4. R.D.H. Murray, J. Mendez, S.A. Brown, The Natural Cou-
marins, Occurrence, Chemistry and Biochemistry (Wiley, New
York, 1982)
Pechmann condensation catalyzed by SnCl4 grafted
on silica gel: general procedure
5. R.L. Shriner, Org. React. 1, 1 (1942)
6. I. Yavari, R. Hekmat-Shoar, A. Zonouzi, Tetrahedron Lett. 39,
2391 (1998)
7. A. Shaabani, R. Ghadari, A. Rahmati, A.H.J. Rezayan, Iran
Chem. Soc. 6, 710 (2009)
8. G. Jones, Org. React. 15, 204 (1967)
9. G. Brufola, F. Fringuelli, O. Piermatti, F. Pizzo, Heterocycles 43,
1257 (1996)
10. J.R. Johnson, Org. React. 1, 210 (1942)
11. W.P. Hong, K.J. Lee, Synthesis 33 (2005)
12. H. Pechmann, C. Duisberg, Chem. Ber. 17, 929 (1884)
13. H. Pechmann, C. Duisberg, Chem. Ber. 16, 2119 (1883)
14. D.S. Bose, A.P. Rudradas, M.H. Babu, Tetrahedron Lett. 43,
9195 (2002)
To a mixture of phenol (10 mmol) and β-ketoester
(11 mmol), SnCl4 grafted on silica gel (5 mol%) was
added and rapidly stirred at 120 °C for the appropriate time
(Table 5). After completion of the reaction, ethanol was
added to the reaction mixture and the mixture was stirred
for 15 min to enable the precipitate dissolved. The mixture
was then filtered to recover the catalyst, washed with etha-
nol, and the ethanol solution was evaporated on a rotatory
evaporator under reduced pressure to obtain the crude prod-
uct. The solid residue was recrystallized from ethanol/water
to afford pure crystals of the proper coumarins in excellent
yields.
15. A.C. Khandekar, B.M. Khadilkar, Synlett 152 (2002)
16. P.R. Singh, D.U. Singh, S.D. Samant, Synlett 1909 (2004)
1 3