JOURNAL OF CHEMICAL RESEARCH 2011 221
Table 3 Cyclisation of different 2’-hydroxychalcones in the
collected by filtration, washed with water and dried in a desiccator
presence of proline and KOHa
to give flavanone 2a. All prepared products are known compounds
1
and were identified by m.p., IR and H NMR. The products did not
show any optical rotation.
2a: M.p. 74–75 °C (lit.5 75–76 °C); IR(KBr): v(C=O) 1715cm−1;
δH(300 MHz, CDCl3) 7.04–7.94 (m, 9H), 5.50 (dd, J = 3.0, 13.0 Hz,
1H), 3.12 (dd, J = 12.9, 16.2, 1H), 2.88 (dd, J = 2.7, 16.2, 1H).
2b: M.p. 96–97 °C (lit.12 95–97 °C); IR(KBr): v(C=O) 1685cm−1;
δH(300 MHz, CDCl3) 7.09–7.89 (m, 8H), 5.66 (dd, J = 2.7, 10.2 Hz,
1H), 2.70–3.15 (m, 2H).
Substrate
Ar
Yield (%)b
2c: M.p. 97–99 °C (lit.13 98–99 °C); IR(KBr): v(C=O) 1695cm−1;
δH(300 MHz, CDCl3) 7.10–7.90 (m, 8H), 5. 44–5.47 (m, 1H), 2.83–
3. 15 (m, 2H).
1a
1b
1c
1d
1e
1f
C6H4
o-ClC6H4
>99
89
94
95
75
95
50
85
m-ClC6H4
p-ClC6H4
o-MeOC6H4
m-MeOC6H4
p-MeOC6H4
p-NO2C6H4
2d: M.p. 94–96 °C (lit.9 95–96 °C); IR(KBr): v(C=O) 1690cm−1;
δH(300 MHz, CDCl3) 7.03–7.65 (m, 8H), 5.43–5.46 (m, 1H), 2.82–
3.06 (m, 2H).
2e: M.p. 81–82 °C (lit.12 80–82 °C); IR(KBr): v(C=O) 1685cm−1;
δH(300 MHz, CDCl3) 6.84–8.60 (m, 8H), 5.75 (dd, J = 12.5, 3.0 Hz,
1H), 3.72 (s, 3H), 2.91 (dd, J = 17.0, 3.0, 1H), 2.83 (dd, J = 17.0, 12.6,
1H).
1g
1h
a All other conditions are the same with Table 1.
b No optical rotation was observed during optical rotation test.
2f: M.p. 79–80 °C (lit.14 78–79 °C); IR(KBr): v(C=O) 1685cm−1;
δH(300 MHz, CDCl3) 6.93–8.55 (m, 8H), 5.75 (dd, J = 12.0, 3.6 Hz,
1H), 3.70 (s, 3H), 2.82–3.12 (m, 2H).
2g: M.p. 86–88 °C (lit.9 87–88 °C); IR(KBr): v(C=O) 1690cm−1;
δH(300 MHz, CDCl3) 6.96–7.91 (m, 8H), 5.40 (dd, J = 2.7, 13.5 Hz,
1H), 3.80 (s, 3H), 2.86–3.15 (m, 2H).
clear relationship between the pKa of the amino group in
amino acid additives and the cyclisation activity. We speculate
that both this property of amino group and steric hinderance of
amino acid additives affect the cyclisation activity.
Some representative examples are listed in Table 3 for the
cyclisation of different 2′-hydroxychalcones in the presence
of L-proline and KOH. The extent of activities appears to be
delicately influenced by the structure and the electron proper-
ties of substrates. Cyclisation of 2′-hydroxychalcone 1a gave
the best activity. When comparing the chloro-substituents,
the steric hinderance clearly influences the catalytic activity,
in the order of p-Cl > m-Cl > o-Cl. However, as in the previous
report,5 electronic properties may play the main role in
substrates possessing a methoxy substituent.
Liquiritigenin 4 is wildly used as an anti-ulcer agent, in the
prevention of atherosclerosis, in the inhibition of monoamine
oxidase, in the treatment of mental depression, anti-virus,
and as an anti-viral agent. However, liquiritigenin has been
prepared in moderate yield at high temperature over a long
time.10,11 Purification of the product in these reports requires
a lot of organic solvent. We applied our optimized catalytic
conditionstothepreparationofliquiritigenin4fromisoliquiriti-
genin 3 (Scheme 1). Liquiritigenin was obtained in high yield
under mild green conditions with simple work-up procedure.
In conclusion, we have shown that different flavanones can
be prepared from 2′-hydroxychalcones very efficiently under
mild green condition. Further work on the mechanism and on
the asymmetric cyclisation employing amino acids and their
derivatives as catalysts is in progress.
2h: M.p. 140–142 °C (Authentic product from TCI 141–142 °C);
IR(KBr): v(C=O) 1685cm−1; δH(300 MHz, CDCl3) 7.02–7.56 (m, 8H),
5.44–5.47 (m, 1H), 2.82–3.12 (m, 2H).
4: M.p. 196–197 °C (lit.10 195–197 °C); IR(KBr): v(C=O) 1660cm−1;
δH(300 MHz, acetone-d6) 9.20 (br, 1H), 8.40 (br, 1H), 7.71 (d, J =
8.5 Hz, 1H), 7.38 (d, J = 8.7 Hz, 2H), 6.84 (d, J = 8.6 Hz, 2H),
6.51 (dd, J = 2.3, 8.8 Hz, 1H), 6.41 (d, J = 2.3 Hz, 1H), 5.44 (dd, J =
3, 12.9 Hz, 1H), 3.06 (dd, J = 12.0, 16.2 Hz, 1H), 2.66 (dd, J = 3,
10.8 Hz, 1H).
This work was supported by grants from Ministry of Educa-
tion of the People’s Republic of China (No. 208119), Innova-
tive Research Team Development Program in University of
Chongqing (No. KJTD201020) and Chongqing Technology
and Business University (No. yjscxx2009-07).
Received 22 January 2011; accepted 11 March 2011
Paper 1100544 doi:10.3184/174751911X13014075196818
Published online: 3 May 2011
References
1
M. Shimokororiyama, The chemistry of flavonoid compounds, ed. T.A.
Geissman, Pergamon, NewYork, 1962, p 286.
J.C.J.M.D.S. Menezes, J.K. Kirtany and S.P. Kamat, J. Chem. Res., 2010,
28.
2
3
4
Z. Chen, Y. Yang and W. Su, J. Chem. Res., 2010, 661.
C.M. Brennan, I. Hunt, T.C. Jarvis, C.D. Johnson and P.D. McDonnell,
Can. J. Chem., 1990, 68, 1780.
5
6
K. Tanaka and T. Sugino, Green Chem., 2001, 3, 133.
B.S. Goud, K. Panneerselvam, D.E. Zacharias and G.R. Desiraju, J. Chem.
Soc., Perkin Trans., 1995, 2, 325.
Experimental
Melting points were measured using a Mel-Temp melting point appa-
ratus and are uncorrected. IR spectra were recorded with a Thermo
Nicolet 370 FTIR Spectrometer using KBr discs. H NMR spectra
were recorded at 300 MHz, and chemical shifts in ppm were reported
relative to internal Me4Si. Optical rotations of products (MeOH
solution) were taken on a Perkin-Elmer Model 341 polarimeter.
Catalytic cyclisation reactions:5 A suspension of a mixture of pow-
dered 2′-hydroxychalcone 1a (1.0 g, 4.5 mmol), KOH (8 M, 0.1 mL)
and L-alanine (0.01 g) in water (10 mL) was stirred at room tempera-
ture for the predetermined time (see Table 2). The crude product was
7
8
Z. Sanicanin and I. Tabakovic, Tetrahedron Lett., 1986, 27, 407.
Y. Maki, K. Shimada, M. Sako and K. Hirota, Tetrahedron, 1988, 44,
3187.
D. Kumar, G. Patel, A. Kumar, R.K. Roy, J. Heterocyclic Chem., 2009, 46,
791.
1
9
10 M. Deodhar, D.S. Black and N. Kumar, Tetrahedron, 2007, 63, 5227.
11 J. Obniska, K. Kaminski, D. Skrzynska and J. Pichor, Eur. J. Med. Chem.,
2009, 44, 2224.
12 Y. Ding, G.F. Yang, Chin. J. Appl. Chem., 2001, 18, 785.
13 K.H. Kumar, P.T. Perumal, Can. J. Chem., 2006, 84, 1079.
14 K. Imafuku, M. Honda, J.F.W. McOmie, Synthesis, 1987, 199.