A green and novel method of synthesizing 2,2′-arylmethylene bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) catalyzed by L-histidine in ionic liquid

Article abstract of DOI:10.1002/cjoc.201090205

An efficient and green approach to the synthesis of 2,2′- arylmethylene bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) using L-histidine as the catalyst is described. In addition, room temperature ionic liquid 1-butyl-3-methylimidazonium tetrafluoroborate [b

Full text of DOI:10.1002/cjoc.201090205

FULL PAPER
A Green and Novel Method of Synthesizing 2,2'-Arylmethylene
Bis(3-hydroxy-5,5-dimethylcyclohex-2-enone)
Catalyzed by L-Histidine in Ionic Liquid
Zhang, Yan(张岩)
Shang, Zhicai*(商志才)
Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China
An efficient and green approach to the synthesis of 2,2'-arylmethylene bis(3-hydroxy-5,5-dimethylcyclohex-2-
enone) using L-histidine as the catalyst is described. In addition, room temperature ionic liquid 1-butyl-3-me-
thylimidazonium tetrafluoroborate [bmim]BF4 was used as green recyclable alternatives to volatile organic solvents
for this condensation reaction. This green catalytic system can be recycled several times with no decreases in yields
and reaction rates.
Keywords condensation reaction, ionic liquid, L-histidine, synthesis, xanthenedione
Introduction
of xanthenediones (Eq. 1).
Green chemistry movement began more than a dec-
ade ago. Specifically, the challenge in chemistry is to
develop new products, processes and services that
achieve the societal, economic and environmental bene-
fits that are required now and tomorrow,1 and the need
for alternative solvents for reactions has been one of the
major issues we have faced. Over the past few years the
room temperature ionic liquids (ILs) which are low-
melting-point (＜100 ℃) salts have received attention
for their promise as alternative reaction media. Ionic
liquids represent a new class of solvents with non-
molecular, ionic character. In addition, ILs can exhibit
certain desirable physical properties, such as high sol-
vency, no effective vapor pressure, nonflammable, as
well as ease of recovery and reuse, which make ILs a
greener alternative to volatile organic solvents in a
number of reactions.2 Thus, the use of ionic liquids as
solvents and/or catalysts for organic chemistry is an
active and important area of current research.3 Or-
gano-catalysis also became a new research area in syn-
thetic chemistry several years ago.4 Developing cheap
and recyclable organocatalysts that promote reactions in
green solvent to expand the scope of organocatalysis
becomes part of an environmentally benign approach to
fine chemical synthesis, especially large scale reactions.
In this paper, we report an environment-frindly direct
condensation reactions between aromatic aldehydes and
5,5-dimethyl-1,3-cyclohexanedione(dimedone) cata-
lyzed by L-histidine, which proceed well in the room
temperature ionic liquid 1-butyl-3-methylimidazonium
tetrafluoroborate to form the ring-opening derivatives
Xanthenediones can be simply obtained by dehydra-
tion cyclization from their ring-opening derivatives 3,
which contain an inbuilt pyran ring in a number of
natural products and occupy a prominent position in
medicinal chemistry,5 such as sauchinone and xan-
thaurine (Figure 1). Many reports describe the synthesis
of xanthenediones or their ring-opening derivatives.6-10
Conventional synthesis of these classes of compounds
usually involves acid or base in order to catalyze the
condensation of appropriate active methylene carbonyl
compounds with aldehydes. However, most of these
reported procedures have some disadvantages, such as
low yields, excessive use of reagents and catalysts, use
of toxic organic solvents, prolonged reaction times and
so forth. So it is still necessary to develop novel and
greener methods for the preparation of this class of
compounds. We are lucky to see that the cheap and ba-
sic amino acid L-histidine is an efficient and reusable
green catalyst for this condensation reaction in room
temperature ionic liquid [bmim]BF4.
*
E-mail: shangzc@zju.edu.cn; Tel.: 0086-0571-8795237; Fax: 0086-0571-87951895
Received January 19, 2010; revised March 3, 2010; accepted March 18, 2010.
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Chin. J. Chem. 2010, 28, 1184— 1188

Synthesizing 2,2'-Arylmethylene Bis(3-hydroxy-5,5-dimethylcyclohex-2-enone)
Table 2 Results of the synthesis of 3 with L-histidine in IL
Time/ Yielda/
Entry
Aldehyde
Product
min
%
1
30
93
Figure 1 Typical compounds containing an inbuilt pyran ring.
Results and discussion
In the initial stage of the experiment, we studied the
synthesis of 2,2'-(furan-2-ylmethylene)bis(3-hydroxy-
5,5-dimethylcyclohex-2-enone) (3m) as a model sub-
strate with using various reaction conditions to achieve
the best results for this condensation reaction (Eq. 1).
Various temperatures have been studied in solution to
determine their effect on the rate of the reaction. We
also examined whether the presence of the catalyst plays
a role in this reaction. The results are summarized in
Table 1. According to our results, as the temperature
increases, the reaction rate speeds up and the yield will
reach the maximum. In addition, the existence of
L-histidine can surely accelerate the reaction rate. The
most satisfactory result was obtained at the temperature
of 60 ℃ in the presence of the catalyst.
2
30
91
3
30
90
Table 1 Optimization of the condensation reaction
Entry Temperature/℃ Catalyst
Time/min Conversiona
4
40
90
1
2
3
4
30
60
80
80
20 mol%
20 mol%
20 mol%
none
40
30
30
40
60%
89%
90%
62%
a Conversions based on HPLC analysis.
With our optimization of the reaction we have been
able to achieve increases in both reaction rates and
yields in a relatively shorter reaction time (30—45 min).
The reaction was investigated using other aromatic al-
dehydes with dimedone under the optimized condition
using 20 mol% of L-histidine in IL. The results are
summarized in the Table 2.
5
40
88
The results in Table 2 show that aromatic aldehydes
with both electron-donating and electron-withdrawing
functionalities afforded high yields of the corresponding
products, which reflects the wide applicability and use-
fulness of the method. What's more, this green catalytic
system can be recovered and reused by dissolving the
post-reaction mixture into dichloromethane and adding
water. It was then possible to extract any unreacted sub-
strates and the product L-histidine is not soluble in di-
chloromethane. So the organics were removed from the
mixture of ionic liquid and water. The ionic liquid could
be recovered by low-pressure rotary evaporation, which
was reused by extracting with dichloromethane again
(Table 3).
6
7
40
45
86
85
Chin. J. Chem. 2010, 28, 1184— 1188
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Zhang & Shang
FULL PAPER
Continued
Table 3 Recycling experiments with the catalytic systema
Time/ Yielda/
Entry
Aldehyde
Product
min
%
Run
1
2
3
8
30 89
Time/min
Yieldb/%
40
86
40
84
40
85
a Reactions performed with furfural (1.0 mmol), dimedone (2.0
mmol), and L-lysine (20 mol%) in IL (2 mL) and stirred for 40
min at 60 ℃; b Isolated yields after column chromatography.
which may contribute to the environmental benign
process.
9
45 91
45 88
45 85
Experimental
General description of the experimental techniques
Melting points were recorded on an electrothermal
digital microscopical melting point apparatus and un-
corrected. The process of reactions was monitored by
1
TLC on silica. H NMR and 13C NMR spectra were re-
10
corded with TMS as internal standard using a Bruker
AMX-500 MHz spectrometer at 500 and 125 MHz, re-
spectively. IR spectra were measured with a Nicolet
Nexus FTIR 670 spectrophotometer. Low-resolution
MS analyses were measured on a Bruke Esquire 3000
spectrometer using ESI (electrospray ionization) tech-
nique.
Typical experimental procedure
11
In a typical experiment, add aldehyde 1 (1 mmol),
dimedone 2 (2 mmol) and L-histidine (20 mol%) to a 15
mL round-bottom flask equipped with efficient mag-
netic stirrer. Then 2 mL of IL [bmim]BF4 is added to the
flask. The reaction is kept at 60 ℃, which is monitored
using thin-layer chromatography (TLC), and stirring is
continued until the end. When the reaction was com-
pleted, add water (5 mL) to the reaction mixture which
was then poured into a separatory funnel and extract
with CH2Cl2 (5 mL×3). The organic layer was sepa-
rated and concentrated, then the residue was purified by
column chromatography eluting with petroleum/ethyl
acetate or ethyl acetate/dichloromethane to give the pure
product.
12
13
45 88
40 86
The physical and spectra data of all the compounds
(Entry 1— 13)
2,2'-((2-Nitrophenyl)methylene)bis(3-hydroxy-5,5-di-
methylcyclohex-2-enone) (3a): Yellow solid, m.p. 172—
174 ℃, Rf＝0.56 [V(EtOAc)∶V(Petroleum), 1∶1]; IR
(KBr) ν: 342－2, 2958, 2872, 1721, 1596, 1524, 1384,
a Isolated yields after column chromatography.
In conclusion, we have described a procedure for the
preparation of 2,2'-arylmethylene bis(3-hydroxy-5,5-
dimethylcyclohex-2-enone) catalyzed by organocatalyst
L-histidine in ionic liquid. The method has many prac-
tical advantages (high yields, green solvent, moderate
temperature, easy recycling of the catalytic system),
1
1065, 788 cm ; 1H NMR (CDCl3, 500 MHz), δ: 1.02 (s,
6H, 2×CH3), 1.10 (s, 6H, 2×CH3), 2.21—2.51 (m, 8H,
4×CH2), 6.04 (s, 1H, CH), 7.24 (d, J＝7.9 Hz, 1H,
ArH), 7.32 (t, J＝7.6 Hz, 1H, ArH), 7.45—7.49 (m, 1H,
1186
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Chin. J. Chem. 2010, 28, 1184— 1188

Synthesizing 2,2'-Arylmethylene Bis(3-hydroxy-5,5-dimethylcyclohex-2-enone)
ArH), 7.54 (q, J＝1.2 Hz, 1H, ArH), 11.6 (br, s, 2H,
OH); 13C NMR (CDCl3, 125 MHz), δ: 191.0, 189.6,
149.9, 132.3, 131.6, 129.8, 127.4, 124.5, 114.8, 47.0,
46.5, 32.1, 30.2, 28.7,－28.4; MS (ESI) m/z: 414.2 ([M＋
H])＋, 412.2 ([M－H]) .
δ: 11.89 (s, 1H, OH), 7.26 (q, J＝7.6 Hz, 2H), 7.17 (d,
J＝7.0 Hz, 1H), 7.09 (d, J＝8.1 Hz, 2H), 5.54 (s, 1H),
2.29—2.48 (m, 8H), 1.23 (s, 6H), 1.10 (s, 6H).
4-(Bis(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-
yl)methyl)benzonitrile (3h): Pale-yellow solid, m.p.
164—166 ℃; Rf＝0.56 [V(EtOAc)∶V(Petroleum), 1∶
4]; IR (KBr) ν: 3484, 2964, 2887, 2225,－1594, 1501,
2,2'-((3-Nitrophenyl)methylene)bis(3-hydroxy-5,5-di-
methylcyclohex-2-enone) (3b): Red-brown oil, Rf＝0.31
[V(EtOAc)∶V(Petroleum), 1∶1]; IR (KBr) ν: 2959,
2870, 1725, 1594, 1529, 1471, 1447, 1377, 1347, 1253,
1
1
1447, 1375, 1306, 1253, 1120, 842 cm ; H NMR
(CDCl3, 500 MHz) δ: 11.86 (broad signal, OH), 7.56 (d,
J＝8.3 Hz, 2H), 7.19 (d, J＝8.1 Hz, 2H), 5.52 (s, 1H),
2.31—2.46 (m, 8H), 1.22 (s, 6H), 1.11 (s, 6H).
－1
1
1074, 803, 734 cm ; H NMR (CDCl3, 500 MHz) δ:
1.25 (d, J＝4.0 Hz, 6H), 1.44 (d, J＝7.6 Hz, 6H),
2.32—2.52 (m, 8H), 5.55 (s, 1H), 7.42 (q, J＝6.2 Hz,
2H), 8.01 (d, J＝1.3 Hz, 2H), 11.86 (s, 1H, OH).
2,2'-((4-Hydroxyphenyl)methylene)bis(3-hydroxy-5,
5-dimethylcyclohex-2-enone) (3i): Red solid, m.p. 188—
190 ℃; Rf＝0.40 [V(EtOAc)∶V(Petroleum), 1∶1]; IR
(KBr) ν: 3392, 2959, 2929, 1730, 1691,－1594, 1512,
2,2'-((4-Nitrophenyl)methylene)bis(3-hydroxy-5,5-di-
methylcyclohex-2-enone) (3c): Yellow solid, m.p.
169—171 ℃; Rf＝0.23 [V(EtOAc)∶V(Petroleum), 1∶
4]; IR (KBr) ν: 3435, 2958, 1594, 1513, 1468,－1451,
1
1
1448, 1375, 1255, 1169, 1071, 834 cm ; H NMR
(CDCl3, 500 MHz) δ: 1.10 (s, 6H), 1.19 (s, 6H), 2.30—
2.43 (m, 8H), 5.47 (s, 1H), 6.71 (d, J＝8.4 Hz, 2H),
6.93 (d, J＝8.0 Hz, 2H), 11.90 (s, 1H, OH); MS (ESI)
m/z: 383.0 ([M－H])－.
1
1
1375, 1345, 1252, 1167, 1154, 1044, 852 cm ; H
NMR (CDCl3, 500 MHz) δ: 11.94 (broad signal, OH),
8.12 (d, J＝8.4 Hz, 2H), 7.25 (d, J＝7.8 Hz, 2H), 5.56
(s, 1H), 2.31—2.46 (m, 8H),＋1.11 (s, 6H), 1.06－(s, 6H);
MS (ESI) m/z: 414.2 ([M＋H]) , 412.2 ([M－H]) .
2,2'-((4-(Dimethylamino)phenyl)methylene)bis(3-hy-
droxy-5,5-dimethylcyclohex-2-enone) (3j): Yellow so-
lid, m.p. 181—183 ℃ ; Rf ＝ 0.68 [V(EtOAc) ∶
V(Petroleum), 1∶1]; IR (KBr) ν: 3410, 2960, 2877,
1601, 1－522, 1449, 1372, 1312, 1258, 1165, 1065, 912,
2,2'-((4-Chlorophenyl)methylene)bis(3-hydroxy-5,5-
dimethylcyclohex-2-enone) (3d): White solid, m.p.
139—141℃; Rf＝0.46 [V(EtOAc)∶V(Petroleum), 1∶
4]; IR (KBr) ν: 3435, 2958, 2872, 1595, 1490, 1468,
1
812 cm ; 1H NMR (CDCl3, 500 MHz) δ: 0.96 (s, 6H, 2
－1
1
1374, 1304, 1253, 830 cm ; H NMR (CDCl3, 500
MHz) δ: 11.86 (s, 1H, OH), 7.22 (d, J＝8.6 Hz, 2H),
7.01 (d, J＝8.4 Hz, 2H), 5.47 (s, 1H), 2.29—2.48 (m,
8H), 1.21 (s, 6H), 1.10 (s, 6H).
×CH3), 1.10 (s, 6H, 2×CH3), 2.29—2.42 (m, 8H, 4×
CH2), 2.90 (s, 6H, 2×CH3), 5.47 (s, 1H, CH), 6.67 (d,
J＝8.2 Hz, 2H, ArH), 6.95 (d, J＝8.4 Hz, 2H, ArH),
11.95 (s, 1H, OH); MS (ESI) m/z: 412.3 ([M＋H])＋.
2,2'-((4-Methoxyphenyl)methylene)bis(3-hydroxy-5,
5-dimethylcyclohex-2-enone) (3k): White solid, m.p.
142—144 ℃; Rf＝0.43 [V(EtOAc)∶V(Petroleum), 1∶
4]; IR (KBr) ν: 3452, 2959, 1593, 1509, 1467,－1452,
2,2'-((4-Bromophenyl)methylene)bis(3-hydroxy-5,5-
dimethylcyclohex-2-enone) (3e): Yellow solid, m.p.
172—174 ℃; Rf＝0.45 [V(EtOAc)∶V(Petroleum), 1∶
5]; IR (KBr) ν: 3420, 2958, 1594, 1486－, 1468, 1450,
1
1
1
1373, 1304, 1265, 1167, 898, 825 cm 1; H NMR
1417, 1375, 1305, 1248, 1179, 1034, 830 cm ; H
NMR (CDCl3, 500 MHz) δ: 11.91 (s, 1H, OH), 6.99 (d,
J＝8.4 Hz, 2H), 6.81 (d, J＝8.7 Hz, 2H), 5.48 (s, 1H),
3.77 (s, 3H), 2.29—2.47 (m, 8H), 1.22 (s, 3H), 1.09 (s,
3H).
(CDCl3, 500 MHz) δ: 11.86 (s, 1H, OH), 7.37 (d, J＝8.6
Hz, 2H), 6.95 (d, J ＝8.0 Hz, 2H), 5.45 (s, 1H),
2.33—2.44 (m, 8H), 1.21 (s, 6H), 1.10 (s, 6H); 13C
NMR (CDCl3, 125 MHz) δ: 190.9, 189.6, 137.5, 131.5,
128.8, 119.9, 115.5, 47.3, 46.7, 32.7, 31.7, 29.8, 27.7;
MS (ESI) m/z: 448.8 ([M＋H])＋.
2,2'-(p-Tolylmethylene)bis(3-hydroxy-5,5-dimethyl-
cyclohex-2-enone) (3l): Yellow solid, m.p. 126—128
℃; Rf ＝0.52 [V(EtOAc)∶V(Petroleum), 1∶4]; IR
(KBr) ν: 2958, 287－1, 1714, 1596, 1511, 1450, 1372,
2,2'-((3-Bromophenyl)methylene)bis(3-hydroxy-5,5-
dimethylcyclohex-2-enone) (3f): Pink solid, m.p. 184—
186 ℃; Rf＝0.50 [V(EtOAc)∶V(Petroleum), 1∶4]; IR
(KBr) ν: 3447, 2955, 2869, 1597, 1471, 1419, 1377, 788,
1
1
1305, 1041, 813 cm ; H NMR (CDCl3, 500 MHz) δ:
11.90 (broad signal, OH), 7.07 (d, J＝8.0 Hz, 2H), 6.97
(d, J＝7.8 Hz, 2H), 5.50 (s, 1H), 2.29—2.47 (m, 11H),
1.22 (s, 6H), 1.09 (s, 6H).
－1
1
725 cm ; H NMR (CDCl3, 500 MHz) δ: 11.88 (broad
signal, OH), 7.29 (t, J＝7.8 Hz, 1H), 7.23 (s, 1H), 7.13
(t, J＝7.8 Hz, 1H), 7.01 (d, J＝7.8 Hz, 1H), 5.49 (s, 1H),
2.29—2.48 (m, 8H), 1.22 (s, 6H), 1.09 (s, 6H); 13C
NMR (CDCl3, 125 MHz) δ: 190.9, 189.7, 141.0, 130.4,
129.9, 129.2, 125.7, 122.7, 115.3, 47.3, 46.7, 32.9, 31.7,
29.8, 27.6; MS (ESI) m/z: 447.2 ([M＋H])＋, 446.8
([M－H])－.
2,2'-(Furan-2-ylmethylene)bis(3-hydroxy-5,5-dimeth-
ylcyclohex-2-enone) (3m): Pale-yellow solid, m.p. 207—
209 ℃; Rf＝0.48 [V(EtOAc)∶V(Petroleum), 1∶1]; IR
(KBr) ν: 3435, 2958, 2930, 1740, 1715, 1641, 1603,
－1
1
1385, 1242, 1044, 755 cm ; H NMR (CDCl3, 500
MHz) δ: 0.86 (s, 3H, CH3), 1.17 (d, J＝1.0 Hz, 9H, 3×
CH3), 2.22 (d, J＝16 Hz, 4H), 2.28 (d, J＝3.1 Hz, 1H),
2.56 (d, J＝3.1 Hz, 1H), 2.62 (q, J＝1.1 Hz, 2H), 4.67
(s, CH, 1H), 6.17 (d, J＝3.2 Hz, 1H), 6.33 (q, J＝1.8 Hz,
1H), 7.40 (d, J＝1.0 Hz, 1H); 13C NMR (CDCl3, 125
MHz) δ: 199.5, 198.9, 193.4, 177.9, 148.9, 143.1, 111.6,
2,2'-(Phenylmethylene)bis(3-hydroxy-5,5-dimethyl-
cyclohex-2-enone) (3g): White solid, m.p. 190—192 ℃;
Rf＝0.50 [V(EtOAc)∶V(Petroleum), 1∶4]; IR (KBr) ν:
3450, 2962, 2872, 1594－, 1492, 1448, 1375, 1302, 1251,
1
1164, 845, 777, 695 cm ; 1H NMR (CDCl3, 500 MHz)
Chin. J. Chem. 2010, 28, 1184— 1188
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Zhang & Shang
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110.3, 110.2, 101.8, 52.9, 51.4, 50.4, 48.4, 37.6, 34.5,
30.9, 30.7, 29.0, 28.6,－26.5; MS (ESI) m/z: 359.2 ([M＋
H])＋, 357.1 ([M－H]) .
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Chin. J. Chem. 2010, 28, 1184— 1188