Improved synthesis of 2,2-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) and 1,8-dioxo-octahydroxanthene derivatives catalyzed by electrogenerated base and sulfuric acid

Article abstract of DOI:10.1002/jccs.201400307

An efficient method has been developed for the synthesis of 1,8-dioxo-octahydroxanthene derivatives in two-step. In the first step, the electrogenerated base (EGB) catalyzed multicomponent transformation of dimedone and aromatic aldehydes in an undivided

Full text of DOI:10.1002/jccs.201400307

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Communication
Improved Synthesis of 2,2¢-Arylmethylene Bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-
1-one) and 1,8-Dioxo-octahydroxanthene Derivatives Catalyzed by Electrogenerated
Base and Sulfuric Acid
Reyhaneh Kazemi-Rad,a* Javad Aziziana and Hassan Kefayatib
aDepartment of Chemistry, Science and Research Branch, Islamic Azad University, Tehran, Iran
bDepartment of Chemistry, Rasht Branch, Islamic Azad University, Guilan, Iran
(Received: Jul. 19, 2014; Accepted: Dec. 26, 2014; Published Online: Mar. 16, 2015; DOI: 10.1002/jccs.201400307)
An efficient method has been developed for the synthesis of 1,8-dioxo-octahydroxanthene derivatives in
two-step. In the first step, the electrogenerated base (EGB) catalyzed multicomponent transformation of
dimedone and aromatic aldehydes in an undivided cell in the presence of sodium bromide as an electrolyte
into 2,2¢-arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) at room temperature. In the
second step, H2SO4 was employed as a dehydrating reagent for the cyclization process to give symmetrical
heterocycles 1,8-dioxo-octahydroxanthene derivatives. Short reaction time, convenient work up, and us-
ing of inexpensive reagents, simple equipment, novel and eco-friendly procedure make this strategy more
useful for the preparation of xanthene derivatives.
Keywords: Electrocatalytic transformation; Electrogenerated base; 1,8-Dioxo-octahydroxanthene;
2,2¢-Arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one); Dimedone.
2,2¢-Arylmethylene bis(3-hydroxy-5,5-dimethyl-2-
cyclohexene-1-one) derivatives are important biologically
active compounds, which can be evaluated as tyrosinase
inhibitors.1 They are also important synthetic intermedi-
ates and can serve as versatile precursors in the synthesis
of xanthenes that are known as an important class of
heterocyclic compounds, widely used as lecodyes,2 pH-
sensitive fluorescent materials for visualization of bio-
molecules3 and are utilized in laser technologies due to
their photochemical and photophysical properties. They
possess diverse biological and therapeutic properties such
as anti-inflammatory,4 antiviral5 and antibacterial activi-
ties.6
chloride,24 and NH2SO3/SDS25 have also been employed
for the preparation of xanthenedione derivatives. Addition-
ally, the above condensation process could proceed in ionic
liquid26-28 or ethylene glycol.29 Recently, Ilangovan et al.
described two-step synthesis of 9-aryl-1,8-dioxooctahy-
droxanthene derivatives by condensation of aryl aldehydes
and dimedone in the presence of CaCl2 and HBr as cata-
lysts.30 However, some of these methodologies have some
disadvantages, such as low yields,14,15 prolonged reaction
time,8,12,17–19,21,30 harsh reaction conditions,7 high tempera-
ture17,18 and the requirement of excess of catalysts21 or spe-
cial apparatus,23 hazard organic solvents, and tedious
workup. Thus, the development of a simple, highly effi-
cient methodology for synthesis of xanthenes has remained
a desired goal.
Therefore, a great number of synthetic methods have
been reported via the condensation of aldehyde with 1,3-
cyclohexanedione or 5,5-dimethyl-1,3-cyclohexanedione
(dimedone) in the presence of protic acids7 or Lewis acids
such as InCl3-4H2O,8 FeCl3-8H2O,9 NaHSO4,10 and hetero-
geneous catalysts, for instance Dowex-50W,11 NaHSO4-
SiO2,12 silica sulfuric acid,13 polyaniline-p-toluenesulfo-
The advances in electro-synthesis have provided or-
ganic chemists with a new and versatile synthetic technique
of significant promise31,32 The electro-organic reaction
took place in good to excellent yields with easy work-up
and do not require the use of harsh conditions such as high
temperature and expensive reagents. To date, no reports
have been published on the electro-synthesis of 2,2¢-
arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohex-
ene-1-one) and 1,8-dioxo-octahydroxanthene.
nate,14 PPA-SiO2,15 TiO2/SO42- 16 Fe3+-montmorillonite,17
,
SbCl3/SiO2,18 Amberlyst-1519 and nano-TiO220 as catalysts.
Other catalysts, such as trimethylsilyl chloride,21 p-dode-
cylbenzenesulfonic acid,22,23 triethylbenzylammonium
* Corresponding author. Tel.: +98 911 2341556; Fax: +98 21 44865767; E-mail: reyhanehkazemi83@gmail.com
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201400307
J. Chin. Chem. Soc. 2015, 62, 311-315
© 2015 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
311

Communication
Kazemi-Rad et al.
Table 1. Electrocatalytic transformation of dimedone (1) and 3-
nitrobenzaldehyde (2a) into 2,2'-(3-nitrophenyl)methyl-
ene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one)
(3a)[a]
All these facts have prompted us to design a conve-
nient and facile multicomponent synthesis of 2,2¢-aryl-
methylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-
1-one) and 1,8-dioxo-octahydroxanthene based on elec-
tro-catalytic transformation of aldehyde and dimedone in
an undivided cell (Scheme 1).
Current
Entry Alcohol I (mA) density
(mAcm-2)
Electricity
passed
(F mol-1)
Time
(min)
Yield
(%)
1
2
3
4
5
6
7
MeOH
EtOH
10
10
10
5
4
4
15
15
15
30
6
0.09
0.09
0.09
0.09
0.09
0.09
0.09
67
40
10
65
70
87
83
Synthesis of 2,2¢-arylmethylene bis(3-hy-
droxy-5,5-dimethyl-2-cyclohexene-1-one)
and 1,8-dioxo-octahydroxanthenes
Scheme 1
n-PrOH
MeOH
MeOH
MeOH
MeOH
4
2
25
50
100
10
20
40
3
1.5
[a] Reaction conditions: dimedone (2 mmol), 3-nitrobenzalde-
hyde (1 mmol), NaBr (0.1 mmol), alcohol (10 mL), iron cathode
(2.5 cm2), platinum anode (2.5 cm2), r.t.
At first, in continuation of our work33,34 on the devel-
opment of efficient and environmentally benign proce-
dures using electrogenerated base, initially we examined
electrocatalytic transformation of dimedone 1 and 3-nitro-
benzaldehyde 2a into 1,8-dioxo-octahydroxanthene 4a, in
methanol in an undivided cell containing an iron electrode
as the cathode and a Pt electrode as the anode under current
density 4 mA/cm2 in the presence of sodium bromide as an
electrolyte at room temperature. Surprisingly, contrary to
our expectation, only intermediate 2,2¢-(3-nitro phen-
yl)methylene bis(3-hydroxy-5,5-dimethyl-2-cyclohex-
ene-1-one) 3a was obtained in 67% yield and cyclized
product 4a was not obtained. Increasing the current density
to 20 mA/cm2, yielded only a mixture of 3a (87%) and 4a
(8%) (Table 1).
dependent on the solvent. When the electrolysis was car-
ried out in MeOH, EtOH, and n-PrOH solvents, the product
3a, after 0.04 F/mol electricity passed, was isolated in 67%,
40%, and 10% yields, respectively (Table 1, entries 1-3).
This result indicated that the yield of 3a is related to the na-
ture of the EGBs in these solvents.
Also, the yield and the rate of this transformation de-
pended on current density in electrochemical cell. As it is
indicated in Table 1 (entries 4-7), When the electrolysis in
MeOH was carried out in the current density 20 mA/cm2 (I
= 50 mA, electrodes surface 2.5 cm2), excellent conver-
sions of starting compounds were obtained. Thus, the cur-
rent density 20 mA/cm2 (I = 50 mA, electrodes surface 2.5
cm2) in methanol at room temperature was found to be opti-
mum for the electrochemically induced chain process and
resulted in the highest yield (87%) of 3a.
The result led us to the use of an acidic dehydrating
agent for this cyclization. We found that, when a few drops
of concd H2SO4, after finishing electrolysis, was added in
the above mixture, the cyclization of 3a proceeded
smoothly to give 1,8-dioxo-octahydroxanthene 4a with
high yield (95%) at room temperature. It was also noticed
that, the condensation of dimedone and 3-nitrobenzalde-
hyde by using H2SO4 without the pre-electrolysis, after 1
day, did not yield the products 3a and 4a in similar condi-
tions.
Under the optimal conditions (current density 20
mA/cm2, MeOH as a solvent) the electrolysis of dimedone
(1) with various aromatic aldehydes 2a-i, bearing electron
withdrawing groups and electron releasing groups, in an
undivided cell gives rise to the corresponding 2,2¢-aryl-
methylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-
one) 3a-i in good yields (57-88%) at room temperature
within 3-30 min (Scheme 1, Table 2). As it is indicated in
Table 2, the reaction of aromatic aldehydes having electron
withdrawing groups reacted very well at faster rate com-
pared with aromatic aldehydes having electron releasing
groups.
In order to optimize the electrolysis conditions, the
electrocatalytic transformation of dimedone 1 (2 mmol)
and 3-nitrobenzaldehyde 2a (1 mmol) into 2,2¢-(3-nitro
phenyl)methylene bis(3-hydroxy-5,5-dimethyl-2-cyclo-
hexene-1-one) 3a, in alcohol solution was studied at room
temperature.
Taking into consideration the above results, the fol-
lowing mechanism for the electrocatalytic chain transfor-
The results showed that, the yield of 3a was strongly
312
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Electrosynthesis of 1,8-Dioxo-octahydroxanthenes
Table 2. Synthesis of 2,2'-Arylmethylene bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-ones) (3a-i)
and 1,8-dioxo-octahydroxanthenes (4a-i) catalyzed by electrogenerated base and sulfuric
acid[a]
Products 3
Time Yield
(min) (%)
Products 4[b]
Mp (ºC)
[18]
Electricity
passed
(F mol-1)
Products
R
Mp (ºC) Yield
Mp (ºC)
Mp (ºC)
[35]
(%)
a
b
c
d
e
f
m-NO2
p-NO2
o-NO2
p-Me
p-OMe
o-Cl
0.09
0.16
0.25
0.78
0.93
0.25
0.22
0.31
0.37
3
5
87
84
76
63
57
88
86
77
74
194-195 190-191
189-191 188-189
191-193 188-189
145-146 142-143
138-139 140-141
200-202 199-200
213-215 189-190
138-139 137-138
188-190 189-190
95
91
89
78
72
94
89
83
81
168-170 165-166
224-226 222-224
258-260 250-252
212-214 215-216
238-240 242-243
229-231 226-227
185-187 183-185
231-232 226-228
202-204 202-203
8
25
30
8
g
h
i
m-Cl
p-Cl
7
10
12
H
[a] Reaction condition: dimedone (1) (2 mmol), arylaldeydes (2a-i) (1 mmol), NaBr (0.1 mmol),
methanol (10 mL), iron cathode (2.5 cm2), platinum anode (2.5 cm2), current density (20 mAcm-2), r.t.
[b] After finishing of the electrolysis a few drops of concd. H2SO4 was added, and the mixture stirred
for 1.5 h at r.t.
mation of dimedone 1 and various aromatic aldehydes 2a-i
A proposed mechanism for the preparation
Scheme 2
of 2,2¢-arylmethylene bis(3-hydroxy-5,5-
dimethyl-2-cyclohexene-1-one) and 1,8-di-
oxo-octahydroxanthene
into 1,8-dioxo-octahydroxanthene 4a-i is proposed. The
deprotonation of methanol at the cathode as result of direct
or indirect cathode process leads to the formation of meth-
oxide anion.36 The subsequent reaction in solution between
methoxide anion and dimedone gives rise to dimedone an-
ion (Scheme 2). Next, Knoevenagel condensation of dime-
done anion with the aromatic aldehyde takes place in the
solution with the elimination of a hydroxide anion and for-
mation of Knoevenagel adduct 5. The subsequent Michael
addition of second dimedone anion to Knoevenagel adduct
5 gives intermediate 6 which results in the formation of the
corresponding 2,2¢-aryl-methylene bis(3-hydroxy-5,5-di-
methyl-2-cyclohexene-1-one) 3 in good yields and cy-
clized products 4 in low yields. Then, intermediate 3 is
cyclized with a few drops of concd H2SO4 at room tempera-
ture to give the expected 1,8-dioxo-octahydroxanthene 4
(Scheme 2).
In conclusion, we have developed a novel and effi-
cient methodology for the synthesis of 2,2¢-aryl-methylene
bis(3-hydroxy-5,5-dimethyl-2-cyclohexene-1-one) and
1,8-dioxo-octahydroxanthene derivatives from dimedone
and aromatic aldehydes. This method has advantages in-
cluding (i) in situ generation of the base and the avoidance
of polluting or hazardous chemicals (ii) a very fast, one-pot
reaction in good to excellent yields under milder condi-
tions, and (iii) the procedure utilizes inexpensive reagents,
simple equipment and convenient work up.
Also, this process is based on the electrocatalytic
transformation representing an eco-friendly benign alter-
native to current chemical processes. We believe that this
economically viable procedure could be successfully ap-
plied to a variety of cyclic 1,3-dicarbonyl compounds as
well as dimedone to variety of xanthene derivatives in ex-
cellent yields.
J. Chin. Chem. Soc. 2015, 62, 311-315
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313

Communication
Kazemi-Rad et al.
EXPERIMENTAL
ACKNOWLEDGMENTS
We gratefully acknowledge financial support from
the Islamic Azad University, Rasht Branch, Iran.
All reagents were purchased from Merck and Fluka and
used without further purification. Melting points were obtained in
open capillary tubes and were measured on an Electrothermal IA
9100 apparatus. IR spectra were recorded on KBr pellets on a
Shimadzu FT-IR 8600 spectrophotometer. 1H and 13C NMR spec-
tra were determined on a Bruker DRX-400 Avance instrument at
400 and 100 MHz. Constant current density was passed through
the solution by Coulometer model ZCM761 made in ZAG Chemie
Company.
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