Electrochemically induced aldol reaction of cyclic 1,3-diketones with isatins

Article abstract of DOI:10.1016/j.electacta.2009.11.045

The electrolysis of isatins and cyclic 1,3-diketones in alcohol in an undivided cell results in the formation of the previously unknown substituted 2-(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)cyclohexane-1,3-diones in 70-85% substance yields and 700-850%

Full text of DOI:10.1016/j.electacta.2009.11.045

Electrochimica Acta 55 (2010) 2129–2133
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochemically induced aldol reaction of cyclic 1,3-diketones with isatins
Michail N. Elinsona,∗, Valentina M. Merkulovaa, Alexey I. Ilovaiskya, Alexander O. Chizhova,
Pavel A. Belyakova, Fructuoso Barbab, Belen Batanerob
a N.D. Zelinsky Institute of Organic Chemistry, Leninsky prospect 47, 119991 Moscow, Russia
b Department of Organic Chemistry, University of Alcalá, 28871 Alcalá de Henares, Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The electrolysis of isatins and cyclic 1,3-diketones in alcohol in an undivided cell results in the formation of
the previously unknown substituted 2-(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)cyclohexane-1,3-
diones in 70–85% substance yields and 700–850% current efficiency. Thus, the simple electrocatalytic
system can produce, under mild conditions the new electrochemically induced aldol reaction of isatins
and cyclic 1,3-diketones.
Received 7 October 2009
Received in revised form
11 November 2009
Accepted 15 November 2009
Available online 20 November 2009
© 2009 Elsevier Ltd. All rights reserved.
Keywords:
Electrolysis
Electrocatalysis
Isatins
1,3-Dicarbonyl compounds
Aldol reaction
2-(3-Hydroxy-2-oxo-2,3-dihydro-1H-
indol-3-yl)cyclohexane-1,3-diones
1. Introduction
dimethylcyclohexane-1,3-dione 1 formation [16]; the second is
the procedure when piperonal together with dimedone were
The aldol reaction is a well-known carbon–carbon bond form-
ing reaction [1,2]. In its usual form, it involves the nucleophilic
addition of aldehyde or ketone enolate to carbonyl group to form ␤-
hydroxycarbonyl compound, which is called aldol, a structural unit
occurring in many natural molecules and pharmaceuticals [3–8].
In aldol condensation and in Knoevenagel condensation a nucle-
ophilic addition of an active hydrogen compound anion to a
carbonyl group is followed by a dehydration reaction [9–12].
One of the important examples of aldol type reaction is Henry
reaction, namely a base-catalyzed reaction between nitroalkanes
and aldehydes or ketones [13,14]. The Henry reaction is also very
useful carbon–carbon bond forming reactions and has wide syn-
thetic applications in organic synthesis [15].
melted, then adsorbed on neutral chromatographic alumina and
shaken at room temperature for 18 h [17]. 2-(Benzo[1,3]dioxol-
5-yl-hydroxymethyl)-5,5-dimethylcyclohexane-1,3-dione 2 was
then extracted by CH2Cl2 [17]. For compound 1 only melting point
is known [16]. Any characteristics of compound 2 in the short
communication are absent [17].
Within the domain of the green chemistry, electrochemical
technology can provide a valuable alternative to the use of the
conventional reagents for fine chemical synthesis [18]. Due to the
electron transfer between an electrode and the substrate molecules
the formation of highly reactive intermediates is achieved under
mild conditions, avoiding reductive or oxidant agents as well as
acids, bases and related waste by-products.
But examples of the aldol reaction of cyclic 1,3-dicarbonyl com-
pounds with carbonyl group yielding aldol (␤-hydroxyketones)
are very rare. As to our knowledge, there are only two papers
which describes two rare examples where the second step,
i.e. Knoevenagel condensation was avoided. One of them is
the addition of dimedone to N-acetyl-2-aminobenzaldehyde
in ethanol with 2 - (2ꢀ- acetylamino- 1 -hydroxybenzyl)-5,5-
Recently, we have published the electrochemically induced
addition of nitromethane to carbonyl compounds in methanol solu-
tion in an undivided cell [19].
Now we wish to report the electrochemically induced addition
of cyclic 1,3-dicarbonyl compounds 3a,b to isatins 4a–f in alcohol
solution in an undivided cell (Scheme 1 and Table 1).
2. Experimental
∗
All melting points were measured with a Gallenkamp melt-
ing point apparatus and are uncorrected. 1H and 13C NMR spectra
Corresponding author. Tel.: +7 499 137 38 42; fax: +7 499 135 53 28.
E-mail address: elinson@ioc.ac.ru (M.N. Elinson).
0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2009.11.045

2130
M.N. Elinson et al. / Electrochimica Acta 55 (2010) 2129–2133
Scheme 1.
Table 1
Electrocatalytic addition of dimedone 3a to isatin 4a with the formation of 2-(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-dimethylcyclohexane-1,3-dione 5aa.
Electrolyte
I (mA)
Current density (mA cm−2
)
Time (min)
32
16
8
4
2
1
2
2
2
Electricity passed (F mol−1
)
Yield of 5a (%)b
NaBr
NaBr
NaBr
NaBr
NaBr
NaBr
NaI
25
50
5
10
20
40
80
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
79 (790)
82 (820)
84 (840)
85 (850)
87 (870)
74 (740)
81 (810)
79 (790)
82 (820)
100
200
400
800
400
400
400
160
80
80
80
KI
NaBrc
a
3a (5 mmol), 4a (5 mmol), electrolyte (0.5 mmol), EtOH (20 mL), iron cathode (5 cm2) graphite anode (5 cm2), 20 ◦C.
Yield of isolated 5a, in parentheses, current efficiency is given.
MeOH as a solvent.
b
c
were recorded with a Bruker Avance II-300 spectrometer at ambi-
ent temperature in DMSO-d6 solutions. Chemical shifts values are
given in ı scale relative to Me4Si. IR spectra were registered with
a SPECORD M82 spectrometer in KBr pellets. The ESI mass spec-
tra were recorded with a Finnigan MAT LCQ instrument with spray
capillary voltage 4530 V. A methanolic solution of the sample was
injected by syringe at 10 ␮L/min; MS spectra were measured at
positive or negative mode (registration range from m/z 100 to m/z
2000); for MS2, helium was used as a collision gas. Interface cap-
illary temperature was 220 ◦C, sheath gas flow (nitrogen) 19.4 a.u.,
auxiliary gas flow 0.4 a.u. Activation time was 30 ms. Activation
energy was 30% from relative max. collision energy. Methanol and
ethanol with less than 1% of water content were used without fur-
ther purification.
2.1. Typical electrolysis procedure
A solution of isatin (5 mmol), cyclic 1,3-diketone (5 mmol) and
sodium bromide (0.05 g, 0.5 mmol) in alcohol (20 mL) was elec-
trolyzed in an undivided cell equipped with a magnetic stirrer,
a graphite anode and an iron cathode at 20 ◦C under a con-
stant current density of 80 mA cm−2 (I = 400 mA, electrodes square
5 cm2) until indicated in Tables 1 and 2 quantity of electricity was
passed. After the electrolysis was finished, the reaction mixture
was evaporated to dryness at 10 mm Hg; evaporation time 30 min,
bath temperature 20 ◦C. The residue obtained was triturated with
water (10 mL) and filtered to isolate the solid product, which was
then washed with water (3 × 10 mL) and dried under reduced
pressure.
Table 2
Electrocatalytic transformation of cyclic diketones (3a,b) and isatins (4a–f) into substituted 2-(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)cyclohexane-1,3-diones (5a–i)a.
Diketone
R1
Isatin
R2
R3
I (mA)
Current density (mA cm−2
)
Time (min)
Electricity passed (F mol−1
)
Product, yield (%)b
3a
3a
3a
3a
3a
3a
Me
Me
Me
Me
Me
Me
4a
4b
4c
4d
4e
4f
H
H
H
H
H
Me
Cl
400
400
400
400
400
400
80
80
80
80
80
80
2
2
2
2
2
2
0.1
0.1
0.1
0.1
0.1
0.1
5a, 87 (870)
5b, 85 (850)
5c, 86 (860)
5d, 71 (710)
5e, 86 (860)
5f, 83 (830)
Me
CH2Ph
Ac
H
H
3b
3b
3b
H
H
H
4a
4b
4f
H
Me
H
H
H
Cl
400
400
400
80
80
80
2
2
2
0.1
0.1
0.1
5g, 72 (720)
5h, 76 (760)
5i, 73 (730)
a
5 mmol of diketones (3a,b), 5 mmol of isatins (4a–f), 0.5 mmol of NaBr, 20 mL of ethanol, iron cathode (5 cm2), graphite anode (5 cm2), 20 ◦C.
Yield of isolated product, in parentheses, current efficiency is given.
b

M.N. Elinson et al. / Electrochimica Acta 55 (2010) 2129–2133
2131
2-(3-Hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-dimethylcy-
clohexane-1,3-dione (5a): white solid; yield 1.25 g (87%); mp
166 ◦C; ıH (300 MHz) 0.98 (s, 6H), 2.15–2.25 (m, 4H), 6.77 (d, J
7.7 Hz, 1H, Ar), 6.87 (t, J 7.5 Hz, 1H, Ar), 7.07 (d, J 7.3 Hz, 1H, Ar),
7.16 (t, J 7.5 Hz, 1H, Ar), 7.50–8.80 (br s, 1H, OH), 10.14 (s, 1H,
NH), 10.50–12.00 (br s, 1H, OH); ıC (75 MHz) 27.5, 31.8, 47.0 (br),
77.8, 109.4, 110.6, 121.2, 123.1, 129.1, 132.3, 142.7, 176.3, 184.0
(br); MS (+): m/z 310 [M+Na]+, 270 [M+H−H2O]+; MS (–): m/z 286
[M−H]−; MS2 (+) (m/z 310): m/z 292 [M+Na−H2O]+; IR (KBr): ꢀmax
3168, 3088, 2960, 1736, 1624, 1472, 1368, 1244 cm−1. Anal. Calcd.
for C16H17NO4 (%): C, 66.89; H, 5.96; N, 4.88. Found (%): C, 66.95;
H, 6.09; N, 4.75.
2-(3-Hydroxy-1-methyl-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-
dimethylcyclohexane-1,3-dione (5b): white solid; yield 1.28 g (85%);
mp 156–158 ◦C; ıH (300 MHz) 0.97 (s, 6H), 2.15–2.25 (m, 4H), 3.10
(s, 3H), 6.95 (d, J 8.0 Hz, 1H, Ar), 6.97 (t, J 7.5 Hz, 1H, Ar), 7.13 (d, J
7.3 Hz, 1H, Ar), 7.28 (t, J 7.5 Hz, 1H, Ar), 9.00–11.00 (br s, 2H, OH); ıC
(75 MHz) 26.0, 27.5, 31.8, 46.6 (br), 77.5, 108.3, 110.6, 122.1, 122.8,
129.4, 131.7, 144.1, 175.0, 186.0 (br); MS (+): m/z 324 [M+Na]+, 284
[M+H−H2O]+; MS (–): m/z 300 [M−H]−; MS2 (+) (m/z 324): m/z
306 [M+Na−H2O]+; IR (KBr): ꢀmax 3192, 2992, 1720, 1604, 1472,
1360, 1304, 1240 cm−1. Anal. Calcd. for C17H19NO4 (%): C, 67.76;
H, 6.36; N, 4.65. Found (%): C, 67.85; H, 6.47; N, 4.48.
141.6, 176.1, 182.0 (br); MS (+): m/z 344, 346 [M+Na]+, 304, 306
[M+H−H2O]+; MS (–): m/z 320, 322 [M−H]−; MS2 (+) (m/z 344):
m/z 326 [M+Na−H2O]+; IR (KBr): ꢀmax 3136, 2960, 1736, 1592,
1448, 1368, 1248 cm−1. Anal. Calcd. for C16H16ClNO4 (%): C, 59.73;
H, 5.01; Cl, 11.02; N, 4.35. Found (%): C, 59.87; H, 5.26; Cl, 10.94; N,
4.23.
2-(3-Hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)cyclohexane-
1,3-dione (5g): white solid; yield 0.93 g (72%); mp 241 ◦C; ıH
(300 MHz) 1.75–1.88 (m, 2H), 2.22–2.36 (m, 4H), 6.76 (d, J 7.3 Hz,
1H, Ar), 6.86 (t, J 7.5 Hz, 1H, Ar), 7.08 (d, J 7.5 Hz, 1H, Ar), 7.15
(t, J 7.5 Hz, 1H, Ar), 8.50–9.50 (br s, 1H, OH), 10.14 (s, 1H, NH),
11.20–12.50 (br s, 1H, OH); ıC (75 MHz) 20.4, 33.0 (br), 77.9, 109.4,
112.0, 121.3, 123.3, 129.2, 132.5, 142.7, 176.5, 187.0 (br); MS (+):
m/z 282 [M+Na]+, 242 [M+H−H2O]+; MS (–): m/z 258 [M−H]−; MS2
(+) (m/z 282): m/z 264 [M+Na−H2O]+; IR (KBr): ꢀmax 3088, 2944,
1700, 1592, 1472, 1364, 1196 cm−1. Anal. Calcd. for C14H13NO4
(%): C, 64.86; H, 5.05; N, 5.40. Found (%): C, 64.98; H, 5.32; N, 5.29.
2-(3-Hydroxy-1-methyl-2-oxo-2,3-dihydro-1H-indol-3-yl)
cyclohexane-1,3-dione (5h): white solid; yield 1.04 g (76%);
mp 158–160 ◦C; ıH (300 MHz) 1.76–1.89 (m, 2H), 2.22–2.38 (m,
4H), 3.09 (s, 3H), 6.94 (d, J 8.0 Hz, 1H, Ar), 6.96 (t, J 7.5 Hz, 1H,
Ar), 7.15 (d, J 7.3 Hz, 1H, Ar), 7.27 (t, J 7.5 Hz, 1H, Ar), 9.50–12.00
(br s, 2H, OH); ıC (75 MHz) 20.3, 26.0, 33.0 (br), 77.5, 108.2, 112.0,
122.0, 122.9, 129.3, 131.7, 144.1, 174.9, 186.0 (br); MS (+): m/z
296 [M+Na]+, 256 [M+H−H2O]+; MS (–): m/z 272 [M−H]−; MS2 (+)
(m/z 296): m/z 278 [M+Na−H2O]+; IR (KBr): ꢀmax 3488, 2952, 1664,
1608, 1472, 1376, 1136 cm−1. Anal. Calcd. for C15H15NO4 (%): C,
65.92; H, 5.53; N, 5.13. Found (%): C, 66.17; H, 5.67; N, 5.02.
2-(5-Chloro-3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-
yl)cyclohexane-1,3-dione (5i): white solid; yield 1.07 g (73%);
mp 129–131 ◦C; ıH (300 MHz) 1.77–1.90 (m, 2H), 2.26–2.38 (m,
4H), 6.77 (d, J 8.1 Hz, 1H, Ar), 7.09 (s, 1H, Ar), 7.21 (d, J 8.1 Hz,
1H, Ar), 9.50–12.00 (br s, 2H, OH), 10.31 (s, 1H, NH); ıC (75 MHz)
20.3, 33.0 (br), 77.8, 110.8, 111.4, 123.4, 125.1, 128.9, 134.5,
141.6, 176.3, 188.0 (br); MS (+): m/z 316, 318 [M+Na]+, 276, 278
[M+H−H2O]+; MS (–): m/z 292, 294 [M−H]−; MS2 (+) (m/z 316):
m/z 298 [M+Na−H2O]+; IR (KBr): ꢀmax 3496, 3208, 1700, 1596,
1480, 1400, 1184 cm−1. Anal. Calcd. for C14H12ClNO4 (%): C, 57.25;
H, 4.12; Cl, 12.07; N, 4.77. Found (%): C, 57.37; H, 4.28; Cl, 11.89; N,
4.62.
2-(1-Benzyl-3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-
dimethylcyclohexane-1,3-dione (5c): white solid; yield 1.62 g (86%);
mp 148–149 ◦C; ıH (300 MHz) 0.99 (s, 6H), 2.16–2.28 (m, 4H), 4.80
(d, J 16.1 Hz, 1H), 4.95 (d, J 16.1 Hz, 1H), 6.66 (d, J 8.0 Hz, 1H, Ar),
6.95 (t, J 7.5 Hz, 1H, Ar), 7.09–7.21 (m, 2H, Ar), 7.23–7.38 (m, 3H,
Ar), 7.52 (d, J 7.3 Hz, 2H, Ar), 8.20–9.50 (br s, 1H, OH), 10.50–12.10
(br s, 1H, OH); ıC (75 MHz) 27.5, 31.8, 42.9, 46.8 (br), 77.5, 108.9,
110.4, 122.1, 122.9, 127.1, 127.2, 128.4, 129.2, 131.7, 136.4, 143.2,
175.0, 184.0 (br); MS (+): m/z 400 [M+Na]+, 360 [M+H−H2O]+; MS
(–): m/z 376 [M−H]−; MS2 (+) (m/z 400): m/z 382 [M+Na−H2O]+; IR
(KBr): ꢀmax 3408, 3344, 2952, 1732, 1600, 1480, 1356, 1248 cm−1
.
Anal. Calcd. for C23H23NO4 (%): C, 73.19; H, 6.14; N, 3.71. Found
(%): C, 73.35; H, 6.29; N, 3.58.
2-(1-Acetyl-3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-
dimethylcyclohexane-1,3-dione (5d): white solid; yield 1.18 g (71%);
mp 178–180 ◦C; ıH (300 MHz) 0.96 (s, 6H), 2.16–2.28 (m, 4H), 2.56
(s, 3H), 7.19 (t, J 7.5 Hz, 1H, Ar), 7.29 (d, J 7.3 Hz, 1H, Ar), 7.34 (t, J
7.5 Hz, 1H, Ar), 8.10 (d, J 8.1 Hz, 1H, Ar), 9.20–11.30 (br s, 2H, OH);
ıC (75 MHz) 26.0, 27.4, 32.0, 46.5 (br), 77.2, 111.3, 115.8, 123.4,
125.2, 129.5, 131.3, 139.9, 170.4, 175.7, 183.0 (br); MS (+): m/z 352
[M+Na]+, 330 [M+H]+, 312 [M+H−H2O]+; MS (–): m/z 328 [M−H]−;
MS2 (+) (m/z 352): m/z 334 [M+Na−H2O]+; IR (KBr): ꢀmax 2968,
2704, 1776, 1712, 1600, 1468, 1364, 1252 cm−1. Anal. Calcd. for
C19H23NO5 (%): C, 65.64; H, 5.81; N, 4.25. Found (%): C, 65.44; H,
5.93; N, 4.11.
3. Results and discussion
In the present study, we report our results on the electrochem-
ically induced addition of cyclic 1,3-dicarbonyl compounds 3a,b to
isatins 4a–f in alcohol solution in an undivided cell (Scheme 1 and
Table 1).
2-(3-Hydroxy-5-methyl-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-
dimethylcyclohexane-1,3-di-one (5e): white solid; yield 1.30 g
(86%); mp 169–171 ◦C; ıH (300 MHz) 0.98 (s, 6H), 2.13–2.25 (m,
4H), 2.25 (s, 3H), 6.65 (d, J 7.3 Hz, 1H, Ar), 6.88 (s, 1H, Ar), 6.96
(d, J 7.3 Hz, 1H, Ar), 8.00–9.00 (br s, 1H, OH), 10.00 (s, 1H, NH),
9.50–11.50 (br s, 1H, OH); ıC (75 MHz) 20.6, 27.5, 31.7, 46.7 (br),
78.0, 109.2, 110.6, 123.7, 129.3, 130.0, 132.4, 140.2, 176.4, 184.0
(br); MS (+): m/z 324 [M+Na]+, 284 [M+H−H2O]+; MS (–): m/z 300
[M−H]−; MS2 (+) (m/z 324): m/z 306 [M+Na−H2O]+; IR (KBr): ꢀmax
3192, 2960, 1728, 1596, 1496, 1368, 1248 cm−1. Anal. Calcd. for
C17H19NO4 (%): C, 67.76; H, 6.36; N, 4.65. Found (%): C, 67.85; H,
6.47; N, 4.50.
2-(5-Chloro-3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)-5,5-
dimethylcyclohexane-1,3-dione (5f): white solid; yield 1.34 g (83%);
mp 187–188 ◦C; ıH (300 MHz) 0.99 (s, 6H), 2.15–2.26 (m, 4H),
6.79 (d, J 8.1 Hz, 1H, Ar), 7.05 (s, 1H, Ar), 7.22 (d, J 8.1 Hz, 1H,
Ar), 9.50–11.50 (br s, 2H, OH), 10.32 (s, 1H, NH); ıC (75 MHz)
27.5, 31.8, 46.8 (br), 77.8, 110.0, 110.9, 123.1, 125.1, 128.9, 134.4,
First, to evaluate the synthetic potential of the procedure
proposed and to optimize the electrolysis conditions, the electro-
catalytic addition of dimedone 3a to isatin 4a in alcohol solution in
an undivided cell was studied (Table 1).
Under the optimal conditions (I = 400 mA, current density
80 mA cm−2, 0.1 F mol−1 passed, time 2 min, NaBr as electrolyte)
the electrolysis of dimedone 3a or cyclohexane-1,3-dione 3b
with isatins 4a–f in ethanol in an undivided cell resulted in the
formation of corresponding substituted 2-(3-hydroxy-2-oxo-2,3-
dihydro-1H-indol-3-yl)cyclohexane-1,3-diones 5a–i in 70–85%
yields (Table 2).
Taking into consideration the data obtained and our previous
results on the electrochemically generated base induced tandem
Knoevenagel–Michael reaction with further cyclization in alco-
hol solution in an undivided cell [20–22] and electrochemically
induced Henry reaction [19], the following reaction scheme for
the electrochemically induced aldol reaction of cyclic 1,3-diketones
3a,b with isatins 4a–f is proposed (Scheme 2). The deprotonation of

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M.N. Elinson et al. / Electrochimica Acta 55 (2010) 2129–2133
Scheme 2.
alcohol at the cathode leads to the formation of alkoxide anion. The
subsequent reaction in solution between alkoxide anion and cyclic
1,3-diketone gives rise to cyclic 1,3-diketone anion (Scheme 2).
Then addition of cyclic 1,3-diketone anion to isatin takes place
in the solution with the formation of the intermediate alkoxide
anion A. The following reaction of alkoxide anion A with alcohol
leads to the formation of the end product of the electrocatalytic
process, i.e. the corresponding 2-(3-hydroxy-2-oxo-2,3-dihydro-
1H-indol-3-yl)cyclohexane-1,3-diones 5a–i with the regeneration
on this stage the new alkoxide anion. This alkoxide anion contin-
ues the catalytic chain process by the interaction with the next
molecule of cyclic 1,3-diketone (Scheme 2). An alternative variant
of the continuation of the catalytic cycle is direct interaction of
anion A with the cyclic 1,3-diketone with the formation of cyclic
1,3-diketone anion, and then once more addition to isatin.
The reaction at anode is usual for the system alcohol –NaBr. The
anode reaction does not participate in our process and was carefully
discussed earlier [23].
biomedically active compounds. The procedure utilizes inexpen-
sive reagents, simple equipment and an undivided cell; it is easy
to carry out, the procedure of the isolation of the final aldol is very
simple and is fully beneficial from the viewpoint of “green” organic
synthesis and large-scale processes.
Acknowledgements
The authors gratefully acknowledge the financial support of the
Russian Foundation for Basic Research (Project No. 09-03-00003)
and of the Presidential Scholarship Program for State Support
of Leading Science Schools of Russian Federation (Project No.
5022.2006.3). The authors also thank ChemBlock Ltd. for providing
an LCQ Finnigan MAT mass spectrometer.
References
[1] L.G. Wade, Organic Chemistry, 6th ed., Prentice-Hall, Upper Saddle River, NJ,
2005.
[2] R. Mahrwald, Modern Aldol Reactions, vols. 1 and 2, Wiley-VCH Verlag, Wein-
heim, 2004.
[3] C.H. Heathcock, in: B.M. Trost (Ed.), Comprehensive Organic Synthesis, vol. 2,
Pergamon, Oxford, 1991 (Chapter 1.5).
4. Conclusions
In conclusion, the simple electrocatalytic system can produce,
under mild conditions in an undivided cell, a fast and selec-
tive previously unknown aldol reaction of cyclic 1,3-dicarbonyl
compounds with isatins to form substituted 2-(3-hydroxy-2-oxo-
2,3-dihydro-1H-indol-3-yl)cyclohexane-1,3-diones in 70–85%
yields and 700–850% current efficiency. This electrocatalytic
chain process is an efficient and convenient way to substituted
2-(3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)cyclohexane-1,3-
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