DABCO catalyzed pseudo multi-component synthesis of functionalized spirooxindoles

Article abstract of DOI:10.1007/s00706-015-1637-y

Abstract: A direct multi-component assembling of isatin, cyclohexanone, and 2?mol of malononitrile in the presence of catalytic amount of DABCO in aq. ethanol leads to functionalized spirooxindoles at ambient temperature. The novelties of the method are m

Full text of DOI:10.1007/s00706-015-1637-y

Monatsh Chem
DOI 10.1007/s00706-015-1637-y
ORIGINAL PAPER
DABCO catalyzed pseudo multi-component synthesis
of functionalized spirooxindoles
1
1
1
Pravin G. Hegade
•
Sarika D. Chinchkar
•
Dattaprasad M. Pore
Received: 7 August 2015 / Accepted: 16 December 2015
Ó Springer-Verlag Wien 2016
Abstract A direct multi-component assembling of isatin,
cyclohexanone, and 2 mol of malononitrile in the presence
of catalytic amount of DABCO in aq. ethanol leads to
functionalized spirooxindoles at ambient temperature. The
novelties of the method are multi-component route, short
time duration, excellent yields of products, mild reaction
conditions, easy work-up procedure, as well as isolation of
product and 100 % carbon economy.
Introduction
The art of performing efficient chemical transformations to
generate molecular complexity and diversity with prede-
fined functionality in natural and biologically relevant
systems is a challenging benchmark which urges chemists
to increase tools of their arsenal [1–3]. In this context,
multi-component reactions (MCRs) by virtue of their
synthetic efficiency [4, 5], the reduction of chemical steps
and energy consumption in organic processes [6], creation
of several bonds in one sequence without changing the
reaction conditions, isolating the intermediates or adding
reagents [7], thus allowing a minimization of waste, cost,
and labor, have emerged as a highly valuable tool for
synthesis of multi-functionalized organic compounds [8,
Graphical abstract
9
]. The last decade has witnessed tremendous develop-
ments in domino multi-component reactions especially in
vinylogous Michael addition-based domino reactions as
they allow a rapid access to highly functionalized carbon
skeleton, offering interesting opportunities for molecular
diversity [10–17].
Keywords Aqueous Ethanol Á 100 % carbon economy Á
Carbonyl compounds Á DABCO Á
Oxindole with a six-membered spirocyclic moiety is a
intriguing subset with potential bioactivity [18] and is
featured in a number of natural products, as exemplified by
gelsemine (I) as well as pharmaceutically relevant com-
pounds with remarkable structural complexity and
interesting biological activities (II, III, and IV, Fig. 1)
Multicomponent reaction Á Spiro compounds
[
19–21]. Specifically, the multi-functionalized spirooxin-
dole family is a promising subset with potential bioactivity
22]. There is a maiden report [23] for the synthesis of
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-015-1637-y) contains supplementary
material, which is available to authorized users.
[
functionalized spirocyclic oxindoles by triethylamine cat-
alyzed two-component reaction of vinyl malononitrile on
isatin-malononitrile via vinylogous Michael addition. To
the best of our knowledge, only this reference exists con-
cerning their synthesis. Thus, a multi-component method to
&
Dattaprasad M. Pore
p_dattaprasad@rediffmail.com
1
Department of Chemistry, Shivaji University, Kolhapur
4
16 004, India
123

P. G. Hegade et al.
pyrolidine, DABCO, p-TSA, and L-proline. It is notewor-
thy to mention that no expected product was detected in the
presence of acidic catalysts, viz. p-TSA and L-proline.
Similar observation was also found in the presence of
KOH. As shown in Table 1, the influence of K PO and
3
4
K CO in the above reaction was marginal (entries 5, 6).
2
3
Table 1 clearly shows that yields were increased under the
influence of N containing bases such as Et NH, morpho-
2
line, pyrrolidine, and DABCO (Table 1, entries 8–11).
Amongst them DABCO was found to be superior one in
terms of yield and time.
To further improve the yields of products, in the context
of our earlier experience with mixed solvent system [26],
we envisioned to design some experiments to optimize the
relative composition of water and ethanol in binary mixture
for the present reaction. Figure 2 illustrates the effect of the
water concentration on the multi-component synthesis of
spirooxindoles in terms of time and yields. As apparent,
when the water content was 70 %, we got the desired
product in 94 % within 8 min. As these reactions proceed
via charged reactive intermediates, we hypothesized that
the corresponding transition state would be stabilized by
water, which has a relatively high static permittivity
(eT = 78.4) [27] and a slight amount of ethanol is required
for solubility of the substrates.
To find the effect of amount of DABCO, the model
reaction was carried out by varying the amount of the
catalyst (Table 1). The conversion of spirooxindole, 5a
increased linearly with the catalyst weight up to 20 mol%
and became almost steady when the amount of catalyst was
further increased beyond this. Therefore 20 mol% of cat-
alyst was sufficient to catalyze the reaction and obtain
expected functionalized spirooxindole in excellent yield.
The reaction procedure is simple. As reaction proceeds a
nearly homogeneous mixture is formed (Fig. 3a) and pro-
duct precipitates from 30 % ethanol (Fig. 3b) which was
Fig. 1 Natural products and biologically active spirooxindoles
synthesize functionalized spirooxindoles operable at
ambient temperature is highly warranted.
Results and discussion
In continuation of our research program dedicated to
development of efficient methods for multi-component
synthesis of spirooxindoles [24, 25], in this paper, we have
reported DABCO catalyzed synthesis of functionalized
spirooxindoles by advocating multi-component reaction of
isatin, malononitirle, and cyclohexanone in ethanol/water
system at ambient temperature (Scheme 1).
1
isolated by simple filtration and confirmed by H NMR
spectrum indicating remarkable singlets at d = 7.60 and
11.42 ppm for –NH and –NH protons, respectively, and a
2
triplet at 5.91 ppm due to heteroannular proton. In the IR
spectrum, the absorption bands at 3410, 3344, and
-1
2218 cm corresponding to N–H stretching of primary
In order to find the best reaction conditions for the
pseudo multi-component synthesis of functionalized
spirooxindoles, our preliminary investigations focused on
the search for a suitable catalyst for the pseudo four-
component reaction of isatin, cyclohexanone, and
malononitrile. To probe the role of catalyst, initially a
blank reaction was conducted for the model reaction in
ethanol/water, the reaction failed to give the expected
product even after employing reflux conditions for 24 h
amine and C–N stretching of cyanide functionality con-
firmed the structure of product.
With optimized reaction conditions in hand, to delineate
this approach, particularly in regard to library construction
(Table 2), this methodology was evaluated by using a
variety of isatin derivatives. Both isatin bearing electron-
-
2
-
–
-
withdrawing substituent Br , I , Cl , F , and NO
2
(Table 2, entries e–i) as well as isatin equipped with
methyl and methoxy groups afforded the product in
excellent yields (Table 2, entries b–d).
(
Table 1, entries 1, 2). At the outset of our studies, we
tested KOH, K CO , K PO , morpholine, diethylamine,
2
3
3
4
1
23

DABCO catalyzed pseudo multi-component synthesis of functionalized spirooxindoles
Scheme 1
Table 1 Screening of catalyst for the multi-component synthesis of 5a
Entry
Catalyst
Catalyst/mol%
Solvent
Time/h
Yield/%
1
2
3
4
5
6
7
8
9
Catalyst-free
Catalyst-free
p-TSA
–
C
2
H
5
OH
24
24
4
NR
NR
NR
NR
55
–
2
H O
20
20
20
20
20
20
20
20
20
20
05
10
15
30
C
C
C
C
C
C
C
C
C
2
H
2
H
2
H
2
H
2
H
2
H
2
H
2
H
2
H
5
OH
OH
OH
OH
OH
OH
OH
OH
OH
L-Proline
5
5
5
5
5
5
5
5
4
K
2
CO
PO
3
4
K
3
4
4
52
KOH
Et NH
4
NR
60
2
4
Morpholine
Pyrrolidine
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
2
76
1
1
1
1
1
1
1
a
0
1
2
3
4
5
6
1
77
1
81
C
2
H
5
OH:H
2
O
0.13
1.2
0.66
0.25
0.13
94
C
C
C
C
2
H
2
H
2
H
2
H
5
OH:H
OH:H
OH:H
OH:H
2
2
2
2
O
O
O
O
80
5
5
5
84
90
94
3
Reaction conditions: isatin (1 mmol), cyclohexanone (1 mmol), malononitrile (2 mmol), 10 cm solvent, RT yields refer to pure isolated
products; NR no reaction; C OH:H O = 30:70 (v/v)
H
2 5
2
Fig. 3 Multi-component reaction between isatin, malononitrile, and
cyclohexanone. a The homogeneous phase at the beginning of the
reaction. b The product precipitated after completion of reaction
Fig. 2 Impact of composition of water–ethanol solvent system on
multi-component synthesis of spirooxindoles in terms of time and
yield
malononitrile under optimized reaction conditions. Grati-
fyingly, reaction took place smoothly and corresponding
spirooxindole was obtained in 85 % yield (Table 2, entry j;
Scheme 3).
We focused our attention towards N-alkylated isatin and
0
finally carried out the reaction of 1,1 -propane-1,3-diyl-
bis(1H-indole-2,3-dione) with cyclohexanone and
To study the mechanism of transformation (Scheme 2),
we have carried out reaction of 1 and 3 in 30 % ethanol
123

P. G. Hegade et al.
Table 2 DABCO catalyzed pseudo multi-component synthesis of functionalized spirooxindoles 5 at ambient temperature
a,b
Entry
Isatin 2
Time/min
Yield/%
1
R = H, R = H
1
R = H, R = 5,7-Me
1
R = H, R = 5-Me
1
R = H, R = 5-OMe
1
R = H, R = 5-Br
1
R = H, R = 5-Cl
1
R = H, R = 5-I
1
R = H, R = 5-NO
a
b
c
d
e
f
8
25
20
15
10
15
20
25
20
40
94
83
90
91
95
93
87
80
94
85
2
g
h
i
2
1
R = H, R = 5-F
j
a
1
All products showed satisfactory spectroscopic data (IR, H and C NMR, MS); Yields refer to pure, isolated products
13
b
Scheme 2
1
23

DABCO catalyzed pseudo multi-component synthesis of functionalized spirooxindoles
Scheme 3
3
furnished isatylidine malononitrile 6 under catalyst-free
conditions. However, reaction of 3 and 2 failed to obtain
respected vinylmalononitrile 7, which was achieved in
presence of catalytic amount of DABCO (4). Thus we
observed, water generates carbanion of malononitrile [28]
and favors formation of isatylidine malononitrile. Carbanion
of vinylmalononitrile 7 is generated in presence of DABCO
for subsequent vinylogous Michael addition to 6 furnish
desired spirooxindole 5 through the transition state 8.
(1 mmol) in 10 cm 30 % ethanol, DABCO (20 mol%)
was added. The reaction mixture was stirred at room
temperature for time mentioned in Table 2 until comple-
tion of reaction, monitored by TLC. After completion of
reaction, the mixture was cooled and filtered to furnish the
desired product in good yields.
0
0 0 0 0
-Amino-5,7-dimethyl-2-oxo-6 ,7 ,8 ,8a’-tetrahydro-2 H-
3
0
0
0
0
spiro[indoline-3,1 -naphthalene]-2 ,2 ,4 -tricarbonitrile
5b, C H N O)
(
2
2 19 5
White solid; m.p.: 236–238 °C; IR (KBr): vꢀ = 3401,
3
339, 3235, 2217, 1740, 1657, 1596, 1479, 1399, 1302,
1
Conclusion
-
1
1276, 1205, 911, 864, 797, 753 cm
;
H NMR
(
(
300 MHz, DMSO-d ): d = 0.43–0.54 (m, 1H), 1.43–1.55
m, 3H), 1.62 (s, 1H), 1.88–1.93 (m, 1H), 2.11 (s, 3H),
6
In summary, we have developed an organocatalyzed pseudo
multi-component reaction which combines isatin, malononi-
trile, and cyclohexanone in a well-defined manner to afford a
functionalized spirooxindoles atambient temperature in 30 %
ethanol. Novelty of the protocol is multi-component route,
operative simplicity, short time duration, avoidance of con-
ventional volatile organic solvents, no waste formation,
2
6
1
.18 (s, 3H), 2.86–2.89 (d, 1H, J = 9 Hz), 5.90 (s, 1H),
.48 (s, 1H), 7.0 (s, 1H), 7.52 (s, 2H, –NH ), 11.31 (s,
2
1
3
H, –NH) ppm;
C NMR (75 MHz, DMSO-d6):
d = 16.86, 20.68, 21.42, 23.90, 24.96, 37.53, 42.70,
5
1
1
5.20, 82.01, 110.73, 111.27, 116.02, 120.27, 122.77,
22.98, 123.91, 125.99, 131.90, 133.09, 139.52, 142.78,
74.19 ppm; MS (EI): m/z = 369.
1
00 % carbon economy, easy separation of highly pure
products. Thus we believethatour findingsportend significant
gains toward achieving ideal transformations.
0
0
0
0
0
3 -Amino-5-methyl-2-oxo-6 ,7 ,8 ,8a’-tetrahydro-2 H-
0
0
0
0
spiro[indoline-3,1 -naphthalene]-2 ,2 ,4 -tricarbonitrile
Experimental
(5c, C H N O)
2
1 17 5
White solid; m.p.: 242–243 °C; IR (KBr): vꢀ = 3332, 3226,
2935, 2217, 1709, 1649, 1490, 1393, 1277, 1085,
IR spectra were recorded on a Agilent cary FT-IR 630
spectrophotometer. NMR spectra were recorded on a
-
1
1
827 cm
;
H
NMR
(300 MHz,
DMSO-d6):
Bruker AC-300 spectrometer in DMSO-d using tetram-
6
d = 0.50–0.54 (m, 1H), 1.44–1.62 (m, 4H), 1.93–1.95 (m,
1H), 2.22 (s, 3H), 2.86–2.90 (d, 1H, J = 12 Hz), 5.91–5.92
(t, 1H, J = 3 Hz), 6.64 (s, 1H), 6.89–6.92 (d, 1H,
J = 9 Hz), 7.17–7.20 (d, 1H, J = 9 Hz), 7.54 (s, 2H,
ethylsilane as an internal standard. Mass spectra were
recorded on a Shimadzu QP2010 GCMS.
1
3
Typical procedure
–NH ), 11.28 (s, 1H, –NH) ppm; C NMR (75 MHz,
2
DMSO-d ): d = 20.68, 21.51, 23.86, 24.96, 37.43, 42.66,
55.07, 82.01, 110.90, 111.18, 116.00, 123.05, 124.02,
6
3
In a 25 cm round bottom flask, to a mixture of isatin
(
1 mmol), malononitrile (2 mmol), and cyclohexanone
123

P. G. Hegade et al.
-
1
1
1
1
25.74, 125.92, 131.66, 132.05, 140.96, 142.75,
829, 827 cm
;
H
NMR (300 MHz, DMSO-d6):
73.65 ppm; MS (EI): m/z = 355.
d = 0.45-0.55 (m, 1H), 1.43–1.57 (m, 1H), 1.61–1.66 (m,
2
1
1
H), 1.89–1.97 (m, 1H), 2.12–2.18 (m, 1H), 2.90–2.93 (d,
0
0 0 0 0
-Amino-5-methoxy-2-oxo-6 ,7 ,8 ,8a’-tetrahydro-2 H-
3
H, J = 6 Hz), 5.94–5.96 (t, 1H, J = 6 Hz), 6.58–6.61 (m,
0
0
0
0
spiro[indoline-3,1 -naphthalene]-2 ,2 ,4 -tricarbonitrile
5d, C H N O )
H), 7.02–7.06 (m, 1H), 7.24–7.31 (m, 1H), 7.62 (s, 2H, –
13
2
(
2
1
17
5
2
NH ), 11.46 (s, 1H, –NH) ppm; C NMR (75 MHz,
White solid; m.p.: 250–252 °C; IR (KBr): vꢀ = 3447, 3345,
284, 2950, 2222, 1742, 1635, 1596, 1448, 1394, 1304,
-
206, 1037, 849, 810, 794 cm ; H NMR (300 MHz,
DMSO-d ): d = 20.60, 23.86, 24.96, 37.35, 42.44, 55.33,
6
3
5
1
1
6.49, 81.86, 110.51, 110.82, 112.76, 113.11, 115.81,
24.24, 124.35, 124.76, 125.36, 139.79, 142.47,
73.55 ppm; MS (EI): m/z = 359.
1
1
1
DMSO-d ): d = 0.47–0.50 (m, 1H), 1.47–1.63 (m, 3H),
.96–2.18 (m, 2H), 2.90 (s, 1H), 3.68 (s, 3H), 5.92 (s, 1H),
6
1
6
–
2
1
1
00 0 0 0 0
1,1 -(Propane-1,3-diyl)bis(3 -amino-2-oxo-6 ,7 ,8 ,8a’-te-
.41 (s, 1H), 6.95 (s, 2H), 7.59 (s, 2H, –NH ), 11.23 (s, 1H,
2
1
3
0
0
0
0
0
NH) ppm; C NMR (75 MHz, DMSO-d ): d = 20.66,
trahydro-2 H-spiro[indoline-3,1 -naphthalene]-2 ,2 ,4 -tri-
6
3.89, 24.99, 37.39, 42.61, 55.21, 55.76, 81.85, 110.63,
11.09, 111.46, 113.27, 114.51, 115.89, 124.15, 124.27,
25.79, 136.49, 142.75, 155.50, 173.42 ppm; MS (EI):
carbonitrile) (5j, C H N O )
3 34 10 2
4
White solid; m.p.: 202–205 °C; IR (KBr): vꢀ = 3347, 3220,
2940, 2871, 2214, 1716, 1611, 1639, 1468, 1356, 1086,
-
1 1
m/z = 371.
879 cm ; H NMR (300 MHz, DMSO-d ): d = 0.38–0.45
6
(
m, 2H), 1.48 (m, 4H), 1.61 (m, 2H), 1.91–1.94 (m, 4H),
0
0 0 0 0
-Amino-5-chloro-2-oxo-6 ,7 ,8 ,8a’-tetrahydro-2 H-
3
2
2
7
.11–2.17 (m, 2H), 2.95 (s, 2H), 3.96–3.98 (m, 4H), 5.93 (s,
0
0
0
0
spiro[indoline-3,1 -naphthalene]-2 ,2 ,4 -tricarbonitrile
5f, C H ClN O)
H), 6.93–6.96 (d, 2H, J = 9 Hz), 7.15–7.20 (m, 2H),
13
.32–7.38 (m, 3H), 7.47–7.58 (m, 5H) ppm; C NMR
(
2
0
14
5
White solid; m.p.: 195–196 °C; IR (KBr): vꢀ = 3327, 3222,
948, 2224, 1712, 1649, 1599, 1475, 1436, 1396, 1314,
1 1
187, 963, 879, 770 cm ; H NMR (300 MHz, DMSO-
(
75 MHz, DMSO-d ): d = 20.55, 23.86, 24.95, 37.51,
6
2
3
1
1
8.33, 42.67, 54.57, 82.06, 110.18, 110.56, 110.98, 115.92,
22.34, 124.25, 124.39, 125.44, 125.71, 131.55, 142.58,
43.70, 143.77, 172.09 ppm.
-
1
d6): d = 0.46–0.54 (m, 1H), 1.48–1.62 (m, 3H), 1.68–1.72
m, 1H), 1.96–1.98 (m, 1H), 2.90–2.93 (d, 1H, J = 9 Hz),
(
5
7
1
.95–5.97 (t, 1H, J = 6 Hz), 6.76–6.77 (d, 1H, J = 3 Hz),
Acknowledgments One of the authors DMP thanks UGC, New
Delhi for financial assistance [F. No.42-394/2013 (SR)].
.04–7.07 (s, 1H), 7.47–7.50 (m, 1H), 7.66 (s, 2H, –NH ),
2
1
1.59 (s, 1H, –NH) ppm; C NMR (75 MHz, DMSO-d6):
3
d = 20.58, 23.86, 24.73, 37.37, 42.43, 55.19, 56.49, 81.81,
1
10.51, 110.75, 112.80, 115.78, 124.78, 125.10, 125.35,
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27.08, 131.47, 139.52, 142.48, 173.34 ppm; MS (EI):
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1
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6
3
221, 2942, 2214, 1712, 1648, 1598, 1470, 1429, 1395,
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2
1
3
H), 11.56 (s, 1H, –NH) ppm; C NMR (75 MHz, DMSO-
1
1
1
d6): d = 20.58, 23.85, 24.96 37.40, 42.47, 54.89, 56.50,
8
1
1.83, 86.22, 110.55, 110.78, 113.58, 115.74, 124.63,
25.41, 133.59, 139.99, 142.51, 143.18, 173.08 ppm; MS
1
(
EI): m/z = 467.
(
0
0
0
0
0
3
-Amino-5-fluoro-2-oxo-6 ,7 ,8 ,8a’-tetrahydro-2 H-
0
0
0
0
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5i, C H FN O)
1
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1
White solid; m.p.: 240–242 °C; IR (KBr): vꢀ = 3328, 3200,
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1
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1
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DABCO catalyzed pseudo multi-component synthesis of functionalized spirooxindoles
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