CuSO4-catalyzed three-component reaction of α-diazo ester, water and isatin: An efficient approach to oxindole derivatives

Article abstract of DOI:10.1039/c2gc36708d

A highly efficient three-component reaction of α-diazo ester, water and isatin was developed by using CuSO₄ as the catalyst. In this reaction, water was used as both a reactant and the solvent. With this highly environmentally benign and economical protocol, a series of 3-hydroxyindolin-2- one derivatives were efficiently produced in good yields with moderate to high diastereoselectivities.

Full text of DOI:10.1039/c2gc36708d

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ARTICLE TYPE
CuSO4 catalyzed three-component reaction of α-diazo ester, water and
isatin : an efficient and green approach to oxindole derivatives
Changcheng Jing, Taoda Shi, Dong Xing, Xin Guo, Wen-Hao Hu*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
synthesis
of
3-alkoxylindolin-2-one
moieties
via
A highly efficient three-component reaction of α-diazo ester,
water and isatin was developed by using CuSO4 as the
catalyst. In this reaction, water was used as both a reactant
and the solvent. With this highly environmentally benign
and economical protocol, a series of 3-hydroxyindolin-2-one
derivatives were efficiently produced in good yields with
moderate to high diastereoselectivities.
diastereoselective trapping of protic oxouim ylide with isatins.14
With this chemistry, we are particularly interested in developing
a
more straightforward strategy for the synthesis of
3-hydroxyindolin-2-one moieties by replacing alcohols with
water. And on the other hand, to replace the toxic dirhodium
catalyst with cheap and less toxic catalyst as well as using water
itself as the solvent so we can make the desired transformation
into a highly green and environmentally benign one.
Green chemistry has gained great attention in organic
community in recent years due to its highly environmentally
benign features from readily available starting materials to
structurally complex molecules of biological activities.1 In
recent years, MCRs (Multi-Component Reactions) have been
developed into highly powerful and atom-efficient strategies to
form multiple chemical bonds from three or more starting
materials in one single step.2 However, it is still a big challenge
in developing green and environmentally benign conditions for
MCRs in modern organic chemistry. Within this context, the use
of abundantly available and less toxic catalysts as well as the
use of water as reaction media would be highly beneficial for us
to develop green and environmentally benign MCRs.3 Herein,
we reported a three-component reaction of -diazo ester, water
and isatin catalyzed by CuSO4. In this transformation, water was
used as both a reactant and the solvent and less toxic and
abundantly available CuSO4 was used as the catalyst. With this
Figure 1. Biologically active alkaloids containing
3-hydroxyindolin-2-one motifs
Firstly, we chose water to react with -diazo ester 1a and
isatin in CH2Cl2 in the presence of Rh(II) catalyst to test
whether the hydroxyl ylide generated from 1a and water15 could
be trapped by isatin to afford 3-hydroxyindolin-2-one 3a. To our
delight, 3a was produced in 84% yield with a 80:20 d.r. ratio
(Table 1, entry 1). Then we replaced the solvent from CH2Cl2 to
water,16 good result was also obtained (Table 1, entry 2)17. To
further increase the green features of this transformation, we
tested the catalytic abilities of a series of cheap and readily
available copper salts.18 We found that CuSO4 was most efficient
to catalyze the desired three-component reaction in water to
provide 3a in 90% yield with similar d.r. ratio (Table 1, entry 7).
Control experiment revealed that CuSO4 is indispensable for
this transformation (Table 1, entry 8). It was more striking that
the product was readily separated by simple extraction of the
reaction mixture with ethyl acetate, while impurities remained
in aqueous phase. After removing the solvent, 3a was obtained
in high purity, and no further isolation or purification steps were
required. The structure as well as the stereochemistry of the
major product was confirmed by single-crystal X-ray analysis as
anti-3a (Figure 2).
highly efficient three component reaction,
3-hydroxyindolin-2-one products was produced.
a series of
The oxindole framework is a key motif in a large spectrum
of bioactive natural products and medicinal agents.4 For
instance, 3-hydroxyindolin-2-one moiety is found in an array of
bioactive alkaloids (Figure 1) .5-11 In general, to generate the two
vicinal stereocenters existing in a 3-hydroxyindolin-2-one
moiety, stepwise synthesis including a nucleophilic addition to
isatin and a following transformation was required.12-13 Our
group has recently developed a highly efficient strategy for the
rapid
Shanghai Engineering Research Centre of Molecular Therapeutics and
New Drug Development, East China Normal University, Shanghai,
200062, China.
E-mail: whu@chem.ecnu.edu.cn
†Electronic Supplementary Information (ESI) available: Experimental
procedures and spectral data for all the compounds. See DOI:
10.1039/b000000x
Table 1 .Optimization of reaction conditions.a
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Entry Catalyst (mol %) Yield (%)b Ratio (anti:syn)c
1d
2
3
4
5
6
7
8
Rh2(OAc)4 (5)
Rh2(OAc)4 (5)
Cu(OAc)2 (5)
CuSO4 (5)
84
80
78
84
83
62
90
<5
80:20
80:20
78:22
80:20
78:22
75:25
80:20
--
.
CuCl2 2H2O (5)
CuI (5)
CuSO4 (10)
--
Entry
1
2
3
3a
Yield (%)d
90
d.r. ratio (anti:syn)e
80:20
1
2b
3
1a 2a
1a 2b 3b
1a 2c
1a 2e
1a 2f
1a 2g
aReaction conditions：Unless otherwise noted, the reaction
was carried out in a 0.5 mmol scale. A mixture of diazoester
1a (2 mmol) and 5 mL water was syringed to the
suspension of isatin 2a (0.5 mmol) and metal catalyst in 2
ml water within one hour via syringe pump; bIsolated yield;
40
85
83:17
89:11
3c
3d
4
65
91:9
5
3e
3f
64
54
66
78
82
92
67
73
66
60
82
68
69:31
72 :28
77:23
80:20
67: 33
63:37
91: 9
58: 42
60:40
64:36
56:44
6
cd.r. ratio were determined by H NMR; CH2Cl2 was used
as the solvent.
1
d
7c
8
1a 2h 3g
1a 2i
1b 2a
1c 2a
1c 2c
1c 2d
1c 2f 3m
1c 2h 3n
1d 2a
3h
3i
3j
3k
3l
9
Figure 2 .X-Ray crystal structure of anti-3a .
10
11
12
13
14
15
16
3o
1e 2a 3p
50:50
aReaction conditions：Unless otherwise noted, the reaction was
carried out in a 0.5 mmol sacle. A mixture of diazoester 1 (2
mmol) and 5 mL water was syringed into the suspension of
isatin 2 (0.5 mmol ) and 10 mol% CuSO4 in 2 ml water within
With the optimized reaction conditions in hand, we began to
explore the substrate scope of diazo esters and isatins. With a
variety of isatins bearing different substituents, the desired
products could be achieved in moderate to high yields (40% –
90%) (Table 2, entries 2-8). When tert-butyl diazoacetate
instead of ethyl diazoacetate was used, the desired product was
obtained in good yield albeit with lower diastereoselectivity
(Table 2, entry 9). With different α-alkyl-substituted
diazoacetates, the reaction went smoothly to provide desired
products in good yields (Table 2, entries 10-17). Different
substituents on isatin had significant effects on the
diastereoselectivities of this transformation, for example, when
5-methyl isatin was used, the products were produced in very
good diastereoselectivities with either ethyl diazoacetate or
tert-butyl diazoacetate (Table 2, entries 3 and 11).
b
one hour via syringe pump; 4 mmol diazoester 1a was used; c3
d
e
mmol diazoester 1a was used. Isolated yield; d.r. ratio were
determined by 1H NMR.
Scheme 1. Plausible mechanism
Table 2. CuSO4-catalyzed three-component reaction of
diazoacetate 1 and isatin 2 in water.a
A plausible mechanism for this transformation is proposed
as shown in Scheme 1. CuSO4-catalyzed decomposition of
diazoester 1 gave corresponding carbenoid 4, which reacted
with water to generate hydroxyl ylide 5. In the presence of isatin,
2
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The hydroxyl ylide 5 could be efficiently trapped to undergo the
solvents could be recycled after distillation.
desired three-component reaction instead of 1,2-proton shift.
The desired product was afforded with an intramolecular proton
shift following the ylide trapping process.
Conclusions
We developed an efficient three-component reaction by trapping
the protic oxonium ylide generated from α-diazo esters and
water in the presence of Cu(II) catalyst with isatin in aqueous
media. This environmentally benign transformation can be
conducted in large scale with simple work up procedures
therefore represents a novel “green” MCR protocol for the
synthesis of diversely substituted 3-hydroxyloxiindole-2-one
derivatives.
One of the most unique features of this CuSO4 catalyzed
three-component reaction is that it is run in aqueous media
under very mild reaction conditions. Moreover, this
transformation is clean and easy to work up. In order to further
demonstrate the scale-up potential of this efficient
transformation, we conducted a gram-scale synthesis of 3a
starting directly from cheap and easily available glycine ethyl
ester through a “telescoped” process. In this protocol, ethyl
diazoacetate was extracted directly from the aqueous
diazotization reaction mixture of glycine ethyl ester (195g) with
petroleum ether and used directly for the CuSO4-catalyzed
three-component reaction in the water/petroleum ether
two-phase solvent media. In this scale-up synthesis, the minor
diastereomer was directly crystalized from the reaction mixture
during the reaction proceeded. And after the completion of the
reaction, simple filtration provided 11.7 g pure syn-3a. The
petroleum ether layer of the mother liquid which contained only
impurities was separated and the solvent could be distilled for
recycling use. The aqueous layer was extracted with ethyl
acetate to finally provide 50.8 g 3a (anti:syn=92:8) after
recrystallization from ethyl acetate/petroleum ether (1:1). After
the whole procedures, the distilled organic solvent could also be
recycled.
Acknowledge
We are grateful for financial support from the National Science
Foundation of China (Grant No. 20932003 and 21125209) and
the MOST of China (2011CB808600).
Experimental
General
procedure
for
the
copper-catalyzed
three-component reaction of diazoesters, water and isatins
To a 10 mL flask with a stir bar was added isatin 2 (0.5 mmol)
and 2 mL water, then the mixture was stirred vigorously to form
suspension to which copper sulfate (0.05 mmol) was added in
one portion. A mixture of diazoester 1 (2 mmol) in 5 mL water
was syringed to the suspension within one hour. Eventually,
colorful suspension turned into a clear solution. When the
reaction was finished as monitored by TLC, the reaction mixture
was washed with petroleum ether (3 × 3 mL) to remove
impurities with low polarity, then extracted with 15 mL ethyl
acetate for 3 times. The combined organic phase was washed
with saturated brine, dried over anhydrous sodium sulfate,
filtered and then concentrated to provide the product, which was
then crystallized from petroleum ether and ethyl acetate.
Scheme 2. Synthesis of 3a in large scale.
Procedure for the scale-up synthesis of 3a from glycine ethyl
ester
To a solution of glycine ethyl ester (195.4 g,1.4 mmol) and conc.
HCl (40 mL) in water (100 mL) was added NaNO2 (115.9 g,
1.68 mmol）in water (150 mL) slowly at -5 ℃ within 30 min.
Then 80 mL petroleum ether was added and the reaction was
stirred for 20 min. The two layers were separated and the
aqueous phase was further extracted with petroleum ether (80
mL). The combined organic layer was washed with brine (40
mL) and directly used for the next step.
To a 1 L three-necked round-bottle flask equipped with a
mechanical stirrer was added isatin 2 (51.5 g，350 mmol) and
160 mL water, the mixture was then stirred vigorously to form a
suspension to which copper sulfate (5.6 g, 0.05 mmol) was
added in one portion. The solution of ethyl diazoester 1a in
petroleum ether was then added dropwise within 1 h. After the
completion of the addition, the reaction mixture was further
stirred for 30 min. During the reaction proceeded, crystal
formation was observed in the two-phase reaction media. When
the reaction is finished as monitored by TLC, the reaction was
filtered and 11.7 g pure cis-3a was obtained as crystals. The
The three-component reaction catalyzed by CuSO4 in
aqueous media generates 3-hydroxyindolin-2-one derivatives,
which are significant structural skeleton presented in a large
number of natural products or medicinal agents. This reaction
protocol embodies several principles of green chemistry. Green
characters of this reaction lie in: 1) this three-component
reaction is atom-economic and step-economic. Multiple
chemical bonds are formed in one single step to provide
complex target molecules and nitrogen gas is the only byproduct;
2) In this reaction abundantly available and less toxic CuSO4
was used as the catalyst to replace the more expensive and toxic
Rh(II) one; 3) water plays dual roles as both a reactant and the
solvent. Water is more direct source of hydroxyl than alcohol
and more friendly to environment than other conventional
volatile organic solvent; 4) this transformation generates almost
no organo wastes, in the scale-up synthesis, the procedures
could be conducted in “telescoped” steps and all organic
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and dried in high vacuo to afford 50.8 g products (d.r. = 92:8).
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