Isocyanide-based multicomponent [2+2+1]-cycloaddition strategy to construct functionalized spirocyclic oxindoles

Article abstract of DOI:10.1055/s-0032-1317030

Isocyanide-based three-component [2+2+1]-cycloaddition reactions from isocyanides, activated alkynes, and isatylidene malononitriles were investigated to provide a new access to spirocyclic oxindole with five-membered carbon rings. The displacement of isatylidene malononitrile with oxindolylideneacetate essentially results in opposite regioselectivity, which adds to its attractiveness. Georg Thieme Verlag Stuttgart ? New York.

Full text of DOI:10.1055/s-0032-1317030

2274▌
LETTER
lIestteor cyanide-Based Multicomponent [2+2+1]-Cycloaddition Strategy to
Construct Functionalized Spirocyclic Oxindoles
Isocyanide-Based Multicomponent [2+2+1]-Cycloaddition
Haohua Jie,a Jian Li,*a Chunju Li,a Xueshun Jia*a,b
a
Department of Chemistry, Shanghai University, Shanghai, 200444, P. R. of China
Fax +86(21)66132408; E-mail: lijian@shu.edu.cn
b
Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, P. R. of China
E-mail: xsjia@mail.shu.edu.cn
Received: 16.06.2012; Accepted: 12.07.2012
Cl
Abstract: Isocyanide-based three-component [2+2+1]-cyclo-
addition reactions from isocyanides, activated alkynes, and isatyli-
dene malononitriles were investigated to provide a new access to
spirocyclic oxindole with five-membered carbon rings. The dis-
placement of isatylidene malononitrile with oxindolylideneacetate
essentially results in opposite regioselectivity, which adds to its
attractiveness.
CN
O
N
H
O
Key words: isocyanide, activated alkyne, isatylidene malono-
welwitindolinone A
NH
O
nitrile, spirocyclic oxindole, oxindolylideneacetate
H
HO
O
Me
N
O
N
Spirocyclic oxindoles are important heterocyclic motifs
that are frequently found in many natural products and
compounds of pharmaceutical significance.1 The appeal-
ing structural characteristics associated with the signifi-
cant biological activities make them interesting and
challenging targets for chemical syntheses.2 Consequent-
ly, a number of successful strategies have emerged for the
construction of such skeletons.3 Apart from the highly ef-
ficient palladium-catalyzed processes,4 synthetic advanc-
es have also been fueled by organocatalysis and other
novel routes.5 However, most synthetic efforts seem to be
devoted to the synthesis of 3,3′-pyrrolidinyl-spiro-
oxindoles, which belong to a large family of alkaloids
with strong bioactivity profiles.6 On the other hand, spiro-
cyclic oxindoles with carbocyclic rings have been com-
paratively less well investigated, despite the fact that these
substructures are widely present in natural products
(Figure 1).7 As a result, there is still much room for the de-
velopment of more efficient syntheses.
paraherquamide A
Me
O
N
O
N
H
Me
gelsemine
Me
N
H
OH
O
N
HN
O
HN
O
Me
cintrinadin A
Figure 1 Natural products containing spirocyclic oxindoles with car-
bocyclic rings
their development. Among the MCRs, isocyanide-based
multicomponent reaction (IMCRs) occupy an outstanding
position, which can be traced back to the exceptional re-
activity of isocyanide.9 Methods starting from isocyanides
often have distinct advantages including high levels of
chemo-, regio-, and stereoselectivity as well as the great
variety of isocyanides that are readily available for use. In
addition, the reactivity of isocyanide can be electronically
and sterically controlled by simply changing the substitu-
ent on the nitrogen, which is very convenient for reaction
optimization. As a result, the past decades have witnessed
considerable progress in the application of isocyanide
chemistry.10
As a result of the intense research efforts of the last few
decades, multicomponent reactions (MCRs) have found
wide application in organic synthesis.8 The key advantage
of MCRs lies in the fact that they can achieve high syn-
thetic efficiency by using more than two reactants to pro-
duce new compounds with maximized number of new
bonds and functionalities. In addition, multicomponent
reactions are characterized by their inherent atom-econo-
my and convergence, which has led to a high demand for
SYNLETT 2012, 23, 2274–2278
Advanced online publication: 14.08.2012
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1
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1
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DOI: 10.1055/s-0032-1317030; Art ID: ST-2012-W0518-L
© Georg Thieme Verlag Stuttgart · New York

LETTER
Isocyanide-Based Multicomponent [2+2+1]-Cycloaddition
2275
Recently, we have focused our attention on the synthesis Among them, we have demonstrated that isocyanide-
of carbocycles and potentially bioactive heterocycles.11 based multicomponent reactions can be used as an effi-
cient method to construct spirocyclic oxindole deriva-
tives.11c–e During the experiments mentioned above, we
have also found that the formation of a zwitterionic inter-
to develop new IMCRs
R2
CO2Et
R1 N=C
+
by the capture of
mediate in situ plays a key role. It is well known that con-
jugated alkynoates are among the most reactive Michael
acceptors, and nucleophiles including tertiary amines12
and phosphines13 have been used to trigger such species in
many multiple-bond-forming processes. Recently, we
have also revealed that isocyanide can also serve as a
nucleophile to trigger the corresponding nucleophilic at-
tack towards conjugated alkynoates, thus providing an op-
portunity for the design of new IMCRs (Scheme 1).11d As
a continuation of our interest in spiro-oxindole com-
pounds, herein we wish to report an efficient and atom-
economical synthesis of spirocyclic oxindole derivatives
by an isocyanide-based three-component [2+2+1]-cyclo-
addition strategy.
third component
1
2
Michael
addition
R1N
C
CO2Et
R2
A
zwitterionic species
Scheme 1
Our initial efforts focused on the use of 2,6-dimethyl-
phenyl isocyanide (1a) as a nucleophilic reagent, and eth-
yl propiolate (2a) and isatylidene malononitrile (3b) as
reactions partners (Scheme 2). During our preliminary ex-
periment, the mixture mentioned above was allowed to re-
act in toluene at 100 °C for 18 hours. The interesting
[2+2+1]-cycloaddition product 4a was isolated in 81%
yield (Table 1, entry 1). Following this encouraging
result, a variety of functionally substituted isatylidene
malononitriles 3 underwent the cycloaddition reaction un-
der the optimal conditions; the results are summarized in
Table 1. Although aromatic isocyanides, especially steri-
cally demanding ones, were considered to be less reactive,
the present reactions proceeded smoothly in all cases; all
Table 1 Three-Component [2+2+1] Cycloaddition of Isocyanide 1,
Conjugated Alkynoate 2, and Isatylidene Malononitrile 3a
Entry
R1
R2
R3
Product Yield
(%)b
81
78
1
2
3
H
H
H
H
4a
79
89
5-fluoro
5-chloro
4b
85
39
4c
4
5
6
7
8
H
H
H
H
H
5-bromo
6-bromo
5-nitro
4d
4e
4f
82
74
90
71
65
1
compounds 4 were fully characterized by H NMR,
1c
13C NMR, and HRMS analyses.14 Moreover, the struc-
tures of compounds 4b (CCDC 884218) and 4f (CCDC
884219) were unambiguously confirmed by single crystal
X-ray analysis (Figure 2).15 As shown in Table 1, sub-
strates 3 with both electron-donating and electron-with-
drawing groups on aromatic rings afforded products 4
with good yields (Table 1, entries 2–8). For instance, re-
action with substrate 3, which contains the nitro group,
produced adduct 4f in 90% yield (Table 1, entry 6). Fur-
thermore, protection of the nitrogen atom of isatylidene
malononitrile 3 was necessary, otherwise the reaction be-
came quite complex. To our delight, the present cycload-
dition reaction was not limited to ethyl propiolate (2a);
even sterically hindered conjugated alkynoates 2b and 2c
5-methoxy
4g
5,7-dimethyl 4h
OMe
9
H
H
4i
62
MeO
1b
10c
11c
12c
13c
14c
15c
H
H
4j
82
75
69
80
70
72
Me
Me
Me
Me
Ph
H
4k
4l
5-fluoro
6-bromo
4m
R1N
1c
NC
NC
R1NC
NC
5,7-dimethyl 4n
5-chloro 4o
CN
O
1
CO2Et
O
toluene
100 °C
R3
R3
CO2Et
+
+
a Reaction conditions: isocyanide 1 (0.5 mmol), conjugated alkynoate
2 (0.6 mmol), isatylidene malononitrile 3 (0.5 mmol), toluene (5 mL),
100 °C in air, 18 h.
N
N
R2
PG
PG
2
3
4
b Yield of product after silica gel chromatography.
c In such cases, the reaction was complete within 10 h.
Scheme 2
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2274–2278

2276
H. Jie et al.
LETTER
R1N
NC
NC
NC
R1NC
1
CN
O
toluene
100 °C
COPh
O
+
R3
+
R3
O
N
N
PG
PG
C
3
5
2d
N
N
N
NC
NC
NC
NC
NC
NC
Cl
COPh
O
COPh
O
COPh
O
N
N
N
Me
Me
5b: 89%
Bn
5c: 70%
5a: 81%
N
N
NC
NC
NC
NC
F
Cl
COPh
O
COPh
O
N
N
Me
5d: 83%
Bn
5e: 66%
Scheme 3
produced the corresponding adducts in satisfactory yields (Scheme 4). To our surprise, nucleophilic addition oc-
(Table 1, entries 11–15), thus greatly expanding the scope curred on the carbon bearing the ester groups (which is the
of the present protocol.
most electrophilic site in the molecule), which led to the
opposite regioselectivity observed in formation of product
4 and 5. Moreover, the structure of compound 7a was un-
ambiguously confirmed by single crystal X-ray analysis
(CCDC 884217).16 It is reasonable to deduce that the elec-
tronic nature of electron-efficient olefins affect the reac-
tion pathway to a significant extent. Furthermore, the
cycloaddition involving isocyanide enabled rapid access
to spirocyclic oxindole-butenolide, which offers new op-
portunities for their application in organic chemistry.
To further demonstrate the utility of the present annula-
tion strategy, 1-phenylprop-2-yn-1-one (2d) was also ex-
amined (Scheme 3). Pleasingly, the cycloaddition
reaction mentioned above proceeded smoothly with 2d to
give product 5 in good yields. In such runs, all reactions
could be finished within 12 hours with exclusive stereo-
selectivity.
With this highly efficient protocol in hand, we investigat-
ed the corresponding cycloaddition reaction by using ox-
indolylideneacetate 3′ as electron-deficient alkenes
NC
EtO2C
CO2Et
N
1a
toluene
R3
O
+
+
CO2Et
O
100 °C
R3
N
Bn
CO2Et
N
Bn
2a
6
7
R3 = 5-Cl
7a: 66% yield
7b: 55% yield
7c: 47% yield
R
R
3 = 5-Br
3 = 5-MeO
Scheme 4
A possible mechanism for the present three-component
cycloaddition reaction is outlined in Scheme 5 to account
Figure 2
Synlett 2012, 23, 2274–2278
© Georg Thieme Verlag Stuttgart · New York

LETTER
Isocyanide-Based Multicomponent [2+2+1]-Cycloaddition
2277
NC
CN
EtO2C
R3
O
R3
O
R1N
N
N
PG
3
PG
6
C
CO2Et
nucleophilic
addition
nucleophilic
addition
R2
A
zwitterionic species
R1N
CO2Et
R2
R2
CO2Et
R1 N=C
+
C
R1N
NC
NC
1
2
CO2Et
O
R3
CO2Et
O
R3
N
PG
N
PG
C
B
R1N
NC
NC
CO2Et
R2
R1N
CO2Et
O
CO2Et
O
R3
R3
N
N
PG
PG
4
7
Scheme 5
for the selective formation of spirocyclic oxindole 4 and mentioned above, the present strategy has the potential to
7. The nucleophilic addition of isocyanide 1 to conjugated be applied in medicinal and synthetic chemistry.
alkynoate 2 essentially leads to the formation of zwitter-
ionic species A,11 which may follow two possible reaction
Acknowledgment
pathways. When A is captured by the carbon–carbon dou-
We thank the National Natural Science Foundation of China
(21002061, 21142012, 20902057), the Key Laboratory of Synthetic
Chemistry of Natural Substances, Chinese Academy of Sciences,
Leading Academic Discipline Project of Shanghai Municipal Edu-
cation Commission (No: J50101). We also thank Dr. Hongmei
Deng and Min Shao of Laboratory for Microstructures, Shanghai
University for the NMR and Single Crystal X-ray analyses.
ble bond of 3, intermediate B is presumably formed. This
intermediate experiences further intramolecular cycliza-
tion to yield stable product 4. On the other hand, an oppo-
site
regioselectivity
will
occur
when
oxindolylideneacetates 6 are employed as electron-defi-
cient olefins. In such cases, nucleophilic addition occurs
on the carbon bearing the ester groups; the corresponding
intermediate C is also quite stable due to the double stabi-
lization of benzylic conjugation and the amide group,
which results in the formation of 7.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
In conclusion, we have described a novel three-compo-
nent [2+2+1]-cycloaddition reaction that can be used to
construct functionalized spirocyclic oxindoles from read-
ily available starting materials with high atom-economy.17
This method is quite flexible with respect to the variable
conjugated alkynes as well as the broad range of electron-
deficient olefins. As a transition-metal-free cycloaddition,
this strategy avoids the formation of any side-products,
thus meeting the requirements of green chemistry. We
have also demonstrated that the regioselectivity of the re-
action could be greatly changed when oxindolylidene-
acetates were used as substrates. Given the advantages
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Synlett 2012, 23, 2274–2278

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(17) General Experimental Procedure for 4: Isatylidene
malononitrile 3 (0.5 mmol) was added to a solution of
isocyanide 1 (0.5 mmol) and alkynoate 2 (0.6 mmol) in
toluene (5 mL). The stirred mixture was heated to 100 °C for
several hours and the progress of the reaction was monitored
by TLC. Upon completion, the reaction mixture was
concentrated under vacuum. The residue was purified by
column chromatography on silica gel (silica: 200–300; PE–
EtOAc) to afford the desired product 4.
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Compound 4a: Yellow solid; mp 194–196 °C. 1H NMR
(500 MHz, CDCl3): δ = 7.53 (t, J = 7.5 Hz, 1 H), 7.46 (d,
J = 7.5 Hz, 1 H), 7.22 (t, J = 7.5 Hz, 1 H), 7.11–7.03 (m,
4 H), 6.86 (s, 1 H), 4.05–3.94 (m, 2 H), 3.37 (s, 3 H), 2.20 (s,
6 H), 1.00 (t, J = 7.0 Hz, 3 H). 13C NMR (125 MHz, CDCl3):
δ = 170.6, 161.8, 161.0, 149.7, 146.4, 144.8, 131.7, 131.5,
128.4, 126.6, 125.7, 125.4, 123.9, 123.1, 111.7, 110.6,
109.5, 68.3, 62.5, 62.4, 48.8, 38.9, 18.0, 13.7. HRMS: m/z
[M + Na]+ calcd for C26H22N4O3: 461.1590; found: 461.1595.
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I.; Luque, F. J.; Lavilla, R. Chem.–Eur. J. 2010, 16, 7904.
(b) Mihara, H.; Xu, Y.; Shepherd, N. E.; Matsunaga, S.;
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Danishefsky, S. J. J. Am. Chem. Soc. 2008, 130, 13225.
Synlett 2012, 23, 2274–2278
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