A novel approach for highly regio- and stereoselective synthesis of (Z)-3-methyleneisoindoline-1-ones in aqueous micellar medium

Article abstract of DOI:10.1016/j.tetlet.2012.10.001

An environmentally benign and operationally simple methodology was developed for the regio- and stereoselective synthesis of (Z)-3- methyleneisoindolinones in aqueous micellar medium from 2-iodo-N-phenyl- benzamides and terminal alkyne by Cu-free domino S

Full text of DOI:10.1016/j.tetlet.2012.10.001

Tetrahedron Letters 53 (2012) 6789–6792
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A novel approach for highly regio- and stereoselective synthesis
of (Z)-3-methyleneisoindoline-1-ones in aqueous micellar medium
Swarbhanu Sarkar a, Samrat Dutta a, Rajdip Dey b, Subhendu Naskar c,
⇑
a Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4 Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India
b Department of Chemistry, Jadavpur University, Jadavpur, Kolkata 700 032, India
c Department of Science & Humanities, Bandwan Government Polytechnic, Madhupur, P.O. Jitan, Purulia 723 129, West Bengal, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An environmentally benign and operationally simple methodology was developed for the regio- and
stereoselective synthesis of (Z)-3-methyleneisoindolinones in aqueous micellar medium from 2-
iodo-N-phenyl-benzamides and terminal alkyne by Cu-free domino Sonogashira reaction followed by
5-exo-dig-cyclization using Pd(CH3CN)Cl2 as catalyst and 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene as
ligand under aerobic condition.
Received 19 August 2012
Revised 30 September 2012
Accepted 1 October 2012
Available online 10 October 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
(Z)-3-Methyleneisoindoline-1-one
Cu-free Sonogashira
5-Exo-dig cyclization
Micelle
Reaction in water
In recent years considerable attention has been perceived
among the synthetic organic chemists to execute organic reactions
in water1 because of its abundance in nature, having virtually no
cost, and being the safest among all available solvents, leading to
environmentally benign chemical processes.2 But limited solubility
of various organic compounds in water actually prevents the exe-
cution of reactions in aqueous media. Introduction of aqueous sur-
factant, in the form of micelles,3 as the reaction medium has
provided a way around this limitation to some extent. In conven-
tional micellar catalysis, the surfactant micelles actually accumu-
late all reacting molecules within the small volume, both by
solubilization due to hydrophobic effect and by counter ion bind-
ing due to electrostatic interactions, resulting in high concentra-
tion of the molecules with different orientations. It actually
influences reaction mechanism, resulting in remarkable differences
with respect to reaction rate and selectivity that is observed in
homogeneous systems.4
Because of the significant biological profile of isoindolin-1-ones
and its derivatives,5 like anti-hypertensive,6 anti-viral,7 anti-
leukemic,8 or anti-inflammatory activity,9 we focused our attention
on this scaffold. Isoindolin-1-ones and its derivatives are found
in the core structure of a number of naturally occurring and
pharmacologically interesting substances like fumaridine,10 len-
noxamine,11 AKS 186,12 pictonamine,13 and pazinaclone.14 Pazina-
clone, pagoclone, and zopiclone showed potent anxiolytic activity,
and are of interest as sedatives, hypnotics, and muscle relaxants.15
The isoindolinone moiety is also found in a group of natural prod-
ucts as exemplified by aristolactam alkaloids.16
The varied biological activities of isoindolinone derivatives have
attracted the attention of organic chemists and a number of syn-
thetic methodologies have been developed for the preparation of
isoindolinone derivatives.17–25 But many such approaches are pla-
gued by constraints26,27 like low yield and long time for comple-
tion, and if the o-iodo benzamides and terminal aryl acetylenes
are used as precursors under Pd–Cu catalysis, acyclic Sonogashira
product or 6-endo-dig cyclized product, that is, isoquinolinones
are formed as side products.
Palladium(II) salts having bidentate N,P- or N,N-ligands have
been established to be efficient catalysts for C–C or C–N bond
forming reaction. The most common catalytic systems used in
the heteroannulation reaction are mainly PdCl2(PPh3)2, Pd(dba)4,
and Pd(dtbpf)Cl2 using amines as solvents or co-solvents with
CuI as the co-catalyst. Although copper-free Sonogashira cross cou-
pling reactions were reported,28,29 they generally employed the use
of a combination of at least one phosphine as ligand or an amine
with tetra-butyl ammonium salts as activator. But under these cir-
cumstances the use of degassed solvents is essential as phosphine
in palladium complexes is often moisture sensitive. We explored a
simple, efficient, and green protocol in aqueous micellar medium
where a domino Sonogashira-5-exo-dig-cyclization reaction has
been used for the complete regio- and stereo-selective synthesis
⇑
Corresponding author. Tel./fax: +91 32 5320 1527.
E-mail address: chemdept2012@gmail.com (S. Naskar).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.10.001

6790
S. Sarkar et al. / Tetrahedron Letters 53 (2012) 6789–6792
Table 1
of isoindolinones in short reaction time. The method allows
domino Sonogashira-cyclization of o-bromo or o-iodo-N-phenyl-
benzamides and terminal alkyne under aerobic conditions using
1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (2) as ligand ( Fig. 1).
The method excludes the use of copper, organic solvents, phos-
phine ligands, or the presence of tetra-butyl ammonium salts as
activator. A library of (Z)-3-methyleneisoindoline-1-ones could
thus be generated in high yield and short reaction time. The nov-
elty of the methodology lies in its eco-friendly operation, forma-
tion of structurally unique molecules, short reaction time, and
excellent yield.
Effect of different surfactants on the yield of 5a
Entrya
Surfactant
Concentration (mM)
Yieldb (%)
1
2
3
4
5
6
7
8
9
None
CTAB
CTAB
CTAB
CTAB
CTAB
TTAB
SDS
—
NRc
25
46
72
92
92
86
75
75
50
60
70
80
90
80
80
80
Triton X-114
a
We envisaged using 2-iodo-N-substituted benzamides to
endow varied acetylenes that could subsequently be used in a
one-pot, two-step synthesis of 3-methyleneisoindoline-1-ones
(Scheme 1). At the outset, we opted 2-iodo-N-phenylbenzamide
(3a) and phenylethyne (4a) as model reactants for the synthesis
of 3-methyleneisoindoline-1-one (5a) and investigated the feasi-
bility of a copper-free Sonogashira coupling-cycloisomerization
domino strategy in aqueous medium (Table 1) to determine the
optimal reaction condition using Pd(CH3CN)2Cl2 (2 mol %) as the
source of palladium. The effect of different hydrazone ligands29
(Fig. 1) was also investigated. Among the ligands, 1a and 1b sound
good as it produces a remarkable yield of 73% and 69%, respec-
tively, whereas the use of bishydrazone ligand 1c, 1d, or 1e having
a seven-membered ring was not found as effective (gave poor to
moderate yield in repetitive experiments). However, the use of
ligand 2 (1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) led to an
excellent yield of 92% for this reaction.
The effect of micelle has also been noticed in the reaction se-
quence. The results summarized in Table 1 revealed that, when
the reaction was carried out in the absence of a surfactant, no prod-
uct was isolated even up to 48 h under aerobic condition. An
encouraging change in the outcome was noticed when cetyltri-
methylammonium bromide (CTAB, 50 mM, cmc 0.92 mM)30 was
introduced in the system. Carrying out the reaction in water at
80 °C for 1 h ensured its completion (monitored by TLC) but gave
a low yield (25%; Table 1, entry 2) of 5a. A drastic change in the
reaction yield was observed when the amount of the surfactant
is increased. The most prominent result (92%) was obtained when
the reaction was performed using CTAB at 80 mM concentration
(Table 1, entry 5). However, no significant increase in the yield
was observed on enhancement of the concentration of CTAB
All the reactions were performed using 3a (1 mmol) and 4a (1.5 mmol) in water
at 80 °C for 1 h under aerobic condition.
b
Yield of isolated pure product; catalyst used Pd(CH3CN)2Cl2 (2 mol %), ligand 2
(2.5 mol %).
c
No reaction.
beyond 80 mM (Table 1, entry 6). Changing to other surfactant,
the reaction yielded a decreased amount of product 5a; with so-
dium dodecylsulfate (SDS: cmc 8.1 mM)31 produced 75% (Table 1,
entry 8) and with tetra-decyltrimethylammonium bromide (TTAB:
cmc value 3.8 mM)32 produced 86% (Table 1, entry 7) both at the
concentration of 80 mM. Even the use of a nonionic surface active
agent such as Triton X-114 (cmc 0.28 mM)33 proved less effective
compared to CTAB or TTAB (Table 1, entry 9).
The effect of different bases, viz. DBU, Et3N, DABCO, DMAP,
K2CO3, and Cs2CO3 has also been envisaged (Table 2). DBU appeared
to be the most effective when employed in 1.5 mol equiv affording
the product in maximum yield. The results concluded that organic
bases worked well in comparison to inorganic bases. It is worth
mentioning that other Pd-sources [Pd/C-PPh3, PdCl2, Pd(PPh3)4,
Pd(dba)2, Pd2(dba)3, Pd-BINAP, Na2PdCl4, and Pd(dtbpf)Cl2] how-
ever gave either very poor or no yield.
To explore the scope and generality of this approach, we used
various aryl or heteroaryl alkynes (Table 3). All the reactions
yielded only Z-3-methylene isomer and no side product was ob-
tained. The structures of all the products were confirmed by IR,
NMR, and MS spectroscopy. Finally, single crystal X-ray analysis
Table 2
Effect of different bases on the yield of 5a
Entrya
Base
Amount (mmol)
Time (h)
Yieldb (%)
Ph
Ph
Ph
CH3
N
N N
N N
CH3
N
N
N N
1
2
3
4
5
6
7
8
Cs2CO3
K2CO3
Et3N
DABCO
DMAP
DBU
1.0
1.0
1.0
1.0
1.0
1.0
1.5
2.0
1
1
1
1
1
1
1
1
40
32
80
82
80
86
92
92
N N
H3C
1a
1c
1b
H
C
N
DBU
DBU
N
N
N N
N
H
C
N N
N N
a
All the reactions were performed using 3a (1 mmol) and 4a (1.5 mmol) in water
at 80 °C for 1 h under aerobic condition in the presence of CTAB (80 mM),
Pd(CH3CN)2Cl2 (2 mol %), and ligand 2 (2.5 mol %).
1d
1e
2
N
b
Yield of isolated pure product.
Figure 1. Ligands used in the study.
O
O
O
Ph
N
H
4a, Pd(CH3CN)2Cl2
Surfactant, H2O, 80 oC,
Base, Ligand
N
Ph
Ph
Ph
N
H
I
3a
Ph
5a
Scheme 1. Synthesis of 5a in aqueous micellar medium.

S. Sarkar et al. / Tetrahedron Letters 53 (2012) 6789–6792
6791
Table 3
Reactions of 2-halobenzamides (3a–c) with terminal alkynes (4a–e) leading to isoindolinones (5a–j) in aqueous micellar medium
Yieldb
(%)
Entrya
Amide
Acetylene
Product
Ref.
O
O
N
Y
Z
HN
Y
X
Z
25b
25b
25b
25b
-
1
2
3
4
5
6
7
3a: X = I, Y = H
3b: X = I, Y = CH3
3c: X = Br, Y = H
4a: Z = H
5a: Y = H, Z = H
5b: Y = CH3, Z = H
5a
5c: Y = H, Z = OCH3
5d: Y = CH3, Z = OCH3
5e: Y = H, Z = C5H11
92
94
83
90
87
80
82
4a
4a
4b: Z = OCH3
4b
4c: Z = C5H11
4c
3a
3b
3a
3b
-
-
5f: Y = CH3, Z = C5H11
O
N
Y
N
N
-
8
9
3a
3b
4d
4d
5g: Y = H
5h: Y = CH3
74
72
-
-
O
Y
N
-
10
11
3a
3b
4e
4e
5i: Y = H
5j: Y = CH3
66
68
-
-
a
Reactions were performed using 3a–c (10 mmol), alkyne (15 mmol), Pd(CH3CN)2Cl2 (2 mol %), ligand 2 (2.5 mol %), and DBU
(15 mmol) in water at 80 °C for 1 h under aerobic condition in the presence of CTAB. Products were characterized by spectroscopic and
analytical data.
b
Isolated yield.
O
O
Pd-catalysis
SiMe3
3a
6
TBAF
N
H
N
H
SiMe3
9
8
3a
O
O
O
N
HN
O
N
Pd
N
SiMe3
7
O
HN
Not obtained
11
10
Scheme 2. Synthesis of dimer 11.

6792
S. Sarkar et al. / Tetrahedron Letters 53 (2012) 6789–6792
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It is notable that, when the aryl substituent on the nitrogen
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is for 2-iodobenzamide, only Sonogashira product is formed. How-
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methylsilyl acetylene (6) under the above condition, the reaction
yielded the desired cyclized product 7.25b But when tetra-butylam-
monium fluoride (50 mol %) was added to the system dimer 1134
was formed as the sole product (Scheme 2).
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factant medium is also envisaged. It is presumed that in aqueous
micellar medium 3a and trimethylsilyl acetylene 6 are in very close
proximity leading to the formation of 2-(trimethylsilyl)ethynyl
benzamide 8 by Sonogashira reaction as predicted. Now fluoride
ion (from tetra-butylammonium fluoride) being negatively charged
lies in the immediate vicinity of the cationic surfactant, and acts as
a desilylating agent to give intermediate 9. The intermediate
immediately undergoes a consecutive Sonogashira reaction to give
the dimer 10, which undergoes an easy cyclization in the presence
of Pd-catalyst to afford dimer 11.
In summary, we have demonstrated an efficient, economical,
environmentally benign, and rapid process for the synthesis of
(Z)-3-methyleneisoindoline-1-one scaffold35,36 in aqueous micellar
medium. We found that, 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadi-
ene was useful as phosphine-free ligand for this reaction. The green
reaction condition, complete regio- and stereo-selectivity, and
excellent yields of products, made this protocol a convenient one
for the preparation of (Z)-3-methyleneisoindoline-1-ones.
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28. For copper and amine-free condition using phosphine follow: (a) Yi, C.; Hua, R.
J. Org. Chem. 2006, 71, 2535; For copper and phosphine-free condition using
amines or tetra-butyl ammonium salts follow: (b) Liang, B.; Dai, M.; Chen, J.;
Yang, Z. J. Org. Chem. 2005, 70, 391.
Acknowledgment
29. (a) Mino, T.; Shirae, Y.; Saito, T.; Sakamoto, M.; Fujita, T. J. Org. Chem. 2006, 71,
9499; (b) Dang, D.; Zheng, Y.; Bai, Y.; Guo, X.; Ma, P.; Niu, J. Cryst. Growth Des.
2012, 12, 3856.
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S.S. and S.D. are thankful to CSIR, Govt. of India for providing
fellowship.
Supplementary data
Supplementary data (1H and 13C NMR spectra of all new com-
pounds associated with this article can be found in the online ver-
sion. Crystallographic data in CIF format are available free of charge
via the Internet at CCDC 866283. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the
Cambridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam.a-
c.uk)) associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.tetlet.2012.10.001. These
data include MOL files and InChiKeys of the most important com-
pounds described in this article.
35. General reaction procedure for the synthesis of isoindolinones: In
a round-
bottomed flask filled with 50 mL of water, aryl amide (3a–c, 1.0 equiv), alkyne
(4a–e, 1.5 equiv), Pd(CH3CN)2Cl2 (0.02 equiv), ligand 2 (0.025 equiv), and DBU
(1.5 equiv) were stirred vigorously at 80 °C for 1 h under aerobic condition in
the presence of CTAB (4 mmol). After completion of the reaction (monitored by
TLC), the contents of the reaction mixture were extracted with ethyl acetate
(3 Â 25 mL) and washed thoroughly with water until free from CTAB and base.
Column chromatography produced pure products (5a–j).
36. Spectral data of Z-3-(2-Pyridinyl)methylidene-N-(4-methylphen-yl)isoindolin-1-
one (5h): Yellow needles (yield: 72%); mp 164–166 °C; IR mmax (KBr): 3001,
1700, 1650, 1559, 1455, 1287, 1175, 1015, 856, 769 cmÀ1 1H NMR (CDCl3,
;
300 MHz): d = 2.44 (s, 3H, CH3), 6.26 (s, 1H), 7.19–7.23 (m, 1H), 7.26–7.37 (m,
5H), 7.54–7.6 (m, 2H), 7.67 (t, J = 7.8 Hz, 1H), 7.94–7.98 (m, 1H), 8.47-8.5 (m,
1H), 8.72 (br s, 1H); 13C NMR (CDCl3, 75 MHz): d = 21.24 (CH3), 111.64 (CH),
121.94 (CH), 123.37 (CH), 125.30 (CH), 125.34 (CH), 128.89 (2 Â CH), 128.89
(C), 130.10 (2 Â CH), 130.22 (CH), 131.84 (C), 132.18 (CH), 134.60 (C), 136.37
(CH), 138.57 (C), 140.88 (C), 149.29 (CH), 154.42 (C), 166.75 (C); HRMS (ESI):
m/z calcd for C21H16ON2 [M+Na]+ 335.1160; found: 335.1172.
References and notes
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