An iodine-promoted one-pot and metal-free access to indolin-2-ones

Article abstract of DOI:10.1177/1747519819875862

A new method for the synthesis of indolin-2-ones has been realized by an I₂-promoted oxidative reaction from 1,2,3,3-tetramethyl-3H-indolium iodides. This transformation proceeded smoothly under metal-free and peroxide-free conditions in a cascade manner.

Full text of DOI:10.1177/1747519819875862

875862CHL0010.1177/1747519819875862Journal of Chemical ResearchZhang et al.
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Journal of Chemical Research
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An iodine-promoted one-pot and
metal-free access to indolin-2-ones
https://doi.org/10.1177/1747519819875862
DOI: 10.1177/1747519819875862
journals.sagepub.com/home/chl
Yong Zhang1 , Xi Zong2 and Min Ji1
Abstract
A new method for the synthesis of indolin-2-ones has been realized by an I2-promoted oxidative reaction from
1,2,3,3-tetramethyl-3H-indolium iodides. This transformation proceeded smoothly under metal-free and peroxide-free
conditions in a cascade manner.
Keywords
I2-promoted, indolin-2-one, metal-free, one-pot, peroxide-free
Date received: 17 May 2019; accepted: 21 August 2019
Recently, due to the need for “greener chemistry,” chem-
Introduction
ists are beginning to develop transformations under metal-
Indolin-2-one rings have been recognized as crucial motifs
free conditions. Iodine, a cheap, nontoxic, and abundant
in diverse natural products and pharmaceutically relevant
halogen, is attracting more and more attention, especially in
entities.1–3 Several drug discovery programs in industry and
oxidative coupling reactions to form new carbon–carbon
academia are anchored around the indolin-2-one scaffold,
(C–C) or carbon–heteroatom (C–X) bonds.19,20 An in situ
and drugs such as Sunitinib and Nintedanib are in clinical
iodination usually occurs in iodine-mediated oxidative cou-
use for targeted anticancer therapies.4,5 A number of meth-
ods for the synthesis of indolin-2-one have been reported.
plings, followed by in situ oxidation to generate an electro-
philicaldehydegroup.21–231,2,3,3-Tetramethyl-3H-indolium
Classical synthetic methods include the derivatization of
iodide, a well-known synthetic agent of many fluorescent
other heterocycles (such as Wolff–Kishner reduction of
dyes, is considered to contain an activated methyl group
isatin and oxidation of indole), Friedel–Crafts cyclizations
which can react with an aldehyde or carbonyl group.24,25 In
of α-haloacetanilides, and variations in the Fischer indole
our previous research, the activated C-2 methyl group
synthesis.6–8 Cyclizations of 2-haloacryloylanilide deriva-
reacted with molecular iodine to form an aldehyde via
tives by a variety of radical initiators have also been used to
Kornblum oxidation in the presence of dimethyl sulfoxide
prepare indolin-2-ones.9–12 In recent years, metal-mediated
(DMSO).26 Based on these results, we report an I2-promoted
activations/cyclizations on precrafted advanced precursors
have been a commonly pursued approach (Scheme 1).
Notable examples are Cu-catalyzed intermolecular C–H
1School of Biological Science and Medical Engineering, Southeast
University, Nanjing, China
2Suzhou Key Laboratory of Biomaterials and Technologies &
Collaborative Innovation Center of Suzhou Nano Science and
Technology, Suzhou, China
cyclization (Scheme 1(a)),13 Pd-catalyzed insertion of
isocyanide (Scheme 1(b)),14 ruthenium-catalyzed intramo-
lecular alkene hydroarylation (Scheme 1(c)),15 and Fe-
mediated hydrometallation-cyclization (Scheme 1(d)).16 In
addition, Ni-catalyzed aromatic C–H alkylation (Scheme
1(e)) and Ir-catalyzed radical cyclization under visible
light (Scheme 1(f)) have also been used to construct indo-
lin-2-one rings.17,18
Corresponding author:
Min Ji, School of Biological Science and Medical Engineering, Southeast
University, Nanjing 210009, China.
Email: jiminseu@163.com

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Journal of Chemical Research 00(0)
Scheme 1. Representative recent approaches for accessing indolin-2-ones.
Source: (a)Theunissen et al.,13 (b) Kong et al.,14 (c) Kilaru et al.,15 (d) Gui et al.,16 (e) Liu et al.,17 and (f) Dong et al.18
one-pot method for the synthesis of indolin-2-ones under and the reaction time was prolonged to 3.0 h (Table 1,
metal-free conditions.
entries 19 and 20). However, the indolin-2-one was not
completely converted into the iodide product. To further
optimize this reaction, we explored the influence of vari-
ous additives (see Table S2 in Supplementary material).
Results and discussion
The reaction is demonstrated by using 1,2,3,3-tetrame- After several experimental iterations, optimum reaction
thyl-3H-indol-1-ium iodide (1a) in the presence of conditions were found: 1a (1.0 mmol), 2a (1.2 mmol), I2
molecular iodine (3.0 equiv.) in DMSO at 100°C for 2 h (2.0 mmol), DMSO (3 mL), and 70°C (Table 1, entry 6).
(Table 1, entry 1). We next studied the effect of the tem-
With optimized conditions in hand, the generality and
perature on reaction (Table 1, entries 2 and 3), and only scope of the reaction were investigated (Table 2).
at a higher temperature was the product obtained. An 1,2,3,3-Tetramethyl-3H-indol-1-ium iodides 1 with elec-
acid, methanesulfonic acid, could effectively promote tron-donating or electron-withdrawing groups on the phe-
the reaction by lowering the reaction temperature (Table nyl ring participated in the reaction to afford the
1, entries
4 and 5). An additive, N-methyl-1,2- corresponding products 3b–m. Compared to electron-
benzenediamine dihydrochloride (2a), was added to the donating groups (e.g. 3b, 3d, and 3h) on the phenyl ring
reaction system and a higher yield was observed (Table or on the fused ring (3i), electron-withdrawing groups
1, entries 6 and 7). Subsequently, the addition of water or (e.g. 3c, 3e, 3f, and 3g) tended to offer the products with
3-Å molecular sieves (Table 1, entries 8 and 9) led to a higher yields. Furthermore, 7-substituted substrates (e.g.
drastic reduction in the yield, suggesting the unusual 3h, 3j, and 3k) participated in the transformation as well,
role of water in the reaction system. We then screened but the yields were slightly lower than those obtained with
the amount of iodine at 70°C (Table 1, entries 12–15) 5-substituted substrates. When the 7-position of the sub-
and found that 2.0 equiv. was optimum. Further increas- strate was substituted by a bromine atom, no iodide prod-
ing the amount of I2 had no effect on the yield, and no uct could be obtained (3j). Finally, a substituent on the
reaction occurred in the absence of I2 (Table 1, entry 15), nitrogen and a bulky group at the 3-position are well toler-
indicating that iodine was essential. When additive was ated, but their reactions afforded the target products in
reduced to catalytic amounts (Table 1, entries 16 and lower yields (3l and 3m).
17), only small amounts of products were obtained. The
To gain more information about the reaction mecha-
addition of pyridine greatly decreased the yield, suggest- nism, a model reaction of 1a (0.2mmol) with I2 (0.4mmol)
ing the importance of acidic conditions (Table 1, entry in DMSO-d6 was tracked by 1H nuclear magnetic resonance
18). In addition, several reactions were performed in dif- (NMR; see Figure S1 in Supplementary material). As the
ferent solvents so as to ascertain the unusual role of reaction proceeded, a signal around 10ppm rapidly
DMSO in this process (see Table S1 in Supplementary appeared, indicating the existence of an aldehyde group
material). The amount of I2 was increased to 7.0 equiv., due to the release of formaldehyde in the reaction system.

Zhang et al.
3
Table 1. Optimization of the reaction conditionsa.
Entry
2a (equiv.)
I2 (equiv.)
Temperature (°C)
Time (h)
Ratio a′/b′b
Yield (%)c
1
2
3
4
5
6
7
8
−
−
−
−
3
2
2
3
2
2
2
2
2
2
2
1
1.5
3
−
2
2
2
5
7
100
70
70
100
70
70
70
70
70
100
50
70
70
70
70
70
70
70
70
70
2
1.5
2
63:37
−
n.d.
50:50
80:20
61:38
40:60
n.d.
25
0
Trace
35d
34d
50
2
−
0.5
0.5
2
0.5
0.5
0.5
1
0.5
0.5
0.5
0.5
0.5
1.5
0.5
1
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
0.1
0.2
1.2
1.2
1.2
45
Tracee
Tracef
42
9
n.d.
10
11
12
13
14
15
16
17
18
19
20
25:75
88:12
77:23
65:35
60:40
−
50:50
56:44
n.d.
14:68h
12:69h
18
35
36
44
0
3
9
Traceg
−
−
3
DMSO: dimethyl sulfoxide; HPLC: high-performance liquid chromatography.
aReaction conditions: 1a (1mmol), 2a, and DMSO (3mL).
bRatio of a′ to b′ in the isolated product is determined by HPLC.
cIsolated yield of 3a. n.d.=not determined.
dMethanesulfonic acid (2.0mmol) was added.
eH2O (1mL) was added.
f3-Å molecular sieves were added.
gPyridine (0.1mL) was added.
hRatio of a′ to b′ in the reaction solution was determined by HPLC.
With the aforementioned results and previous reports in
mind,26 a possible mechanism is proposed in Scheme 2
using 1,2,3,3,5-pentamethyl-3H-indol-1-ium iodide 1b as
an example. Initially, the substrate indolium iodide 1b
reacted with I2 to afford the intermediate 2-iodomethyl
indolium iodide A. Subsequently, the intermediate A under-
went a nucleophilic substitution reaction with the nucleo-
philic oxygen atom of DMSO to form the alkoxysulfonium
salt B, which was then attacked by H2O to give the interme-
diate C. Under the reaction conditions, intermediate C was
unstable and underwent C–C bond cleavage to give the
final indolin-2-one 3b, along with the release of formalde-
hyde and dimethyl sulfide.
In conclusion, a molecular I2 promoted C–C bond cleav-
age has been developed to construct indolin-2-ones from
simple and readily available indolinium iodides. In addition,
the reaction performs well in the absence of any metal or
peroxide. Further studies to elucidate a detailed mechanism
and further explorations of this I2/DMSO-promoted oxida-
tive reaction are currently underway in our laboratory.
Experimental analysis
All reagents and solvents were obtained from commercial
suppliers and were used without further purification. The
method of preparing starting compounds 1 is given in
Supplementary material. NMR spectra were recorded on a
Bruker FT-NMR 400 spectrometer with chemical shifts
reported in ppm relative to the internal standard tetra-
methylsilane (TMS). HRMS was determined on a Waters
GCT Premier spectrometer.
General procedure for the synthesis of
indolin-2-ones 3
A mixture of quaternary salt 1 (1.0mmol), 2a (1.2mmol),
and iodine (2mmol) in DMSO (3mL) was stirred at 70°C.
After the reaction was complete (monitored by thin-layer
chromatography (TLC)), the mixture was cooled to room
temperature and quenched with saturated aqueous Na2S2O3,
then extracted with ethyl acetate (3×20mL). The

4
Journal of Chemical Research 00(0)
Scheme 2. A plausible reaction mechanism.
Table 2. Substrate scopea.
Entry
Substrate 1 (R1)
Product 3 (R1)
Yield (%)b
1
2
3
4
5
6
7
1b (5-Me)
1c (5-Cl)
1d (5-OMe)
1e (5-Br)
1f (5-CF3)
1g (5,7-diCl)
1h (5,7-diMe)
3b (5-Me)
3c (5-Cl)
3d (5-OMe)
3e (5-Br)
3f (5-CF3)
3g (5,7-diCl)
3h (5,7-diMe)
43
55
40
56
52
54
39
8
42
9
10
1j (7-Br)
1k (7-Me)
3j (7-Br)
45
41c
11
12
40c
41c
DMSO: dimethyl sulfoxide; NMR: nuclear magnetic resonance.
aReaction was performed with 1 (1.0mmol), 2a (1.2mmol), and I2 (2mmol) in DMSO (3mL) at 70°C for 0.5h.
bYields of isolated products.
cThe ratio was determined by 1H NMR spectroscopy.

Zhang et al.
5
combined organic layers were washed with brine, dried (s, 6H); 13C NMR (100MHz, DMSO-d6): δC 180.7, 140.4,
over anhydrous Na2SO4, and evaporated. The residue was 137.9, 129.1, 127.2, 122.7, 115.1, 44.3, 29.5, 24.3; HRMS
purified by column chromatography using ethyl acetate and (ESI+): m/z [M+H]+ calcd for C11H12Cl2NO+: 244.0290,
petroleum ether to yield the desired pure product.
found: 244.0290.
1,3,3-Trimethylindolin-2-one and 7-iodo-1,3,3-trimethyl-
1,3,3,5,7-Pentamethylindolin-2-one (3h):16 Yellow oil,
1
indolin-2-one (mixture obtained from entry 7 in Table 1, 3a): 39% yield; H NMR (400MHz, DMSO-d6): δH 7.00 (s,
1
Brown oil, 50% yield; H NMR (400MHz, DMSO-d6): δH 1H), 6.83 (s, 1H), 3.35 (s, 3H), 2.52 (s, 3H), 2.25 (s, 3H),
7.71 (d, J=1.7Hz, 1H), 7.61 (dd, J=8.2, 1.8Hz, 1H), 7.35– 1.23 (s, 6H); 13C NMR (100MHz, DMSO-d6): δC 181.1,
7.31 (m, 0.67H), 7.26 (td, J=7.7, 1.3Hz, 0.67H), 7.04 (td, 138.1, 136.4, 131.9, 131.4, 121.4, 119.7, 43.2, 29.3, 24.9,
J=7.6, 1.3Hz, 0.67H), 7.00 (d, J=7.8Hz, 0.67H), 6.87 (d, 20.9, 18.8; HRMS (ESI+): m/z [M+H]+ calcd for
J=8.2Hz, 1H), 3.13 (s, 2H), 3.11 (s, 3H), 1.26 (s, 10H); 13
NMR (100MHz, DMSO-d6): δC 180.6, 180.1, 142.9, 142.8,
C
C13H18NO+: 204.1383, found: 204.1391.
1,1,3-Trimethyl-1,3-dihydro-2H-benzo[e]indol-2-one
138.4, 136.6, 135.7, 131.4, 128.1, 122.8, 122.6, 111.4, 108.8, (3i):Yellow oil, 42% yield; 1H NMR (400MHz, DMSO-d6):
85.8, 44.0, 26.5, 26.4, 24.6, 24.3; LC-MS: tR =3.94min, δH 8.02 (d, J=8.5Hz, 1H), 7.98 (s, 1H), 7.96 (s, 1H), 7.57–
m/z=176.1 [M+H]+; tR =4.48min, m/z=302.0 [M+H]+; 7.53 (m, 1H), 7.47 (d, J=8.6Hz, 1H), 7.39 (t, J=7.5Hz,
HRMS (ESI+): m/z [M+H]+ calcd for C11H14NO+ and 1H), 3.28 (s, 3H), 1.54 (s, 6H); 13C NMR (100MHz,
C11H13INO+: 176.1075 and 302.0042, found: 176.1074 and DMSO-d6): δC 181.7, 140.5, 130.5, 130.0, 129.3, 129.1,
302.0040.
127.5, 126.6, 123.7, 122.4, 110.9, 45.4, 26.7, 24.1; HRMS
1,3,3,5-Tetramethylindolin-2-one (3b):16 Brown oil, (ESI+): m/z [M+H]+ calcd for C15H16NO+: 226.1226,
1
43% yield; H NMR (400MHz, DMSO-d6): δH 7.18 (s, found: 226.1230.
1H), 7.09 (d, J=7.9Hz, 1H), 6.91 (d, J=7.9Hz, 1H), 3.13
7-Bromo-1,3,3-trimethylindolin-2-one (3j): Light yel-
(s, 3H), 2.31 (s, 3H), 1.27 (s, 6H); 13C NMR (100MHz, low oil, 45% yield; H NMR (400MHz, DMSO-d6): δH
DMSO-d6): δC 180.5, 140.5, 135.7, 131.5, 128.2, 123.5, 7.44 (d, J=8.1Hz, 1H), 7.40 (d, J=7.2Hz, 1H), 7.00 (t,
108.5, 43.9, 26.4, 24.6, 21.2; HRMS (ESI+): m/z [M+H]+ J=7.7Hz, 1H), 3.49 (s, 3H), 1.30 (s, 6H); 13C NMR
1
calcd for C12H16NO+: 190.1226, found: 190.1230.
(100MHz, DMSO-d6): δC 181.1, 140.0, 139.1, 133.4,
5-Chloro-1,3,3-trimethylindolin-2-one (3c):16 White 124.4, 122.5, 101.9, 43.7, 29.8, 24.7; HRMS (ESI+): m/z
solid, 55% yield; m.p. 141–143°C (lit.16 140–143°C); H [M+H]+ calcd for C11H13BrNO+: 254.0175, found:
1
NMR (400MHz, DMSO-d6): δH 7.52 (d, J=2.1Hz, 1H), 254.0174.
7.35 (dd, J=8.3, 2.2Hz, 1H), 7.06 (d, J=8.3Hz, 1H), 3.15
1,3,3,7-Tetramethylindolin-2-one and 5-Iodo-1,3,3,7-
(s, 3H), 1.30 (s, 6H); 13C NMR (100MHz, DMSO-d6): δC tetramethylindolin-2-one (mixture, 3k): Yellow oil, 41%
180.3, 141.8, 137.8, 127.9, 126.8, 123.4, 110.3, 44.2, 26.5, yield; 1H NMR (400MHz, DMSO-d6): δH 7.56 (d,
24.2; HRMS (ESI+): m/z [M+H]+ calcd for C11H13ClNO+: J=1.3Hz, 0.68H), 7.41 (s, 0.68H), 7.18 (d, J=7.1Hz, 1H),
210.0680, found: 210.0683.
7.02 (d, J=7.5Hz, 1H), 6.94 (t, J=7.5Hz, 1H), 3.43 (s,
5-Methoxy-1,3,3-trimethylindolin-2-one (3d):16 Yellow 3H), 3.40 (s, 2H), 2.57 (s, 3H), 2.53 (s, 2H), 1.25 (s, 10H);
oil, 40% yield; 1H NMR (400MHz, DMSO-d6): δH 7.02 (d, 13C NMR (100MHz, DMSO-d6): δC 181.2, 180.7, 140.6,
J=2.5Hz, 1H), 6.90 (d, J=8.4Hz, 1H), 6.81 (dd, J=8.4, 140.5, 139.5, 138.9, 136.3, 131.6, 129.3, 123.0, 122.5,
2.5Hz, 1H), 3.72 (s, 3H), 3.09 (s, 3H), 1.24 (s, 6H); 13C 120.7, 120.0, 85.9, 43.3, 43.1, 29.3, 24.9, 24.6, 19.0, 18.4;
NMR (100MHz, DMSO-d6): δC 180.3, 156.0, 137.0, 136.2, HRMS (ESI+): m/z [M+H]+ calcd for C12H16NO+ and
112.3, 110.4, 109.1, 56.0, 44.3, 26.4, 24.5; HRMS (ESI+): C12H15INO+: 190.1226 and 316.0193, found: 190.1228 and
+
m/z [M+H]+ calcd for C12H16NO2 : 206.1176, found: 316.0192.
206.1183.
1-Ethyl-3,3-dimethylindolin-2-one and 1-Ethyl-5-
5-Bromo-1,3,3-trimethylindolin-2-one (3e):16 White iodo-3,3-dimethylindolin-2-one (mixture, 3l): Yellow oil,
solid, 56% yield; m.p. 152–154°C (lit.16 152–154°C); H 40% yield; H NMR (400 MHz, DMSO-d6): δH 7.76 (d,
NMR (400MHz, DMSO-d6): δH 7.63 (s, 1H), 7.47 (d, J = 1.5 Hz, 0.8H), 7.63 (dd, J = 8.2, 1.5 Hz, 0.8H), 7.38 (d,
J=8.2Hz, 1H), 7.01 (d, J=8.3Hz, 1H), 3.14 (s, 3H), 1.29 J = 7.3 Hz, 1H), 7.28 (d, J = 7.5 Hz, 1H), 7.09–7.06 (m,
(s, 6H); 13C NMR (100MHz, DMSO-d6): δC 180.2, 142.3, 2H), 6.96 (d, J = 8.2 Hz, 0.8H), 3.78–3.67 (m, 3.6H), 1.29
138.2, 130.7, 126.0, 114.6, 110.8, 44.2, 26.5, 24.2; HRMS (s, 10.8H), 1.19–1.13 (m, 5.4H); 13C NMR (100 MHz,
(ESI+): m/z [M+H]+ calcd for C11H13BrNO+: 254.0175, DMSO-d6): δC 180.3, 179.7, 141.8,141.6, 138.6, 136.6,
1
1
found: 254.0174.
135.9, 131.6, 128.1, 123.0, 122.4, 111.5, 108.9, 85.7,
1,3,3-Trimethyl-5-(trifluoromethyl)indolin-2-one (3f):27 44.0, 43.8, 34.4, 34.3, 24.5, 24.2, 13.0, 12.9; HRMS
Light yellow solid, 52% yield; m.p. 38–40°C (lit.27 37– (ESI+): m/z [M + H]+ calcd for C12H16NO+ and
1
39°C); H NMR (400MHz, DMSO-d6): δH 7.80 (s, 1H), C12H15INO+: 190.1226 and 316.0193, found: 190.1226
7.68 (d, J=8.2Hz, 1H), 7.22 (d, J=8.2Hz, 1H), 3.20 (s, and 316.0190.
3H), 1.33 (s, 6H); 13C NMR (100MHz, DMSO-d6): δC
1′-Methylspiro[cyclohexane-1,3′-indolin]-2′-one
and
180.8, 146.5, 136.6, 126.0, 125.9, 123.3, 122.9, 120.0, 5′-Iodo-1′-methylspiro [cyclohexane-1,3′-indolin]-2′-one
109.1, 44.0, 26.6, 24.1; HRMS (ESI+): m/z [M+H]+ calcd (mixture, 3m): Yellow oil, 41% yield; 1H NMR (400MHz,
for C12H13F3NO+: 244.0944, found: 244.0943.
DMSO-d6): δH 7.69 (d, J=1.6Hz, 0.42H), 7.57 (dd, J=8.2,
5,7-Dichloro-1,3,3-trimethylindolin-2-one (3g): Yellow 1.7Hz, 0.42H), 7.43 (d, J=7.3 Hz, 1H), 7.24–7.20 (m, 1H),
oil, 54% yield; 1H NMR (400MHz, DMSO-d6): δH 7.56 (d, 6.99–6.93 (m, 2H), 6.81 (d, J=8.2Hz, 0.42H), 3.06 (s, 3H),
J=1.9Hz, 1H), 7.44 (d, J=1.9Hz, 1H), 3.46 (s, 3H), 1.31 3.03 (s, 1.26H), 1.88–1.43 (m, 14.2H); 13C NMR (100MHz,

6
Journal of Chemical Research 00(0)
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DMSO-d6): δC 179.9, 179.2, 143.0, 142.8, 137.9, 136.5,
135.2, 132.0, 127.9, 123.9, 122.2, 111.3, 108.7, 85.5, 46.9,
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Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
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Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: This
work was supported by the National Natural Science Foundation
of China (Grant No. 81671745).
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Supplemental material
Supplemental material for this article, which contains the NMR
spectra and preliminary study of reaction mechanism, is available
online.
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