Tert -Butoxide-Mediated Arylation of 1-Acetylindolin-3-ones with Diaryliodonium Salts

Article abstract of DOI:10.1055/s-0035-1560575

A procedure for the 2-arylations of indolinone derivatives with diaryliodonium salts mediated by potassium tert-butoxide is developed. Various monoarylated indolinone derivatives are readily obtained in 24-70% yield via this method. The alkylation of monoarylated indolinone derivatives with allyl bromide or benzyl bromide affords the corresponding 2,3-disubstituted products in 60% and 70% yield, respectively.

Full text of DOI:10.1055/s-0035-1560575

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© Georg Thieme Verlag Stuttgart · New York
2015, 26, 2593–2597
letter
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Letter
Synlett
tert-Butoxide-Mediated Arylation of 1-Acetylindolin-3-ones with
Diaryliodonium Salts
Yanxia Zhanga,b
Jianwei Han*b
Zhen-Jiang Liu*a
O
O
KOtBu (1 equiv)
THF, 30 °C, 10 h
[Ar1IAr2]+X–
Ar1(/2)
+
R
R
N
N
a School of Chemical and Environmental Engineering, Shanghai
Institute of Technology, 100 Haiquan Road, Shanghai 201418,
P. R. of China
Ac
Ac
22 examples
24–70% yield
zjliu@sit.edu.cn
b Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis,
Shanghai Institute of Organic Chemistry, The Chinese Academy
of Sciences, 345 Ling Ling Road, Shanghai 200032,
P. R. of China
jianweihan@sioc.ac.cn
Received: 06.07.2015
Accepted after revision: 27.08.2015
Published online: 22.09.2015
with other valuable nucleophiles has experienced a renais-
sance in recent years.6 Manetsch reported a metal-free
arylation of ethyl acetoacetate for the synthesis of 3-aryl-
4(1H)-quinolones.7 Furthermore, a mild protocol for the C-4
arylation of 4-substituted pyrazolin-5-ones with diaryl-
iodonium salts promoted by 4-(N,N-dimethylamino)pyri-
dine (DMAP) has been described.8 On the other hand, the
indolinone moiety is found frequently in a wide-spectrum
of naturally occurring bioactive products and compounds of
pharmaceutical interest. 2-Arylated indolin-3-ones have
been used as important building blocks for further synthet-
ic transformations.9 However, the reported approach for the
preparation of 2-arylated indolinones is via Baeyer–Villiger
oxidation of indole derivatives which are substituted with a
phenyl group at C-3 (Scheme 1, A and B). Obviously, this
method is restricted by the limited number of available
substrates.10 In 1992, Mérour and Finet reported a brief
method for the direct arylation of indolin-3-ones with aryl-
lead triacetates, but only electron-rich polymethoxyphenyl-
lead reagents could be employed in the reaction (Scheme 1,
C).11 To the best of our knowledge, direct metal-free aryl-
ations at position C-2 of indolin-3-ones, with a wide reac-
tion scope, remains unexplored. Herein, we present a tert-
butoxide-mediated arylation of indolin-3-ones using diaryl-
iodonium(III) salts to provide access to diverse 2-arylindo-
lin-3-ones (Scheme 1, D).
DOI: 10.1055/s-0035-1560575; Art ID: st-2015-w0513-l
Abstract A procedure for the 2-arylations of indolinone derivatives
with diaryliodonium salts mediated by potassium tert-butoxide is devel-
oped. Various monoarylated indolinone derivatives are readily obtained
in 24–70% yield via this method. The alkylation of monoarylated indoli-
none derivatives with allyl bromide or benzyl bromide affords the corre-
sponding 2,3-disubstituted products in 60% and 70% yield, respectively.
Key words arylation, diaryliodonium salts, metal-free, indolinone,
alkylation
Arylations under transition-metal-free conditions have
recently attracted significant attention due to the draw-
backs of toxicity, cost and pollution problems associated
with organometallic chemistry.1 Iodine(III) reagents such as
diaryliodonium salts possess similar properties to those of
transition-metal-complexes, and hence can be employed as
alternative metal-free reactants in reaction pathways that
typically require heavy-metal reagents.2 For example, aryl–
metal reagents such as Ar4Sn, Ar2Pb(OAc)2, Ar3Bi, Ar2TlCl,
ArB(OH)2 and so on, are efficient arylating agents. Similarly,
a diaryliodonium salt can transfer one of its aryl groups to
various nucleophiles to furnish arylated products, this be-
ing a result of their highly electron-deficient nature and the
excellent leaving ability of the aryl iodide.2,3 As such, several
methods for C-, N-, O- and S-arylations using diaryliodoni-
um salts as arylating reagents have been reported by sever-
al research groups.3 Most of the recent developments in
C-arylations have focused on coupling reactions of aromatic
nucleophiles such as electron-rich aromatic heterocycles
and naphthalene.4
Our investigation commenced with a set of experiments
to evaluate the arylation of 1-acetylindolin-3-one (1a), in
which the 1-acetyl protecting group is essential for its sta-
bilization, with diphenyliodonium triflate (2a) in order to
optimize the reaction conditions (Table 1). Initially, we ex-
amined a range of bases and solvents at 30 °C. It was found
that the desired monoarylated product 3aa could be ob-
tained in 58% yield together with small amounts of the di-
arylated product 4 (Figure 1) when using one equivalent of
Although C(sp3)-arylations of carbonyl compounds us-
ing hypervalent iodonium salts were reported in the early
1960s,5 interest in simple, mild and metal-free arylations
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2593–2597

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Table 1 Optimization of the Reaction Conditions for the Arylation of
Indolinonesa
Ph
N
A
O
Ac
O
1. MoO5, HMPA
MeOH
2. SnCl4
base (1 equiv)
[Ph2I]+X–
9%
O
Ph
+
N
solvent, 30 °C
N
Ac
Ac
1a
2
3aa
O
CHO
Ph
m-CPBA
CH2Cl2
Entry Base
X–
OTf
Solvent
Yield (%)b
[Ar2I]+X–
base
Ar
1
2
t-BuOK
THF
58
25%
N
N
N
D
Ac
Ac
Ac
KOH
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTs
BF4
PF6
Br
THF
45
B
3
K2CO3
THF
41
this work
ArPb(OAc)3
pyridine
4
NaOMe
THF
30
70%
O
5
NaHMDS
THF
35
6
Proton-sponge
DBU
THF
43
7
THF
43
N
8
DMAP
THF
trace
trace
56
Ar = 2,4-(MeO)2C6H3
C
Ac
9
Et3N
THF
Scheme 1 Different approaches toward the synthesis of 2-arylated in-
dolinones
10
11
12c
13
14
15
16
17
18d
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
MeOH
toluene
CH2Cl2
t-BuOH
THF
37
50
potassium tert-butoxide (t-BuOK) as the promoter and tet-
rahydrofuran as the solvent. Other alkali bases such as po-
tassium hydroxide (KOH), potassium carbonate (K2CO3), so-
dium methoxide (NaOMe), and sodium hexamethyldi-
silazide (NaHMDS) gave 3aa in slightly lower yields of 30–
45% under similar conditions (Table 1, entries 1–5).
trace
58
THF
55
THF
61
THF
57
OTf
THF
60
O
Ac
O
a Reaction conditions: 1a (0.2 mmol, 1.0 equiv), 2 (0.2 mmol, 1.0 equiv),
base (0.2 mmol, 1.0 equiv), solvent (2 mL), 30 °C, 10 h; unless otherwise
specified.
N
Ph
Ph
N
b Yield of isolated product.
N
c Organic dye 5 was isolated.
Ac
O
Ac
d Freshly sublimated t-BuOK was employed.
4
5
Figure 1 Byproducts 4 and 5
the diphenyliodonium species showed that the nature of
the counteranion did not have a significant influence on the
yield of the desired product (Table 1, entries 14–17).
A range of organic bases including triethylamine (Et3N),
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 4-(N,N-dimethyl-
amino)pyridine and Proton-sponge were screened, with the
results showing that the strong bases 1,8-diazabicy-
clo[5.4.0]undec-7-ene and Proton-sponge were effective in
the reaction, while almost no conversion was observed in
the presence of triethylamine and 4-(N,N-dimethylami-
no)pyridine in tetrahydrofuran as the solvent after 10 hours
(Table 1, entries 6–9).
Next, a solvent screen revealed that the conversion into
3aa was also efficient in methanol and dichloromethane
(Table 1, entries 10–13). However, a purple dye (5; Figure 1)
was also isolated, apparently via dimerization of 1a in di-
chloromethane. Furthermore, an evaluation of the anions of
It is worth noting that enol–keto tautomerism of 3aa to
give an equilibrium mixture with 3aa′ was observed by
1H NMR spectroscopy after a solution of 3aa had been al-
lowed to stand for a couple of hours (Scheme 2). The insta-
bility of 3aa might be the reason behind the generally low
yields of this arylation reaction. Furthermore, these find-
ings also hampered our initial target of achieving asymmet-
ric monoarylations of 1-acetylindolin-3-ones.
With optimized conditions in hand, we subsequently
examined the structural diversity of various iodonium salts
as coupling partners in the arylation of 1-acetylindolin-3-
one. As shown in Table 2, a wide variety of functionalities
with diverse electronic nature, such as electron-donating
methoxy and electron-withdrawing nitro groups on the ar-
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2595
Y. Zhang et al.
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used in the reaction. It was interesting to find that 2-nitro-
phenyl product 3an was isolated exclusively in 46% yield
(Table 2, entry 13). Unsymmetric [ArI(mesityl)]OTf trans-
ferred both the aryl and mesityl groups to give mixtures of
products in different ratios (Table 2, entries 14–17). Nota-
bly, in each case, mesitylated indolinone 3al was obtained
as the major product.
To further probe the scope of this reaction, a range of
substituted 1-acetylindolin-3-ones was phenylated under
the standard conditions with diphenyliodonium triflate
(Table 3). Generally, the conditions proved to be effective for
a variety of 1-acetylindolin-3-one derivatives bearing dif-
ferent substituents on the indolinone skeleton. Substituents
including halogens, methyl and methoxy groups on each
position of the benzene ring of the indolinone framework
were tolerated. The reactions gave the corresponding phe-
nylated products 3ba–ja in good yields ranging from 24–
70%.
To illustrate the scope for the potential utility of this re-
action, monosubstituted 1-acetyl-indolin-3-ones 4a,b were
phenylated with diphenyliodonium triflate (2a) to generate
products 5a,b, which possess quaternary carbon centers, in
quantitative yields (Scheme 3, eq. 1). Moreover, we per-
formed the vinylation and alkynylation of 1-acetylindolin-
3-one (1a) using iodonium salts 6 under the standard con-
ditions; only disubstituted products 7a and 7b were afford-
ed in 23% and 45% yield, respectively (Scheme 3, eq. 2). In-
spired by these results, a final set of investigations focused
on further transformation of mono-2-phenylated indolin-
3-one (3aa) was carried out. Specifically, we attempted the
alkylation of 3aa with allyl bromide and benzyl bromide,
and pleasingly found that these reactions under the opti-
mized conditions provided alkylated products 9a and 5b in
60% and 70% yield, respectively (Scheme 3, eq. 3).
In summary, we have developed a method for the 2-aryl-
ation of indolinone derivatives with diaryliodonium salts.
The procedure is tolerant of a variety of substituents, and
various monoarylated indolinones can be readily obtained
via this protocol.12 Moreover, the further transformation of
monoarylated indolinone derivatives with various electro-
philes has been demonstrated, which could provide an ac-
cess to bioactive compounds bearing the 2-arylated indoli-
none core.
O
OH
Ph
Ph
N
N
Ac
Ac
3aa
3aa'
Scheme 2 Enol–keto tautomerism of 3aa to give an equilibrium mix-
ture with 3aa′
omatic ring, were tolerated (Table 2, entries 1–10). Howev-
er, steric factors severely affected the reactivity: almost no
reaction took place with bis-(2,4,6-trimethyldiphenyl)iodo-
nium triflate as the arylating reagent (Table 2, entry 11).
When [(2-thienyl)2)I]OTs was employed under the standard
conditions, the heterocyclic thiophene ring was unfortu-
nately not transferred to furnish the desired product (3am).
Table 2 Scope of the Iodonium Salts in the Arylation of Indolinone 1aa
O
O
KOtBu (1 equiv)
THF, 30 °C
[Ar1IAr2]+X–
Ar1(/2)
+
N
N
Ac
Ac
3
1a
2
Entry Ar1
Ar2
X–
Product
Yield (%)b
1
2
4-MeC6H4
4-FC6H4
4-MeC6H4
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
PF6
3ab
3ac
3ad
3ae
3af
41
4-FC6H4
36
3
4-ClC6H4
4-BrC6H4
4-t-BuC6H4
4-MeOC6H4
2-MeC6H4
3-MeC6H4
3-FC6H4
4-ClC6H4
4-BrC6H4
4-t-BuC6H4
4-MeOC6H4
2-MeC6H4
3-MeC6H4
3-FC6H4
37
4
41
5
40
6
3ag
3ah
3ai
27
7
55
8
57
9
3aj
26
10
11
12
13
14
15
16
17
3-O2NC6H4
mesityl
3-O2NC6H4
mesityl
3ak
3al
50
OTf
OTs
OTf
OTf
OTf
OTf
OTf
trace
trace
46:0
5:10
12:17
12:21
6:10
2-thienyl
4-O2NC6H4
4-ClC6H4
4-BrC6H4
4-MeC6H4
3-MeC6H4
2-thienyl
4-MeOC6H4
mesityl
3am
3an/3ag
3ad/3al
3ae/3al
3ab/3al
3ai/3al
mesityl
Acknowledgment
mesityl
This work was supported by grants from the National Nature Science
Foundation of China (NSFC Nos. 21472213, 21202186), as well as by
the Croucher Foundation (Hong Kong) in the form of a CAS-Croucher
Foundation Joint Laboratory Grant and the Innovation Program of
Shanghai Municipal Education Commission (No. 14YZ144). This re-
search program was performed under the auspices of Professor Henry
N. C. Wong, whom we thank for helpful discussions and generous
support.
mesityl
a Reaction conditions: 1a (0.2 mmol), 2 (0.2 mmol, 1.0 equiv), t-BuOK (0.2
mmol, 1.0 equiv), THF (2 mL), 30 °C, 10 h.
b Yield of isolated product.
In connection with the influence of the electronic prop-
erties on the ability to transfer different aromatic rings, un-
symmetric 4-methoxy-4′-nitrodiphenyliodonium (2n) was
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2593–2597

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Y. Zhang et al.
Letter
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Table 3 Phenylation of Different Indolinone Derivatives under the Optimized Reaction Conditionsa,b
O
O
t-BuOK
Ph2I+–OTf
R
Ph
+
R
THF, 30 °C
N
N
Ac
Ac
1
3
2a
O
O
O
Me
Me
Ph
Ph
Ph
N
N
N
MeO
Ac
Ac
3da, 60%
Ac
Me
3ba, 37%
3ca, 47%
O
O
O
HO
Cl
Ph
Ph
Ph
N
N
N
Br
Ac
Ac
Ac
3ga, 57%
3fa, 70%
3ea, 24%
Cl
O
O
O
I
F
Ph
Ph
Ph
N
N
N
Ac
Ac
Ac
3ha, 52%
3ia, 48%
3ja, 59%
a Reaction conditions: 1 (0.2 mmol, 1.0 equiv), 2a (0.2 mmol, 1.0 equiv), t-BuOK (0.2 mmol, 1.0 equiv), THF (2 mL), 30 °C, 10 h.
b Yields are those of isolated products.
O
O
cinchonine (10 mol%)
R
KOH (1.5 equiv)
[Ph2I]+OTf-
R
+
Ph
(1)
(2)
(3)
N
N
toluene, r.t., 10 h
Ac
Ac
4a,b
2a
5a: R = Me, 98%
5b: R = Bn, 99%
O
O
R
X
KOtBu (1 equiv)
THF, r.t., 10 h
R
I
+
Ph
R
N
N
Ac
Ac
1a
6
7a: R = PhCH=CH-, X = OTf, 23%
7b: R = PhC C-, X = OTs, 45%
O
O
R
KOtBu (1 equiv)
THF, r.t.,10 h
Ph
Br
R
Ph
N
+
N
Ac
Ac
8
3aa
9a: R = CH2=CHCH2-, 60%
5b: R = Bn, 70%
Scheme 3 Related transformations with indolinone derivatives
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Supporting Information
(5) (a) Beringer, F. M.; Forgione, P. S.; Yudis, M. D. Tetrahedron
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S. A.; Rubin, G. J. Org. Chem. 1966, 31, 4315. (e) Ryan, J. H.; Stang,
P. J. Tetrahedron Lett. 1997, 38, 5061.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1560575.
S
u
p
p
ortiInfogrmoaitn
S
u
p
p
ortioInfgrmoaitn
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(12) Compounds 3ba−ja; General Procedure
Indolinone 1 (0.2 mmol, 1 equiv) and t-BuOK (22.4 mg, 0.2
mmol, 1.0 equiv) were added to a Schlenk tube. THF (2 mL) was
added using a syringe and the mixture was stirred for 15 min.
Next, iodonium salt 2 (0.0860 g, 0.2 mmol, 1.0 equiv) was added
and the mixture was stirred at 30 °C for 10 h. After cooling to
r.t., the solvent was removed in vacuo and the residue was puri-
fied over silica gel (EtOAc–hexane) to afford the desired prod-
uct. Analytical data for representative sample 3aa is provided
below.
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(e) Guo, F.; Han, J.; Mao, S.; Li, J.; Geng, X.; Yu, J.; Wang, L. RSC
Adv. 2013, 3, 6267.
1-Acetyl-2-phenylindolin-3-one (3aa)
Yield: 29.2 mg (58%); white solid; mp 125–128 °C. 1H NMR (300
MHz, CDCl3): δ = 8.67 (d, J = 7.8 Hz, 1 H), 7.80–7.65 (m, 2 H),
7.44–7.32 (m, 3 H), 7.30–7.22 (m, 3 H), 5.19 (s, 1 H), 2.05 (s,
3 H). 13C NMR (75 MHz, CDCl3): δ = 195.2, 169.5, 154.1, 137.8,
134.8, 129.7, 129.0, 126.0, 125.0, 123.0, 118.7, 107.9, 69.9, 24.8.
HRMS (ESI): m/z [M + H]+ calcd for C16H13NO2: 252.1025; found:
252.1025.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 2593–2597