1,2-Alkylarylation of Activated Alkenes with Two C-H Bonds by Using Visible-Light Catalysis

Article abstract of DOI:10.1055/s-0033-1340956

A new visible-light promoted strategy for the difunctionalization of activated alkenes with two C-H bonds has been developed. In the presence of [Ru(bpy)₃Cl₂], 4-MeOC₆H₄N ₂BF₄, Na₂CO₃ and 36 W compact fluorescent light, a variety of N-arylacrylamides underwent the 1,2-alkylarylation reaction with acetonitrile or acetone to give the corresponding functionalized oxindoles in moderate to good yields. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1340956

LETTER
▌1031
letter
1,2-Alkylarylation of Activated Alkenes with Two C–H Bonds by Using
Visible-Light Catalysis
1,2-Alkylarylation of Activated Alkenes
Jia-Ling Zhang, Yu Liu, Ren-Jie Song, Guo-Fang Jiang,* Jin-Heng Li*
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha
410082, P. R. of China
Fax +(86)73188713642; E-mail: jhli@hnu.edu.cn; E-mail: gfjiang@hnu.edu.cn
Received: 15.01.2014; Accepted after revision: 17.02.2014
CH2R4
R3
Abstract: A new visible-light promoted strategy for the difunction-
alization of activated alkenes with two C–H bonds has been devel-
oped. In the presence of [Ru(bpy)3Cl2], 4-MeOC6H4N2BF4, Na2CO3
and 36 W compact fluorescent light, a variety of N-arylacrylamides
underwent the 1,2-alkylarylation reaction with acetonitrile or ace-
tone to give the corresponding functionalized oxindoles in moderate
to good yields.
R3
Ru(bpy)3Cl2
visible light
H
CH2R4
+
O
4-MeOC6H4N2BF4
Na2CO3, 50 °C
Ar, 20 h
N
R2
O
R1
N
R1
R4 = CN, COMe
R2
Scheme 1 The 1,2-alkylarylation of alkenes
Key words: alkylarylation, alkenes, acetonitrile, acetone, visible-
light catalysis, oxindoles
Our investigation commenced with the reaction between
N-methyl-N-phenylmethacrylamide (1a) with acetonitrile
(2a; Table 1).10 Initially, the reaction of substrate 1a with
2a, 4-MeOC6H4N2BF4 (2 equiv.) and Na2CO3 (2 equiv.)
gave the desired product 3a in 36% yield (entry 1). The
yield decreased to 19% with the addition of 4-
MeOC6H4N2BF4 (1 equiv.) and no reaction was observed
in the absence of 4-MeOC6H4N2BF4 (entries 2 and 3). It
has been reported that 4-MeOC6H4N2BF4 could be readily
converted into an aryl radical by using visible-light catal-
ysis.7,8 As expected, the yield of product 3a dramatically
increased to 77% in the presence of [Ru(bpy)3Cl2] and vis-
ible light (entry 4). Subsequently, two other aryldiazoni-
um salts, 4-NO2C6H4N2BF4 and 4-BrC6H4N2BF4, were
examined, and the results showed that they were less effi-
cient than 4-MeOC6H4N2BF4 (entries 5 and 6). The reac-
tion did not take place without aryldiazonium salts or
bases (entries 7 and 8). A series of other bases, including
NaOAc, NaHCO3 and Et3N, were tested (entries 9–11) but
all were less active than Na2CO3, and the use of Et3N re-
sulted in no detectable product 3a. A study on the effect
of reaction temperature revealed that conducting the reac-
tion at 50 °C gave the best results (entries 4, 12 and 13).
The use of [Ir(ppy)3] or Eosin Y instead of [Ru(bpy)3Cl2]
was also evaluated (entries 14 and 15) and it was found
that the reaction was successful with both catalysts, but
Eosin Y was less active. It was noted that the reactivity of
substrate 1a decreased in the absence of either visible
light or visible-light catalysts (entries 16 and 17). In con-
trast to the results reported by the group of Fu, Fu and
Zhou,6m the product from diarylation of acrylamide 1a
with 4-MeOC6H4N2BF4, 3-(4-methoxybenzyl)-1,3-dime-
thylindolin-2-one, was observed as a side-product (<5%
yield) under the present reaction conditions; this is pre-
sumably because the present reaction was carried out un-
der basic conditions using highly reactive α-hydrogen-
atom-containing solvents.
Difunctionalization of alkenes has proven to be an effi-
cient and versatile synthetic approach to the construction
of a range of synthetic intermediates and important bioac-
tive compounds.1 As a result, the development of new
methods for alkene difunctionalization has been an active
area of research. Recent alkene difunctionalizations in-
volving C–H functionalization are particularly attractive
because of their efficiency and because prefunctionaliza-
tion processes can be avoided.2–6 However, available
methods for alkene difunctionalizations involving C–H
functionalization are still limited. Remarkably, methods
for the difunctionalization of alkenes with two C–H bonds
are quite rare and most focus on a C–H oxidative function-
alization strategy.2–5 For example, the group of Liu report-
ed the first oxidative arylalkylation of an activated alkene
with an aryl C(sp2)–H bond and an α-C(sp3)–H bond of al-
kyl nitriles by using the Pd(OAc)2/PhI(OAc)2 catalytic
system.2 Subsequently, the group of Guo and Duan,3 the
group of Liu,4 and our group5 independently employed
other C(sp3)–H bonds of ethers, aryl methanes and cy-
cloalkanes to react with alkenes followed by cyclization
with aryl C(sp2)–H bonds using peroxides. Nevertheless,
it would still be highly desirable to develop new alkene di-
functionalization methods by using the double C–H func-
tionalization strategy. Herein, we describe a new visible-
light catalysis strategy for the synthesis of functionalized
oxindoles through 1,2-alkylarylation of activated alkenes
with acetonitrile and aryl C(sp2)–H bonds (Scheme 1).7,8
In addition, this strategy can be expanded to acetone for
1,2-alkylarylation of activated alkenes. Notably, the oxin-
dole unit is a ubiquitous constituent in many natural prod-
ucts and bioactive molecules.9
SYNLETT 2014, 25, 1031–1035
Advanced online publication: 14.03.2014
DOI: 10.1055/s-0033-1340956; Art ID: ST-2014-W0037-L
© Georg Thieme Verlag Stuttgart · New York
With the optimal conditions in hand,10 a variety of N-aryl-
acrylamides 1b–r were then investigated to determine the
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

1032
J.-L. Zhang et al.
LETTER
scope of the 1,2-alkylarylation protocol (Scheme 2). In the gioselective isomers 3f in 70% total yield with 1.5:1 ratio.
presence of [Ru(bpy)3Cl2], 4-MeOC6H4N2BF4, Na2CO3 By using bulky N-methyl-N-o-tolylmethacrylamide, good
and 36 W compact fluorescent light, the reaction of N-Bn- yield of product 3g was still achieved. Both Cl or F groups
substituted substrate 1b was successful with acetonitrile could be tolerated (products 3j, 3k and 3n), thereby facil-
(2a) to give the desired product 3b in 61% yield. The re- itating additional modifications at the halogenated posi-
activity of N-Ac-substituted substrate 1c was less, and tion. We found that N-(2,3-dihydro-1H-inden-5-yl)-N-
only 21% yield of the corresponding product 3c was iso- methylmethacrylamide (1o) was viable for the reaction,
lated. However, N-phenylmethacrylamide 1d, with a free and a mixture of two regioselective isomers 3o was
N–H bond, was unreactive and no product 3d was ob- formed in 64% total yield with 1.6:1 ratio. The optimal
served. Gratifyingly, several substituents, including Me, conditions could also be applied to substrates with a Ph,
n-Bu, MeO, Cl, F, CF3 and SMe, on the aromatic ring of CH2OH or CH2OAc group at the 2-position of the acryl-
the N-aryl moiety were compatible with the optimal con- amide moiety (products 3p–r). However, the use of butyro-
ditions, and the reaction gave the expected products 3e–n. nitrile (2b) and 2-phenylacetonitrile (2c) instead of
For example, substrate 1e, with a p-Me group, underwent acetonitrile (2a) was not successful, and substrate 1a did
the reaction smoothly to afford 3e in good yield. Notably, not react with 2b under the optimal conditions (products
substrate 1f, with a m-Me group, gave a mixture of two re- 3s and 3t).
Table 1 Screening Optimal Conditionsa
CH2CN
[M]
visible light
+
H
CH2CN
2a
O
ArN2BF4, base
N
O
N
Me
1a
Me
3a
Entry
[M] (mol%)
ArN2BF4
Base
T (°C)
Yield (%)b,c
1d
2d,e
3d
4
–
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
–
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
–
50
50
50
50
50
50
50
50
50
50
50
25
80
50
50
50
50
36
19
0
–
–
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (5)
Ru(bpy)3Cl2 (2)
Ir(ppy)3 (5)
Eosin Y (5)
Ru(bpy)3Cl2 (5)
–
4-MeOC6H4N2BF4
4-NO2C6H4N2BF4
4-BrC6H4N2BF4
–
77
15
38
trace
0
5
6
7
8
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
4-MeOC6H4N2BF4
9
NaOAc
NaHCO3
Et3N
70
50
0
10
11
12
13
14
15
16d
17
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
trace
23
75
49
34
38
a Reaction conditions: 1a (0.3 mmol), 2a (1 mL), [M], 4-MeOC6H4N2BF4 (2 equiv), base (2 equiv), 36 W compact fluorescent light, argon at-
mosphere, 20 h.
b Some side products, including 3-(4-methoxybenzyl)-1,3-dimethylindolin-2-one (diarylation of acrylamide 1a with aryl diazonium salt) and
4,4′-dimethoxybiphenyl, were observed by GC-MS analysis.
c Isolated yield.
d Without additional light.
e 4-MeOC6H4N2BF4 (1 equiv) was used.
Synlett 2014, 25, 1031–1035
© Georg Thieme Verlag Stuttgart · New York

LETTER
1,2-Alkylarylation of Activated Alkenes
1033
Interestingly, this 1,2-alkylarylation protocol could be To help understand the mechanism of this 1,2-alkylaryla-
applied to acetone (2d; Scheme 3). Thus, treatment of tion protocol, the quantum yield was determined
N-methyl-N-phenylmethacrylamide (1a) with 2d, (Figure S1 in the Supporting Information). The quantum
[Ru(bpy)3Cl2], 4-MeOC6H4N2BF4, Na2CO3 and 36 W yield (Φx) was found to be approximately 0.099, suggest-
compact fluorescent light afforded the desired product 4a ing that the 1,2-alkylarylation protocol proceeded through
in 63% yield. The reactions with 2d were also successful a photoinduced mechanism.11
with substrates 1j and 1l, giving the corresponding prod-
ucts 4j and 4l in moderate yields. Unfortunately, attempts
at the 1,2-alkylarylation of 1a with other ketones, such as
acetylbenzene or cyclohexanone, failed.
Consequently, the mechanism outlined in Scheme 4 is
proposed.2–4 The 4-methoxyphenyl radical is readily
formed from 4-MeOC6H4N2BF4 under the action of the
base/[Ru(bpy)3Cl2]/visible-light system under heating.4,5
Subsequent selective hydrogen atom abstraction by the 4-
R5
R3
CHCN
Ru(bpy)3Cl2
visible light
R4
R3
R4
O
+
H
CH(R5)CN
2a
4-MeOC6H4N2BF4
Na2CO3, 50 °C
Ar, 20 h
N
R2
1
O
R1
N
R2
R1
CH2CN
CH2CN
R2 = Bn, 3b, 61%
R
R
2 = Ac, 3c, 21%
2 = H, 3d, trace
O
O
N
N
R2
Me
3e, 75%
CH2CN
CH2CN
CH2CN
+
O
O
O
N
N
N
Me
Me
Me
3f, 70% (1.5:1)
3g, 75%
CH2CN
CH2CN
CH2CN
Cl
MeO
n-Bu
O
O
O
N
N
N
Me
3j, 60%
Me
3i, 69%
Me
3h, 55%
CH2CN
CH2CN
CH2CN
F3C
F
O
O
O
N
N
N
Me
3m, 42%
CH2CN
Me
3l, 63%
Me
3k, 73%
SMe
CH2CN
CH2CN
O
O
+
O
N
N
N
Me
Cl
Me
Me
3n, 54%
3o, 64% (1.6:1)
R5
CHCN
CH2CN
CH2CN
CH2CN
HOH2C
AcOH2C
Ph
O
O
O
O
N
N
N
Me
N
Me
Me
Me
R5 = CH3(CH2)2, 3s, 0%
3p, 50%
3q, 54%
3r, 55%
R
5 = Ph, 3t, 0%
Scheme 2 Scope of the reaction with N-arylacrylamides 1. Reagents and conditions: 1 (0.3 mmol), 2a (1 mL), [Ru(bpy)3Cl2] (5 mol%), 4-
MeOC6H4N2BF4 (2 equiv), Na2CO3 (2 equiv), 36 W compact fluorescent light, argon atmosphere, 50 °C, 20 h.
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1031–1035

1034
J.-L. Zhang et al.
LETTER
Acknowledgment
O
We thank the Hunan Provincial Natural Science Foundation of Chi-
na (No. 13JJ2018), the Specialized Research Fund for the Doctoral
Program of Higher Education (No. 20120161110041), and the Na-
tural Science Foundation of China (No. 21172060) for financial
support.
Ru(bpy)3Cl2
visible light
O
+
4-MeOC6H4N2BF4
Na2CO3, 50 °C
Ar, 20 h
N
O
R1
O
2d
Me
1
N
R1
Me
4
O
O
O
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
Cl
F3C
References and Notes
O
O
O
N
N
N
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Me
Me
4l, 45%
Me
4a, 63%
4j, 53%
Scheme 3 1,2-Alkylarylation of alkenes (1) with acetone (2d)
methoxyphenyl radical from either CH3CN or cation rad-
ical A, which is generated in situ from CH3CN (2a)
through visible-light catalysis, yields the ·CH2CN radical.
Addition of the ·CH2CN radical to the activated alkene
gives radical intermediate B, intramolecular cyclization of
which then produces radical intermediate C. Finally, hy-
drogen atom abstraction from the CH3CN cation radical A
by radical intermediate C takes place to generate the
·CH2CN radical and product 3a. The ·CH2CN radical can
be formed directly from the reaction between CH3CN (2a)
and 4-methoxyphenyl radical in the presence of a base un-
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In summary, we have disclosed a new visible-light catal-
ysis strategy for the difunctionalization of activated al-
kenes with alkyl C(sp3)–H bonds (acetonitrile or acetone)
and aryl C(sp2)–H bonds. This strategy provides a new
route to functionalized oxindoles from N-arylacrylamides
and either acetonitrile or acetone. The measured quantum
yield for the process (Φx = 0.099) indicates that the 1,2-
alkylarylation protocol proceeds through a photoinduced
mechanism.
CH2CN
CH2CN
CH2CN
CH3CN
A
O
O
N
O
N
N
CH2CN
Me
Me
3a
Me
C
B
visible light
N
O
2+
2+
Ru(bpy)3
Ru(bpy)3
Me
1a
MeO
MeO
MeO
N2BF4
CH2CN
CH3CN
A
H
CH3CN
2a
MeO
3+
Ru(bpy)3
CH3CN
2a
+ N2 + base BF4
Δ
MeO
MeO
N2BF4
N2 + base BF4
Scheme 4 Possible mechanism
Synlett 2014, 25, 1031–1035
© Georg Thieme Verlag Stuttgart · New York

LETTER
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(10) 1,2-Alkylarylation of Activated Alkenes with
Acetonitrile; Typical Procedure: To a Schlenk tube were
added N-methyl-N-phenylmethacrylamide (1a; 0.3 mmol),
4-MeOC6H4N2BF4 (2 equiv), [Ru(bpy)3Cl2] (5 mol%),
Na2CO3 (2 equiv), and acetonitrile (2a; 1 mL). The tube was
charged with argon and the mixture was stirred at 50 °C (oil
bath temperature) under irradiation with a 36 W compact
fluorescent light for the indicated time until complete
consumption of starting material was observed (reaction
monitored by TLC and/or GC-MS analysis).Upon
completion, the reaction mixture was cooled to room
temperature, diluted in Et2O (3 mL), and washed with brine
(3 mL). The aqueous phase was re-extracted with Et2O
(3 mL) and the combined organic extracts were dried over
Na2SO4, concentrated in vacuum, and the resulting residue
was purified by silica gel column chromatography (hexane–
EtOAc, 5:1) to afford the desired product 3a.
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3-(1,3-Dimethyl-2-oxoindolin-3-yl)propanenitrile (3a):2
Brown oil. 1H NMR (400 MHz, CDCl3): δ = 7.34–7.30 (m,
1 H), 7.18 (d, J = 7.2 Hz 1 H), 7.11 (t, J = 7.6 Hz, 1 H), 6.88
(d, J = 7.6 Hz, 1 H), 3.22 (s, 3 H), 2.34–2.29 (m, 1 H), 2.11–
1.98 (m, 3 H), 1.39 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ
= 178.8, 143.1, 131.6, 128.6, 123.0, 122.6, 118.8, 108.5,
47.3, 33.4, 26.3, 23.4, 12.8. MS (EI, 70 eV): m/z (%) = 214
(37) [M]+, 161 (35), 160 (100).
(8) For pioneering papers on the use of aryldiazonium salts in
organic synthesis, see: (a) Sandmeyer, T. Ber. Dtsch. Chem.
Ges. 1884, 17, 1633. (b) Sandmeyer, T. Ber. Dtsch. Chem.
(11) (a) Gorner, H.; Khun, H. J. J. Chem. Soc., Perkin Trans. 2
1999, 2671. (b) Pelliccioli, A. P.; Wirz, J. Photochem.
Photobiol. Sci. 2002, 1, 441.
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Synlett 2014, 25, 1031–1035

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