Tert-Butoxide-Mediated Arylation of 2-Substituted Cyanoacetates with Diaryliodonium Salts

Article abstract of DOI:10.1002/adsc.201501013

A transition metal-free direct arylation of 2-substituted cyanoacetates with diaryliodonium salts was developed. With this approach, a wide range of α-tolunitrile derivatives has been synthesized in good to excellent yields of 45-92%. Furthermore, the practicability of this approach is further manifested in the synthesis of a related bioactive agent of glutarimide.

Full text of DOI:10.1002/adsc.201501013

FULL PAPERS
DOI: 10.1002/adsc.201501013
tert-Butoxide-Mediated Arylation of 2-Substituted Cyanoacetates
with Diaryliodonium Salts
Xiaofei Qian,a Jianwei Han,b,* and Limin Wanga,*
a
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and
Technology, 130 Meilong Road, Shanghai 200237, Peopleꢀs Republic of China
Fax: (+86)-21-6425-3881, phone: (+86)-21-6425-3881; e-mail: wanglimin@ecust.edu.cn
Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry, The Chinese
b
Academy of Sciences, 345 Ling Ling Road, Shanghai 200237, Peopleꢀs Republic of China
Fax: (+86)-21-5492-5383; e-mail: jianweihan@sioc.ac.cn
Received: November 4, 2015; Revised: December 23, 2015; Published online: February 17, 2016
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201501013.
Abstract: A transition metal-free direct arylation of in the synthesis of a related bioactive agent of glu-
2-substituted cyanoacetates with diaryliodonium salts tarimide.
was developed. With this approach, a wide range of
a-tolunitrile derivatives has been synthesized in good
to excellent yields of 45–92%. Furthermore, the Keywords: a-arylacetonitriles; arylation; diaryliodo-
practicability of this approach is further manifested nium salts; metal-free conditions; nitriles
Introduction
coupling reaction between aryl halides and simple 2-
alkylcyanoacetates such as ethyl 2-methylcyanoace-
Nitriles are valuable synthons that can serve as pre- tate proved to be a practically difficult task with these
cursors to amines, carboxylic acids, carboxamides, al- catalytic systems.[5c]
dehydes, ketones, and even hetercycles.[1] Further-
Recently, our laboratory has reported the metal-
more, over 50 nitrile-containing agents are prescribed free C-arylation of tetrahydrocarbazoles, pyrazolin-5-
for either medicinal indications as pharmaceuticals or ones and 1-acetylindolin-3-ones.[6] In recent years,
undergoing clinical development.[2] Particularly, a- other valuable nucleophiles such as ethyl acetoace-
arylacetonitriles containing the nitrile group on a qua-
ternary carbon adjacent to an aromatic ring, are struc-
turally interesting in medical research. For example,
anastrazole, verapamil, and piritramide are widely
prescribed for treating estrogen-dependent breast
cancer, angina and postoperative pain, respectively.[3]
Cilomilast is one of the well studied nitrile-containing
leads as an anti-inflammatory and antiasthmatic agent
(Figure 1).[4]
With regard to the preparation of versatile synthons
of 2-alkyl-2-arylcyanoacetates, several powerful ap-
proaches essentially involving transition metal (such
as palladium or copper) catalyzed a-arylation of 2-cy-
anoacetate esters with aryl halides, are well record-
ed.[5] But the requirement of heavy metals with spe-
cial ligands in these arylation reactions limits the
practical applications due to the major problems
caused by purification and economic cost. Further-
more, functional group tolerance in these catalytic
systems with labile metal-phosphine complexes also
Figure 1. Selected examples of pharmaceutical agents con-
received much consideration.[5] Notably, the direct taining a-arylacetonitriles.
940
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2016, 358, 940 – 946

FULL PAPERS
tert-Butoxide Mediated Arylation of 2-Substituted Cyanoacetates
tates, azlactones and nitro compounds were arylated well in dichloromethane (CH2Cl2), which give 3a in
using diaryliodonium salts in a basic reaction environ- a high yield of 92% (Table 1, entry 5). Screening vari-
ment.[7] Very recently, Gaunt reported two cases of ous bases revealed that strong base potassium tert-
the fluoride counteranion within the diaryliodonium butoxide in CH2Cl2 delivered the desired product 3a
salts triggered C-arylation of a-cyano-a-phenyl esters in the most efficient manner (Table 1, entries 5–9).
in good yields under metal-free reaction conditions.[8] We also tried the reaction under air conditions, the
In the context of our general interest in the synthesis yield of 3a was slightly decreased (Table 1, entry 10).
of medically useful compounds by arylation of nucleo- Furthermore, we evaluated different anions of the di-
philes using iodonium salts, we were intrigued by the phenyliodonium salts, a negligible influence was ob-
possibility of metal-free arylation towards nitrile-con- served on the yield of desired product of 3a (Table 1,
taining 2-arylcyanoacetates. Herein we present the entries 11–13).
potassium tert-butoxide-mediated arylation of 2-sub-
With the optimal conditions established, we subse-
stiuted cyanoacetates, giving an efficient access to 2- quently examined various diaryliodonium salts as ary-
arylcyanoacetates.
lation partners. Generally, as shown in Table 2, this
reaction system could tolerate a variety of functional
groups on the diphenyliodonium salts, and the reac-
tions were completed in the short time of fifteen mi-
nutes as determined by thin-layer chromatography.
Results and Discussion
We began our study using diphenyliodonium triflate For symmetrical diaryliodonium salts, the reaction
(2a) and ethyl 2-methylcyanoacetate (1a) to optimize was significantly affected by the electronic nature of
the conditions (Table 1). We were pleased to find that the aromatic rings (Table 2, entries 1–11). It was ob-
the reaction gave the desired product ethyl 2-cyano-2- served that diaryliodonium salts bearing electron-do-
phenylpropanoate (3a) in 70% yield in the presence nating substituents, such as methoxy, alkyl and halo
of potassium tert-butoxide as the base and toluene as groups on the phenyl ring, favoured the reaction in
solvent at 08C. As shown in Table 1, after examining terms of isolated yields of desired products. While
several solvents, it is found that the reaction worked substrates with electron-withdrawing groups ester or
Table 1. Screening of reaction conditions for the arylation of
Table 2. Scope of iodonium salts in the arylation of ethyl 2-
ethyl 2-methylcyanoacetate.[a]
methylcyanoacetate.[a]
Entry
X[b]
Base
Solvent
Yield [%][c]
70
Entry Ar1(Ar2)
X[b] Product Yield [%][c]
1
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTs
BF4
PF6
t-BuOK
t-BuOK
t-BuOK
t-BuOK
t-BuOK
K2CO3
toluene
DCE
MeCN
THF
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
1
(4-t-BuC6H4)2
OTf 3b
OTf 3c
OTf 3d
OTf 3e
OTf 3f
OTf 3g
PF6 3h
PF6 3i
BF4 3j
BF4 3k
PF6 3l
OTf 3a
73
86
90
65
85
77
34
43
83
68
72
68
51
32
64
2[d]
3
46
58
33
92
40
64
68
30
75
84
90
91
2
3
4
(4-MeC6H4)2
(4-MeOC6H4)2
(4-FC6H4)2
4
5
6
7
8
9
5
(4-ClC6H4)2
6
(4-BrC6H4)2
NaOH
NaH
7
8
9
10
11
12
13
14
15
(3-CO2EtC6H4)2
(3-NO2C6H4)2
(4-CF3C6H4)2
(3,4-Cl2C6H3)2
(2,4-Me2C6H3)2
Ph (mesityl)
4-CO2EtC6H4 (mesityl) OTf 3m
3-CO2EtC6H4 (mesityl) OTf 3h
4-BrC6H4 (mesityl)
DMAP
t-BuOK
t-BuOK
t-BuOK
t-BuOK
10[e]
11
12
13
[a]
Unless otherwise specified, reaction conditions: 1a
(0.5 mmol), 2 (0.55 mmol, 1.1 equiv.), base (0.55 mmol,
1.1 equiv.) and solvent (2 mL); 08C; 15 min; under nitro-
gen.
OTf=trifluoromethansulfonate;
nate.
Isolated yield.
DCE=1,2-dichloroethane.
Under air.
OTf 3g
[a]
Unless otherwise specified, reaction conditions: 1a
(0.5 mmol), diaryliodonium salt (0.55 mmol, 1.1 equiv.),
base (0.55 mmol, 1.1 equiv.) and solvent (2 mL); 08C;
15 min; under nitrogen.
OTf=trifluoromethansulfonate;
nate.
[b]
OTs=4-toluenesulfo-
[c]
[d]
[e]
[b]
[c]
OTs=4-toluenesulfo-
Isolated yield.
Adv. Synth. Catal. 2016, 358, 940 – 946
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
941

FULL PAPERS
Xiaofei Qian et al.
Table 3. Arylation of 2-substituted cyanoacetates 1.[a,b]
nitro groups on the meta-position of benzene ring,
gave relatively low yields of 34% and 43%, respec-
tively (Table 2, entries 7 and 8). For the unsymmetri-
cal diaryliodonium salts, [Ar-I-mesityl]OTf, to test the
steric effect on the reactivity, as expected,[9] the less
sterically demmanding aromatic group Ar was trans-
ferred preferably to the desired products of 3. No me-
sitylated product 3 was observed (Table 2, entries 12–
15). In comparison with the iodonium salt [4-
CO2EtC6H4-I-Mesityl]OTf bearing an ester group on
the para-position, the ester groups on the meta-posi-
tion of diaryliodonium salt gave a relative low yield
(32% yield of 3h vs. 51% yield of 3m; Table 2, en-
tries 13 and 14).
To further investigate the scope of this reaction,
a variety of ethyl cyanacetate derivatives were pheny-
lated in the presence of potassium tert-butoxide at the
temperature of 08C. These conditions proved to be ef-
ficient in the phenylation as shown in Table 3. Gener-
ally, 2-phenyl-2-alkylcyanoacetates 4 were obtained in
excellent yields of 77–92% when the R of 1 is alkyl
(Table 3, entries 1–7). Among them, when R is fluo-
roalkyl or allyl, 4e and 4f can be furnished in good
yields of 81% and 77%, respectiviely. Moreover,
when 1 bearing benzyl and aromatic rings were em-
ployed, the phenylated products 4h–4n were readily
prepared in the good yields of 65–82% (Table 3, en-
tries 8–14). When R of 1 is phenacyl, the phenylation
product 4o was provided in a moderate yield of 45%
(Table 3, entry 15).
Although it is difficult to draw a precise mechanism
at this stage, according to the previous reports, the
metal-free arylation using diaryliodonium salts can
proceed either through an SET mechanism[10a] or via
a ligand exchange pathway.[10b,c] Therefore, as shown
in Scheme 1, deprotonation of 1a by t-BuOK generat-
ed 5 and/or the corresponding enolate 6 in the basic
environment. Two pathways via different intermedi-
ates 7 or 8 by electronic attack with diaryliodonium
salts could give the final product 3a along with an aryl
iodide, respectively.
[a]
[b]
Unless otherwise specified, reaction conditions:
(0.5 mmol), diphenyliodonium salt (0.55 mmol,
1.1 equiv.), base (0.55 mmol, 1.1 equiv.) and solvent
(2 mL); 08C; 15 min; under nitrogen.
Isolated yield.
1
Finally, utilization of the arylation for conversion of
the products into useful molecules was attempted
(Scheme 2). Glutarimides were reported to possess
neuroplegic, immunomodulatory and anticancer activ-
ity.[11] According to the reported synthetic route,[12] 2-
phenylbutanenitrile is an important intermediate to
prepare glutethimide. The direct arylation of alkyl ni-
triles had been attempted firstly, while it led to the
decomposition of the diaryliodonium salts, no aryla-
tion product was observed. Hence, the arylation of
methyl 2-cyanobutanoate 9 was conducted under the
standard conditions. The desired product 10 was ob-
tained in the yield of 84%. The decarboxylation of 10
delivered the key intermediate 11 in 92% yield. The
further synthetic procedure involving Michael addi-
tion with acrylic ester, two steps of hydrolysis and cyc- Scheme 1. Proposed mechanism.
942
asc.wiley-vch.de
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2016, 358, 940 – 946

FULL PAPERS
tert-Butoxide Mediated Arylation of 2-Substituted Cyanoacetates
Institute of Organic Chemistry. Column chromatography
was performed on silica gel (Huang-hai, 300–400 mesh).
Typical Procedure for Arylation of 2-Substiuted
Cyanoacetates
An oven-dried Schlenk tube was charged with 2-substituted
cyanoacetate (0.5 mmol, 1 equiv.), the tube was evacuated
and backfilled with nitrogen, then 2 mL anhydrous CH2Cl2
and potassium tert-butoxide (61.7 mg, 0.55 mmol, 1.1 equiv.)
were added, the mixture was stirred at 08C for 5 min. The
solution of diaryliodonium salt (0.55 mmol, 1.1 equiv.) in
2 mL anhydrous CH2Cl2 was added through a syringe subse-
quently for 5 min. the reaction was stirred for another
15 min. The reaction mixture was quenched with 20 mL
water, and then extracted with ethyl acetate (30 mL). The
combined extracts were washed with brine, dried over
Na2SO4 and filtered. After the solvent was removed under
vacuum, the residue was purified by flash chromatography
to give the desired product.
Scheme 2. Synthesis of glutethimide.
Ethyl 2-cyano-2-phenylpropanoate (3a):[5c] Colorless oil;
1
yield: 93.5 mg (92%). H NMR (400 MHz, CDCl3): d=7.54–
7.52 (m, 2H), 7.43–7.35 (m, 3H), 4.30–4.17 (m, 2H), 1.95 (s,
3H), 1.25 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3):
d=167.9, 135.8, 129.2 128.8, 125.7, 119.6, 63.3, 48.3, 24.9,
13.8.
lization gave the final product of 13 for which the an-
alytical data corresponded to those in the litera-
ture.[12,13]
Ethyl 2-(4-tert-butylphenyl)-2-cyanopropanoate (3b): Col-
orless oil; yield: 94.6 mg (73%). 1H NMR (400 MHz,
CDCl3): d=7.46–7.40 (m, 4H), 4.29–4.19 (m, 2H), 1.94 (s,
3H), 1.32 (s, 9H), 1.27 (t, J=7.2 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=168.1, 151.9, 132.8, 126.1, 125.5,
119.7, 63.2, 47.9, 34.6, 31.2, 24.9, 13.8; HR-MS (EI): m/z=
259.1574, calcd. for C16H21NO2 [M]+: 259.1572.
Conclusions
In summary, we have demonstrated a direct arylation
of ethyl 2-cyanobutanoate derivatives by using diary-
liodonium salts under transition metal-free conditions.
The synthetic method was extended to substrates
bearing a variety of functional groups. As such, vari-
ous 2-substituted a-arylacetonitriles were prepared in
good yields, which are valuable chemical intermedi-
ates in medical research. Furthermore, glutethimide
was prepared by using this approach as the key step,
which demonstrates the potential applications of this
method in organic synthesis.
Ethyl 2-cyano-2-p-tolylpropanoate (3c):[15a] Colorless oil;
1
yield: 93.4 mg (86%). H NMR (400 MHz, CDCl3): d=7.42–
7.40 (m, 2H), 7.21 (d, J=8.2 Hz, 2H), 4.27–4.18 (m, 2H),
2.36 (s, 3H), 1.93 (s, 3H), 1.25 (t, J=7.2 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=168.1, 138.8, 132.9, 129.8, 125.6,
119.7, 63.2, 47.9, 24.8, 21.0, 13.8.
Ethyl 2-cyano-2-(4-methoxyphenyl)propanoate (3d):[15a]
Colorless oil; yield: 105.0 mg (90%). 1H NMR (400 MHz,
CDCl3) d=7.47–7.43 (m, 2H), 6.94–6.90 (m, 2H), 4.27–4.19
(m, 2H), 3.81 (s, 3H), 1.93 (s, 3H), 1.25 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=168.2, 159.9, 127.7, 127.0,
119.81, 114.4, 63.2, 55.4, 47.6, 24.8, 13.8.
Ethyl 2-cyano-2-(4-fluorophenyl)propanoate (3e):[15a] Col-
orless oil; yield: 71.9 mg (65%). 1H NMR (400 MHz,
CDCl3): d=7.54–7.51 (m, 2H), 7.13–7.08 (m, 2H), 4.29–4.20
(m, 2H), 1.95 (s, 3H), 1.26 (t, J=7.2 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=167.8, 162.8 (d, J=247.3 Hz), 131.6
(d, J=3.4 Hz), 127.8 (d, J=8.4 Hz), 119.4, 116.1 (d, J=
22.0 Hz), 63.4, 47.7, 24.8, 13.8.
Experimental Section
General Methods
All reagents were obtained from commercial sources with-
out further purification and the solvents were purified by
standard techniques. The diaryliodonium salts were pre-
pared according to the literature report.[14] All reactions
were performed in oven-dried glassware containing
a Teflon-coated stirrer bar and dry septum under a nitrogen
atmosphere. 1H NMR and 13C NMR spectra were respec-
tively recorded at 400 and 100 MHz, using tetramethylsilane
as an internal reference. Chemical shifts (d) and coupling
constants (J) were expressed in parts per million and hertz,
respectively. High-resolution mass spectrometry (HR-MS)
was performed on an EI-TOF spectrometer. Mass spectra
were recorded by the mass spectrometry service of Shanghai
Ethyl 2-(4-chlorophenyl)-2-cyanopropanoate (3f):[5c] Col-
orless oil; yield: 101.0 mg (85%). 1H NMR (400 MHz,
CDCl3): d=7.50–7.48 (m, 2H), 7.40–7.38 (m, 2H), 4.31–4.18
(m, 2H), 1.94 (s, 3H), 1.26 (t, J=7.2 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=167.6, 135.0, 134.3, 129.3, 127.3,
119.2, 63.5, 47.8, 24.8, 13.8.
Ethyl 2-(4-bromophenyl)-2-cyanopropanoate (3g): Color-
1
less oil; yield: 108.6 mg (77%). H NMR (400 MHz, CDCl3):
d=7.56–7.53 (m, 2H), 7.43–7.40 (m, 2H), 4.31–4.18 (m,
2H), 1.94 (s, 3H), 1.26 (t, J=7.2 Hz, 3H); 13C NMR
Adv. Synth. Catal. 2016, 358, 940 – 946
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
943

FULL PAPERS
Xiaofei Qian et al.
(101 MHz, CDCl3): d=167.6, 134.8, 132.3, 127.6, 123.2,
119.1, 63.5, 47.9, 24.8, 13.8; HR-MS (EI): m/z=281.0056,
calcd. for C12H12BrNO2 [M]+: 281.0051.
2.81 (dt, J=13.4, 6.8 Hz, 1H), 1.26–1.22 (m, 6H), 0.80 (d,
J=6.8 Hz, 3H); 13C NMR (101 MHz, CDCl3): d=167.8,
133.9, 129.0, 128.8, 126.5, 116.8, 63.0, 61.1, 36.1, 19.4, 17.3,
13.9; HR-MS (EI): m/z=231.1260, calcd. for C14H17NO2
[M]+: 231.1259.
Ethyl 3-(2-cyano-1-ethoxy-1-oxopropan-2-yl) benzoate
(3h): Colorless oil; yield: 46.8 mg (34%). 1H NMR
(400 MHz, CDCl3): d=8.19 (t, J=1.8 Hz, 1H), 8.08 (ddd,
J=7.8, 5.0, 1.6 Hz, 1H), 7.75 (ddd, J=8.0, 2.0, 1.0 Hz, 1H),
7.52 (dd, J=9.8, 5.8 Hz, 1H), 4.43–4.38 (m, 2H), 4.30–4.22
(m, 2H), 2.00 (s, 3H), 1.41 (t, J=7.2 Hz, 3H), 1.27 (t, J=
7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3): d=167.6, 165.7,
136.3, 131.6, 130.3, 130.0, 129.3, 126.8, 119.2, 63.5, 61.4, 48.1,
24.7, 14.3, 13.8; HR-MS (EI): m/z=275.1159, calcd. for
C15H17NO4 [M]+: 275.1158.
Ethyl 2-cyano-2-phenylhexanoate (4c): Colorless oil;
yield: 112.8 mg (92%).1H NMR (400 MHz, CDCl3): d=
7.56–7.53 (m, 2H), 7.43–7.34 (m, 3H), 4.30–4.16 (m, 2H),
2.41–2.22 (m, 1H), 2.15–2.07(m, 1H), 1.42–1.35 (m, 4H),
1.25 (t, J=7.2 Hz, 3H), 0.91 (t, J=7.2 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=167.7, 134.8, 129.1, 128.8, 125.7,
118.5, 63.1, 54.2, 37.9, 27.6, 22.4, 13.8 (d, J=8.7 Hz); HR-MS
(EI): m/z=245.1415, calcd. for C15H19NO2 [M]+: 245.1416.
Ethyl 5-chloro-2-cyano-2-phenylpentanoate (4d): Color-
Ethyl 2-cyano-2-(3-nitrophenyl)propanoate (3i): Colorless
1
1
oil; yield: 53.4 mg (43%). H NMR (400 MHz, CDCl3): d=
less oil; yield: 112.9 mg (85%). H NMR (400 MHz, CDCl3):
8.41 (t, J=2.0 Hz, 1H), 8.27 (ddd, J=8.2, 2.2, 1.0 Hz, 1H),
7.94 (ddd, J=8.0, 2.0, 1.0 Hz, 1H), 7.66 (t, J=8.2 Hz, 1H),
4.36–4.23 (m, 2H), 2.04 (s, 3H), 1.29 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=167.0, 148.6, 137.8, 132.2,
130.4, 124.0, 121.2, 118.5, 63.9, 48.0, 24.8, 13.8; HR-MS (EI):
m/z=248.0789, calcd. for C12H12N2O4 [M]+: 248.0797..
d=7.59–7.50 (m, 2H), 7.48–7.33 (m, 3H), 4.37–4.12 (m,
2H), 3.56 (t, J=6.4 Hz, 2H), 2.52 (ddd, J=13.8, 11.8,
4.6 Hz, 1H), 2.33 (ddd, J=13.8, 12, 4.6 Hz, 1H), 2.02–1.79
(m, 2H), 1.24 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz,
CDCl3): d=167.3, 134.1, 129.3, 129.1, 126.0, 118.1, 63.4, 53.6,
44.0, 35.5, 28.4, 13.8; HR-MS (EI): m/z=265.0872, calcd. for
C14H16ClNO2 [M]+: 265.0870.
Ethyl
2-cyano-2-[4-(trifluoromethyl)phenyl]propanoate
(3j): Colorless oil; yield: 112.5 mg (83%). 1H NMR
(400 MHz, CDCl3): d=7.70 (s, 4H), 4.34–4.21 (m, 2H), 2.00
(s, 3H), 1.28 (t, J=7.1 Hz, 3H).13C NMR (101 MHz,
CDCl3): d=167.3, 139.7, 131.1 (q, J=32.9 Hz), 126.4, 126.1
(q, J=3.7 Hz), 123.7 (q, J=273.3 Hz), 118.8, 63.6, 48.2, 24.8,
13.7; HR-MS (EI): m/z=272.0904, calcd. for C13H12F3NO2
[M+H]+: 272.0898.
Ethyl 2-cyano-2-(3,4-dichlorophenyl)propanoate (3k):
Colorless oil; yield: 92.5 mg (68%). 1H NMR (400 MHz,
CDCl3): d=7.64 (d, J=2.4 Hz, 1H), 7.50 (d, J=8.6 Hz, 1H),
7.39 (dd, J=8.6, 2.4 Hz, 1H), 4.33–4.20 (m, 2H), 1.95 (s,
3H), 1.28 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3):
d=167.2, 135.8, 133.4, 131.1, 128.0, 125.4, 118.7, 63.7, 47.6,
24.7, 13.8; HR-MS (EI): m/z=271.0168, calcd. for
C12H11Cl2NO2 [M]+: 271.0167.
Ethyl
2-cyano-5,5,6,6,7,7,8,8,8-nonafluoro-2-phenylocta-
noate (4e): Colorless oil; yield: 176.3 mg (81%). 1H NMR
(400 MHz, CDCl3): d=7.56–7.53 (m, 2H), 7.48–7.40 (m,
3H), 4.33–4.20 (m, 2H), 2.68 (td, J=13.2, 4.2 Hz, 1H), 2.47
(td, J=13.2, 4.2 Hz, 1H), 2.31–2.21 (m, 1H), 2.20–2.05 (m,
1H), 1.25 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3):
d=166.6, 133.3, 129.5 (d, J=10.2 Hz), 125.8, 120.2 (t, J=
32.2 Hz), 118.7 (t, J=33.5 Hz), 117.9–117.3 (m), 115.9 (t, J=
33.1 Hz), 112.9–107.7 (m), 63.7, 52.9, 29.1, 27.4 (t, J=
22.4 Hz), 13.6; 19F NMR (376 MHz, CDCl3): d=À81.31 (d,
J=8.8 Hz, 3F), À114.35 to À114.43 (m, 2F), À124.27 (d, J=
4.6 Hz, 2F), À126.22 to À126.30 (m, 2F); HR-MS (EI):
m/z=435.0882, calcd. for C17H14F9NO2 [M]+: 435.0881.
Ethyl 2-cyano-2-phenylpent-4-enoate (4f):[5c] Colorless oil;
yield: 88.3 mg (77%). H NMR (400 MHz, CDCl3): d=7.57–
1
Ethyl 2-cyano-2-(2,4-dimethylphenyl)propanoate (3l):
Colorless oil; yield: 83.3 mg (72%).1H NMR (400 MHz,
CDCl3): d=7.26 (t, J=6.8 Hz, 1H), 7.07- 7.04 (m, 2H),
4.31–4.24 (m, 2H), 2.36 (s, 3H), 2.31 (s, 3H), 2.03 (s, 3H),
1.28 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3): d=
169.4, 138.8, 136.3, 133.0, 130.6, 127.3, 126.0, 119.6, 63.2,
46.6, 23.9, 20.9, 19.9, 13.9; HR-MS (EI): m/z=231.1260,
calcd. for C14H17NO2 [M]+: 231.1259..
7.53 (m, 2H), 7.43–7.35 (m, 3H), 5.80–7.70 (m, 1H), 5.29–
5.21 (m, 2H), 4.30–4.17 (m, 2H), 3.12 (dd, J=14.0, 7.4 Hz,
1H), 2.85 (dd, J=14.0, 7.0 Hz, 1H), 1.24 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3) d=167.1, 134.1, 130.7, 129.2,
128.9, 126.2, 121.2, 118.0, 63.2, 54.13, 42.3, 13.9.
Ethyl 2-cyano-2-cyclohexyl-2-phenylacetate (4g): Color-
1
less oil; yield: 108.6 mg (80%). H NMR (400 MHz, CDCl3):
d=7.54 (d, J=7.2 Hz, 2H), 7.30 (dd, J=16.4, 8.6 Hz, 3H),
4.19–4.05 (m, 2H), 2.35 (t, J=11.0 Hz, 1H), 1.75 (d, J=
10.4 Hz, 2H), 1.60 (d, J=8.8 Hz, 2H), 1.41 (d, J=11.8 Hz,
1H), 1.27 (d, J=11.2 Hz, 1H), 1.29–1.00 (m, 7H); 13C NMR
(101 MHz, CDCl3): d=167.7, 133.4, 129.0, 128.7, 126.6,
117.3, 63.0, 60.5, 45.3, 29.8, 27.2, 26.0 (d, J=8.7 Hz), 25.8,
13.9; HR-MS (EI): m/z=271.1573, calcd. for C17H21NO2
[M]+: 271.1572.
Ethyl
4-(2-cyano-1-ethoxy-1-oxopropan-2-yl)benzoate
(3m):[15b] Colorless oil; yield: 70.2 mg (51%). 1H NMR
(400 MHz, CDCl3): d=8.10 (d, J=8.6 Hz, 2H), 7.63 (d, J=
8.6 Hz, 2H), 4.40 (q, J=7.2 Hz, 2H), 4.30–4.22 (m, 2H),
1.99 (s, 3H), 1.41 (t, J=7.2 Hz, 3H), 1.26 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=167.4, 165.7, 140.3, 131.1,
130.3, 125.9, 119.0, 63.5, 61.3, 48.4, 24.8, 14.3, 13.8.
Ethyl 2-cyano-2-phenylbutanoate (4a):[5c] Colorless oil;
Ethyl 2-cyano-2,3-diphenylpropanoate (4h):[5c] Colorless
1
1
yield: 90.2 mg (83%). H NMR (400 MHz, CDCl3): d=7.56–
oil; yield: 114.5 mg (82%). H NMR (400 MHz, CDCl3): d=
7.53 (m, 2H), 7.43–7.34 (m, 3H), 4.30–4.17 (m, 2H), 2.43
(dq, J=14.6, 7.4 Hz, 1H), 2.17 (dq, J=14.8, 7.4 Hz, 1H),
1.25 (t, J=7.2 Hz, 3H), 1.07 (t, J=7.4 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=167.6, 134.5, 129.1, 128.8, 126.1,
118.3, 63.1, 55.1, 31.6, 13.8, 9.8.
7.55–7.53 (m, 2H), 7.39–7.37 (m, 3H), 7.25–7.23 (m, 3H),
7.17–7.14 (m, 2H), 4.25–4.15 (m, 2H), 3.70 (d, J=13.6 Hz,
1H), 3.32 (d, J=13.6 Hz, 1H), 1.18 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=167.4, 134.5, 134.2, 130.5,
129.1, 129.0, 128.4, 127.8, 126.4, 118.0, 63.3, 55.83, 44.2, 13.8.
Ethyl 2-cyano-2-phenyl-3-p-tolylpropanoate (4i): Colorless
Ethyl 2-cyano-3-methyl-2-phenylbutanoate (4b): Colorless
1
1
oil; yield: 92.5 mg (80%). H NMR (400 MHz, CDCl3): d=
oil; yield: 115.9 mg (79%). H NMR (400 MHz, CDCl3): d=
7.63–7.61 (m, 2H), 7.42–7.36 (m, 3H), 4.30–4.13 (m, 2H),
7.54 (dd, J=8.0, 1.6 Hz, 2H), 7.38–7.36 (m, 3H), 7.04 (s,
944
asc.wiley-vch.de
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2016, 358, 940 – 946

FULL PAPERS
tert-Butoxide Mediated Arylation of 2-Substituted Cyanoacetates
4H), 4.23–4.15 (m, 2H), 3.66 (d, J=13.6 Hz, 1H), 3.27 (d,
J=13.6 Hz, 1H), 2.28 (s, 3H), 1.18 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=167.4, 137.4, 134.5, 131.1,
130.3, 129.1, 129.1, 128.9, 126.4, 118.1, 63.3, 56.0, 43.8, 21.2,
13.8; HR-MS (EI): m/z=293.1417, calcd. for C19H19NO2
[M]+: 293.1416.
nyliodonium salt (21.51 g, 55 mmol, 1.1 equiv.) in 100 mL an-
hydrous CH2Cl2 was added subsequently for about 15 min.
After being stirred for another 30 min the reaction mixture
was poured into 200 mL H2O and then extracted with ethyl
acetate. The combined extracts were washed with brine,
dried over Na2SO4, and filtered. After the solvent was re-
moved under vacuum, the residue was purified by flash
chromatography to give 10; yield: 8.53 g (84%).
Step 2: The product 10 (8.53 g) was dissolved in 80 mL
MeOH, 6.91 gK2CO3 were dissolved in 20 mL H2O and
poured into the reaction solution. The contents were stirred
for 1 h until TLC analysis indicated complete formation of
11. MeOH was removed under vacuum and the mixture was
poured into 100 mL H2O and then extracted with ethyl ace-
tate. The combined extracts were washed with brine, dried
over Na2SO4, and filtered, then the solvent removed to give
11; yield: 5.56 g (92%).
Step 3: The compound 11 (5.56 g) was dissolved in 50 mL
1,4-dioxane under 08C, 3.63 g methyl acrylate and 7.05 g
benzyltrimethylammonium hydroxide (Triton B, 50% solu-
tion in MeOH) were added subsequently, followed by a fur-
ther 3 h stirring to complete the reaction. 1,4-Dioxane was
removed under vacuum and the reactor contents were
cooled to 08C, a solution of NaOH (3.06 g, 2 equiv.) in
water/MeOH (5 mL/50 mL) was added, and the mixture
heated to 508C and maintained at this temperature for 3 h
to hydrolyze the intermediate. MeOH was removed under
vacuum and water was added to maintain the volume. The
solution was washed with CH2Cl2 (30 mL”3) to remove any
non-acidic organic impurities. The aqueous basic layer was
acidified to pH 1–2 with 25% w/w H2SO4 to precipitate the
product 12; yield: 7.55 g (90%).
Ethyl
3-(4-bromophenyl)-2-cyano-2-phenylpropanoate
(4j): Colorless oil; 139.7 mg (78%). 1H NMR (400 MHz,
CDCl3): d=7.52–7.50 (m, 2H), 7.40–7.35 (m, 5H), 7.01 (d,
J=8.4 Hz, 2H), 4.28–4.15 (m, 2H), 3.64 (d, J=13.8 Hz,
1H), 3.27 (d, J=13.8 Hz, 1H), 1.20 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=167.1, 134.1, 133.2, 132.2,
131.5, 129.2, 129.1, 126.3, 122.0, 117.8, 63.5, 55.5, 43.5, 13.8;
HR-MS (EI): m/z=357.0366, calcd. for C18H16BrNO2 [M]+:
357.0364.
Ethyl
2-cyano-3-(4-fluorophenyl)-2-phenylpropanoate
(4k): Colorless oil; yield: 104.1 mg (70%). 1H NMR
(400 MHz, CDCl3): d=7.53–7.51 (m, 2H), 7.41–7.37 (m,
3H), 7.13–7.10 (m, 2H), 6.95–6.90 (m, 2H), 4.28–4.15 (m,
2H), 3.66 (d, J=13.8 Hz, 1H), 3.29 (d, J=13.8 Hz, 1H),
1.19 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3): d=
167.2, 162.5 (d, J=247.3 Hz), 134.1, 132.1 (d, J=8.1 Hz),
129.9 (d, J=2.8 Hz), 129.2, 129.1, 126.3, 117.9, 115.2 (d, J=
21.4 Hz), 63.4, 55.8 (d, J=1.2 Hz), 43.3, 13.8; HR-MS (EI):
m/z=297.1166, calcd. for C18H16FNO2 [M]+: 297.1165..
Ethyl 2-cyano-2,2-diphenylacetate (4l):[15c] Colorless oil;
1
yield: 86.2 mg (65%). H NMR (400 MHz, CDCl3): d=7.32–
7.29 (m, 10H), 4.26 (q, J=7.2 Hz, 2H), 1.22 (t, J=7.2 Hz,
3H); 13C NMR (101 MHz, CDCl3): d=167.2, 135.9, 129.0,
128.0, 118.8, 63.7, 58.9, 13.9.
Ethyl 2-cyano-2-phenyl-2-p-tolylacetate (4m): Colorless
1
oil; yield: 97.8 mg (70%). H NMR (400 MHz, CDCl3): d=
7.41–7.35 (m, 5H), 7.29–7.27 (m, 2H), 7.19 (d, J=8.2 Hz,
2H), 4.33 (q, J=7.2 Hz, 2H), 2.35 (s, 3H), 1.30 (t, J=
7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3): d=167.4, 139.0,
136.1, 132.9, 129.7, 128.9, 128.9, 128.0, 127.9, 118.9, 63.7,
58.6, 21.1, 13.9. HR-MS (EI): m/z=279.1260, calcd. for
C18H17NO2 [M]+: 279.1259.
Step 4: The product 12 (7.55 g) was dissolved in 50 mL
toluene and concentrated H2SO4 (0.68 g, 0.2 equiv.) was
added, the mixture was heated to reflux for 4 h. After that,
the reaction was poured into 200 g ice, then extracted with
ethyl acetate, the solvent removed and the residue crystal-
lized in ether to give glutethimide 13; yield: 5.28 g (70%).
Methyl 2-cyano-2-phenylbutanoate (10):[15d] Colorless oil;
Ethyl 2-(4-bromophenyl)-2-cyano-2-phenylacetate (4n):[8]
Colorless oil; yield: 117.0 mg (68%). 1H NMR (400 MHz,
CDCl3): d=7.54–7.51 (m, 2H), 7.42–7.37 (m, 5H), 7.30–7.26
(m, 2H), 4.35 (q, J=7.2 Hz, 2H), 1.32 (t, J=7.2 Hz, 3H);
13C NMR (101 MHz, CDCl3): d=166.8, 135.4, 135.0, 132.1,
129.8, 129.2, 129.2, 127.8, 123.4, 118.3, 63.9, 58.3, 13.9.
Ethyl 2-cyano-4-oxo-2,4-diphenylbutanoate (4o): White
solid; yield: 69.1 mg (45%). 1H NMR (400 MHz, CDCl3):
d=7.80–7.95 (m, 2H), 7.68–7.59 (m, 3H), 7.50–7.42 (m,
5H), 4.38 (dd, J=10.8, 7.2 Hz, 1H), 4.27 (dd, J=10.8,
7.2 Hz, 1H), 4.18 (d, J=18.0 Hz, 1H), 3.76 (d, J=18.0 Hz,
1H), 1.32 (t, J=7.2 Hz, 3H); 13C NMR (101 MHz, CDCl3):
d=194.3, 167.3, 135.3, 134.0, 133.6, 129.4, 129.2, 128.83,
128.2, 126.1, 118.5, 63.5, 50.0, 48.4, 13.8; HR-MS (EI): m/z=
307.1206, calcd. for C19H17NO2 [M]+: 307.1208.
1
yield: 8.53 g (84%). H NMR (400 MHz, CDCl3): d=7.47–
7.44 (m, 2H), 7.34–7.27 (m, 3H), 3.68 (d, J=0.8 Hz, 3H),
2.35 (dq, J=14.8, 7.4 Hz, 1H), 2.09 (dq, J=14.8, 7.4 Hz,
1H), 0.97 (t, J=7.4 Hz, 3H); 13C NMR (101 MHz, CDCl3):
d=167.1, 133.3, 128.1, 127.8, 125.1, 117.2, 53.9, 52.8, 30.6,
8.8.
2-Phenylbutanenitrile (11):[15e] Colorless oil; yield: 5.60 g
1
(92%). H NMR (400 MHz, CDCl3): d=7.39–7.29 (m, 5H),
3.73 (t, J=7.2 Hz, 1H), 1.96–1.89 (m, 2H), 1.06 (t, J=
7.4 Hz, 3H); 13C NMR (101 MHz, CDCl3): d=135.8, 129.0,
128.0, 127.3, 120.8, 38.9, 29.2, 11.5.
4-Cyano-4-phenylhexanoic acid (12): White solid; yield:
1
7.55 g (90%). H NMR (400 MHz, CDCl3): d=9.58 (b, 1H),
7.42–7.32 (m, 5H), 2.57–2.49 (m, 1H), 2.39–2.31 (m, 1H),
2.19–1.94 (m, 4H), 0.92 (t, J=7.3 Hz, 3H); 13C NMR
(101 MHz, CDCl3): d=178.3, 136.9, 129.2, 128.1, 126.0,
121.5, 48.3, 35.1, 34.3, 30.2, 9.7; HR-MS (EI): m/z=
217.1106, calcd. for C13H15NO2 [M]+: 217.1103.
Procedure for the Synthesis of Glutethimide
Step 1: An oven-dried, 100-mL, three-necked, round-bottom
flask was charged with methyl 2-cyanobutanoate (6.35 g,
50 mmol, 1 equiv.), the flask was evacuated and backfilled
with nitrogen, then 50 mL anhydrous CH2Cl2 and potassium
tert-butoxide (6.17 g, 55 mmol, 1.1 equiv.) were added. The
mixture was stirred at 08C for 5 min. The solution of diphe-
3-Ethyl-3-phenylpiperidine-2,6-dione (13):[15f] White solid;
1
yield: 5.28 g (70%). H NMR (400 MHz, CDCl3): d=8.64 (s,
1H), 7.38–7.34 (m, 2H), 7.28 (d, J=7.8 Hz, 3H), 2.63–2.58
(m, 1H), 2.45–2.36 (m, 2H), 2.27–2.20 (m, 1H), 2.11–2.02
(m, 1H), 1.98–1.88 (m, 1H), 0.87 (t, J=7.4 Hz, 3H);
Adv. Synth. Catal. 2016, 358, 940 – 946
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
945

FULL PAPERS
Xiaofei Qian et al.
13C NMR (101 MHz, CDCl3): d=175.4, 172.8, 138.9, 129.0,
127.6, 126.2, 51.1, 32.9, 29.3, 27.1, 9.1.
Yang, X. Qian, S. Wu, J. Han, L. Wang, RSC Adv. 2015,
5, 36390–36393; c) Y. Zhang, J. Han, Z.-J. Liu, Synlett
2015, 26, 2593–2597.
[7] a) Z. Chai, B. Wang, J.-N. Chen, G. Yang, Adv. Synth.
Catal. 2014, 356, 2714–2718; b) A. Monastyrskyi, N. K.
Namelikonda, R. Manetsch, J. Org. Chem. 2015, 80,
2513–2520. For a review, see: c) E. A. Merritt, B. Olofs-
son, Angew. Chem. 2009, 121, 9214–9234; Angew.
Chem. Int. Ed. 2009, 48, 9052–9070.
Acknowledgements
This work was supported by grants from the National Nature
Science Foundation of China (NSFC Nos. 21272069,
21472213, 21202186) and the Fundamental Research Funds
for the Central Universities, Key Laboratory of Organofluor-
ine Chemistry, Shanghai Institute of Organic Chemistry, Chi-
nese Academy of Sciences.
[8] L. Chan, A. McNally, Q. Y. Toh, A. Mendoza, M. J.
Gaunt, Chem. Sci. 2015, 6, 1277–1281.
[9] J. Malmgren, S. Santoro, N. Jalalian, F. Himo, B. Olofs-
son, Chem. Eur. J. 2013, 19, 10334–10342.
[10] a) P. O. Norrby, T. B. Petersen, M. Bielawski, B. Olofs-
son, Chem. Eur. J. 2010, 16, 8251–8254; b) T. Dohi, M.
Ito, N. Yamaoka, K. Morimoto, H. Fujioka, Y. Kita,
Angew. Chem. 2010, 122, 3406–3409; Angew. Chem.
Int. Ed. 2010, 49, 3334–3337; c) C. Dey, E. Lindstedt, B.
Olofsson, Org. Lett. 2015, 17, 4554–4557.
References
[1] For reviews, see: a) D. T. Mowry, Chem. Rev. 1948, 42,
189–283; b) V. Y. Kukushkin, A. J. L. Pombeiro, Inorg.
Chim. Acta 2005, 358, 1–21; c) F. F. Fleming, Z. Zhang,
Tetrahedron 2005, 61, 747–789.
´
[11] a) D. Michalska, B. Morzyk, D. C. Bienko, W. Wojcie-
chowski, Med. Hypotheses 2000, 54, 472–474; b) M.-Y.
Chang, B.-R. Chang, H.-M. Tai, N.-C. Chang, Tetrahe-
dron Lett. 2000, 41, 10273–10276.
[2] F. F. Fleming, L. Yao, P. C. Ravikumar, L. Funk, B. C.
Shook, J. Med. Chem. 2010, 53, 7902–7917.
[3] T. Jackson, L. W. Lawrence Woo, M. N. Trusselle, S. K.
Chander, A. Purohit, M. J. Reed, B. V. L. Potter, Org.
Biomol. Chem. 2007, 5, 2940–2952.
[4] N. F. Badham, J.-H. Chen, P. G. Cummings, P. C. Del-
l’Orco, A. M. Diederich, A. M. Eldridge, W. L. Mendel-
son, R. J. Mills, V. J. Novack, M. A. Olsen, A. M.
Rustum, K. S. Webb, S. Yang, Org. Process Res. Dev.
2003, 7, 101–108.
[5] a) S. R. Stauffer, N. A. Beare, J. P. Stambuli, J. F. Hart-
wig, J. Am. Chem. Soc. 2001, 123, 4641–4642; b) J. You,
J. G. Verkade, Angew. Chem. 2003, 115, 5205–5207;
Angew. Chem. Int. Ed. 2003, 42, 5051–5053; c) X.
Wang, A. Guram, E. Bunel, G.-Q. Cao, J. R. Allen,
M. M. Faul, J. Org. Chem. 2008, 73, 1643–1645;
d) C. C. C. Johansson, T. J. Colacot, Angew. Chem.
2010, 122, 686–718; Angew. Chem. Int. Ed. 2010, 49,
676–707; e) P. Y. Yeung, K. H. Chung, F. Y. Kwong,
Org. Lett. 2011, 13, 2912–2915; f) G. Wu, Y. Deng, C.
Wu, Y. Zhang, J. Wang, Angew. Chem. 2014, 126,
10678–10682; Angew. Chem. Int. Ed. 2014, 53, 10510–
10514; g) S. H. Kim, W. Jang, M. Kim, J. G. Verkade, Y.
Kim, Eur. J. Org. Chem. 2014, 6025–6029.
[12] M. J. Bunegar, U. C. Dyer, G. R. Evans, R. P. Hewitt,
S. W. Jones, N. Henderson, C. J. Richards, S. Sivapra-
sad, B. M. Skead, M. A. Stark, E. Teale, Org. Process
Res. Dev. 1999, 3, 442–450.
[13] E. Tagmann, E. Sury, K. Hoffmann, Helv. Chim. Acta
1952, 35, 1541–1548.
[14] a) M. Bielawski, Z. Zhu, B. Olofsson, Adv. Synth.
Catal. 2007, 349, 2610–2618; b) T. Kitamura, J. Mat-
suyuki, H. Taniguchi, Synthesis 1994, 147–148; c) A. M.
Wagner, A. J. Hickman, M. S. Sanford, J. Am. Chem.
Soc. 2013, 135, 15710–15713.
[15] a) S. Xie, P. Qin, M. Li, X. Zhang, Y. Jiang, D. Ma, Tet-
rahedron Lett. 2013, 54, 3889–3891; b) R. C. Anand, A.
Milhotra, Chem. Commun. 1999, 1415–1415; c) N. A.
Beare, J. F. Hartwig, J. Org. Chem. 2002, 67, 541–555;
d) A. H. Mermerian, G. C. Fu, Angew. Chem. 2005,
117, 971–974; Angew. Chem. Int. Ed. 2005, 44, 949–952;
e) B. Gaspar, E. M. Carreira, Angew. Chem. 2007, 119,
4603–4606; Angew. Chem. Int. Ed. 2007, 46, 4519–4522;
f) H. Takaya, K. Yoshida, K. Isozaki, H. Terai, S. Mura-
hashi, Angew. Chem. 2003, 115, 3424–3426; Angew.
Chem. Int. Ed. 2003, 42, 3302–3304.
[6] a) F. Guo, L. Wang, P. Wang, J. Yu, J. Han, Asian J.
Org. Chem. 2012, 1, 218–221; b) S. Mao, X. Geng, Y.
946
asc.wiley-vch.de
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2016, 358, 940 – 946