An Iron-Catalyzed Direct Approach to Amides from Benzyl Azides via C-C Bond Cleavage

Article abstract of DOI:10.1055/s-0034-1380222

A novel iron-catalyzed transformation of benzyl azides to give the corresponding amides via C-C bond cleavage under mild reaction conditions is developed. This method provides a new synthetic tool for the construction of amides and the opportunity to accomplish C-C functionalization under mild conditions.

Full text of DOI:10.1055/s-0034-1380222

SYNTHESIS
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©
Georg Thieme Verlag Stuttgart · New York
2015, 47, 2971–2975
2971
special topic
Synthesis
Y. Ou et al.
Special Topic
An Iron-Catalyzed Direct Approach to Amides from Benzyl Azides
via C–C Bond Cleavage
Yang Oua
Chong Qina
Song Songa
Ning Jiao*a,b
a
State Key Laboratory of Natural and Biomimetic Drugs, Peking
University, Xue Yuan Road 38, Beijing 100191, P. R. of China
State Key Laboratory of Organometallic Chemistry, Chinese
b
Academy of Sciences, Ling Ling Rd. 345, Shanghai 200032,
P. R. of China
jiaoning@bjmu.edu.cn
6
Received: 12.05.2015
fonyl azides. In addition, our group has realized the gold-
catalyzed nitrogenation of alkynes to give amides, promot-
ed by Brønsted acids.7 Hong and co-workers have devel-
oped a ruthenium N-heterocyclic carbene (NHC) catalyzed
Accepted after revision: 05.06.2015
Published online: 06.08.2015
DOI: 10.1055/s-0034-1380222; Art ID: ss-2015-c0307-st
Abstract A novel iron-catalyzed transformation of benzyl azides to
give the corresponding amides via C–C bond cleavage under mild reac-
tion conditions is developed. This method provides a new synthetic tool
for the construction of amides and the opportunity to accomplish C–C
functionalization under mild conditions.
8
synthesis of amides from organic azides and alcohols. Fur-
thermore, an elegant synthesis of amides from vinyl azides
and imines was reported by Chiba.9 Recently, our group
demonstrated iron-catalyzed C–H and C–C bond cleavage of
benzyl hydrocarbons for the synthesis of amides (Scheme 1,
Key words C–C bond cleavage, azides, amides, rearrangement
10
a). However, despite the novelty of this transformation,
only diarylmethane and 1,3-diphenylpropene substrates
were tolerated. In order to prepare an N-acylaniline via this
strategy, and further, to prove the mechanism of the nitro-
Amides are versatile building blocks in synthetic organ-
ic chemistry, and are found in a wide number of biologically
active molecules and natural products. They are common-
1
10
genation reaction, we envisioned that alkyl-substituted
ly formed via reactions of carboxylic acids with amines.
However, the unification of these two functional groups
does not occur spontaneously at ambient temperature. For
the most part, these reactions require the activation of the
carboxylic acid partner by coupling agents such as acid
chlorides, anhydrides, carbonic anhydrides or active esters.
Although these methods are easily performed and highly
efficient, the conditions are usually harsh involving the use
of toxic, corrosive and/or expensive coupling reagents, with
azides would show potential as precursors for the synthesis
of amides. Herein, we describe an iron-catalyzed oxidative
rearrangement of alkyl-substituted benzyl azides for the di-
rect preparation of N-acylanilines (Scheme 1, b).
2
poor atom economy. Hence, the development of new
methods for the synthesis of amides is still attractive.
Significant progress has been made on the direct ap-
proach to nitrogen-containing compounds proceeding
3
through transition-metal-catalyzed selective C–H and C–
4
C bond cleavage. Among the various nitrogen sources uti-
lized for amide synthesis, organic azides have attracted
considerable attention for reasons of high atom economy.
Aubé et al. have developed Lewis acid mediated Schmidt re-
actions of ketones with 2-azidoethanols or 3-azidopropa-
5
nols for the synthesis of amides. Chang has reported cop-
per-catalyzed hydrative amide synthesis by employing sul-
Scheme 1 Synthesis of amides from: (a) benzyl hydrocarbons, and (b)
organic azides
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Special Topic
We commenced our studies by employing (1-azidopro-
pyl)benzene (1a) as a model substrate in order to optimize
the reaction conditions (Table 1). Treatment of (1-azidopro-
pyl)benzene (1a) with water (2.0 equiv), iron(II) chloride
fyingly, it was found that the reaction could be performed
in good yield when benzoic acid was employed as an addi-
tive (Table 1, entry 15). After extensive screening of other
parameters, the optimum reaction conditions were deter-
mined as follows: benzyl azide (0.5 mmol, 1.0 equiv),
iron(II) chloride (10 mol%), 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (1.2 equiv), water (2.0 equiv), benzoic acid
(5.0 equiv), 60 °C, argon atmosphere.
(
FeCl ) (10 mol%) and 2,3-dichloro-5,6-dicyano-1,4-benzo-
2
10
quinone (DDQ) (1.2 equiv) in acetic acid at 60 °C resulted
in a 15% yield of the desired product, N-phenylpropion-
amide (2a) (Table 1, entry 1). Solvent screening showed that
1
,2-dichloroethane (DCE) was the most efficient for this
With optimized reaction conditions in hand, we next
explored the scope of this reaction using various alkyl- and
aryl-substituted benzyl azides (Scheme 2). Benzyl azides
with different alkyl groups (ethyl, propyl, butyl, isopropyl,
cyclohexyl and methyl) were transformed into the corre-
sponding amides (2a–j) in moderate to good yields. In our
previous study,10 only benzanilides were accessible via the
transformation (Table 1, entries 2–6). Next, we examined
the effects of different catalysts on this reaction. Iron(II)
bromide (FeBr ), iron(III) bromide (FeBr ) and copper(II) tri-
2
3
flate [Cu(OTf) ] led to low yields of 2a (Table 1, entries 7–9).
2
Several common oxidants, including tert-butyl hydroperox-
ide (TBHP), cerium(IV) ammonium nitrate (CAN) and
phenyliodonium diacetate (PIDA), showed low efficiencies
in this reaction (Table 1, entries 10–12).
In our previous studies, we found that the addition of an
appropriate Brønsted acid usually played an important role
in the reaction system.
acetic acid (AcOH), trifluoroacetic acid (TFA) and benzoic
acid (PhCOOH) were employed to test their activity. Grati-
FeCl2 (10 mol%)
N3
H
N
DDQ (1.2 equiv)
PhCOOH (5.0 equiv)
H2O (2.0 equiv)
R2
R2
O
4e,7,10
Hence, Brønsted acids such as
R1
R1
DCE (2 mL)
1
2
H
N
H
N
H
N
Table 1 Optimization of the Reaction Conditionsa
O
O
O
O
2
a 78%
2b 70%
2c 54%
N3
catalyst (10 mol%)
oxidant (1.2 equiv)
H2O (2.0 equiv)
H
N
H
N
H
N
H
N
O
solvent, Ar, 60 °C
O
1a
2a
O
2
e 52%
2f 43%
2
d 37%
Entry Catalyst
Oxidant Solvent
Acid
Yield (%)b
H
N
H
H
N
N
1
2
3
4
5
6
7
8
9
FeCl
FeCl
FeCl
FeCl
FeCl
FeCl
2
2
2
2
2
2
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
TBHP
CAN
PIDA
DDQ
DDQ
DDQ
DDQ
DDQ
AcOH
MeCN
toluene
DCE
–
–
–
–
–
–
–
–
–
–
–
–
15
<5
<5
51
0
O
O
O
2g 62%
2h 73%
2i 72%
F
H
H
N
DMF
DMSO
DCE
N
H
N
0
O
O
O
Cl
F
FeBr
2
3
35
32
32
0
2
j 30%
2k 76%
2l 87%
FeBr
DCE
Cu(OTf)
2
DCE
H
H
N
N
79%
1
0
1
2
3
4
5
6
7
FeCl
FeCl
FeCl
FeCl
FeCl
2
2
2
2
2
DCE
O
(1.53:1)
O
1
1
1
1
1
1
DCE
0
2m
2m'
DCE
0
Cl
DCE
AcOH
50
18
78
71
52
H
H
62%
(1.23:1)
N
N
DCE
TFA
O
FeCl
2
DCE
PhCOOH
Cl
O
FeCl
2
2
DCE
4-MeOC COOH
6
H
4
2n
2n'
1
FeCl
DCE
4-O NC H COOH
2
6 4
Scheme 2 Substrate scope of the FeCl -catalyzed synthesis of amides
from benzyl azides. Reaction conditions: benzyl azide 1 (0.5 mmol), H
2
a
Reaction conditions: 1a (0.5 mmol), H
2
O (1.0 mmol, 2.0 equiv), catalyst
2
O
(
0.05 mmol, 10 mol%), oxidant (0.6 mmol, 1.2 equiv), solvent (2 mL), 60 °C,
(1.0 mmol, 2.0 equiv), FeCl (0.05 mmol, 10 mol%), DDQ (0.6 mmol,
2
Ar, 12 h.
1.2 equiv), PhCOOH (5.0 equiv), DCE (2 mL), 60 °C, Ar, 12 h.
b
Yield of isolated product.
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1a, DDQ
N
OH
Fe(II)
OH
O
N
N
N
+
–
Cl
CN
CN
D
Cl
+
2a
Fe(II)
H2O
A
+
N
N
C
+ N
N
N2
B
Scheme 3 Proposed mechanism for the FeCl -catalyzed synthesis of amides
2
nitrogenation of diarylmethenes; however, the present
strategy has expanded the scope to alkyl-substituted
amides. The efficiency of this process was influenced by the
nature of the substituents on the aromatic ring. An elec-
tron-withdrawing group resulted in a slightly decreased
yield, while an electron-donating group increased the yields
gen is the only by-product of this transformation, which
demonstrates good atom economy. This procedure not only
provides a new synthetic tool for amide construction, but
also permits C–C functionalization under mild conditions.
(
see products 2g–j). Satisfactory results were obtained in
All reactions were carried out under an inert atmosphere with anhy-
drous solvents under anhydrous conditions unless otherwise stated.
Petroleum ether (PE) refers to the fraction boiling in the 60–90 °C
range. Chemicals obtained from commercial suppliers were used
without further purification unless otherwise noted. All manipula-
tions were conducted in Schlenk tubes. Column chromatography was
performed using Qingdao Ocean brand silica gel (200–300 mesh). H
NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded on a
Bruker AVIII-400 spectrometer. Chemical shifts (in ppm) are refer-
the reaction of diarylmethyl azides 2k and 2l. When un-
symmetrical diphenylmethyl azides, such as 1-[azido(phe-
nyl)methyl]-4-methylbenzene (1m) and 1-[azido(phe-
nyl)methyl]-4-chlorobenzene (1n) were employed, two re-
gioisomeric products (2m,m′ and 2n,n′) were obtained in
ratios of 1.53:1 and 1.23:1, respectively.
On the basis of our previous work, a tentative reaction
mechanism is shown in Scheme 3. Initially, the oxidation of
1
1
enced to CDCl3 or DMSO-d . Low-resolution mass spectra were ob-
6
tained using an Agilent PE SCLEX QSTAR GC-MS instrument.
a by the iron/2,3-dichloro-5,6-dicyano-1,4-benzoquinone
11
oxidative system, assisted by the azido group, affords the
corresponding benzylic azide cation A. Subsequent isomeri-
zation of this benzylic azide cation leads to intermediate B.
Next, a Beckmann rearrangement occurs with migration of
the phenyl group from carbon to the adjacent nitrogen to
generate nitrile cation C. Subsequent nucleophilic attack of
water leads to the intermediate D, isomerization of which
N-Phenylpropionamide (2a);13 Typical Procedure
To a Schlenk tube (25 mL) were added sequentially FeCl (6.3 mg, 0.05
mmol), DDQ (136 mg, 0.6 mmol), PhCOOH (305 mg, 2.5 mmol), (1-
2
azidopropyl)benzene (1a) (80.5 mg, 0.5 mmol), H O (18 μL, 1.0 mmol)
2
and dry DCE (2 mL). The resulting mixture was stirred at 60 °C under
an argon atmosphere for 24 h. The mixture was filtered, concentrated
and purified by flash chromatography on silica gel (PE–EtOAc, 10:1)
to afford amide 2a.
12
gives the final product 2a.
In summary, we have reported a novel iron-catalyzed
transformation of benzyl azides into the corresponding am-
ides via C–C bond cleavage under mild reaction conditions.
The inclusion of benzoic acid in the reaction is very import-
ant to improve the efficiency of this transformation. Com-
pared to our previous work, this method expands the prod-
uct scope to benzanilides and N-phenylalkylamides. Nitro-
Yield: 58.1 mg (78%); white solid; mp 106–108 °C.
1
H NMR (400 MHz, DMSO-d ): δ = 9.84 (s, 1 H), 7.60 (d, J = 8.0 Hz, 2
6
H), 7.28 (t, J = 8.0 Hz, 2 H), 7.03 (d, J = 7.6 Hz, 1 H), 2.39–2.27 (m, 2 H),
1.10 (t, J = 7.6 Hz, 3 H).
13
C NMR (100 MHz, DMSO-d ): δ = 172.5, 139.9, 129.1, 123.3, 119.5,
6
30.0, 10.1.
MS (EI, 70 eV): m/z (%) = 149.0 (100) [M]+.
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N-Phenylbutyramide (2b)7
1
H NMR (400 MHz, DMSO-d ): δ = 9.73 (br s, 1 H), 7.44 (s, 1 H), 7.38
6
(
2
d, J = 7.6 Hz, 1 H), 7.15 (t, J = 8.0 Hz, 1 H), 6.83 (d, J = 7.6 Hz, 1 H),
.35–2.25 (m, 2 H), 2.26 (s, 3 H), 1.08 (t, J = 7.2 Hz, 3 H).
Yield: 57.1 mg (70%); white solid.
1
H NMR (400 MHz, DMSO-d ): δ = 9.83 (s, 1 H), 7.60 (d, J = 8.0 Hz, 2
6
1
3
C NMR (100 MHz, DMSO-d ): δ = 172.4, 139.7, 138.2, 128.9, 124.1,
H), 7.27 (t, J = 8.0 Hz, 2 H), 7.01 (t, J = 7.6 Hz, 1 H), 2.28 (t, J = 7.6 Hz, 2
H), 1.67–1.53 (m, 2 H), 0.91 (t, J = 7.6 Hz, 3 H).
6
1
20.0, 116.7, 30.0, 21.6, 10.1.
MS (EI, 70 eV): m/z (%) = 163.0 (100) [M]+.
13
C NMR (100 MHz, DMSO-d ): δ = 171.5, 139.7, 129.7, 123.4, 119.5,
6
3
8.8, 19.0, 14.1.
N-(p-Tolyl)propionamide (2i)14
MS (EI, 70 eV): m/z (%) = 163.0 (100) [M]+.
Yield: 58.9 mg (72%); white solid.
N-Phenylpentanamide (2c)14
1
H NMR (400 MHz, DMSO-d ): δ = 9.76 (br s, 1 H), 7.49 (d, J = 8.0 Hz, 2
6
H), 7.09 (d, J = 8.0 Hz, 2 H), 2.35–2.23 (m, 2 H), 2.24 (s, 3 H), 1.09 (t,
J = 7.6 Hz, 3 H).
Yield: 47.8 mg (54%); white solid.
1
H NMR (400 MHz, DMSO-d ): δ = 9.83 (br s, 1 H), 7.58 (d, J = 8.0 Hz, 2
6
13
C NMR (100 MHz, DMSO-d ): δ = 172.2, 137.4, 132.2, 129.5, 119.5,
H), 7.27 (t, J = 8.0 Hz, 2 H), 7.01 (t, J = 7.6 Hz, 1 H), 2.30 (t, J = 7.6 Hz, 2
H), 1.61–1.52 (m, 2 H), 1.38–1.25 (m, 2 H), 0.90 (t, J = 7.6 Hz, 3 H).
6
29.9, 20.8, 10.2.
MS (EI, 70 eV): m/z (%) = 163.0 (100) [M]+.
13
C NMR (100 MHz, DMSO-d ): δ = 171.2, 139.2, 128.6, 122.9, 119.0,
6
3
6.1, 27.2, 21.8, 13.7.
N-(4-Chlorophenyl)propionamide (2j)14
MS (EI, 70 eV): m/z (%) = 177.0 (100) [M]+.
Yield: 27.3 mg (30%); white solid.
N-Phenylisobutyramide (2d)14
1
H NMR (400 MHz, DMSO-d ): δ = 9.98 (br s, 1 H), 7.63 (d, J = 8.8 Hz, 2
6
H), 7.31 (d, J = 8.8 Hz, 2 H), 2.39–2.29 (m, 2 H), 1.09 (t, J = 7.2 Hz, 3 H).
Yield: 30.2 mg (37%); white solid.
13
1
C NMR (100 MHz, DMSO-d ): δ = 172.6, 138.8, 129.0, 126.9, 121.0,
H NMR (400 MHz, DMSO-d ): δ = 9.81 (br s, 1 H), 7.60 (d, J = 8.0 Hz, 2
6
6
30.0, 10.0.
H), 7.29 (t, J = 8.0 Hz, 2 H), 7.03 (d, J = 7.6 Hz, 1 H), 2.60 (t, J = 7.6 Hz, 1
H), 1.10 (d, J = 7.2 Hz, 6 H).
MS (EI, 70 eV): m/z (%) = 183.0 (100) [M]+.
13
C NMR (100 MHz, DMSO-d ): δ = 175.2, 139.4, 128.6, 122.9, 119.1,
6
34.9, 19.5.
N-Phenylbenzamide (2k)14
MS (EI, 70 eV): m/z (%) = 163.0 (100) [M]+.
Yield: 74.8 mg (76%); white solid.
1
H NMR (400 MHz, DMSO-d ): δ = 10.25 (s, 1 H), 7.96 (d, J = 7.6 Hz, 2
6
N-Phenylcyclohexanecarboxamide (2e)15
H), 7.79 (d, J = 8.0 Hz, 2 H), 7.61–7.51 (m, 3 H), 7.36 (t, J = 7.6 Hz, 2 H),
7
.10 (t, J = 7.6 Hz, 1 H).
Yield: 52.9 mg (52%); white solid.
13
1
C NMR (100 MHz, DMSO-d ): δ = 166.0, 139.5, 135.4, 132.0, 129.1,
H NMR (400 MHz, DMSO-d ): δ = 9.77 (s, 1 H), 7.61 (d, J = 7.6 Hz, 2
6
6
128.9, 124.1, 120.8.
H), 7.28 (t, J = 7.6 Hz, 2 H), 7.01 (t, J = 7.6 Hz, 1 H), 2.36–2.29 (m, 1 H),
.81–1.75 (m, 4 H), 1.67–1.64 (m, 1 H), 1.46–1.38 (m, 2 H), 1.32–1.17
MS (EI, 70 eV): m/z (%) = 197.1 (100) [M]+.
1
(m, 3 H).
13
4-Fluoro-N-(4-fluorophenyl)benzamide (2l)16
C NMR (100 MHz, DMSO-d ): δ = 174.8, 140.0, 129.0, 123.3, 119.5,
6
4
5.3, 29.6, 25.9, 25.7.
Yield: 101.3 mg (87%); white solid.
MS (EI, 70 eV): m/z (%) = 203.1 (100) [M]+.
1
H NMR (400 MHz, DMSO-d ): δ = 10.31 (br s, 1 H), 8.05–8.02 (m, 2
6
H), 7.79–7.77 (m, 2 H), 7.40–7.36 (m, 2 H), 7.23–7.19 (m, 2 H).
N-Phenylacetamide (2f)7
13
C NMR (100 MHz, DMSO-d ): δ = 164.8, 164.6 (d, J = 250.0 Hz),
6
Yield: 29.0 mg (43%); white solid.
158.8 (d, J = 237.5 Hz), 135.9, 131.7, 130.8, 122.7, 115.8 (d, J = 25.0
Hz), 115.6 (d, J = 12.5 Hz).
MS (EI, 70 eV): m/z (%) = 233.1 (100) [M]+.
1
H NMR (400 MHz, DMSO-d ): δ = 8.27 (br s, 1 H), 7.51 (d, J = 8.0 Hz, 2
6
H), 7.27 (t, J = 7.6 Hz, 2 H), 7.08 (t, J = 7.6 Hz, 1 H), 2.13 (s, 3 H).
13
C NMR (100 MHz, DMSO-d ): δ = 168.9, 138.0, 128.8, 124.2, 120.0,
6
2
4.3.
N-(p-Tolyl)benzamide (2m) and 4-Methyl-N-phenylbenzamide
(2m′)
14
MS (EI, 70 eV): m/z (%) = 135.0 (100) [M]+.
Yield: 83.0 mg (79%); ratio 2m/2m′ = 1.53:1; white solid.
N-(p-Tolyl)acetamide (2g)14
2m
Yield: 46.2 mg (62%); white solid.
1H NMR (400 MHz, DMSO-d
H), 7.67 (d, J = 8.4 Hz, 2 H), 7.60–7.48 (m, 3 H), 7.16 (d, J = 8.4 Hz, 2
H), 2.28 (s, 3 H).
): δ = 10.18 (br s, 1 H), 7.95 (d, J = 7.6 Hz,
1
6
H NMR (400 MHz, DMSO-d ): δ = 7.77 (br s, 1 H), 7.37 (d, J = 7.6 Hz, 2
6
2
H), 7.09 (d, J = 8.4 Hz, 2 H), 2.30 (s, 3 H), 2.13 (s, 3 H).
13
C NMR (100 MHz, DMSO-d ): δ = 168.6, 135.3, 133.8, 129.3, 120.1,
6
2
4.3, 20.8.
2
1
m′
MS (EI, 70 eV): m/z (%) = 149.1 (100) [M]+.
H NMR (400 MHz, DMSO-d ): δ = 10.17 (br s, 1 H), 7.88 (d, J = 8.2 Hz,
6
2
H), 7.79 (d, J = 8.2 Hz, 2 H), 7.39–7.30 (m, 4 H), 7.10 (t, J = 7.4 Hz, 1
N-(m-Tolyl)propionamide (2h)14
H), 2.39 (s, 3 H).
Yield: 59.1 mg (73%); white solid.
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N-(4-Chlorophenyl)benzamide (2n) and 4-Chloro-N-phenylbenz-
amide (2n′)
Angew. Chem. Int. Ed. 2013, 52, 11862. (f) Fan, Y.; Wan, W.; Ma,
G.; Gao, W.; Jiang, H.; Zhu, S.; Hao, J. Chem. Commun. 2014, 50,
14
5733. (g) Deng, Q.-H.; Bleith, T.; Wadepohl, H.; Gade, L. H. J. Am.
Yield: 71.6 mg (62%); ratio 2n/2n′ = 1.23:1; white solid.
Chem. Soc. 2013, 135, 5356. (h) Chen, H.; Yang, W.; Wu, W.;
Jiang, H. Org. Biomol. Chem. 2014, 12, 3340. (i) Shin, K.; Baek, Y.;
Chang, S. Angew. Chem. Int. Ed. 2013, 52, 8031. (j) Kim, J. Y.;
Park, S. H.; Ryu, J.; Cho, S. H.; Kim, S. H.; Chang, S. J. Am. Chem.
Soc. 2012, 134, 9110. (k) Qin, C.; Jiao, N. J. Am. Chem. Soc. 2010,
2
n
1
H NMR (400 MHz, DMSO-d ): δ = 10.38 (br s, 1 H), 7.96 (d, J = 7.6 Hz,
6
2
H), 7.84 (d, J = 8.0 Hz, 2 H), 7.62–7.56 (m, 1 H), 7.56–7.45 (m, 2 H),
7.41 (d, J = 8.8 Hz, 2 H).
132, 15893. (l) Zheng, Q.-Z.; Feng, P.; Liang, Y.-F.; Jiao, N. Org.
Lett. 2013, 15, 4262. (m) Zhou, W.; Zhang, L.; Jiao, N. Angew.
Chem. Int. Ed. 2009, 48, 7094. (n) Chen, F.; Huang, X.; Cui, Y.;
Jiao, N. Chem. Eur. J. 2013, 19, 11199. (o) Ou, Y.; Jiao, N. Chem.
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Angew. Chem. Int. Ed. 2014, 53, 6528. (s) Tang, C.; Yuan, Y.; Jiao,
N. Org. Lett. 2015, 17, 2206.
2
n′
1
H NMR (400 MHz, DMSO-d ): δ = 10.32 (br s, 1 H), 8.00 (d, J = 8.4 Hz,
6
2
2
H), 7.78 (d, J = 8.0 Hz, 2 H), 7.60 (d, J = 7.2 Hz, 2 H), 7.35 (t, J = 7.8 Hz,
H), 7.11 (t, J = 7.2 Hz, 1 H).
Acknowledgment
(
4) For some recent examples with azides, see: (a) Chen, F.; Qin, C.;
Cui, Y.; Jiao, N. Angew. Chem. Int. Ed. 2011, 50, 11487. (b) Shen,
T.; Wang, T.; Qin, C.; Jiao, N. Angew. Chem. Int. Ed. 2013, 52,
6677. (c) Wang, T.; Jiao, N. J. Am. Chem. Soc. 2013, 135, 11692.
(d) Tang, C.; Jiao, N. Angew. Chem. Int. Ed. 2014, 53, 6528. (e) Qin,
C.; Shen, T.; Tang, C.; Jiao, N. Angew. Chem. Int. Ed. 2012, 51,
6971.
Financial support from the National Basic Research Program of China
(973 Program) (grant No. 2015CB856600), the National Natural Sci-
ence Foundation of China (Nos. 21325206, 21172006), the National
Young Top-notch Talent Support Program, and the Programs Founda-
tion of the Ministry of Education of China (No. 20120001110013) is
greatly appreciated
(5) (a) Katz, C. E.; Aubé, J. J. Am. Chem. Soc. 2003, 125, 13948.
(
b) Sahasrabudhe, K.; Gracias, V.; Furness, K.; Smith, B. T.; Katz,
C. R.; Reddy, D. S.; Aubé, J. J. Am. Chem. Soc. 2003, 125, 7914.
c) Desai, P.; Schildknegt, K.; Agrios, K. A.; Mossman, C.;
Milligan, G. L.; Aubé, J. J. Am. Chem. Soc. 2000, 122, 7226.
d) Gracias, V.; Frank, K. E.; Milligan, G. L.; Aubé, J. Tetrahedron
997, 53, 16241.
6) (a) Cho, S. H.; Chang, S. Angew. Chem. Int. Ed. 2007, 46, 1897.
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Supporting Information
(
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1380222.
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Georg Thieme Verlag Stuttgart · New York — Synthesis 2015, 47, 2971–2975