An Efficient Catalytic Amidation of Esters Promoted by N-Heterocyclic Carbenes

Article abstract of DOI:10.1055/s-0037-1610355

An efficient NHC-catalyzed amidation between esters and amines or hydrazines is described. This strategy was tolerant for a wide scope of substrates, affording a series of amides (or hydrazides) in good to excellent yields (60-96%) under simple conditions. The approach was also used to synthesize the pharmaceutically relevant antidepressant moclobemide in 85% yield.

Full text of DOI:10.1055/s-0037-1610355

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2018, 50, A–H
paper
A
en
L.-Y. Chen, M.-F. Wu
Paper
Synthesis
An Efficient Catalytic Amidation of Esters Promoted by N-Heterocyclic
Carbenes
Ling-Yan Chen*
Mei-Fang Wu
0
0
0
0-
0
0
0
1-6
1
2
5-6
8
8
4
O
O
N
N
R3
R2
R1
N
R3
HN
R2
R1
OAr
+
THF, r.t., 30 min
College of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, 333 Longteng Road,
Shanghai 201620, China
primary and secondary amines compatible
28 examples, 60–97% yield
lingyan.chen@hotmail.com
Received: 23.08.2018
Accepted after revision: 13.11.2018
Published online: 19.12.2018
O
O
Cl
N
N
N
DOI: 10.1055/s-0037-1610355; Art ID: ss-2018-h0563-op
H
N
MeO
O
N
H2N
O
OMe
Abstract An efficient NHC-catalyzed amidation between esters and
amines or hydrazines is described. This strategy was tolerant for a wide
scope of substrates, affording a series of amides (or hydrazides) in good
to excellent yields (60–96%) under simple conditions. The approach was
also used to synthesize the pharmaceutically relevant antidepressant
moclobemide in 85% yield.
itopride
metoclopramide
N
O
N
O
N
N
N
H
O
O
Key words N-heterocyclic carbenes, amidation, catalytic reaction,
N
NH2
amides, nucleophilic addition
copanlisib (approved by FDA in 2017)
Figure 1 Selected examples of pharmaceutical products with amide
bonds
Amidation is one of the most important transformations
in organic synthesis, since amide compounds are abundant-
ly found in biologically active compounds, pharmaceutical
products, proteins, and natural products (Figure 1).1–5 For
example, itopride is indicated for the treatment of function-
al dyspepsia, metoclopramide is commonly used to treat
and prevent nausea and vomiting, while copanlisib is a new
drug approved by the U.S. Food and Drug Administration
(FDA) in 2017 for the treatment of recurrent follicular lym-
phoma. Consequently, it is important to develop different
methods for the synthesis of amide compounds.
The traditional methods for the synthesis of amides fo-
cus on the condensation between carboxylic acids and
amines, using more reactive acyl chlorides or esters,6,7 or
using alternative intermediates without use of metals,8a,b
followed by nucleophilic substitutions with amines, but
they often need elevated temperatures in the absence of
any catalyst, and the substrates could not completely be
transformed even after long time. Therefore, it is highly de-
sirable to seek suitable catalysts to facilitate faster amida-
tion. Recently, enormous catalytical methods for preparing
amides have been developed such as transition-metal-cata-
lyzed9 and N-heterocyclic carbenes (NHC)-catalyzed8c–i oxi-
dative amidation, radical initiated amidation through the
formation of activated intermediates,10 and photocatalysis
through radical process,11 which even directly used alde-
hydes as the starting material instead of carboxylic acids or
their derivatives. However, these direct oxidative amidation
of aldehydes often need oxidants or other extra additives
with obvious restrictions on substrate scope. Thus, trans-
forming to acid derivatives still should be the major effi-
cient and simple approach to produce the amide com-
pounds if suitable catalysts are chosen.
In the past several decades, N-heterocyclic carbenes
(NHCs) have emerged as efficient organocatalysts in organ-
ic synthesis.12 In 2005, Movassaghi reported the amidation
between unactivated esters and amino alcohol.13 As the hy-
droxy group was necessary for the reaction, the reaction
suffered from the limited substrate scope. Recently, Du and
co-workers explored the amidation between vinyl ester and
aromatic amines (Scheme 1). However, this method needed
elevated temperature (60 °C), and did not mention the use
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

B
L.-Y. Chen, M.-F. Wu
Paper
Synthesis
of secondary amines or aliphatic amines.14 We envisioned
whether the aliphatic amines (including secondary amines)
or hydrazines could form the corresponding amides under
mild conditions. As a result, we herein report an efficient
approach for amidation between aryl esters and different
amines or hydrazines promoted by NHCs, which is a useful
supplementary method for preparing amide compounds
(Scheme 1). Our approach was performed at room tempera-
ture in very short time, which is more efficient and easier
to handle.
Cs2CO3 and K2CO3 gave promising results as well (90% and
92%, respectively, entries 11 and 12). However, if other bas-
es such as DMAP, Et3N, t-BuOK, DABCO, and DIPEA were
used, there was a significant decrease in yields (entries 10,
13–16). In addition, to our delight, when using THF instead
of CH2Cl2 as the solvent, the desired amide was obtained in
97% yield in 30 minutes (entry 18). For other solvent such
as toluene, methanol, acetonitrile, the yields were all poor
Table 1 Investigation of the Effects of Different NHC Precursors, Bases
and Solvents on the Amidation Reactiona
Previous work
(a) 200513: Movassaghi et al.
O
O
Mes
O
Mes
N
O
N
Ar
OH
N
O
PreNHC/base
solvent
OH
R1
N
R2
H2N
H
HN
R2
+
n
R1
+
OMe
n
THF, 23 °C, 1.5–24 h
amino alcohol necessary
1
2a
3a
1a Ar = Ph
66–99% yield
1b Ar = 4-NO2C6H4
(b) 201514: Du et al.
R
R
Mes
Mes
O
N
N
N
X
N
X
R2
N
N
BF4
NH2
O
R2
R1
N
N
N
R
N
R
R
R1
O
+
toluene, 60 °C
14–40 h
H
suitable for aromatic primary amines 58–92% yield
4 R = Me, X = I
5 R = Ph, X = Cl
6 R = Me, X = I
7 R = Ph, X = Cl
9 R = Ph
10 R = Mes
This work
8 R = naphth, X = Cl
O
O
N
N
R3
R2
R1
N
R3
HN
R2
Entry
1
PreNHC Base
Solvent
Time
Yield (%)b
R1
OAr
+
THF, r.t., 30 min
1
2
1a
1a
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
–
4
4
5
6
7
8
9
10
4
4
4
4
4
4
4
4
4
4
4
4
–
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
toluene
THF
10 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
30 min
10 h
1 h
3 h
23
68
93
41
63
32
trace
80
66
88
90
92
61
59
63
62
50
97
–
efficient catalytic amidation
wide scope: primary and secondary amines compatible
60–96% yield
DBU
3
DBU
Scheme 1 NHC-catalyzed amidation of esters
4
DBU
5
DBU
According to NHC-catalyzed saturated ester process de-
veloped by Chi group,15 our investigation started from the
amidation between benzoate 1a and benzylamine (2a) in
CH2Cl2 at room temperature (Table 1). In the absence of cat-
alyst, the reaction proceeded so slow that the yield was low
even after 10 hours (Table 1, entry 1). As anticipated, when
in the presence of 20% NHC precursor 4 and DBU, the reac-
tion proceeded quickly, affording the desired amide in 68%
yield in 1 hour (entry 2). When benzoate 1b was used in-
stead of 1a, the yield rose to 93% (entry 3). Several other
different NHC precursors 5–10 were also examined. The re-
action showed strong dependence on the types of the cata-
lysts or substituents on the catalysts (entries 3–10). For im-
idazole-based and benzimidazole-based NHC precursors, if
the aromatic group was used instead of alkyl group, the
yield decreased dramatically (entries 3–8). NHC precursor 8
even resulted only in trace amount of the product. For tri-
azole-based NHC precursor, the yield was moderate (entries
9, 10). In order to further optimize the reaction, other pa-
rameters such as base and solvents were also screened. The
results indicated that different bases had obvious effect on
yields of the reaction. Importantly, DBU was proved to be
the most efficient base providing the best result, while both
6
DBU
7
DBU
8
DBU
9
DBU
10
11
12
13
14
15
16
17
18
19
20
21c
DMAP
Cs2CO3
K2CO3
Et3N
t-BuOK
DABCO
DIPEA
DBU
DBU
DBU
MeOH
MeCN
THF
DBU
60
88
DBU
a Unless otherwise noted, all reactions were carried out using 1b (0.5
mmol), 2a (0.6 mmol), NHC precursor (0.1 mmol), and base (0.1 mmol) in
solvent (2 mL) for 30 min to 10 h.
b Isolated yield.
c NHC precursor (0.05 mmol) and base (0.05 mmol) were used.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

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L.-Y. Chen, M.-F. Wu
Paper
Synthesis
(entries 17, 19, and 20). Besides, if the catalyst loading was
cut to half, the reaction needed longer time with slightly
lower yield.
could also afford the desired amide in quite good yields (3p,
3q, and 3r: 85%, 75% and 92%, respectively). If the substrate
containing a hydroxy group was used, no transesterifica-
tion product was observed in the reaction. Additionally, hy-
drazines could also smoothly produce its corresponding
acylhydrazides 3m–o in good yields. For aliphatic hydra-
zine, it was worth noting that the reaction preferred to take
place at the NH close to the alkyl group (3o). If there was a
chiral center in the substrate, the enantiomeric excess could
be evaluated by HPLC analysis (3s). However, aromatic
amines like aniline or its derivatives could not undergo the
amidation at room temperature.
Under the optimized conditions, the scope of amidation
promoted by NHC was further explored. A wide range of
amines were tested. Scheme 2 shows that the reaction de-
pended on both electronic and steric factors in some way,
although almost all the reactions proceeded quite well and
gave good to excellent yields. On the one hand, amines con-
taining electron-withdrawing group like Cl, led to lower
chemical yields than that with electron-donating group like
Me and MeO. It is worth noting that secondary amines
O
NO2
R1
R2
N
N
O
R1
N
H
N
I
4
R2
O
+
DBU, THF
1b
2
3a–s
O
O
O
OMe
OMe
N
N
N
H
H
H
OMe
3b 95%
3c 96%
3a 97%
Cl
O
O
O
N
H
N
H
N
H
OMe
3e 95%
3f 85%
3d 86%
Me
O
O
O
N
H
N
H
N
H
OH
3g 86%
3h 83%
3i 90%
O
O
O
N
N
H
N
H
OMe
N
H
3k 88%
3l 87%
3j 80%
O
H
N
N
H
O
O
H
N
NH2
N
H
N
Me
3m 81%
3n 75%
3o 60%
O
N
O
O
N
N
N
3r 92%
3q 75%
3p 85%
COOMe
O
HN
3s 65%
Scheme 2 The scope of amidation with different amines (or hydrazines) promoted by NHC. Reagents and conditions: Unless otherwise noted, all reac-
tions were carried out using 1b (0.5 mmol), 2 (0.6 mmol), NHC precursor 4 (0.1 mmol), and DBU (0.1 mmol) in THF (2 mL) for 30 min.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

D
L.-Y. Chen, M.-F. Wu
Paper
Synthesis
O
NO2
N
N
O
NH2
I
R3
N
4
+
R3
O
H
DBU, THF
3t–ab
2a
1
O
O
O
N
N
N
H
H
H
Me
MeO
Cl
3t 92%
3u 95%
3v 80%
F
O
NO2
O
O
H
N
N
H
N
H
O
3w 88%
3x 77%
3y 90%
O
O
O
N
H
N
H
N
H
S
3z 89%
3aa 91%
3ab 81%
Scheme 3 The scope of amidation with different esters promoted by NHC. Reagents and conditions: Unless otherwise noted, all reactions were carried
out using 1 (0.5 mmol), 2a (0.6 mmol), NHC precursor 4 (0.1 mmol), and DBU (0.1 mmol) in THF (2 mL) for 30 min.
O
O
NO2
+
O
4 (20 mol%)
DBU (20 mol%)
O
N
N
N
H
O
H2N
THF (0.25 M), r.t., 30 min
Cl
13 moclobemide 85%
12
11
Cl
Scheme 4 Synthesis of antidepressant moclobemide
O
Further, we studied the substrate scope with respect to
different esters for the synthesis of amides. The results are
summarized in Scheme 3. Different esters, no matter from
aromatic or aliphatic carboxylic acid, could smoothly afford
the amidation to the corresponding amides in good yields.
However, if there was an electron-donating group in the es-
ters, the results were slightly better than that with elec-
tron-withdrawing group (Scheme 3, 3t–ab). In order to ex-
pand on the potential of this approach to be used in practi-
cal applications, the synthesis of pharmaceutically relevant
antidepressant moclobemide was performed smoothly to
obtain the desired product in 85% yield (Scheme 4).
Ar
R3
O
R3
O
N
N
N
N
ArOH
+
O
R1
R1
NH
R2
Based on the NHC-catalyzed saturated ester process, a
plausible mechanism is proposed for this amidation using
esters and amines (or hydrazines) in Scheme 5, which was
similar to those described in other NHC-catalyzed reactions
in the reported literature.15 As esters and NHC were mixed
before adding the amines, NHC catalyst only underwent a
nucleophilic attack at the carbonyl group of the esters to
form even more reactive intermediate, followed by the sub-
sequent attack of amines to afford the desired amides or hy-
drazides, which avoided or reduced the interactions be-
tween the amine and NHC.
R3
N
R2
Scheme 5 Proposed mechanism for the amidation
In summary, we have demonstrated an efficient and
convenient approach for amidation between aromatic es-
ters and aliphatic amines catalyzed by NHC. This strategy
tolerated a wide range of amines (including primary amines
and secondary amines) or hydrazines with good to excel-
lent yields in very short time, which is a valuable alterna-
tive approach for the synthesis of amides. Further explora-
tions of NHCs are in progress.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

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L.-Y. Chen, M.-F. Wu
Paper
Synthesis
N-(1-Phenylethyl)benzamide (3d)17
1H NMR and 13C NMR spectra were recorded in CDCl3 operating at 400
MHz and 100 MHz. 1H NMR chemical shifts are reported relative to
the residual proton signals of the deuterated solvent CDCl3 (7.26
ppm). 13C NMR chemical shifts were internally referenced to the deu-
terated solvent signals in CDCl3 (77.16 ppm). Data are represented as
follows: chemical shift, multiplicity (standard abbreviations), cou-
pling constant in hertz (Hz), and integration. IR spectra were recorded
on a PerkinElmer spectrometer. Mass spectra were recorded on a
time-of-flight mass spectrometer with an ESI source. High-perfor-
mance liquid chromatography (HPLC) was performed using a chro-
matograph equipped with a Chiralpak column (250 mm × 4.6 mm)
with hexane/i-PrOH as the eluent. Products were identified by com-
parison to spectral data reported in the literature. Unless otherwise
noted, all reagents were purchased from commercial supplies and
used without further purification.
White solid; yield: 96.9 mg (86%); mp 120–121 °C.
IR (neat): 3338, 2925, 2360, 1635, 1539, 1457, 1311, 694 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.80 (d, J = 8.0 Hz, 2 H), 7.51–7.48 (m, 1
H), 7.41–7.29 (m, 7 H), 6.69 (d, J = 8.0 Hz, 1 H), 5.39–5.30 (m, 1 H),
1.61 (d, J = 8.0 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 166.7, 143.4, 134.6, 131.4, 128.7,
128.5, 127.4, 127.1, 126.3, 49.3, 21.8.
MS (ESI): m/z = 248.1 [M + Na]+.
.
N-(3-Methoxyphenethyl)benzamide (3e)18
Colorless oil; yield: 121.2 mg (95%).
IR (neat): 3314, 2921, 2361, 1639, 1541, 1489, 1319, 784, 695 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.71 (d, J = 8.0 Hz, 2 H), 7.43 (t, J = 8.0
Hz, 1 H), 7.34 (t, J = 8.0 Hz, 2 H), 7.19 (t, J = 8.0 Hz, 1 H), 6.77 (t, J = 8.0
Hz, 2 H), 6.69 (s, 1 H), 3.74 (s, 3 H), 3.66 (dd, J1 = 8.0 Hz, J2 = 12.0 Hz, 2
H), 2.87 (t, J = 8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 167.6, 160.0, 140.6, 134.7, 131.5,
129.8, 128.6, 127.0, 121.2, 114.5, 112.1, 55.3, 41.2, 35.8.
Amidation Promoted by PreNHC 4; General Procedure
An oven-dried 10 mL Schlenk tube was charged with ester 1 (0.50
mmol), NHC precursor 4 (22 mg, 0.1 mmol), and DBU (15 mg, 0.1
mmol) in THF (2.0 mL). The mixture was stirred for 20 min, and the
amine 2 (0.6 mmol) was added. The reaction mixture was stirred at
r.t. until the full consumption of the ester 1 (typically, about 30 min).
The mixture was concentrated under reduced pressure and washed
with aq 1% NaHCO3 (3 ×) and purified by column chromatography on
silica gel (PE/EtOAc as the eluent, typically 5:1 to 10:1) to furnish the
corresponding amide.
MS (ESI): m/z = 256.1 [M + H]+.
N-(4-Chlorophenethyl)benzamide (3f)18
White solid; yield: 110.4 mg (85%); mp 148–149 °C.
IR (neat): 3346, 2921, 2359, 1640, 1534, 1487, 1311, 1091, 714, 693
cm–1
.
N-Benzylbenzamide (3a)8g
White solid; yield: 102.5 mg (97%); mp 60–61 °C.
IR (neat): 3285, 2366, 1653, 1558, 1489, 1316, 726, 693 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.79 (d, J = 4.0 Hz, 2 H), 7.50–7.46 (m, 1
H), 7.42–7.38 (m, 2 H), 7.34–7.25 (m, 5 H), 6.65 (s, 1 H), 4.61 (d, J = 8.0
Hz, 2 H).
1H NMR (400 MHz, CDCl3): δ = 7.70 (d, J = 8.0 Hz, 2 H), 7.49 (t, J = 8.0
Hz, 1 H), 7.40 (t, J = 8.0 Hz, 2 H), 7.28 (d, J = 8.0 Hz, 2 H), 7.15 (d, J = 8.0
Hz, 2 H), 6.32 (s, 1 H), 3.67 (dd, J1 = 6.7 Hz, J2 = 13.2 Hz, 2 H), 2.90 (t, J =
8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 162.0, 138.9, 138.2, 130.1, 128.9,
128.3, 128.0, 127.7, 44.1.
.
13C NMR (100 MHz, CDCl3): δ = 167.3, 138.2, 134.3, 131.5, 128.7,
127.5, 127.8, 127.5, 126.9, 44.0.
MS (ESI): m/z = 260.1 [M + H]+.
MS (ESI): m/z = 212.1 [M + H]+.
N-(3-Methoxypropyl)benzamide (3g)19
White solid; yield: 102.9 mg (86%); mp 96–97 °C.
N-(4-Methoxybenzyl)benzamide (3b)16
IR (neat): 3326, 2374, 1639, 1541, 1458, 1307, 1311, 1192, 805, 692
White solid; yield: 114.6 mg (95%); mp 95.8–96.2 °C.
cm–1
.
IR (neat): 3326, 2361, 1653, 1558, 1238, 719 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.70 (d, J = 8.0 Hz, 2 H), 7.44 (t, J = 8.0
Hz, 1 H), 7.36 (t, J = 8.0 Hz, 2 H), 7.10 (s, 4 H), 6.48 (s, 1 H), 3.65 (dd,
J1 = 8.0 Hz, J2 = 12.0 Hz, 2 H), 2.86 (t, J = 8.0 Hz, 2 H), 2.31 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 167.6, 136.1, 135.9, 134.8, 131.3,
129.4, 128.7, 128.5, 126.9, 41.3, 35.3, 21.0.
1H NMR (400 MHz, CDCl3): δ = 7.76 (d, J = 7.2 Hz, 2 H), 7.44 (t, J = 7.2
Hz, 1 H), 7.34 (t, J = 7.6 Hz, 2 H), 7.21 (d, J = 8.0 Hz, 2 H), 6.93 (s, 1 H),
6.81 (d, J = 8.0 Hz, 2 H), 4.49 (d, J = 4.0 Hz, 2 H), 3.74 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 167.5, 159.0, 134.5, 131.4, 130.5,
129.1, 128.4, 127.1, 114.0, 55.2, 43.4.
MS (ESI): m/z = 240.1 [M + H]+.
MS (ESI): m/z = 242.1 [M + H]+.
N-(2-Hydroxy-2-phenylethyl)benzamide (3h)18
N-(3,4-Dimethoxybenzyl)benzamide (3c)17
White solid; yield: 100.1 mg (83%); mp 164–166 °C.
IR (neat): 3301, 2929, 2361, 1617, 1541, 1316, 1063, 705, 693 cm–1
1H NMR (400 MHz, DMSO-d6): δ = 8.50 (s, 1 H), 7.83 (d, J = 8.0 Hz, 2
H), 7.51- 7.25 (m, 8 H), 5.52 (d, J = 4.0 Hz, 1 H), 4.81–4.77 (m, 1 H),
3.52–3.46 (m, 1 H).
13C NMR (100 MHz, DMSO-d6): δ = 166.9, 144.3, 135.0, 131.6, 128.7,
128.5, 127.7, 127.5, 126.5, 71.7, 48.2.
MS (ESI): m/z = 242.1 [M + H]+.
White solid; yield: 130.2 mg (96%); mp 116–117 °C.
.
IR (neat): 3330, 2925, 2359, 1636, 1527, 1427, 1264, 1140, 800, 690
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.80 (d, J = 8.0 Hz, 2 H), 7.47–7.44 (m, 1
H), 7.36 (t, J = 8.0 Hz, 2 H), 7.03 (s, 1 H), 6.85 (t, J = 4.0 Hz, 2 H), 6.77 (d,
J = 4.0 Hz, 1 H), 4.52 (d, J = 4.0 Hz, 2 H), 3.81 (s, 3 H), 3.78 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 167.7, 136.6, 134.8, 131.5, 128.6,
127.5, 127.0 122.3, 119.6, 118.8, 113.0, 111.5, 40.4, 25.4.
MS (ESI): m/z = 272.1 [M + H]+.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

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L.-Y. Chen, M.-F. Wu
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Synthesis
N-(Cyclopropylmethyl)benzamide (3i)18
IR (neat): 3242, 1647, 1511, 1483, 1327, 1245, 1070, 914, 820, 707,
693 cm–1
.
White solid; yield: 78.9 mg (90%); mp 78–80 °C.
IR (neat): 3309, 3097, 1632, 1543, 1493, 1296, 695 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.80 (d, J = 8.0 Hz, 2 H), 7.47 (t, J = 8.0
Hz, 1 H), 7.39 (t, J = 8.0 Hz, 2 H), 6.68 (s, 1 H), 3.29 (dd, J1 = 4.0 Hz, J2 =
8.0 Hz, 2 H), 1.08–1.02 (m, 1 H), 0.52 (dd, J1 = 4.7 Hz, J2 = 10.6 Hz, 2 H),
0.25 (dd, J1 = 4.7 Hz, J2 = 10.6 Hz, 2 H).
1H-NMR (400 MHz, DMSO-d6): δ = 10.34 (d, J = 2.8 Hz, 1 H), 7.92 (d, J =
3.2 Hz, 2 H), 7.73 (d, J = 3.2 Hz, 1 H), 7.59–7.55 (m, 1 H), 7.52–7.48 (m,
2 H), 6.97 (d, J = 8.4 Hz, 2 H), 6.72 (d, J = 8.4 Hz, 2 H), 2.16 (s, 3 H).
13C NMR (100 MHz, DMSO-d6): δ = 166.2, 147.2, 133.1, 131.5, 129.1,
128.4, 127.2, 112.6.
.
MS (ESI): m/z = 227.1 [M + H]+.
13C NMR (100 MHz, CDCl3): δ = 167.6, 134.8, 131.3, 128.5, 127.0, 44.9,
10.8, 3.5.
MS (ESI): m/z = 198.1 [M + Na]+.
N-Isopropylbenzohydrazide (3o)22
Yellow solid; yield: 53.5 mg (60%); mp 57–58 °C.
N-Butylbenzamide (3j)8g
IR (neat): 3431, 3300, 2970, 2929, 1638, 1541, 1341, 1071, 900, 694
cm–1
.
Yellow oil; yield: 70.9 mg (80%).
1H NMR (400 MHz, CDCl3): δ = 7.77–7.75 (m, 1 H), 7.51–7.39 (m, 4 H),
4.0 (d, J = 3.2 Hz, 2 H), 3.25–3.19 (m, 1 H), 1.18 (d, J = 8.0 Hz, 3 H), 1.10
(d, J = 8.0 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 167.5, 133.1, 131.8, 129.8, 128.7,
128.6, 127.0, 126.7, 51.5, 20.9.
IR (neat): 3317, 2962, 1637, 1541, 1490, 1308, 694 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.79–7.76 (m, 2 H), 7.47–7.36 (m, 3 H),
6.66 (s, 1 H), 3.41 (dd, J1 = 4.0 Hz, J2 = 12.0 Hz, 2 H), 1.61–1.54 (m, 2 H),
1.42–1.33 (m, 2 H), 0.92 (t, J = 8.0 Hz, 3 H).
13C NMR (100 MHz, CDCl3): δ = 167.7, 135.0, 131.2, 128.5, 127.0, 39.9,
31.8, 20.2, 13.8.
MS (ESI): m/z = 179.1 [M + H]+.
MS (ESI): m/z = 200.1 [M + Na]+.
N-Benzyl-N-methylbenzamide (3p)17
Colorless oil; yield: 95.7 mg (85%).
IR (neat): 3248, 1633, 1482, 1399, 1069, 719, 697 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.47–7.17 (m, 10 H), 4.76 (s, 1 H), 4.51
(s, 1 H), 2.95 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 171.4, 170.8, 136.6, 136.3, 135.8,
129.0, 128.2, 127.8, 127.6, 126.9, 126.4, 54.5, 50.2, 36.3, 32.5.
MS (ESI): m/z = 248.1 [M + Na]+.
N-(3-Methoxypropyl)benzamide (3k)18
.
Colorless oil; yield: 85.0 mg (88%).
IR (neat): 3338, 2925, 1636, 1541, 1381, 1307, 1120, 915, 695 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.78–7.76 (m, 2 H), 7.48–7.37 (m, 3 H),
7.23 (s, 1 H), 3.56–3.50 (m, 4 H), 3.35 (s, 3 H), 1.90–1.84 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 167.4, 134.8, 131.2, 128.4, 126.9, 72.0,
58.8, 38.6, 29.0.
.
MS (ESI): m/z = 194.1 [M + H]+.
(1H-Benzo[d]imidazol-1-yl)phenylmethanone (3q)23
White solid; yield: 83.3 mg (75%); mp 71–72 °C.
IR (neat): 3301, 2917, 2360, 1647, 1539, 1459, 1358, 749, 711 cm–1
N-(1-Benzylpiperidin-4-yl)benzamide (3l)20
.
White solid; yield: 128.7 mg (87%); mp 171.5–172.5 °C.
1H NMR (400 MHz, CDCl3): δ = 8.23–8.19 (m, 2 H), 7.86–7.80 (m, 3 H),
7.70 (t, J = 8.0 Hz, 1 H), 7.60 (t, J = 8.0 Hz, 2 H), 7.48–7.42 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 167.3, 144.2, 143.2, 133.4, 133.0,
132.3, 129.7, 129.2, 125.9, 125.5, 120.7, 115.6.
MS (ESI): m/z = 223.1 [M + H]+.
IR (neat): 3309, 2913, 2786, 2366, 1634, 1541, 1340, 739, 695 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.76 (d, J = 4.0 Hz, 2 H), 7.47–7.27 (m, 8
H), 6.23 (d, J = 8.0 Hz, 1 H), 4.01 (s, 1 H), 3.52 (s, 2 H), 2.86 (d, J = 12.0
Hz, 2 H), 2.17 (t, J = 12.0 Hz, 2 H), 2.01 (d, J = 12.0 Hz, 2 H), 1.60 (dd,
J1 = 8.0 Hz, J2 = 20.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 166.9, 138.3, 134.8, 131.3, 129.1,
128.5, 128.2, 127.1, 127.0, 63.0, 52.3, 47.1, 32.2.
Phenyl(pyrrolidin-1-yl)methanone (3r)8g
MS (ESI): m/z = 295.1 [M + H]+.
Colorless oil; yield: 80.6 mg (92%).
IR (neat): 2974, 1623, 1575, 1419, 792, 718, 700 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.52–7.39 (m, 5 H), 3.64 (t, J = 8.0 Hz, 2
H), 3.42 (t, J = 8.0 Hz, 2 H), 1.99–1.92 (m, 2 H), 1.89–1.83 (m, 2 H).
.
N′-Phenylbenzohydrazide (3m)21
Orange solid; yield: 86.0 mg (81%); mp 165–167 °C.
IR (neat): 3326, 2921, 2357, 1643, 1496, 1303, 691 cm–1
.
13C NMR (100 MHz, CDCl3): δ = 169.7, 137.2, 129.7, 128.2, 127.0, 49.5,
1H NMR (400 MHz, CDCl3): δ = 8.07 (s, 1 H), 7.83 (d, J = 8.0 Hz, 2 H),
7.55 (t, J = 8.0 Hz, 1 H), 7.46 (t, J = 8.0 Hz, 2 H), 7.24 (t, J = 8.0 Hz, 2 H),
6.91 (d, J = 8.0 Hz, 3 H).
46.1, 26.3, 24.4.
MS (ESI): m/z = 198.1 [M + Na]+.
13C NMR (100 MHz, DMSO-d6): δ = 166.9, 150.1, 133.5, 132.1, 129.3,
Methyl Benzoyl-L-phenylalaninate (3s)18
129.0, 127.8, 119.2, 112.8.
MS (ESI): m/z = 213.1 [M + H]+.
Colorless oil; yield: 92.1 mg (65%).
IR (neat): 3308, 2952, 1745, 1647, 1624, 1573, 1478, 1437, 1358,
1217, 1092, 1030, 914, 700 cm–1
.
N′-(p-Tolyl)benzohydrazide (3n)21
White solid; yield: 84.8 mg (75%); mp 134–135 °C.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

G
L.-Y. Chen, M.-F. Wu
Paper
Synthesis
1H NMR (400 MHz, CDCl3): δ = 7.72 (d, J = 8.0 Hz, 2 H), 7.49 (t, J = 8.0
Hz, 1 H), 7.40 (t, J = 8.0 Hz, 2 H), 7.30–7.24 (m, 3 H), 7.14 (d, J = 4.0 Hz,
2 H), 6.68 (s, 1 H), 5.11–5.06 (m, 1 H), 3.75 (s, 3 H), 3.29 (dd, J1 = 4.0
Hz, J2 = 12.0 Hz, 1 H), 3.22 (dd, J1 = 4.0 Hz, J2 = 16.0 Hz, 1 H),
1H NMR (400 MHz, CDCl3): δ = 8.03 (d, J = 8.0 Hz, 1 H), 7.64 (d, J = 8.0
Hz, 1 H), 7.57–7.49 (m, 2 H), 7.37–7.33 (m, 5 H), 6.28 (s, 1 H), 4.61 (d,
J = 4.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 166.5, 146.4, 137.6, 133.7, 132.8,
130.5, 128.8, 128.0, 127.7, 124.5, 44.1.
13C NMR (100 MHz, CDCl3): δ = 172.1, 167.0, 136.0, 134.0, 131.8,
129.4, 128.7, 127.2, 127.1, 53.7, 52.4, 38.0.
MS (ESI): m/z = 284.1 [M + H]+.
MS (ESI): m/z = 257.1 [M + H]+.
N-Benzyl-2-oxo-2-phenylacetamide (3y)26
N-Benzyl-4-methylbenzamide (3t)17
White solid; yield: 107.7 mg (90%); mp 96–97 °C.
White solid; yield: 103.6 mg (92%); mp 132–133 °C.
IR (neat): 3309, 2917, 2366, 1639, 1558, 1507, 1319, 721, 694 cm–1
1H NMR (400 MHz, CDCl3): δ = 7.71 (s, 2 H), 7.37–7.24 (m, 7 H), 6.53
(s, 1 H), 4.65 (s, 2 H), 2.42 (s, 3 H).
IR (neat): 3256, 2925, 2353, 1646, 1558, 1454, 1226, 726, 688 cm–1
.
.
1H NMR (400 MHz, CDCl3): δ = 7.82 (d, J = 8.0 Hz, 2 H), 7.53–7.50 (m, 1
H), 7.45–7.41 (m, 2 H), 7.37–7.31 (m, 5 H), 6.65 (s, 1 H), 4.65 (d, J = 8.0
Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 166.7, 143.3, 134.7, 131.4, 128.7,
13C NMR (100 MHz, CDCl3): δ = 187.7, 161.8, 137.3, 134.5, 133.5,
128.5, 127.4, 127.1, 126.3, 49.3, 21.8.
131.3, 128.9, 128.6, 128.0, 127.9, 43.6.
MS (ESI): m/z = 226.1 [M + H]+.
MS (ESI): m/z = 262.1 [M + Na]+.
N-Benzyl-4-methoxybenzamide (3u)17
N-Benzyl-3-phenylpropanamide (3z)8a
White solid; yield: 114.6 mg (95%); mp 137–139 °C.
White solid; yield: 106.5 mg (89%); mp 87–89 °C.
IR (neat): 3252, 2361, 1631, 1541, 1507, 1328, 1248, 1025, 842, 723
IR (neat): 3293, 2921, 2366, 1638, 1542, 1458, 1311, 740, 694 cm–1
.
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.31–7.25 (m, 5 H), 7.22–7.18 (m, 3 H),
7.13 (d, J = 8.0 Hz, 2 H), 5.73 (s, 1 H), 4.38 (d, J = 8.0 Hz, 2 H), 2.98 (t, J =
8.0 Hz, 2 H), 2.50 (t, J = 8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 172.1, 140.8, 138.3, 128.6, 128.6,
128.4, 127.7, 127.4, 126.2, 43.5, 38.4, 31.7.
1H NMR (400 MHz, CDCl3): δ = 7.78 (d, J = 8.0 Hz, 2 H), 7.33 (d, J = 8.0
Hz, 4 H), 7.32–7.27 (m, 1 H), 6.89 (d, J = 8.0 Hz, 2 H), 6.51 (s, 1 H), 4.62
(d, J = 4.0 Hz, 2 H), 3.82 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 167.1, 162.4, 138.6, 128.9, 128.8,
128.0, 127.6, 126.8, 113.9, 55.5, 44.2.
MS (ESI): m/z = 242.1 [M + H]+.
MS (ESI): m/z = 240.1 [M + H]+.
N-Benzylthiophene-2-carboxamide (3aa)17
N-Benzyl-4-chlorobenzamide (3v)17
White solid; yield: 98.9 mg (91%); mp 102.5–103.5 °C.
White solid; yield: 98.3 mg (80%); mp 161.5–162.5 °C.
IR (neat): 3305, 2913, 2359, 1634, 1541, 1340, 1105, 743, 699 cm–1
.
IR (neat): 3314, 2921, 2366, 1637, 1541, 1487, 1328, 1082, 845, 712
1H NMR (400 MHz, CDCl3): δ = 7.48 (dd, J1 = 4.0 Hz, J2 = 20.0 Hz, 2 H),
7.34–7.26 (m, 5 H), 7.05 (t, J = 4.0 Hz, 1 H), 6.43 (s, 1 H), 4.60 (d, J = 8.0
Hz, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 166.6, 139.0, 135.0, 131.5, 131.2,
131.0, 128.6, 127.5, 41.0, 34.8.
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.72 (d, J = 8.0 Hz, 2 H), 7.40 (d, J = 8.0
Hz, 2 H), 7.37–7.31 (m, 5 H), 6.56 (s, 1 H), 4.61 (d, J = 4.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 166.5, 138.1, 137.9, 132.9, 129.0,
128.6, 128.0, 127.8, 44.4.
MS (ESI): m/z = 268.1 [M + Na]+.
MS (ESI): m/z = 218.1 [M + H]+.
N-Benzylcyclohexanecarboxamide (3ab)27
N-Benzyl-2-fluorobenzamide (3w)24
White solid; yield: 88.0 mg (81%); mp 113–114 °C.
White solid; yield: 100.9 mg (88%); mp 67–69 °C.
IR (neat): 3301, 2921, 1647, 1528, 1453, 1300, 1217, 755, 698 cm–1
IR (neat): 3424, 2924, 2859, 1635, 1459, 1041, 494 cm–1
.
.
1H NMR (400 MHz, CDCl3): δ = 7.34–7.24 (m, 5 H), 5.90 (s, 1 H), 4.41
(d, J = 8.0 Hz, 2 H), 2.15–2.07 (m, 1 H), 1.89–1.86 (m, 2 H), 1.80–1.76
(m, 2 H), 1.66–1.63 (m, 1 H), 1.51–1.41 (m, 2 H), 1.31–1.16 (m, 3 H).
13C NMR (100 MHz, CDCl3): δ = 176.1, 138.7, 128.8, 127.8, 127.5, 45.6,
43.4, 29.8, 25.8.
1H NMR (400 MHz, CDCl3): δ = 8.11 (t, J = 8.0 Hz, 1 H), 7.47–7.46 (m, 1
H), 7.35–7.25 (m, 6 H), 7.13 (dd, J1 = 8.0 Hz, J2 = 12.0 Hz, 2 H), 4.67 (d,
J = 8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 163.4, 160.7 (d, J = 246.0 Hz), 138.2,
133.4 (d, J = 9.0 Hz), 132.2, 128.8, 127.8, 127.6, 124.9 (d, J = 3.0 Hz),
121.2 (d, J = 11.0 Hz), 116.1 (d, J = 25.0 Hz), 44.2.
MS (ESI): m/z = 218.2 [M + H]+.
MS (ESI): m/z = 230.1 [M + H]+.
4-Chloro-N-(2-morpholinoethyl)benzamide (13)11
White solid; yield: 114.2 mg (85%); mp 136–137 °C.
N-Benzyl-2-nitrobenzamide (3x)25
IR (neat): 3285, 2925, 2357, 1635, 1558, 1458, 1311, 1117, 1082,
Brown solid; yield: 98.7 mg (77%); mp 121–122 °C.
1017, 866, 731, 682 cm–1
.
IR (neat): 3280, 2925, 2366, 1653, 1540, 1489, 1345, 871, 726, 693
1H NMR (400 MHz, CDCl3): δ = 7.70 (d, J = 8.0 Hz, 2 H), 7.37 (d, J = 8.0
Hz, 2 H), 6.89 (s, 1 H), 3.70 (t, J = 4.0 Hz, 4 H), 3.51 (dd, J1 = 4.0 Hz, J2 =
12.0 Hz, 2 H), 2.57 (t, J = 8.0 Hz, 2 H), 2.48 (s, 4 H).
cm–1
.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

H
L.-Y. Chen, M.-F. Wu
Paper
Synthesis
13C NMR (100 MHz, CDCl3): δ = 166.4, 137.7, 133.0, 128.9, 128.5, 77.5,
77.2, 76.8, 67.0, 57.0, 53.4, 36.2.
MS (ESI): m/z = 291.1 [M + Na]+.
(10) For selected examples, see: (a) Yao, H.; Yamamoto, K. Chem.
Asian J. 2012, 7, 1542. (b) Yao, H.; Tang, Y.; Yamamoto, K. Tetra-
hedron Lett. 2012, 53, 5094. (c) Pilo, M.; Porcheddu, A.; De Luca,
L. Org. Biomol. Chem. 2013, 11, 8241. (d) Dettori, G.; Gaspa, S.;
Porcheddu, A.; De Luca, L. Adv. Synth. Catal. 2014, 356, 2709.
(e) Tan, B.; Toda, N.; Barbas, C. F. Angew. Chem. Int. Ed. 2012, 51,
12538.
Funding Information
(11) Iqbal, N.; Cho, E. J. J. Org. Chem. 2016, 81, 7453.
(12) For selected reviews, see: (a) Enders, D.; Niemeier, O.; Henseler,
A. Chem. Rev. 2007, 107, 5606. (b) Bugaut, X.; Glorius, F. Chem.
Soc. Rev. 2012, 41, 3511. (c) Ryan, S. J.; Candish, L.; Lupton, D. W.
Chem. Soc. Rev. 2013, 42, 4906. (d) Ye, S.; Chen, X.-Y. Synlett
2013, 24, 1614. (e) Mahatthananchai, J.; Bode, J. W. Acc. Chem.
Res. 2014, 47, 696. (f) Flanigan, D. M.; Romanov-Michailidis, F.;
White, N. A.; Rovis, T. Chem. Rev. 2015, 115, 9307. (g) Wang, M.
H.; Scheidt, K. A. Angew. Chem. Int. Ed. 2016, 55, 14912.
(h) Reyes, E.; Uria, U.; Carrillo, L.; Vicario, J. L. Synthesis 2017, 49,
451. (i) Kathleen, J. R.; Murauski, A.; Jaworski, A.; Scheidt, K. A.
Chem. Soc. Rev. 2018, 47, 1773.
The authors are grateful for financial support from the Scientific Re-
search Foundation for the Returned Overseas Chinese Scholars, State
Education Ministry, and the Students Innovation Program in Shanghai
University of Engineering Science (cs1704005).()
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1610355.
S
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p
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orti
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gInformati
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H