Highly efficient and facile synthesis of β-enaminones catalyzed by diphenylammonium triflate

Article abstract of DOI:10.1007/s11696-019-00838-2

Abstract: The catalytic performance of diphenylammonium triflates as an organocatalyst in the synthesis of β-enaminones from various substituted β-diketones and amides (or amines) were evaluated. A wide range of β-enaminones were efficiently synthesized in good to excellent yields under mild reaction conditions. Applying diphenylammonium triflate (DPAT) as catalyst makes this protocol cost-effective, low corrosive and easy to handle. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s11696-019-00838-2

Chemical Papers
https://doi.org/10.1007/s11696-019-00838-2
ORIGINAL PAPER
Highly efcient and facile synthesis of β‑enaminones catalyzed
by diphenylammonium trifate
Ting‑Ting Zhao1 · Jiang‑Long Song1 · Feng‑Qing Hong2 · Jian‑Sheng Xia2 · Jian‑Jun Li1
Received: 7 March 2019 / Accepted: 28 May 2019
© Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
The catalytic performance of diphenylammonium trifates as an organocatalyst in the synthesis of β-enaminones from various
substituted β-diketones and amides (or amines) were evaluated. A wide range of β-enaminones were efciently synthesized
in good to excellent yields under mild reaction conditions. Applying diphenylammonium trifate (DPAT) as catalyst makes
this protocol cost-efective, low corrosive and easy to handle.
Graphic abstract
Keywords Ammonium trifates · Diphenylammonium trifate · β-enaminones · Organocatalyst
Introduction
β-enaminones are important precursors for the construc-
tion of a variety of pharmaceutical compounds, including
anti-convulsivant, anti-infammatory agents, anti-cancer
agents, and quinoline antibacterials (Edafogho et al. 2006;
Tabatabaeian et al. 2014; Zhang et al. 2014). In addition,
substituted β-enaminones are commonly used as interme-
diates in the synthesis of heterocycles, such as pyridines
(Chen et al. 2017), indoles (Li et al. 2018), pyrroles (Zhao
et al. 2017) and isoxazole derivatives (Fatima and Adel
2005). Due to the extensive application of β-enaminones
in organic synthesis and drug development, much attention
has been given to development of facile, green, and practical
methods for the preparation of β-enaminones. The classical
method to synthesize β-enaminones synthesis involves direct
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-019-00838-2) contains
supplementary material, which is available to authorized users.
* Jian-Jun Li
lijianjun@zjut.edu.cn
1
National Engineering Research Center for Process
Development of Active Pharmaceutical Ingredients,
College of Pharmaceutical Sciences, Zhejiang
University of Technology, Hangzhou 310014,
People’s Republic of China
2
TianTai YiSheng Biochemical Co., Ltd, 197 Fengze Road,
Tiantai 317299, People’s Republic of China
Vol.:(0123456789)
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condensation of corresponding amine with 1,3-dicarbonyl
compounds via catalysis of strong protonic acid (Baraldi
et al. 1983; Martin et al. 1961). Subsequently, greener meth-
ods which employed the metal as catalysts such as NaAuCl4
(Arcadi et al. 2003), Zn(ClO4)2·6H2O (Bartoli et al. 2004),
Er(OTf)3 (Dalpozzo et al. 2006), Zn[aminoacid]2 (Winck
et al. 2014) and Ca(CF3COO)2 (Harrad et al. 2010), to pre-
pare β-enaminones were developed. Although great progress
has been achieved in past decades, most of them sufer from
one or more of limitations, such as unsatisfactory yields,
the use of expensive or less easily available reagents, highly
corrosive, and longer reaction time. Until now, studies on
the synthesis of β-enaminones involved the condensation of
β-ketoesters with less active amides has rarely been reported
(Ovenden and Capon 1999; Guin et al. 2007; Klapars et al.
2005). Consequently, developing the green and highly ef-
cient methods for synthesis of a wide range of β-enaminones
under less hazardous conditions is of prime importance.
Ammonium trifates have been used as a novel type of
organocatalyst in a variety of reactions (Wakasugi et al.
2000; Mercs et al. 2007; Li et al. 2012; Mahjoob and Mon-
tazeri 2012; Li and Gui 2014; Jiang et al. 2018) and have dis-
played great catalytic activity and efciency. Compared with
strong protonic acid or metal catalyst, it has the advantages
of reusable, cost-efective, operational simplicity and low
corrosive. Despite the considerable success that has been
achieved, we wished to expand the application of ammonium
trifate to the preparation of β-enaminones. Herein, we report
a green, mild and efcient method for the condensation of
β-ketoesters with amines or amides (sulfonamides) to syn-
thesize a variety of β-enaminones in good to excellent yields,
catalyzed by DPAT (Scheme 1).
Results and discussion
To begin our study, we chose benzamide and ethyl acetoac-
etate as model reactants to examine and optimized the con-
ditions of this condensation. The transformation was ini-
tially carried out in toluene under refuxing for 6 h without
adding any catalyst and the experimental result showed that
no desired product was detected. A variety of ammonium
trifates (Fig. 1, Table 1) such as piperidinium trifate (PT),
morpholinium trifate (MorT), (1-ethylpyrrolidin-2-yl)meth-
anaminium trifate (EPMAT), p-methoxyanilinium trifate
(p-MOAT), p-nitroanilinium trifate (p-NAT), 1-phenyle-
than-1-aminium trifate (1-PEAT), tributylaminium trifate
(TBAT) and diphenylammonium trifate (DPAT) were then
tested for this reaction. To our delight, DPAT showed an
excellent catalytic activity and the corresponding product
was obtained in 96% yield. Subsequently, we also explored
whether the amounts of DPAT would afect the efciency
of this reaction. It was observed that increasing or decreas-
ing the amount of DPAT all led to a slight decrease in the
yield (Table 1, entries 10, 11). Furthermore, various com-
monly used solvents including CH3CH2OH, THF, CH3CN,
cyclohexane, methylcyclohexane and p-xylene (Table 1,
entries 13–18) were examined. However, none of them gave
a better result than toluene.
On the basis of the screening of the reaction conditions, it
was concluded that this condensation should be performed
in toluene by employing DPAT as catalyst (10 mol%) under
refuxing for 6 h. To demonstrate the generality of this
method, the scope of the reaction was investigated under
the optimized conditions, and the results are summarized
in Table 2. This method was found to be applicable to a
wide range of β-diketones (β-ketoesters) and amides, deliv-
ering the desired product in moderate to excellent yields.
Moreover, β-diketones (β-ketoesters) and amides resulted
(Z)-β-enaminones with high stereoselectivity (Z/E > 20:1,
determined by 1H NMR spectroscopy of the crude reaction
Scheme 1 Diferent strate-
gies for the synthesis of
β-enaminones
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Fig. 1 Ammonium trifates
Table 1 Optimization of the reaction conditions
Entry
Catalyst (mol%)
Solvent
Yield (%)a
1
2
3
4
5
6
7
8
None
PT(10)
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
C2H5OH
THF
Trace
Trace
Trace
Trace
11
17
9
Trace
96
92
93
68
56
51
64
91
92
87
MorT(10)
EPMAT(10)
p-MOAT(10)
p-NAT(10)
1-PEAT(10)
TBAT(10)
DPAT(10)
DPAT(5)
DPAT(15)
DPAT(10)
DPAT(10)
DPAT(10)
DPAT(10)
DPAT(10)
DPAT(10)
DPAT(10)
9
10
11
12b
13
14
15
16
17
18
CH3CN
Cyclohexane
Methylcyclohexane
p-xylene
Reaction conditions: benzamide (0.6 mmol), ethyl acetoacetate (0.5 mmol) in refuxing solvent (2 mL), catalyst (5-15 mol %), 6 h
aIsolated yields after column chromatography based on ethyl acetoacetate
bAt 80 °C
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Table 2 Synthesis of
β-enaminones catalyzed by
DPATa
aReaction conditions: amides or amines (0.6 mmol), β-dicarbonyl compounds (0.5 mmol), and DPAT
(0.05 mmol), all reactions were stirred in refuxing toluene (2 mL), 6 h
b8 h
cUrea (0.6 mmol), β-dicarbonyl compounds (0.5 mmol), under optimized conditions
mixture). The occurrence of (Z)-selectivity was probably
due to feasible hydrogen-bond formation between (N)H
and O(=C). For example, the screened β-ketoesters were
all efective substrates examined, which could proceed this
condensation well with aromatic amides or aliphatic amides
to gave the corresponding products in 51–98% yields. Aro-
matic amides bearing electron-donating groups at 4-position
of aromatic ring such as methoxy 2b provided the desired
products in 93% yield. The electron-withdrawing substitu-
ents at 4-position of aryl group such as chloro or nitro, seem
to disfavor this transformation, as the yield was reduced to
79%, 51%. β-Diketone substrate was also tolerated well for
this transformation and provided the desired product 3h
in 86% yield. However, it failed to give the product when
1,3-cyclohexanedione or 1,3-diphenylpropane-1,3-dione
was used as β-diketone substrate mainly due to their steric
hindrance and inherent low reactivity (Table 2). Satisfac-
torily, amides substrate including the aromatic amides,
aliphatic amide and benzylamide were all compatible for
this protocol, providing a series of products β-enaminones
via condensation with β-diketones (β-ketoesters) (Table 2).
Furthermore, an unprotected β-amino product was observed
when urea was used as substrate. Urea successfully functions
as a latent scafold for amino group. Products 3i, 3j and 3k,
the intermediates for synthesis of sitagliptin that is an active
ingredient of antidiabetic drug used in the treatment of type
2 diabetes mellitus (T2DM) (Enguzel-Alperen et al. 2018),
could be synthesized via the condensation with amides
under optimized conditions in satisfied yields. Further-
more, aromatic amines and benzylamine were investigated
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for this reaction and the results are given in Table 2. Screen-
ing revealed that the reactions between aromatic amines and
1,3-diketones or β-ketoesters could proceeded smoothly and
provided the desired products 3v–3z in 47–95% yields. The
general applicability of our method was then extended to the
condensation of α-ketoesters with acetamide or benzamide
(Scheme 2). α-Ketoesters with acetamide only led to the
synthesis of desired products 4a and 4d in moderate yields.
Moreover, it only selectively gave the product 4d when
the condensation between acetamide and ethyl 2,4-dioxo-
pentanoate was proceeded under optimized conditions. To
our surprise, except for the desired product 4b (46%), an
unexpected bis(benzamide) byproduct 4c was also obtained
between the condensation of benzamide with ethyl pyruvate
in 21% yield (Scheme 2). Interestingly, a similar result was
obtained when using 2,4-dioxovalerate as substrate instead
of ethyl pyruvate. Besides the isolation of the desired prod-
uct 4e in a yield of 45%, the coupling product 4f was isolated
in 21% yield. Finally, it was delight to fnd that this approach
was also applicable to sulfonamides though its activity was
inferior to amides, such as 4-methoxybenzenesulfonamide,
giving the corresponding products in 31 to 61% yields
(Scheme 3, 5a–5d).
To gain mechanistic insight into the transformation of
4c, the control experiment was carried out (Scheme 4).
Scheme 2 Reaction between
acetamide (benzamide) and
α-ketoester
Scheme 3 Condensation reac-
tion between 4-methoxyben-
zenesulfonamide and α- and
β-keto compounds
Scheme 4 Control experiment
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Scheme 5 Proposed mechanism
(a)
(b)
The condensation of benzamide with 4b was conducted
and provided the desired product 4c in 28% yield.
the imine A is generated after the condensation of benza-
mide with ethyl pyruvate in the presence of DPAT. Subse-
quently, the imine A is attacked by the benzamide to form
the coupling product 4c. Meanwhile, A is also transformed
into the more stable product 4b by removing the catalyst
DPAT (Scheme 5b). In addition, no bis-addition product was
detected between the reaction of acetamide with α-ketoesters
(Scheme 2), suggesting that the imine intermediate formed
by acetamide and α-ketoesters is probably unstable due to
lack of large conjugated system.
According to the above mentioned observations, a pos-
sible mechanism for the DPAT-catalyzed synthesis of 3a
and 4c has been proposed in Scheme 5. Initially, the 3aʹ
is formed after condensation between benzamide and ethyl
acetoacetate in the presence of DPAT, followed by elimina-
tion of a molecule of H2O to generate the imine intermediate
3aʺ. After removing the catalyst DPAT, the 3aʺ is trans-
formed into the desired product 3a (Scheme 5a). Similarly,
Scheme 6 Gram-scale synthesis
of product 3a and 3i
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To further demonstrate the practicality of this transforma-
tion, a gram-scale experiment of 1a and 1i were carried out.
The result is shown in the Scheme 6, 3a and 3i was obtained
in 94% and 82% yields, respectively, which indicated the
easy scale up of this transformation.
(Z)‑Ethyl 3‑benzamidobut‑2‑enoate (3a)
White solid; m.p.: 47.3–47.6 °C. (lit. of Aberhart and Lin
1981)
1H NMR (400 MHz, CDCl3) δ 12.03 (s, 1H), 7.92–7.90
(m, 2H), 7.49 (d, J=7.2 Hz, 1H), 7.43 (t, J=8.0 Hz, 2H),
5.00 (s, 1H), 4.17 (q, J=7.2 Hz, 2H), 2.52 (s, 3H), 1.30 (t,
J=7.2 Hz, 3H).
Conclusions
13C NMR (100 MHz, CDCl3) δ 169.2, 165.0, 155.1,
133.8, 132.1, 128.6, 127.4, 97.2, 59.9, 22.1, 14.4.
MS (ESI): m/z=234.1 [M+H]+.
DPAT is widely used as organocatalyst in various chemical
transformations (Wakasugi et al. 2000; Li et al. 2012). In
this work, we have developed a novel method for the synthe-
sis of β-enaminones using DPAT as the metal-free catalyst.
This protocol featured by its environmentally benign, simple
work-up procedure, easy manipulation and highly efcient,
which make it an attractive and useful addition to the exist-
ing methods for the synthesis of β-enaminones. Notably, this
reaction can be run on the gram-scale, giving the desired
products in 94% and 82% yields. Moreover, the amides and
sulfonamides were well compatible for this protocol. Further
applications of DPAT are ongoing in our laboratory.
(Z)‑Ethyl 3‑(4‑methoxybenzamido)but‑2‑enoate
(3b)
White solid; m.p.: 108.5–109.8 °C.
1H NMR (400 MHz, CDCl3) δ 12.09 (s, 1H), 7.97 (d,
J=9.2 Hz, 2H), 7.00 (d, J=9.2 Hz, 2H), 5.02 (d, J=0.8 Hz,
1H), 4.22 (q, J = 7.2 Hz, 2H), 3.88 (s, 3H), 2.54 (d,
J=0.8 Hz, 3H), 1.32 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 169.6, 164.9, 162.9,
155.7, 129.7, 126.3, 114.1, 96.8, 59.9, 55.4, 22.1, 14.3.
HRMS (ESI): C14H17NNaO4 [M + Na]+; calculated:
286.1050, found: 286.1050.
Experimental
(Z)‑Ethyl 3‑(4‑chlorobenzamido)but‑2‑enoate (3c)
All reagents were purchased from commercial suppliers
and used without further purifcation. The fash column
chromatography was carried out over silica gel (200–400
mesh), purchased from Qingdao Haiyang Chemical Co., Ltd.
Melting points were determined on a Büchi B-540 capil-
lary melting point apparatus and uncorrected. 1H NMR and
13C NMR spectra were recorded at VARIAN-400, using
DMSO-d6 or CDCl3 as the solvent with tetramethylsilane
(TMS) as an internal standard. Chemical shifts are given
in δ relative to TMS, the coupling constants J are given
in Hz. Mass spectra were measured with Thermo Finnigan
LCQ-Advantage. High resolution mass spectral (HRMS)
analyze were measured on an Agilent 6210 TOF LC/MS
and Q-Exactuve(Thermo USA) UHPLC-Q-Orbitrap using
ESI techniques.
White solid; m.p.: 88.3–89.1 °C.
1H NMR (400 MHz, CDCl3) δ 12.17 (s, 1H), 7.94 (d,
J=8.8 Hz, 2H), 7.48 (d, J=8.4 Hz, 2H), 5.07 (d, J=0.8 Hz,
1H), 4.22 (q, J=7.2 Hz, 2H), 2.54 (d, J=0.8 Hz, 3H), 1.32
(t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 169.6, 164.2, 155.2,
138.8, 132.4, 129.1, 129.0, 97.7, 60.1, 22.0, 14.3.
HRMS (ESI): C13H14ClNNaO3 [M + Na]+; calculated:
290.0554 found: 290.0566.
(Z)‑Ethyl 3‑(4‑nitrobenzamido)but‑2‑enoate (3d)
Yellow solid; m.p.: 122.3–123.0 °C.
1H NMR (400 MHz, CDCl3) δ 12.36 (s, 1H), 8.36 (d,
J=8.4 Hz, 2H), 8.16 (d, J=8.8 Hz, 2H), 5.13 (s, 1H), 4.23
(q, J=7.2 Hz, 2H), 2.56 (s, 3H), 1.33 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 169.6, 163.2, 154.7,
150.0, 139.5, 128.8, 124.0, 98.7, 60.3, 21.9, 14.3.
HRMS (ESI): C13H14N2NaO5 [M + Na]+; calculated:
301.0795 found: 301.0797.
General procedures for the synthesis
of β‑enaminones
A mixture of amides (amines) (0.6 mmol), 1,3-dicarbonyl
compounds (0.5 mmol), and DPAT (0.05 mmol) was stirred
in refuxing toluene for 6 h. After completion of the reaction
(Reaction progress was monitored by TLC), the mixture was
washed with water (3×10 mL). The organic layer was dried
over anhydrous Na2SO4, fltered and evaporated. Purifcation
by column chromatography on silica gave the product 3, 4, 5.
(Z)‑Ethyl 3‑(picolinamido)but‑2‑enoate (3e)
White solid; m.p.: 76.7–77.3 °C.
1H NMR (400 MHz, CDCl3) δ 13.00 (s, 1H), 8.77 (d,
J=4.4 Hz, 1H), 8.22 (d, J=8.0 Hz, 1H), 7.91–7.87 (m, 1H),
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7.52–7.46 (m, 1H), 5.09 (s, 1H), 4.26 (q, J =7.2 Hz, 2H),
2.56 (s, 3H), 1.32 (t, J=7.2 Hz, 3H).
(dm, JF = 15.0 Hz), 118.4 (dm, JF = 20.0 Hz), 105.5 (tm,
JF =24.0 Hz), 98.1 (d, JF =4.0 Hz), 51.5, 32.7.
HRMS (ESI): C18H13F3NO3 [M-H]−; calculated:
348.0853, found: 348.0861.
13C NMR (100 MHz, CDCl3) δ 168.5, 163.4, 153.4,
149.9, 148.8, 137.4, 126.6, 122.9, 98.9, 59.9, 22.1, 14.4.
HRMS (ESI): C12H14N2NaO3 [M + Na]+; calculated:
257.0897 found: 257.0911.
(Z)‑Methyl
3‑(2‑phenylacetamido)‑4‑(2,4,5‑trifuorophenyl)
but‑2‑enoate (3j)
(Z)‑Methyl 3‑benzamidobut‑2‑enoate (3f)
White solid; m.p.: 104.2–104.3 °C.
White solid; m.p.: 55.2–55.7 °C. (lit. of Holz et al. 2003)
1H NMR (400 MHz, CDCl3) δ 12.08 (s, 1H), 7.98–7.95
(m, 2H), 7.56–7.52 (m, 1H), 7.50–7.46 (m, 2H), 5.04 (s,
1H), 3.74 (s, 3H), 2.54 (s, 3H).
1H NMR (400 MHz, CDCl3) δ 11.11 (s, 1H), 7.35–7.25
(m, 5H), 6.99–6.93 (m, 1H), 6.91–6.84 (m, 1H), 4.80 (s,
1H), 4.11 (s, 2H), 3.66 (s, 3H), 3.63 (s, 2H).
13C NMR (100 MHz, CDCl3) δ 169.5, 168.7, 155.8 (dm,
JF = 244.0 Hz), 154.1, 148.9 (dm, JF = 235.0 Hz), 146.5
(dm, JF = 241.0 Hz), 133.4, 129.1, 128.7, 127.3, 120.1
(dm, JF = 20.0 Hz), 118.1 (dm, JF = 20.0 Hz), 105.4 (tm,
JF =19.0 Hz), 98.0, 51.3, 45.6, 32.5.
13C NMR (100 MHz, CDCl3) δ 169.6, 165.1, 155.4,
133.8, 132.2, 128.7, 127.5, 96.8, 51.2, 22.2.
MS (ESI): m/z=242.4 [M+Na]+.
(Z)‑Tert‑butyl 3‑benzamidobut‑2‑enoate (3g)
HRMS (ESI): C19H15F3NO3 [M-H]−; calculated:
362.1010, found: 362.0998.
White solid; m.p.: 80.2–80.7 °C.
1H NMR (400 MHz, CDCl3) δ 12.14 (s, 1H), 7.97–7.95
(m, 2H), 7.54–7.47 (m, 3H), 4.95 (s, 1H), 2.50 (s, 3H), 1.50
(s, 9H).
(Z)‑Methyl 3‑acetamido‑4‑(2,4,5‑trifuorophenyl)
but‑2‑enoate (3k)
13C NMR (100 MHz, CDCl3) δ 168.9, 165.2, 154.0,
134.0, 132.1, 128.6, 127.5, 99.2, 80.4, 28.4, 22.1.
HRMS (ESI): C15H20NO3 [M + H]+; calculated:
262.1438, found: 262.1435.
White solid; m.p.: 102.6–102.8 °C.
1H NMR (400 MHz, CDCl3) δ 11.04 (s, 1H), 7.03–6.96
(m, 1H), 6.89–6.83 (m, 1H), 4.78 (s, 1H), 4.11 (s, 2H), 3.68
(s, 3H), 2.13 (s, 3H).
13C NMR (100 MHz, CDCl3) δ 169.0, 168.6, 155.8 (dm,
JF = 243.0 Hz), 154.4, 149.0 (dm, JF = 248.0 Hz), 146.5
(dm, JF = 241.0 Hz), 120.2 (dt, JF = 19.0, 5.0 Hz), 118.2
(dt, JF = 19.0, 5.0 Hz), 105.4 (tm, JF = 26.0 Hz), 97.2 (d,
JF =4.0 Hz), 51.3, 32.4, 25.3.
(Z)‑N‑(4‑oxo‑4‑phenylbut‑2‑en‑2‑yl)benzamide (3h)
Yellow solid; m.p.: 108.6–109.2 °C. (lit. of Sugiura et al.
2009)
1H NMR (600 MHz, CDCl3) δ 13.87 (s, 1H), 8.14–8.13
(m, 2H), 7.99–7.98 (m, 2H), 7.62 (t, J = 7.2 Hz, 1H),
7.59–7.55 (m, 3H), 7.50 (t, J = 7.8 Hz, 2H), 6.21 (s, 1H),
2.71 (s, 3H).
HRMS (ESI): C13H11F3NO3 [M-H]−; calculated:
286.0697, found: 286.0691.
(Z)‑Methyl 3‑amino‑4‑methylpent‑2‑enoate (3l)
13C NMR (150 MHz, CDCl3) δ 191.9, 166.2, 158.2,
138.8, 133.8, 132.7, 132.5, 129.0, 128.6, 128.1, 127.7,
102.6, 22.8.
Yellow oil.
1H NMR (600 MHz, CDCl3) δ 4.53 (s, 1H), 3.61 (s, 3H),
2.30 (m, 1H), 1.12 (d, J=7.8 Hz, 6H).
13C NMR (150 MHz, CDCl3) δ 171.0, 169.7, 80.3, 50.0,
34.8, 21.1.
MS (ESI): m/z=288. 1 [M+Na]+.
(Z)‑Methyl 3‑benzamido‑4‑(2,4,5‑trifuorophenyl)
but‑2‑enoate (3i)
HRMS (ESI): C7H14NO2 [M+H]+; calculated: 144.1019,
found: 144.1021.
Yellow solid; m.p.: 119.8–120.0 °C.
1H NMR (400 MHz, CDCl3) δ 12.04 (s, 1H), 7.91–7.89
(m, 2H), 7.51 (t, J=7.6 Hz, 1H), 7.44 (t, J=8.0 Hz, 2H),
7.10–7.04 (m, 1H), 6.92–6.86 (m, 1H), 4.91 (s, 1H), 4.29 (s,
2H), 3.72 (s, 3H).
(Z)‑Ethyl 3‑acetamidobut‑2‑enoate (3m)
White solid; m.p.: 63.1–63.6 °C. (lit. of Lee and Zhang
2002)
1H NMR (400 MHz, CDCl3) δ 11.10 (s, 1H), 4.88 (s, 1H),
4.14 (q, J=7.2 Hz, 2H), 2.37 (s, 3H), 2.14 (s, 3H), 1.28 (t,
J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 169.4, 165.0, 156.0 (dm,
JF = 247.0 Hz), 155.0, 149.0 (dm, JF = 246.0 Hz), 146.5
(dm, JF = 242.0 Hz), 133.4, 132.5, 128.8, 127.6, 120.4
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13C NMR (100 MHz, CDCl3) δ 168.9, 168.6, 154.8, 96.3,
59.8, 25.3, 22.0, 14.4.
(Z)‑Methyl 3‑(benzylamino)but‑2‑enoate (3r)
MS (ESI): m/z=172.0 [M+H]+.
White solid; m.p.: 35.2–35.6 °C. (lit. of Hebbache et al.
2008).
1H NMR (400 MHz, CDCl3) δ 8.91 (s, 1H), 7.34–7.23
(m, 5H), 4.53 (s, 1H), 4.42 (d, J=6.4 Hz, 2H), 3.63 (s, 3H),
1.92 (s, 3H).
(Z)‑N‑(4‑oxo‑4‑phenylbut‑2‑en‑2‑yl)acetamide (3n)
13C NMR (100 MHz, CDCl3) δ 170.6, 161.6, 138.5,
128.6, 127.2, 126.5, 82.8, 50.0, 46.8, 19.4.
MS (ESI): m/z=206.1 [M+H]+.
Yellow solid; m.p.: 97.8–98.9 °C. (lit. of Sugiura et al. 2009)
1H NMR (500 MHz, CDCl3) δ 12.82 (s, 1H), 7.92 (d,
J=7.0 Hz, 2H), 7.55 (t, J=7.5 Hz, 1H), 7.47 (t, J=8.0 Hz,
2H), 6.05 (s, 1H), 2.53 (s, 3H), 2.24 (s, 3H).
13C NMR (125 MHz, CDCl3) δ 191.4, 169.9, 157.6,
138.7, 132.4, 128.6, 127.6, 101.6, 25.5, 22.5.
(Z)‑Ethyl 3‑(benzylamino)but‑2‑enoate (3s)
MS (ESI): m/z=226.1 [M+Na]+
White solid; m.p.: 22.1–22.6 °C. (lit. of Hebbache et al.
2008).
1H NMR (400 MHz, CDCl3) δ 8.93 (s, 1H), 7.34–7.23
(m, 5H), 4.52 (s, 1H), 4.42 (d, J = 6.4 Hz, 2H), 4.08 (q,
J=7.2 Hz, 2H), 1.91 (s, 3H), 1.26 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 170.3, 161.5, 138.6,
128.6, 127.2, 126.5, 83.2, 58.4, 46.8, 19.4, 14.7.
MS (ESI): m/z=220.4 [M+H]+.
(Z)‑Ethyl 3‑acetamido‑3‑phenylacrylate (3o)
White solid; m.p.: 42.5–44.8 °C. (lit. of Lee and Zhang
2002)
1H NMR (600 MHz, CDCl3) δ 10.67 (s, 1H), 7.43–7.36
(m, 5H), 5.30 (s, 1H), 4.25 (q, J=7.2 Hz, 2H), 2.19 (s, 3H),
1.34 (t, J=7.2 Hz, 3H).
13C NMR (150 MHz, CDCl3) δ 168.6, 168.4, 154.5,
135.9, 129.6, 128.0, 127.1, 101.1, 60.3, 24.8, 14.3.
MS (ESI): m/z=256.2 [M+Na]+
(Z)‑Tert‑butyl 3‑(benzylamino)but‑2‑enoate (3t)
Yellow oil. (lit. of Hebbache et al. 2008)
1H NMR (400 MHz, CDCl3) δ 8.87 (s, 1H), 7.34–7.22 (m,
5H), 4.45 (s, 1H), 4.40 (d, J=6.4 Hz, 2H), 1.87 (s, 3H), 1.46
(s, 9H).
(Z)‑Methyl 3‑acetamido‑4‑methylpent‑2‑enoate
(3p)
13C NMR (100 MHz, CDCl3) δ 170.4, 159.2, 138.9,
128.6, 127.1, 126.6, 85.0, 77.9, 46.8, 28.8, 19.4.
MS (ESI): m/z=248.2 [M+H]+.
Yellow oil. (lit. of Wu et al. 2011)
1H NMR (600 MHz, CDCl3) δ 11.15 (s, 1H), 5.07 (s, 1H),
3.87 (m, 1H), 3.71 (s, 3H), 2.15 (s, 3H), 1.12 (d, J=6.6 Hz,
6H).
13C NMR (150 MHz, CDCl3) δ 170.1, 168.4, 165.7, 92.3,
51.1, 29.3, 25.6, 21.3.
(Z)‑4‑(benzylamino)pent‑3‑en‑2‑one (3u)
MS (ESI): m/z=208.1 [M+H]+.
White solid; m.p.: 25.1–25.3 °C. (lit. of Chen et al. 2010)
1H NMR (400 MHz, CDCl3) δ 11.13 (s, 1H), 7.34–7.22
(m, 5H), 5.03 (s, 1H), 4.45 (d, J=6.4 Hz, 2H), 2.03 (s, 3H),
1.91 (s, 3H).
(Z)‑Ethyl 3‑(2‑(2‑oxopyrrolidin‑1‑yl)butanamido)
but‑2‑enoate (3q)
13C NMR (100 MHz, CDCl3) δ 195.0, 162.8, 137.8,
128.6, 127.2, 126.5, 95.8, 46.7, 28.9, 18.9.
MS (ESI): m/z=190.0 [M+H]+.
White solid; m.p.: 60.2–60.6 °C.
1H NMR (400 MHz, CDCl3) δ 11.42 (s, 1H), 4.92 (d,
J = 1.0 Hz, 1H), 4.66 (dd, J1 = 10.8 Hz, J2 = 4.8 Hz, 1H),
4.13 (q, J=7.2 Hz, 2H), 3.42–3.32 (m, 2H), 2.66–2.59 (m,
1H), 2.51–2.41 (m, 1H), 2.36 (d, J=1.0 Hz, 3H), 2.22–2.00
(m, 4H), 1.25 (t, J=7.2 Hz, 3H), 0.92 (t, J=7.6 Hz, 3H).
13C NMR (100 MHz, CDCl3): δ 176.6, 169.6, 168.9,
154.0, 98.2, 60.2, 57.7, 43.8, 31.0, 22.1, 21.3, 18.3, 14.7,
11.2.
(Z)‑4‑(phenylamino)pent‑3‑en‑2‑one (3v)
White solid; m.p.: 50.3–50.7 °C. (lit. of Chen et al. 2010).
1H NMR (400 MHz, CDCl3) δ 12.44 (s, 1H), 7.32 (t,
J=8.0 Hz, 2H), 7.17 (t, J=7.6 Hz, 1H), 7.11–7.06 (m, 2H),
5.18 (s, 1H), 2.10 (s, 3H), 1.99 (s, 3H).
13C NMR (100 MHz, CDCl3) δ 195.7, 159.9, 138.6,
128.9, 125.3, 124.6, 97.5, 29.2, 19.9.
HRMS (ESI): C14H21N2O4 [M + H]+; calculated:
281.1507, found: 281.1493.
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Chemical Papers
MS (ESI): m/z=176.2 [M+H]+.
1H NMR (500 MHz, CDCl3) δ 7.83 (s, 1H, NH), 6.46
(s, 1H, =CH), 5.77 (d, J = 1.0 Hz, 1H, =CH), 4.18 (q,
J=7.0 Hz, 2H), 2.03 (s, 3H), 1.23 (t, J=7.0 Hz, 3H).
13C NMR (125 MHz, CDCl3) δ 168.7, 163.8, 131.0,
108.1, 61.8, 24.2, 13.8.
(Z)‑Ethyl 3‑((4‑methoxyphenyl)amino)but‑2‑enoate
(3w)
MS (ESI): m/z=158.0 [M+H]+.
White solid; m.p.: 40.6–41.2 °C. (lit. of Zhang et al. 2006)
1H NMR (400 MHz, CDCl3) δ 10.17 (s, 1H), 7.04 (d,
J = 8.8 Hz, 2H), 6.87 (d, J = 8.8 Hz, 2H), 4.67 (s, 1H),
4.16 (q, J=7.2 Hz, 2H), 3.82 (s, 3H), 1.90 (s, 3H), 1.30 (t,
J=7.2 Hz, 3H).
Ethyl 2‑benzamidoacrylate (4b)
Yellow oil. (lit. of Yang et al. 2018)
13C NMR (100 MHz, CDCl3) δ 170.5, 160.0, 157.4,
132.2, 126.8, 114.2, 84.7, 58.6, 55.5, 20.1, 14.6.
MS (ESI): m/z=236.2 [M+H]+.
1H NMR (400 MHz, CDCl3) δ 8.55 (s, 1H, NH),
7.84–7.81 (m, 2H), 7.55–7.51 (m, 1H), 7.49–7.44 (m, 2H),
6.77 (s, 1H, =CH), 5.99 (d, J=1.6 Hz, 1H, =CH), 4.33 (q,
J=7.2 Hz, 2H), 1.38 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 165.4, 164.0, 134.2,
131.8, 131.1, 128.6, 126.8, 108.4, 62.3, 14.2.
MS (ESI): m/z=220.1 [M+H]+.
(Z)‑Ethyl 3‑((4‑chlorophenyl)amino)but‑2‑enoate
(3x)
White solid; m.p.: 51.0–52.0 °C. (lit. of Zhang et al. 2006)
1H NMR (400 MHz, CDCl3) δ 10.37 (s, 1H), 7.34–7.28
(m, 2H), 7.03 (d, J = 8.8 Hz, 2H), 4.73 (s, 1H), 4.17 (q,
J=7.2 Hz, 2H), 2.00 (s, 3H), 1.30 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 170.4, 158.4, 138.0,
130.3, 129.2, 125.5, 86.9, 58.9, 20.2, 14.6.
Ethyl 2,2‑bis(benzamido)propanoate (4c)
White solid; m.p.: 132.0–133.0 °C.
1H NMR (400 MHz, CDCl3) δ 7.82 (s, 2H), 7.78–7.75
(m, 4H), 7.50–7.46 (m, 2H), 7.39 (t, J=7.6 Hz, 4H), 4.35
(q, J=7.2 Hz, 2H), 2.08 (s, 3H), 1.32 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 170.9, 168.7, 133.5,
131.8, 128.4, 127.1, 67.3, 62.9, 23.8, 14.2.
MS (ESI): m/z=240.1 [M+H]+.
(Z)‑Ethyl 3‑((4‑nitrophenyl)amino)but‑2‑enoate (3y)
HRMS (ESI): C19H20N2O4Na [M + Na]+; calculated:
363.1315, found: 363.1316.
Green solid; m.p.: 112.0–112.8 °C. (lit. of Zhang et al. 2006)
1H NMR (400 MHz, CDCl3) δ 10.96 (s, 1H), 8.23 (d,
J=8.8 Hz, 2H), 7.17 (d, J=8.8 Hz, 2H), 4.93 (s, 1H), 4.22
(q, J=7.2 Hz, 2H), 2.26 (s, 3H), 1.34 (t, J=7.2 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 170.0, 155.7, 145.8,
142.8, 125.3, 120.6, 91.6, 59.5, 21.0, 14.4.
(Z)‑Ethyl 4‑acetamido‑2‑oxopent‑3‑enoate (4d)
Yellow oil.
1H NMR (400 MHz, CDCl3) δ 11.18 (s, 1H), 5.75 (s, 1H),
4.33 (q, J=7.2 Hz, 2H), 2.27 (s, 3H), 2.18 (s, 3H), 1.35 (t,
J=7.2 Hz, 3H).
MS (ESI): m/z=251.1 [M+H]+.
(Z)‑Ethyl 3‑(naphthalen‑2‑ylamino)but‑2‑enoate
(3z)
13C NMR (100 MHz, CDCl3) δ 200.6, 168.4, 163.9,
142.7, 106.3, 62.3, 31.0, 23.4, 13.8.
HRMS (ESI): C9H12NO4 [M-H]−; calculated: 198.0772,
found: 198.0777.
Yellow oil; (lit. of Chen et al. 2010)
1H NMR (400 MHz, CDCl3) δ 10.61 (s, 1H), 8.10 (d,
J=7.6 Hz, 1H), 7.93–7.91 (m, 1H), 7.79 (d, J=8.4 Hz, 1H),
7.62–7.54 (m, 2H), 7.49 (t, J=8.0 Hz, 1H), 7.36–7.32 (m,
1H), 4.86 (s, 1H), 4.26 (q, J=7.2 Hz, 2H), 1.90 (s, 3H), 1.38
(t, J=7.2 Hz, 3H).
(Z)‑Ethyl 2‑benzamido‑4‑oxopent‑2‑enoate (4e)
Yellow solid; m.p.: 107.2–107.8 °C.
13C NMR (100 MHz, CDCl3) δ 170.7, 160.5, 135.4,
134.3, 130.5, 128.2, 126.7, 126.6, 126.4, 125.3, 123.6,
122.8, 85.7, 58.8, 20.0, 14.7.
1H NMR (400 MHz, CDCl3) δ 12.26 (s, 1H), 7.95–7.93
(m, 2H), 7.58 (t, J=7.6 Hz, 1H), 7.49 (t, J=8.0 Hz, 2H),
5.85 (s, 1H), 4.39 (q, J=7.2 Hz, 2H), 2.30 (s, 3H), 1.37 (t,
J=7.6 Hz, 3H).
MS (ESI): m/z=256.2 [M+H]+.
13C NMR (100 MHz, CDCl3) δ 200.9, 165.7, 163.1,
143.5, 133.0, 132.6, 128.8, 128.0, 106.5, 62.6, 29.8, 14.2.
HRMS (ESI): C14H16NO4 [M + H]+; calculated:
262.1074, found: 262.1075.
Ethyl 2‑acetamidoacrylate (4a)
Yellow oil. (lit. of Yamashita et al. 2014)
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Chemical Papers
HRMS (ESI): C18H18NO5S [M-H]−; calculated:
360.0911, found: 360.0909.
Diethyl 3,4‑diacetyl‑2,5‑bis(benzamido)
hex‑3‑enedioate (4f)
Yellow solid; m.p.: 103.2–103.4 °C.
Ethyl 2‑((4‑methoxyphenyl)sulfonamido)acrylate
1H NMR (400 MHz, CDCl3) δ 13.32 (s, 2H), 8.06 (d,
J=7.6 Hz, 4H), 7.59 (t, J=7.6 Hz, 2H), 7.49 (t, J=7.6 Hz,
4H), 6.28 (s, 2H), 4.36 (q, J = 7.2 Hz, 4H), 2.68 (s, 6H),
1.41 (t, J = 7.2 Hz, 6H).
(5d)
Yellow solid; m.p.: 96.1–97.9 °C.
1H NMR (600 MHz, CDCl3) δ 7.82 (d, J=9.0 Hz, 2H),
7.13 (s, 1H), 6.98 (d, J=8.4 Hz, 2H), 5.66 (s, 2H), 4.22 (q,
J=7.2 Hz, 2H), 3.88 (s, 3H), 1.28 (t, J=7.2 Hz, 3H).
13C NMR (150 MHz, CDCl3) δ 163.4, 163.2, 131.1,
129.9, 129.8, 114.2, 106.6, 62.5, 55.7, 14.0.
13C NMR (100 MHz, CDCl3) δ 200.9, 164.6, 163.9,
143.6, 133.0, 131.5, 128.8, 128.0, 62.5, 31.2, 22.9, 14.1.
HRMS (ESI): C28H30N2O8Na [M + Na]+; calculated:
545.1894, found: 545.1902.
HRMS (ESI): C12H14NO5S [M-H]−; calculated:
284.0598, found: 284.0605.
(Z)‑4‑methoxy‑N‑(4‑oxo‑4‑phenylbut‑2‑en‑2‑yl)
benzenesulfonamide (5a)
Acknowledgements This work was supported by the National Natural
Science Foundation of China (Nos. 21776254 and 21406203).
Yellow solid; m.p.: 70.8–72.0 °C. (lit. of Lee et al. 2017)
1H NMR (600 MHz, CDCl3) δ 13.34 (s, 1H), 7.93–7.88
(m, 4H), 7.55 (t, J = 7.8 Hz, 1H), 7.47 (t, J = 7.8 Hz, 2H),
7.02 (d, J = 9.0 Hz, 2H), 6.05 (s, 1H), 3.89 (s, 3H), 2.23
(s, 3H).
Compliance with ethical standards
Conflict of interest There is no confict of interest.
13C NMR (150 MHz, CDCl3) δ 191.1, 163.4, 156.3,
138.0, 132.6, 132.0, 129.5, 128.6, 127.7, 114.6, 100.5,
55.7, 20.2.
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