Synthesis and photoreaction of 2-amino-3-cyano-4-aryl-4H-pyrans

Article abstract of DOI:10.1071/CH14113

A series of 2-amino-3-cyano-4-aryl-4H-pyrans (1) were synthesised by reacting malononitrile, ethyl acetoacetate, and aromatic aldehydes under ultrasound irradiation. The photochemical properties, including the photostability and photoreaction of 1, were i

Full text of DOI:10.1071/CH14113

CSIRO PUBLISHING
Aust. J. Chem. 2015, 68, 273–281
Full Paper
http://dx.doi.org/10.1071/CH14113
Synthesis and Photoreaction of 2-Amino-3-cyano-
4-aryl-4H-pyrans
A
A
A B
,
A
Wuji Sun, Yangye Jiang, Hong Yan,
and Xiuqing Song
A
College of Life Science and Bioengineering, Beijing University of Technology,
Pingleyuan Street No. 100, Chaoyang District, Beijing 100124, China.
Corresponding author. Email: hongyan@bjut.edu.cn
B
A series of 2-amino-3-cyano-4-aryl-4H-pyrans (1) were synthesised by reacting malononitrile, ethyl acetoacetate, and
aromatic aldehydes under ultrasound irradiation. The photochemical properties, including the photostability and
photoreaction of 1, were investigated in conventional solvents. The results indicated that compounds 1 were unstable
and underwent a photoreaction to the 1,3-butadienes under irradiation with UV light. A mechanism for the photoreaction is
proposed and investigated using electron spin resonance spectroscopic techniques. The 1,3-butadiene structures were
determined by 1H and 13C NMR spectra, high-resolution mass spectrometry, and single crystal X-ray diffraction analysis.
Manuscript received: 3 March 2014.
Manuscript accepted: 25 April 2014.
Published online: 4 June 2014.
Introduction
investigated. The photoreaction products were determined by
1H and 13C NMR spectroscopy, high-resolution mass spectro-
metry, and single crystal X-ray diffraction analysis.
4H-Pyrans are very important heterocyclic compounds that
frequently exhibit a variety of biological activities.[1] In addi-
tion, 4H-pyrans are useful intermediates for the synthesis of
various compounds, such as pyranopyridine derivatives, poly-
azanaphthalenes, and pyridin-2-ones.[2] However, the prepara-
tions of 4H-pyrans have many drawbacks, such as longer
reaction times, unsatisfactory yields, harsh reaction conditions,
and excessive use of reagents and catalysts.[3] Therefore, a more
convenient method of preparing 4H-pyrans is essential. Ultra-
sound has become a highly useful method for performing a wide
range of chemical reactions and processes. The application of
ultrasound irradiation in organic reactions is also rapidly
increasing, and a large number of organic reactions can be
performed with a higher yield, shorter reaction time, and milder
conditions.[4] To expand the application of ultrasound in the
synthesis of organic compounds, we report a novel and efficient
method for the synthesis of 1 by use of malononitrile, ethyl
acetoacetate, and aromatic aldehydes using a sodium ethoxide
catalyst under ultrasound irradiation (Scheme 1).
Results and Discussion
Synthesis of 2-Amino-3-cyano-4-aryl-4H-pyrans
To achieve suitable conditions for the synthesis of 2-amino-3-
cyano-4-aryl-4H-pyrans (1), the reactions have been investi-
gated for the preparation of 1a. The effects of the catalyst,
solvent, reaction temperature, and intensity power of ultrasound
were examined. Initially, to search for the optimal catalyst, the
reaction was examined using triethylamine, piperidine, sodium
hydroxide, and sodium ethoxide as the catalysts. Under ultra-
sound irradiation in ethanol at 508C and 150 W, 10 mol %
sodium ethoxide in ethanol resulted in the best yield (i.e. 85 %)
(Table 1). The reaction was then performed in ethanol,
dichloromethane, acetonitrile, and dimethylformamide, and
the desired product was obtained in 85, 37, 65, and 80 % yield,
respectively. Therefore, ethanol was chosen as the solvent for
the reaction. Next, the optimal reaction temperature and ultra-
sound intensity power were evaluated at 30, 50, and 808C with
80, 150, and 250 W of power. When the reaction was performed
at 508C and 150 W, the best yield of the desired product was
Although the photochemical properties of heterocyclic
compounds have been studied,[5] 1 has received very little
attention. To evaluate the photochemical properties, the photo-
stability, photoreaction, and reaction mechanism of 1 have been
R
R
O
O
Ultrasound irradiation
ϩ
ϩ
EtOOC
CN
NC
CN
Catalyst
O
CHO
O
NH2
1
Scheme 1. Synthesis of 2-amino-3-cyano-4-aryl-4H-pyrans.
Journal compilation Ó CSIRO 2015
www.publish.csiro.au/journals/ajc

274
W. Sun et al.
Table 1. Yields of 1a under different reaction conditions
EntryA
Cat. (conc. [mol %])
Solvent
Temp. [8C]
Power [W]
Time [min]
Yield [%]B
1
Triethylamine (10)
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
CH2Cl2
CH3CN
DMF
80
80
80
80
80
80
80
80
80
30
50
50
50
150
150
150
150
150
150
150
150
150
150
150
50
30
15
10
10
30
10
60
60
15
10
10
10
10
60
78
82
85
30
83
37
65
80
34
86
80
77
2
Piperidine (10)
3
Sodium hydroxide (10)
Sodium ethoxide (10)
Sodium ethoxide (5)
Sodium ethoxide (15)
Sodium ethoxide (10)
Sodium ethoxide (10)
Sodium ethoxide (10)
Sodium ethoxide (10)
Sodium ethoxide (10)
Sodium ethoxide (10)
Sodium ethoxide (10)
4
5
6
7
8
9
10
11
12
13
Ethanol
Ethanol
Ethanol
Ethanol
250
AReaction conditions: malononitrile (10 mmol), ethyl acetoacetate (10 mmol), and benzaldehyde (10 mmol), solvent (15 mL),
and catalyst under ultrasound irradiation.
BIsolated yield.
2.0
Table 2. Yields of 2-amino-3-cyano-4-aryl-4H-pyrans
1a
1b
Entry
R
Time [min]
Yield [%]A
1.5
1.0
0.5
0
1c
1d
1e
1a
1b
1c
1d
1e
1f
H
10
10
5
86
86
87
89
92
90
89
91
65
p-CH3
p-F
m-Cl
10
5
p-Br
3,4-diF
3,5-diCF3
p-NO2
p-OCH3
10
10
5
1g
1h
1i
30
AIsolated yield.
220
270
320
370
420
Wavelength [nm]
obtained (i.e. 86 %). As shown in Table 1, the best reaction
conditions involved the presence of sodium ethoxide (10 mol %)
in ethanol as the solvent at 508C and 150 W. Under the optimised
conditions, a series of 1 was obtained, and the results are shown
in Table 2.
Fig. 1. The UV-vis absorption spectra in THF at a concentration of
5 ꢀ 10ꢁ5 M.
As shown in Table 2, all of the reactions proceeded efficiently,
and the desired products were obtained in good to excellent
yields (65–92 %). For example, 1a was obtained in 86 % yield
after 10 min of ultrasound irradiation, whereas 1a was isolated in
80 % yield after 3 h with a traditional heating method.[6]
photostability of the 2-amino-3-cyano-4-aryl-4H-pyrans and
was irradiated at different wavelengths (i.e. 256, 280–300,
300–320, 320–350, 350–360, and 360–370 nm) in THF for the
same time (40 h). Compound 1a was unstable and yielded
polymers with UV irradiation at ,300 nm (i.e. 256 and
280–300 nm). At 300–370 nm, 1a yields products 2a and 3a
(Scheme 2), the yields of which increase at 300–320 nm. The
photostability was investigated by the changes of UV-vis
absorption spectrum irradiated under UV (300–320 nm) irradia-
tion in THF at a concentration of 5 ꢀ 10ꢁ5 M (Fig. 2). After
irradiation for 40 h, the two wavelength maxima of 1a (224–234
and 284–296 nm) changed dramatically from those taken before
the irradiation. In particular, the wavelength maximum at
224–234 nm decreased in magnitude, and new peaks appeared
at 258–266 and 322–332 nm. The changes in the UV-vis absorp-
tion spectra may be caused by the fragmenting of the pyran ring
and the formation of conjugated dienes during irradiation.
Photochemical Properties of the 2-Amino-3-cyano-
4-aryl-4H-pyrans
Photostability of 2-Amino-3-cyano-4-aryl-4H-pyrans
The UV-vis absorption spectra of 1a, 1b, 1c, 1d, and 1e in
THF at a concentration of 5 ꢀ 10ꢁ5 M are shown in Fig. 1.
Several absorption peaks were observed in the linear absorption
spectra for all of the molecules in the wavelength range of 220 to
450 nm, while almost no linear absorption was observed beyond
370 nm. The shapes of the spectra are similar because these
compounds have the same stem nuclei of the 2-amino-3-cyano-
4-aryl-4H-pyran structure. The maximum absorptions range
from 224 to 234 and 284 to 296 nm and are similar to the
UV-vis absorption spectra of 1a.
Photoreaction of the 2-Amino-3-cyano-4-aryl-4H-pyrans
According to the absorption spectroscopic characteristics, 1a
was chosen as a representative compound to investigate the
Because the photoreaction of 1a yielded products 2a and 3a,
it is necessary to explore the photoreaction conditions of 1a.

2-Amino-3-cyano-4-aryl-4H-pyrans
275
R
R
EtOOC
H
H2NOC
EtOOC
NC
hv
ϩ
CN
EtOOC
NC
H
R
H2NOC
O
NH2
1
2
3
Scheme 2. Photoreaction of 2-amino-3-cyano-4-aryl-4H-pyrans.
1.5
the benzene ring was small, the yield of 2 was higher (i.e. for 1a
(R ¼ H) and 1b (R ¼ p-CH3)), and in some cases 3 could not be
obtained (i.e. for 1c (R ¼ p-F) and 1i (R ¼ p-OCH3)). When the
steric hindrance was large, the yield of 3 was better (i.e. for 1d
(R ¼ m-Cl) 1e (R ¼ p-Br), and 1f (R ¼ 3,4-diF)) and 2 was
not obtained (i.e. for 1g (R ¼ 3,5-diCF3)). In addition, 1h
(R ¼ p-NO2) produced none of the desired products, which is
most likely a result of the nitro group being sensitive to UV light
resulting in a nitroso free radical.[7]
1a before irradition
1a after irradition for 10 h
1a after irradition for 30 h
1a after irradition for 40 h
1.0
0.5
0
Photoreaction Mechanism of the 2-Amino-3-
cyano-4-aryl-4H-pyrans
To the best of our knowledge, the pyran ring transformation
to 1,3-butadiene is novel. The mechanism outlined in Scheme 3
was proposed to account for the formation of products 2 and 3. It
involves intramolecular single-electron transfer from the enam-
ino moiety to the ester within the resulting zwitterion-biradical
4, followed by transannular bond formation to afford the
zwitterion 5, which collapses to cyclobutene 6 by the cleavage
of the carbon–oxygen bond. Cyclobutene 6, which is a four-
membered ring, is destabilised under irradiation to yield 2 and 3.
The existence of cyclobutene 6 was accepted based on the work
of Armesto et al.,[8] which examined the photoreaction of
2-amino-3,5-dicyano-4-alkyl-4H-pyrans to cyclobutenes. The
main difference between the two photoreactions is the substitu-
ent on the reactant at C-4 of the pyran ring. The reactant used by
Armesto et al. had an alkyl substituent, while 1 had an aryl
substituent. The aryl substituent may make cyclobutene 6 more
unstable than the alkyl and result in the formation of 2 and 3 by
cleavage of the carbon–carbon bond.
Electron spin resonance (ESR) spectroscopic techniques can
be used to investigate the characteristics of radical generation. It
is difficult to observe radical 4 because the lifetime of this
radical is extremely short. Radical 4 was confirmed using a
combination of spin trapping reagents and ESR with phenyl-
tert-butyl nitrone (PBN) as the trapping agent.[9] The reaction of
radical 4 with PBN generated PBN adduct PBN-4 (Scheme 4).
The obtained ESR signals involved a six-line spectrum with
1a/PBN (Fig. 3). No signals were observed with 1a or PBN
alone. These results demonstrated that radical 4 was generated in
the photoreaction. The ESR signals correspond to a triplet from
the a-nitrogen that is further split into a doublet by the b-proton.
220
270
320
370
420
Wavelength [nm]
Fig. 2. The UV-vis absorption spectra of 1a before and after irradiation.
Table 3. Yields of products 2 and 3
Entry
R
Yield of 2 [%]A
Yield of 3 [%]A
1a
1b
1c
1d
1e
1f
H
41.0
46.0
45.1
29.3
21.5
30.2
–
26.0
24.4
–
p-CH3
p-F
m-Cl
31.4
29.4
36.1
48.2
–
p-Br
3,4-diF
3,5-diCF3
p-NO2
p-OCH3
1g
1h
1i
–
18.8
–
AIsolated yield.
The primary factor affecting the photoreaction is the solvents.
Conventional solvents, such as dichloromethane, THF, acetone,
and methanol, were evaluated in the photoreaction of 1a under
UV (300–320 nm) irradiation for 50 h. Different solvents pro-
duced 2a and 3a in different yields (2a: 15.0–41.0 %, 3a: 11.0–
26.0 %). The best results were obtained in THF with a 41.0 %
yield for 2a and a 26.0 % yield for 3a.
Compounds 1b–1i were irradiated in THF under the UV
(300–320 nm) irradiation for 50 h, and the results are shown in
Table 3. Like 1a (R ¼ H), 1b (R ¼ p-CH3), 1d (R ¼ m-Cl), 1e
(R ¼ p-Br), and 1f (R ¼ 3,4-diF) also yielded 2 and 3 with
different yields (2: 21.5–46.0 %, 3: 24.4–36.1 %). It is important
to note that 1c (R ¼ p-F) and 1i (R ¼ p-OCH3) only yielded 2
with 18.8 and 45.1 % yields and 1g (R ¼ 3,5-diCF3) only yielded
3g with a 48.2 % yield. The differences of the yields of 2 and 3
may be related to the steric hindrance of the substituents on the
benzene ring. When the steric hindrance of the substituents on
Structure Determination of Products 2 and 3
The structures of products 2 and 3 were verified by 1H and
13C NMR spectroscopy, and high-resolution mass spectrometry
(HRMS). Products 2a and 3a will be used as representative
examples for discussing structural details. In the 1H NMR
spectrum of 2a, there were signals corresponding to the five
protons on the benzene ring in the range of 7.281–7.411 ppm,
a signal from the alkene at 7.660 ppm, a signal from the
methyl at 2.294 ppm, signals from the ethoxy group at 1.322

276
W. Sun et al.
R
R
R
hv
CN
EtOOC
EtOOC
CN
CN
EtOOC
Ϫ
Ϫ
ϩ
ϩ
O
NH2
O
NH2
O
NH2
5
1
4
R
R
EtOOC
H
EtOOC
H2NOC
EtOOC
ϩ
NC
NC
H
CN
CONH2
H2NOC
R
2
3
6
Scheme 3. Proposed mechanism for the formation of products 2 and 3.
R
R
R
EtOOC
CN
Ϫ
Ϫ
ϩ
O
CN
EtOOC
O
EtOOC
CN
α-H
β-N
CH
NH2
Ϫ
Ϫ
ϩ
ϩ
N
C
ϩ
ϩ
O
N
ϩ
O
H
O
NH2
O
NH2
N
C
H
α-H
β-N
PBN
4
PBN-4
Scheme 4. Reaction of 4 with phenyl-tert-butyl nitrone (PBN).
600000
cyano carbon resided at 116.34 ppm, the signal corresponding to
the methyl appeared at 14.18 ppm, the two signals attributable to
the ethoxy group appeared at 24.64 and 61.53 ppm, and the
signals from the benzene ring were observed at 129.61–
133.72 ppm. The remaining signals were attributed to the alkene
carbons (109.81, 131.49, 138.03, and 165.92 ppm). HRMS
(ESIþ) of 2a showed a molecular ion peak at m/z 285.1235,
which is consistent with the calculated value (i.e. m/z 285.1239)
for 2a [M þ H]þ.
400000
200000
0
3440 3450 3460 3470 3480 3490 3500 3510 3520 3530 3540 3550 3560
Ϫ200000
Ϫ400000
Ϫ600000
The NMR and HRMS data for 3a was similar to the data for
100000
0
1
2a. In the H NMR spectrum of 3a, there were signals corre-
sponding to the five protons on the benzene ring in the range of
7.266–7.393 ppm, a signal from the alkene at 7.169 ppm, a
signal from the methyl at 2.507 ppm, signals from the ethoxy
group at 1.180 and 4.221 ppm, and signals from the amino group
at 5.723 and 6.290 ppm. In the 13C NMR spectra of 3a, only 14
signals were observed because of the symmetry of the benzene
ring. The carbonyl carbons resided at 164.43 and 156.35 ppm,
the cyano carbon resided at 115.44 ppm, the signal of the methyl
appeared at 14.08 ppm, the two signals attributable to the ethoxy
group appeared at 21.64 and 61.33 ppm, and the signals from the
benzene ring were observed at 128.76–133.92 ppm. The remain-
ing signals were attributed to the alkene carbons (109.68,
131.69, 138.02, and 166.88 ppm). HRMS (ESIþ) of 3a showed
a molecular ion peak at m/z 285.1228, which is consistent with
the calculated value (i.e. m/z 285.1239) for 3a [M þ H]þ.
3440 3450 3460 3470 3480 3490 3500 3510 3520 3530 3540 3550 3560
Ϫ100000
Ϫ200000
Ϫ300000
Ϫ400000
Ϫ500000
Fig. 3. ESR spectrum of 1a/phenyl-tert-butyl nitrone (PBN) and 1a or
PBN alone.
and 4.280 ppm, and signals from the amino group at 5.739 and
6.160 ppm. In the 13C NMR spectra of 2a, only 14 signals
were observed as a result of the symmetry of the benzene ring.
The carbonyl carbons resided at 164.45 and 161.25 ppm, the

2-Amino-3-cyano-4-aryl-4H-pyrans
277
these results, 2 and 3 were geometric isomers with (2Z,4E) and
(2E,4Z) at the double bond positions. However, only two
geometric isomers were obtained in this reaction among the
possible conformers. This may be correlated with the mecha-
nism of this reaction. In the photoreaction, the cyclobutene 6 is
formed in the more stabilised spatial structure. Cyclobutenes 6
undergo ring-opening reactions under irradiation conditions to
yield 1,3-butadienes. The ring-opening activation enthalpies
and barrier for 2 (2Z,4E) and 3 (2E,4Z) are presumably lower
than other conformers, which may be the reason why only 2
(2Z,4E) and 3 (2E,4Z) are obtained in this reaction.
C11
C10
C9
C12
C13
C8
C7
C5
C4
C6
Conclusion
O3
C14
A series of 2-amino-3-cyano-4-aryl-4H-pyrans were synthe-
sised by reaction of malononitrile, ethyl acetoacetate, and aro-
matic aldehydes in the presence of sodium ethoxide in ethanol at
508C and 150 W under ultrasound irradiation. The photostability
of the 2-amino-3-cyano-4-aryl-4H-pyrans was investigated with
a variety of wavelengths, and the 2-amino-3-cyano-4-aryl-4H-
pyrans were determined to be unstable under irradiation at
300–320 nm. The photoreaction conditions were investigated in
different conventional solvents, and better yields were obtained
in THF for ,50 h. The main products (i.e. 1,3-butadienes) were
isolated, and their structures were determined by 1H and
13C NMR spectra and HRMS. The single crystal X-ray dif-
fraction analysis indicated that the 1,3-butadienes had (2Z,4E)
and (2E,4Z) conformations. The proposed reaction mechanism
involved a photoinduced free radical reaction and the decompo-
sition of the unstable intermediate cyclobutene to 1,3-butadienes.
The radical was observed using ESR spectroscopy using the
spin-trapping method with PBN as the trapping agent.
O1
C3
C1
N2
C2
N1
C15
C16
O2
Fig. 4. ORTEP diagram of the crystal structure of 2a (drawn at 50 %
thermal ellipsoids).
Br1
C4
C3
C11
C2
C10
C5
Experimental
C6
C1
All of the chemicals were purchased from commercial sources
and were used without further purification. Ultrasound irradia-
tion was performed in a GEX750-5C ultrasonic instrument
(ACE GLASS Inc., Vineland N.J., USA). Thin-layer chroma-
tography (TLC) was conducted on silica gel 60 F254 plates
O1
O2
C9
C8
C7
1
(Merck KGaA). H and 13C NMR spectra were recorded on a
N1
Bruker Avance 400 spectrometer at 400 and 100 MHz, respec-
tively, using CDCl3 or DMSO-d6 as the solvent and tetra-
methylsilane (TMS) as the internal standard. The melting points
were determined on a XT-5A digital melting point apparatus and
are uncorrected. HRMS was performed using an Agilent
G3250AA LC/MSD TOF mass spectrometer. The ESR spin-
trapping experiment was conducted using a Bruker A300
X-band spectrometer with a 100 kHz magnetic field modulation.
Irradiation for the photochemical properties and photoreactions
was conducted using a PHILIPS PL-S 11W/10/2P mercury
lamp.
C15
C12
C13
C14
N2
C16
O3
Procedure for the Synthesis of 2-Amino-3-cyano-4-
Fig. 5. ORTEP diagram of the crystal structure of 3e (drawn at 50 %
aryl-4H-pyrans (1a–1i)
thermal ellipsoids).
In a 100 mL flask, malononitrile (10 mmol), ethyl acetoacetate
(10 mmol), an aromatic aldehyde (10 mmol), and ethanol
(15 mL) were thoroughly mixed with a catalytic amount of
sodium ethoxide (1 mmol). The reaction mixture was sonicated
at 508C and at 150 W. After the completion of the reaction
(monitored by TLC), the reaction was allowed to cool to room
temperature, and the generated solid was filtered and recrys-
tallised from ethanol to yield pure products 1a–1i.
The 3D structures of 2 and 3 were confirmed by single crystal
X-ray diffraction. The single crystal X-ray diffraction data for
2a (CCDC number 958698) confirmed that 2a was (2Z,4E)-2-
cyano-4-ethylformyl-3-methyl-5-phenyl-2,4-dienamide (Fig. 4).
The single crystal X-ray diffraction data for 3e (CCDC number
958794) confirmed that it was (2E,4Z)-2-cyano-4-ethylformyl-
3-methyl-5-(4-bromophenyl)-2,4-dienamide (Fig. 5). Based on

278
W. Sun et al.
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
phenyl-4H-pyran (1a)
(4-nitrophenyl)-4H-pyran (1h)
Yield 2.44 g (86 %); white solid; mp 176.4–177.28C (Lit.[3]
176.08C). dH (400 MHz, DMSO-d6) 1.026 (m, 3H, CH2CH3),
2.314 (s, 3H, CH3), 3.966 (m, 2H, CH2CH3), 4.296 (s, 1H,
Ar-CH), 6.902 (s, 2H, NH2), 7.138–7.233 (m, 3H, Ar-H), 7.293–
7.330 (t, 2H, Ar-H).
Yield 2.99 g (91 %); yellow solid; mp 181.4–182.28C
(Lit.[13] 180.0–182.08C). dH (400 MHz, DMSO-d6) 1.034
(m, 3H, CH2CH3), 2.350 (s, 3H, CH3), 3.958 (m, 2H, CH2CH3),
4.474 (s, 1H, Ar-CH), 7.111 (s, 2H, NH2), 7.433–7.455 (d, 2H,
Ar-H), 8.187–8.209 (d, 2H, Ar-H).
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-
(4-methoxyphenyl)-4H-pyran (1i)
4-(4-methylphenyl)-4H-pyran (1b)
Yield 2.04 g (65 %); pale yellow solid; mp 110.8–111.48C
(Lit.[3] 110.08C). dH (400 MHz, DMSO-d6) 1.061 (m, 3H,
CH2CH3), 2.287 (s, 3H, CH3), 3.719 (s, 3H, OCH3), 3.956
(m, 2H, CH2CH3), 4.239 (s, 1H, Ar-CH), 6.853 (s, 2H, NH2),
6.870–6.873 (d, 2H, Ar-H), 7.042–7.063 (d, 2H, Ar-H).
Yield 2.56 g (86 %); pale yellow solid; mp 176.1–177.18C
(Lit.[10] 177.0–179.08C). dH (400 MHz, DMSO-d6) 1.052 (m,
3H, CH2CH3), 2.258 (s, 3H, Ar-CH3), 2.304 (s, 3H, CH3), 3.961
(m, 2H, CH2CH3), 4.265 (s, 1H, Ar-CH), 6.893 (s, 2H, NH2),
7.024–7.043 (d, 2H, Ar-H), 7.102–7.121 (d, 2H, Ar-H).
Procedure for Determining Photochemical Stability
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-
4-(4-fluorophenyl)-4H-pyran (1c)
Different wavelengths of light (i.e. 256, 300–320, 320–350,
350–360, 360–370, 370–380, 380–390, 390–400, and 400–
410 nm) were produced by PHILIPS PL-S 11W/10/2P mercury
lamps. The samples were dissolved in THF and were irradiated
in quartz cuvettes.
Yield 2.63 g (87 %); white solid; mp 166.6–167.28C (Lit.[11]
168.08C). dH (400 MHz, DMSO-d6) 1.028 (m, 3H, CH2CH3),
2.306 (s, 3H, CH3), 3.964 (m, 2H, CH2CH3), 4.315 (s, Ar-CH),
6.952 (s, 2H, NH2), 7.109–7.199 (m, 4H, Ar-H).
Procedure for the Photoreaction of 2-Amino-3-cyano-
4-aryl-4H-pyrans
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
(3-chlorophenyl)-4H-pyran (1d)
2-Amino-3-cyano-4-aryl-4H-pyrans (1) (1 mmol) were dis-
solved in THF (100 mL) and irradiated with UV light
(300–320 nm) for 40 h. After completion of the reaction, the
solvent was removed under reduced pressure, and the residue
was purified by chromatography on silica gel to yield products
2 and 3.
Yield 2.83 g (89 %); white solid; mp 177.9–178.78C
(Lit.[12] 177.0–178.08C). dH (400 MHz, DMSO-d6) 1.028
(m, 3H, CH2CH3), 2.322 (s, 3H, CH3), 3.981 (m, 2H, CH2CH3),
4.332 (s, Ar-CH), 7.020 (s, 2H, NH2), 7.119–7.373 (m, 4H,
Ar-H).
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
(4-bromophenyl)-4H-pyran (1e)
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-
phenyl-2,4-dienamide (2a)
Yield 3.34 g (92 %); pale yellow solid; mp 172.8–173.28C
(Lit.[13] 172.0–174.08C). dH (400 MHz, DMSO-d6) 1.038 (m,
3H, CH2CH3), 2.315 (s, 3H, CH3), 3.971 (m, 2H, CH2CH3),
4.036 (s, 1H, Ar-CH), 6.961 (s, 2H, NH2), 7.109–7.128 (d, 2H,
Ar-H), 7.496–7.517 (d, 2H, Ar-H).
Yield 116 mg (41.0 %); mp 87.5–88.48C. dH (400 MHz,
CDCl3) 1.322 (m, 3H, CH2CH3), 2.294 (s, 3H, CH3), 4.280 (s,
2H, CH2CH3), 5.739, 6.160 (s, 2H, NH2), 7.281–7.411 (m, 5H,
Ar-H), 7.660 (s, 1H, CH). dC (100 MHz, CDCl3) 14.18, 24.64,
61.53, 109.81, 116.34, 128.96, 129.61, 129.89, 131.49, 133.72,
138.03, 161.25, 164.45, 165.92. m/z 285.1235. HRMS Anal.
Calc. for C16H17N2O3: 285.1239. X-Ray diffraction analysis
(Fig. 2). The CCDC number for this product is 958698.
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
(3,4-difluorophenyl)-4H-pyran (1f)
Yield 2.88 g (90 %); white solid; mp 171.6–172.38C. dH
(400 MHz, DMSO-d6) 1.030 (m, 3H, CH2CH3), 2.320 (s, 3H,
CH3), 3.969 (m, 2H, CH2CH3), 4.364 (s, 1H, Ar-CH), 7.023
(s, 2H, NH2), 7.179–7.412 (m, 3H, Ar-H). dC (100 MHz,
DMSO-d6) 14.14, 18.68, 38.60, 57.15, 60.67, 106.87, 116.51,
117.80, 119.89, 124.38, 143.31, 147.48, 149.91, 157.78, 158.92,
165.68. m/z 321.1045. HRMS Anal. Calc. for C16H15F2N2O3:
321.1051.
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-(4-
methylphenyl)-2,4-dienamide (2b)
Yield 137 mg (46.0 %); mp 85.5–86.28C. dH (400 MHz,
CDCl3) 1.304 (m, 3H, CH2CH3), 2.297 (s, 3H, CH3), 2.380 (s,
3H, CH3), 4.259 (m, 2H, CH3CH2), 5.989, 6.147 (s, 2H, NH2),
7.178–7.279 (m, 4H, Ar-H), 7.621 (s, 1H, CH). dC (100 MHz,
CDCl3) 14.16, 21.42, 24.52, 61.42, 110.00, 116.33, 129.72,
129.74, 130.36, 130.84, 138.17, 140.42, 161.77, 164.64,
165.64. m/z 299.1392. HRMS Anal. Calc. for C17H19N2O3:
299.1396.
2-Amino-3-cyano-5-ethoxycarbonyl-6-methyl-4-
[3,5-bis(trifluoromethyl)phenyl]-4H-pyran (1g)
Yield 3.74 g (89 %); white solid; mp 167.8–168.28C. dH
(400 MHz, DMSO-d6) 0.955 (m, 3H, CH2CH3), 2.346 (s, 3H,
CH3), 3.933 (m, 2H, CH3CH2), 4.659 (s, 1H, Ar-CH), 7.161
(s, 2H, NH2), 7.814 (s, 2H, Ar-H), 8.009 (s, 1H, Ar-H). dC
(100 MHz, DMSO-d6) 13.79, 18.75, 38.91, 56.46, 60.69,
106.01, 119.61, 125.06, 128.58, 130.70, 131.02, 149.14,
158.76, 159.05, 165.42. m/z 421.0980. HRMS Anal. Calc. for
C18H15N2O3F6: 421.0987.
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-(4-
fluorophenyl)-2,4-dienamide (2c)
Yield 136 mg (45.1 %); mp 132.4–133.28C. dH (400 MHz,
CDCl3) 1.313 (m, 3H, CH2CH3), 2.284 (s, 3H, CH3), 4.270
(t, 2H, CH2CH3), 5.813, 6.185 (s, 2H, NH2), 7.069–7.388 (m,
4H, Ar-H), 7.611 (s, 1H, CH). dC (100 MHz, CDCl3) 14.15,
24.52, 61.56, 110.06, 116.10, 129.93, 131.32, 131.52, 131.60,

2-Amino-3-cyano-4-aryl-4H-pyrans
279
136.70, 161.27, 162.18, 164.32, 165.48. m/z 303.1139. HRMS
Anal. Calc. for C16H16FN2O3: 303.1145.
129.72, 129.72, 129.78, 130.36, 130.83, 140.17, 142.42,
155.77, 164.74, 167.67. m/z 299.1391. HRMS Anal. Calc. for
C17H19N2O3: 299.1396.
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-
(3-chlorophenyl)-2,4-dienamide (2d)
(2E,4Z)-2-Cyano-4-ethylformyl-3-methyl-5-
(3-chlorophenyl)-2,4-dienamide (3d)
Yield 93 mg (29.3 %); mp 125.5–126.28C. dH (400 MHz,
CDCl3) 1.347 (m, 3H, CH2CH3), 2.599 (s, 3H, CH3), 4.353
(m, 2H, CH2CH3), 5.678, 6.123 (s, 2H, NH2), 7.267–7.402 (m,
4H, Ar-H), 7.738 (s, 1H, CH). dC (100 MHz, CDCl3) 14.14,
24.64, 61.67, 109.99, 116.06, 127.16, 129.51, 129.74, 130.19,
133.11, 134.92, 135.61, 136.07, 161.10, 164.09, 165.27. m/z
319.0851. HRMS Anal. Calc. for C16H16N2O3Cl: 319.0850.
Yield 100 mg (31.4 %); mp 140.6–141.38C. dH (400 MHz,
CDCl3) 1.324 (m, 3H, CH2CH3), 2.277 (s, 3H, CH3), 4.284 (m,
2H, CH2CH3), 5.662, 6.163 (s, 2H, NH2), 7.203 (s, 1H, CH),
7.280–7.572 (m, 4H, Ar-H). dC (100 MHz, CDCl3) 13.71, 20.56,
61.93, 107.46, 116.77, 127.11, 128.83, 129.50, 129.60, 134.31,
135.42, 135.76, 138.76, 162.51, 164.91, 166.56. m/z 319.0850.
HRMS Anal. Calc. for C16H16N2O3Cl: 319.0850.
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-
(4-bromophenyl)-2,4-dienamide (2e)
(2E,4Z)-2-Cyano-4-ethylformyl-3-methyl-5-
(4-bromophenyl)-2,4-dienamide (3e)
Yield 78 mg (21.5 %); mp 69.2–70.18C. dH (400 MHz,
CDCl3) 1.311 (m, 3H, CH2CH3), 2.273 (s, 3H, CH3), 4.270 (s,
2H, CH2CH3), 5.837, 6.188 (s, 2H, NH2), 7.175–7.536 (m, 4H,
Ar-H), 7.567 (d, 1H, CH). dC (100 MHz, CDCl3) 14.14, 24.54,
61.63, 110.08, 116.11, 124.31, 130.92, 132.24, 132.31, 132.66,
136.43, 161.42, 164.26, 165.23. m/z 363.0333. HRMS Anal.
Calc. for C16H16BrN2O3: 363.0344.
Yield 106 mg (29.4 %); mp 126.8–127.68C. dH (400 MHz,
CDCl3) 1.223 (m, 3H, CH2CH3), 2.516 (s, 3H, Ar-CH3), 4.241
(m, 2H, CH2CH3), 5.667, 6.273 (s, 2H, NH2), 7.076 (s, 1H, CH),
7.279–7.535 (m, 4H, Ar-H). dC (100 MHz, DMSO-d6) 13.97,
19.96, 61.94, 110.50, 116.43, 123.36, 131.26, 131.98, 133.75,
133.83, 138.12, 156.50, 163.38, 166.11. m/z 363.0334. HRMS
Anal. Calc. for C16H16BrN2O3: 363.0344. X-Ray diffraction
analysis (Fig. 3). The CCDC number for this product is 958794.
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-
(3,4-difluorophenyl)-2,4-dienamide (2f)
(2E,4Z)-2-Cyano-4-ethylformyl-3-methyl-5-
(3,4-difluorophenyl)-2,4-dienamide (3f)
Yield 96 mg (30.2 %); mp 71.0–71.98C. dH (400 MHz,
CDCl3) 1.313 (m, 3H, CH2CH3), 2.282 (s, 3H, CH3), 4.356
(m, 2H, CH2CH3), 5.821, 6.207 (s, 2H, NH2), 7.085–7.278 (m,
3H, Ar-H), 7.533 (s, 1H, CH). dC (100 MHz, CDCl3) 14.16,
24.54, 61.72, 109.23, 115.97, 117.95, 118.54, 125.97, 130.87,
135.25, 139.19, 149.11, 151.60, 162.03, 164.04, 166.14. m/z
321.1042. HRMS Anal. Calc. for C16H15F2N2O3: 321.1051.
Yield 115 mg (36.1 %); mp 107.7–108.78C. dH (400 MHz,
CDCl3) 1.246 (m, 3H, CH2CH3), 2.515 (s, 3H, Ar-CH3), 4.262
(q, 2H, CH2CH3), 5.702, 6.271 (s, 2H, NH2), 7.033 (s, 1H, CH),
7.165–7.353 (m, 3H, Ar-H). dC (100 MHz, CDCl3) 13.77, 20.58,
61.95, 107.51, 116.75, 117.24, 118.03, 125.97, 130.83, 135.00,
138.19, 148.73, 151.21, 162.50, 164.68, 166.62. m/z 321.1039.
HRMS Anal. Calc. for C16H15F2N2O3: 321.1051.
(2Z,4E)-2-Cyano-4-ethylformyl-3-methyl-5-
(4-methoxyphenyl)-2,4-dienamide (2i)
(2E,4Z)-2-Cyano-4-ethylformyl-3-methyl-5-
(3,5-bis(trifluoromethyl)phenyl)-2,4-dienamide (3g)
Yield 59 mg (18.8 %); mp 267.5–268.48C. dH (400 MHz,
CDCl3) 1.305 (m, 3H, CH2CH3), 2.320 (s, 3H, CH3), 3.850 (s,
3H, OCH3), 4.257 (m, 2H, CH2CH3), 5.878, 6.163 (s, 2H, NH2),
6.893–7.300 (m, 4H, Ar-H), 7.61 (s, 1H, CH). dC (100 MHz,
CDCl3) 14.20, 24.49, 55.38, 61.39, 109.98, 114.51, 116.40,
126.14, 128.71, 131.63, 138.08, 161.06, 161.51, 164.69,
165.79. m/z 315.1352. HRMS Anal. Calc. for C17H19N2O4:
315.1345.
Yield 202 mg (48.2 %); mp 117.9–118.98C. dH (400 MHz,
CDCl3) 1.186 (m, 3H, CH2CH3), 2.551 (s, 3H, Ar-CH3), 4.228
(m, 2H, CH2CH3), 5.874, 6.307 (s, 2H, NH2), 7.166 (s, 1H, CH),
7.822–7.896 (m, 3H, Ar-H). dC (100 MHz, CDCl3) 13.55, 20.64,
62.26, 108.18., 116.47, 127.06, 12128.30, 128.84, 131.33,
130.22, 136.11, 137.01, 162.37, 164.01, 165.80. m/z 421.0976.
HRMS Anal. Calc. for C18H15N2O3F6: 421.0987.
(2E,4Z)-2-Cyano-4-ethylformyl-3-methyl-5-
phenyl-2,4-dienamide (3a)
ESR Spin-Trapping Experiment
Yield 73 mg (26.0 %); mp 141.6–142.48C. dH (400 MHz,
CDCl3) 1.180 (m, 3H, CH2CH3), 2.507 (s, 3H, CH3), 4.221
(m, 2H, CH2CH3), 5.723, 6.290 (s, 2H, NH2), 7.169 (s, 1H, CH),
7.266–7.393 (m, 5H, Ar-H). dC (100 MHz, CDCl3) 14.08, 21.64,
61.33, 109.68, 115.44, 128.76, 129.66, 129.89, 131.69, 133.92,
138.02, 156.35, 164.43, 166.88. m/z 285.1228. HRMS Anal.
Calc. for C16H17N2O3: 285.1239.
THF solutions containing 5 ꢀ 10ꢁ4 mol Lꢁ1 1a and 5 ꢀ 10ꢁ4
mol Lꢁ1 PBN were added to quartz, cylindrical ESR tubes and
were deoxygenated with N2 for 15 min. Each sample was irra-
diated with UV light (300–320 nm) for 10 min and immediately
subjected to ESR analysis. The magnetic parameters were
measured by reference to the signals of tetra-
cyanoquinodimethane lithium salt (TCNQ-Li, g ¼ 2.00252)
and Mn2þ/MgO. The experiment was conducted at room
temperature.
(2E,4Z)-2-Cyano-4-ethylformyl-3-methyl-5-
(4-methylphenyl)-2,4-dienamide (3b)
X-Ray Diffraction Analysis for 2a (Fig. 4 and Table 4)
and 3e (Fig. 5 and Table 5)
Yield 72 mg (24.4 %); mp 122.6–123.58C. dH (400 MHz,
CDCl3) 1.232 (m, 3H, CH2CH3), 2.388 (s, 3H, Ar-CH3), 2.507
(s, 3H, CH3), 4.255 (m, 2H, CH2CH3), 5.720, 6.293 (s, 2H,
NH2), 7.135 (s, 1H, CH), 7.181–7.343 (m, 4H, Ar-H). dC
(100 MHz, CDCl3) 12.16, 18.52, 21.42, 61.72, 110.03, 116.33,
Crystals of 2a and 3e suitable for X-ray diffraction analysis were
obtained by the slow evaporation of an ethyl acetate solution
of 2a and 3e at room temperature. The single crystal X-ray

280
W. Sun et al.
Table 4. Crystal data and structure refinement for 2a
program.[16] All of the hydrogen atoms were geometrically fixed
using the riding model. Details, including the crystal data, data
collection, and structure refinements, are summarised in Table 4
and Table 5. CCDC-958698 and CCDC-958794 contain the
supplementary crystallographic data for this paper. These data
can be obtained, free of charge, from www.ccdc.cam.ac.uk/
conts/retrieving.html.
Parameter
2a
Empirical formula
Formula weight
C16H17N2O3
284.31
Temperature
113 K
Wavelength
0.71073
Crystal system, space group
Unit cell dimensions
Triclinic, P-1
˚
a 5.8653(13) A
˚
b 9.968(2) A
Supplementary Material
1H and 13C NMR spectra of all new compounds and H NMR
1
˚
c 13.817(3) A
a 72.367(15)o
b 88.41(3)o
g 81.50(2)o
spectra of all known compounds are available on the Journal’s
website.
3
˚
Volume
761.2(3) A
Acknowledgements
Z
2
This work was financially supported by the Key Projects in the National
Science & Technology Pillar Program (No. 2012ZX10001007-008-002) and
the Doctoral Fund of Innovation of Beijing University of Technology.
Calculated density
Absorption coefficient
F(000)
1.240 Mg mꢁ3
0.087 mmꢁ1
300.0
0.30 ꢀ 0.18 ꢀ 0.16 mmꢁ3
Crystal size
y range for data collection
Index ranges
1.58–27.98
References
ꢁ7 # h # 6, ꢁ13 # k # 13, ꢁ16 # l # 18
7860/3569 [Rint ¼ 0.0423]
3569/0/200
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Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
R indices (all data)
Largest diff. peak and hole
0.894
R1 ¼ 0.0590, wR2 ¼ 0.0777
ꢁ3
˚
0.233 and ꢁ0.233 e A
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Table 5. Crystal data and structure refinement for 3e
Parameter
3e
Empirical formula
Formula weight
C16H15BrN2O3
363.21
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Temperature
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Wavelength
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Crystal system, space group
Unit cell dimensions
Triclinic, P-1
˚
a 7.478(3) (13) A
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J.ULTSONCH.2013.04.008
˚
b 8.842(3) A
˚
c 12.389(5) A
a 107.386(9)o
b 93.652(5)o
g 90.037(6)o
3
˚
Volume
779.9(5) A
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Z
2
Calculated density
Absorption coefficient
F(000)
1.547 Mg mꢁ3
2.649 mmꢁ1
368.0
0.20 ꢀ 0.18 ꢀ 0.12 mmꢁ3
Crystal size
y range for data collection
Index ranges
1.78–27.98
ꢁ9 # h # 9, ꢁ11 # k # 11, ꢁ16 # l # 16
8250/3689 [Rint ¼ 0.0333]
3689/3/209
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
R indices (all data)
Largest diff. peak and hole
1.002
R1 ¼ 0.0383, wR2 ¼ 0.0542
ꢁ3
˚
0.377 and ꢁ0.650 e A
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˚
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j scanning mode. An empirical absorption correction was
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[16] G. Sheldrick, SHELXL-97 program 1997 (University of Go¨ttingen:
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