Structural tuning enables piezochromic and photochemical properties in N-aryl-β-enaminones

Article abstract of DOI:10.1039/c9ra07598d

An efficient synthesis of N-aryl-β-enaminones via Et₃N-mediated, one-pot three-component reaction of 4-hydroxycoumarin/dimedone, β-nitrostyrene/2-(2-nitrovinyl)thiophene, and arylamine in toluene under refluxed conditions is herein presented. Some prepared compounds were found to exhibit piezochromic properties. The XRD and SEM measurements of the piezochromic compound showed substantial crystal packing and morphology changes before and after grinding. Further, one prepared compound was found to be light-sensitive and can be converted to a furo[3,2-b]pyridin-2(4H)-one derivative upon UV irradiation. A plausible mechanism for this photochemical reaction was proposed.

Full text of DOI:10.1039/c9ra07598d

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PAPER
Structural tuning enables piezochromic and
photochemical properties in N-aryl-b-
enaminones†
Cite this: RSC Adv., 2019, 9, 34088
*
*
Wan-Chi Hsieh, Kiran B. Manjappa
and Ding-Yah Yang
An efficient synthesis of N-aryl-b-enaminones via Et3N-mediated, one-pot three-component reaction of
4-hydroxycoumarin/dimedone, b-nitrostyrene/2-(2-nitrovinyl)thiophene, and arylamine in toluene under
refluxed conditions is herein presented. Some prepared compounds were found to exhibit piezochromic
properties. The XRD and SEM measurements of the piezochromic compound showed substantial crystal
packing and morphology changes before and after grinding. Further, one prepared compound was
found to be light-sensitive and can be converted to a furo[3,2-b]pyridin-2(4H)-one derivative upon UV
irradiation. A plausible mechanism for this photochemical reaction was proposed.
Received 19th September 2019
Accepted 14th October 2019
DOI: 10.1039/c9ra07598d
rsc.li/rsc-advances
preparation of N-aryl-b-enaminones via base-mediated, one-pot
three-component reaction of 4-hydroxycoumarin/dimedone, b-
1 Introduction
nitrostyrene/2-(2-nitrovinyl)thiophene, and arylamine in
toluene under reuxed conditions. The functional and photo-
chemical properties of the prepared compounds such as pie-
zochromism10 are also investigated.
The b-enaminones represent a crucial molecular skeleton that
is present in various natural products.1 They were found to be
associated with a wide range of pharmacological activities,
including antimicrobial,2 antibacterial,3 anti-inammatory,4
and anti-leukemia5 properties. Owing to their diverse biolog-
ical activities, quite a few methodologies for the synthesis of b-
enaminones have been reported in the literature.6 Most of them
focused on the preparation of N-alkyl-b-enaminones; the
synthesis of N-aryl-b-enaminones is much less explored. As
a result, the photochemical and functional properties of N-aryl-
b-enaminones have never been reported. Scheme 1 lists the
previous syntheses of N-aryl-b-enaminones. While they can be
readily prepared by either condensation7 of dimedone,
orthoester, and aniline or dehydration8 of 3-acetyl-4-
hydroxycoumarin and arylamine, the scope of these reactions
is rather limited. Recently, Banerjee9 and coworkers reported
a highly atom-economical and efficient method for the prepa-
ration of N-aryl-b-enaminones via CuO–ZnO NPs-catalyzed, one-
pot three-component reaction of 4-hydroxycoumarin/
dimedone, b-nitrostyrene, and arylamine. Nevertheless, the
CuO-doped ZnO nanoparticles are currently not commercially
available, and the self-prepared nanomaterials need to be
analyzed by sophisticated spectroscopic and analytical tech-
niques. Thus, the development of the simple methodology for
the preparation of N-aryl-b-enaminones with readily available
reagents remains desirable. Here, we report the modied
2 Results and discussion
Our initial efforts toward the preparation of N-aryl-b-enami-
nones called for the base-mediated, one-pot three-component
Department of Chemistry, Tunghai University, No. 1727, Sec. 4, Taiwan Boulevard,
Xitun District, Taichung 40704, Taiwan. E-mail: kiran@thu.edu.tw; yang@thu.edu.tw
† Electronic supplementary information (ESI) available. CCDC 1913301, 1913302,
1953598, and 1953599. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c9ra07598d
Scheme 1 Previous and modified synthesis of N-aryl-b-enaminones.
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Table 1 Optimization of reaction parameters for 4a
the inuence of different organic bases and solvents. To our
delight, we found that the reaction can proceed smoothly in the
presence of one equiv. of triethylamine as a base in toluene
under reuxed conditions for 1.5 h (Entry 4, Table 1). These
optimization reaction conditions were then subsequently
employed to the preparation of other N-aryl-b-enaminones with
different substituents.
Fig. 1 lists the structures of the prepared N-aryl-b-enami-
nones and their yields. The molecular structures of 4a–s were
elucidated by 1H and 13C NMR spectroscopy. Compounds 4g
and 4j were further veried by X-ray crystallography, as depicted
in Fig. 2.12 An intramolecular hydrogen bonding between the
amine hydrogen and carbonyl oxygen atom is clearly observed
for both of the compounds. Generally, the N-aryl-b-enaminones
with electron-donating group substituted at benzene or
coumarin moiety gave better yields compared to their unsub-
stituted counterparts. The opposite was true for N-aryl-b-
enaminones with electron-withdrawing group substituted at
benzene or coumarin moiety. Further, when the substrate 4-
hydroxycoumarin (1) was replaced by dimedone, the yield of the
corresponding product (4q, 56%) was less than that of unsub-
stituted coumarin counterpart (4a, 76%), indicating that 4-
hydroxycoumarin is a better substrate than that of dimedone for
this multicomponent reaction.
Entry
Base (equiv.)
Solvent
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
K2CO3 (1.0)
DABCO (1.0)
DMAP (1.0)
Et3N (1.0)
Et3N (0.5)
Et3N (1.0)
Et3N (1.0)
Et3N (1.0)
Et3N (1.0)
Toluene
Toluene
Toluene
Toluene
Toluene
EtOH
CH3CN
DCE
Toluene
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
3.0
31
68
20
76
53
21
30
44
76
a
Isolated yield.
reaction of 4-hydroxycoumarin, aldehyde, and arylamine in the
presence of DABCO as a base in nitromethane under reuxed
conditions.11 Although the desired product was indeed isolated,
this reaction suffered from moderate to low yields. Further, the
reaction scope for the substrates was somewhat limited. Alter-
natively, we pursued the target compound synthesis by modi-
fying the three-component reaction conditions reported by
Wang.6c Table 1 lists the optimization for condensation of 4-
hydroxycoumarin (1), b-nitrostyrene (2), and aniline (3) under
With the availability of N-aryl-b-enaminones 4a–s, their
functional properties were then investigated. Interestingly,
compounds 4g–j were found to be sensitive to pressure, espe-
cially for 4g. Upon grinding, compound 4g changes from yellow
to red. It can be swily reverted to the original color aer
exposed to methylene chloride vapor, as shown in Fig. 3.
Fig. 1 Structures and yields of the prepared N-aryl-b-enaminones 4a–s.
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Fig. 2 ORTEP crystal structure of 4g (left) and 4j (right).
illustrating the presence of a crystalline structure (Fig. 4a).
Nevertheless, the diffraction peaks of 4g became substantially
weaker aer grinding (Fig. 4b). The sharp and strong diffraction
peaks were recovered when the ground powder of 4g was
exposed to CH2Cl2 vapor for 10 s (Fig. 4c).
To obtain more information about the morphology of
different aggregated states of 4g prior to and aer grinding, the
scanning electron microscopy (SEM) images were also recorded,
as illustrated in Fig. 5. Before grinding, the prepared 4g showed
regular plate crystals with a relatively smooth surface (Fig. 5a).
However, the smooth surface became rough aer grinding
(Fig. 5b). This external stimuli-induced damage to the surface
topography was swily repaired by exposing to CH2Cl2 vapor
(Fig. 5c). While the detailed piezochromic mechanism of 4g–j
remains to be investigated, the presence of an N,N-dimethyla-
mino substituent on b-nitrostyrene substrate seems to be
required for their color change upon grinding. The discovery of
piezochromism from the prepared N-aryl-b-enaminones 4g–j
suggests that multicomponent reactions may serve as a useful
tool not only to prepare compounds with potential biological
and pharmaceutical activities but also to unearth molecules
with novel functional properties.
Fig. 3 Color transition of 4g (a) before grinding; (b) after grinding; (c)
after exposed to fuming CH2Cl2.
As for their photochemical properties, the prepared N-aryl-b-
enaminones 4a–r were all found to be light-insensitive even
aer prolonged (more than 30 min) irradiation with UV light,
except for compound 4s. Upon UV irradiation in acetonitrile
under aerobic conditions for half an hour, compound 4s was
Fig. 4 XRD spectra of 4g (a) before grinding; (b) after grinding; (c) after
fuming with CH2Cl2.
converted to furo[3,2-b]pyridin-2(4H)-one
5 in 56% yield
(Scheme 2). Both of the molecular structures of 4s and 5 were
conrmed by the X-ray crystallography, as shown in Fig. 6.12
While the detailed photochemical mechanism for this trans-
formation is currently unclear, this photo-oxidation substan-
tially alters the molecular structure of 4s by opening up two
rings, that is, thiophene and dimedone, and forming of a new
fused ring, that is, furopyridinone. To gain insights into the
mechanism of this photo-oxidation, compound 4s was sub-
jected to EPR measurement under UV irradiation, and the result
turned out to be EPR-silent. Further, the yield of the photore-
action was not affected by the presence of a radical scavenger
like TEMPO. These observations suggest the photo-oxidation
might not proceed with the radical mechanism. Scheme 3
depicts the plausible intermediates involved in this photo-
oxidation. It presumably starts with light-mediated ring-
opening of thiophene ring to give the thiol 6, which
Fig. 5 SEM image of 4g (a) before grinding; (b) after grinding (c) after
fuming with CH2Cl2.
To investigate the phase transition during the piezochromic
process, the X-ray diffraction (XRD) patterns of 4g in different
solid states were recorded, as depicted in Fig. 4. Several sharp
and strong peaks were observed for the crystal sample of 4g,
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reaction of 4-hydroxycoumarin/dimedone, b-nitrostyrene/2-(2-
nitrovinyl)thiophene, and arylamine in the presence of trime-
thylamine as a base in toluene under reuxed conditions.
Moreover, compounds 4g–j were found to exhibit piezochromic
properties, whereas compound 4s was found to be sensitive to
light and could be converted to the furo[3,2-b]pyridin-2(4H)-one
upon UV irradiation. Further exploration of other functional
properties such as photochromism via structural tuning of N-
aryl-b-enaminones is currently underway and will be reported in
due course.
Scheme 2 Photochemical reaction of 4s.
4 Experimental
4.1 General
Melting points were determined on a Mel-Temp melting point
apparatus in open capillaries and are uncorrected. Infrared (IR)
spectra were recorded using 1725XFT-IR spectrophotometer.
High-resolution mass spectra (HRMS) were obtained on
a Thermo Fisher Scientic Finnigan MAT95XL spectrometer
using magnetic sector analyzer. X-ray diffraction (XRD) spectra
were recorded using PHILIPS X’PERT Pro MPD. Scanning elec-
tron microscopy (SEM) images were recorded on a JEOL JSM-
6500F. 1H NMR (400 MHz) and 13C NMR (100 or 150 MHz)
spectra were recorded on a Bruker 400 or Agilent Technologies
DD2 600 spectrometer. Chemical shis were reported in parts
per million on the d scale relative to an internal standard (tet-
ramethylsilane, or appropriate solvent peaks) with coupling
constants given in hertz. 1H NMR multiplicity data are denoted
by s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet).
Analytical thin-layer chromatography (TLC) was carried out on
Merck silica gel 60G-254 plates (25 mm) and developed with the
solvents mentioned. Visualization was accomplished by using
portable UV light, ninhydrin spray, or iodine chamber. Flash
chromatography was performed in columns of various diame-
ters with Merck silica gel (230–400 mesh ASTM 9385 kieselgel
60H) by elution with the solvent systems. Solvents, unless
otherwise specied, were reagent grade and distilled once prior
to use. All new compounds exhibited satisfactory spectroscopic
and analytical data.
Fig. 6 ORTEP crystal structure of 4s (left) and 5 (right).
Scheme 3 Proposed intermediates for the formation of 5 from 4s.
undergoes enol–keto tautomerization to yield the thiolactone 7.
The keto–enol tautomerization of ketone 7 and the subsequent
intramolecular cyclization furnish the hemithioketal 8. The
elimination of hydrogen sulde from 8 yields benzofuropyr-
idinone 9. Final oxidative cleavage of the double bond of vinyl
ether 9 affords the furopyridinone 5. The fact that compound 4s
is light-sensitive and compound 4r is not implies that the
methyl substituent on the thiophene moiety of 4s plays a crucial
role in its photochemical properties.
4.2 General procedure for the synthesis of b-nitrostyrene
derivatives
To a solution of NH4OAc (10.4 g, 135 mmol, 2.4 equiv.) and
acetic acid (100 mL) was added nitromethane (23.8 g,
389 mmol, 6.9 equiv.) and appropriate aldehyde (56.4 mmol, 1
equiv.) at room temperature. The resulting mixture was then
ꢀ
heated at 100 C for 6 h. Aer cooled down to room tempera-
ture, the reaction mixture was poured into water (300 mL). The
pH of the solution was adjusted to 7 with 2 M NaOH(aq) and the
product was then extracted with EtOAc (5 ꢁ 150 mL). The
organic layers were combined, washed with brine (1 ꢁ 150 mL),
dried over MgSO4, ltered, and concentrated in vacuo. The
3 Conclusions
In summary, we have demonstrated that N-aryl-b-enaminones crude product was puried by column chromatography (EtOAc/
4a–s can be efficiently synthesized via one-pot three-component hexanes) to obtain the title compound.
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8.0 Hz, 2H), 6.89 (d, J ¼ 8.0 Hz, 2H), 6.58 (d, J ¼ 8.0 Hz, 2H), 2.99 (s,
6H); 13C NMR (CDCl3, 150 MHz) d 172.8, 154.1, 151.7 (2C), 137.1
(2C), 134.1, 132.1, 130.4, 126.4, 126.0, 123.6, 120.7, 119.9, 118.3,
116.7, 111.2, 97.8, 39.9; IR n (ATR) 3401, 2897, 1715, 1604, 1340,
750 cmꢂ1; HRMS (EI) m/z calcd for C24H20N2O3 [M+] 384.1474
found 384.1471.
4.3 General procedure for the synthesis of 4
To a mixture of 4-hydroxycoumarin (1.00 mmol, 1 equiv.) in
toluene (10 mL) was added b-nitrostyrene (1 equiv.), amine (1
equiv.), and Et3N (1 equiv.) at room temperature. The resulting
mixture was then reuxed for 1.5 h. The progress of the reaction
was monitored by TLC. Aer cooled down to room temperature,
the ltrate was concentrated in vacuo. The crude product was
puried by column chromatography (EtOAc/hexanes) to give the
desired compound 4.
4.3.1 (E)-3-(Phenyl(phenylamino)methylene)chromane-2,4-
dione (4a). Rf ¼ 0.5 (15% EtOAc/hexanes); light yellow solid;
yield 76%; mp 152–153 ꢀC; 1H NMR (CDCl3, 400 MHz) d 15.65 (s,
1H), 8.13 (d, J ¼ 7.6 Hz, 1H), 7.58 (t, J ¼ 7.6 Hz, 1H), 7.42–7.34
(m, 3H), 7.30–7.12 (m, 7H), 6.85 (d, J ¼ 7.6 Hz, 2H); 13C NMR
(CDCl3, 150 MHz) d 182.6, 173.2, 161.1, 154.4, 136.9, 134.4,
133.0, 129.8, 128.9, 128.4, 127.6, 127.1, 126.0, 125.0, 123.6,
120.2, 116.8, 97.8; IR n (ATR) 3060, 1719, 1548, 1339, 1060,
759 cmꢂ1; HRMS (EI) m/z calcd for C22H15NO3 [M+] 341.1052
found 341.1050.
4.3.6 (E)-3-(((4-(Dimethylamino)phenyl)amino)(phenyl)
methylene) chromane-2,4-dione (4f). Rf ¼ 0.6 (25% EtOAc/
1
ꢀ
hexanes); orange solid; yield 69%; mp 190–191 C; H NMR
(CDCl3, 400 MHz) d 15.64 (s, 1H), 8.11 (d, J ¼ 7.6 Hz, 1H), 7.55
(d, J ¼ 7.6 Hz, 1H), 7.41–7.36 (m, 3H), 7.27–7.19 (m, 4H), 6.67
(d, J ¼ 9.2 Hz, 2H), 6.44 (d, J ¼ 9.2 Hz, 2H), 2.89 (s, 6H); 13C
NMR (CDCl3, 150 MHz) d 182.0, 171.2, 161.3, 154.3, 149.0,
133.9, 133.6, 129.5, 128.5, 127.5, 125.9, 125.6, 125.4, 123.5,
120.4, 116.8, 111.8, 97.3, 40.2; IR n (ATR) 3412, 2921, 1719,
1605, 1346, 958, 756 cmꢂ1; HRMS (EI) m/z calcd for
C
24H20N2O3 [M+] 384.1474 found 384.1475.
4.3.7 (E)-3-((4-(Dimethylamino)phenyl)((4-(dimethyl amino)
phenyl) amino)-methylene)chromane-2,4-dione (4g). Rf ¼ 0.3 (25%
EtOAc/hexanes); yellow solid; yield 68%; mp 251–252 ꢀC; 1H NMR
(CDCl3, 400 MHz) d 14.84 (bs, 1H), 8.08 (dd, J ¼ 7.6, 1.6 Hz, 1H),
7.53 (td, J ¼ 7.6, 1.6 Hz, 1H), 7.25–7.20 (m, 2H), 7.14 (d, J ¼ 8.8 Hz,
2H), 6.75 (d, J ¼ 9.2 Hz, 2H), 6.62 (d, J ¼ 8.8 Hz, 2H), 6.50 (d, J ¼
9.2 Hz, 2H), 3.00 (s, 6H), 2.91 (s, 6H); 13C NMR (CDCl3, 150 MHz)
d 181.1, 171.2, 162.5, 154.1, 151.3, 148.6, 133.5, 130.1, 126.7, 125.9,
125.4, 123.3, 121.0, 119.6, 116.6, 112.0, 111.3, 97.2, 40.3, 40.0; IR n
(ATR) 3420, 2888, 2810, 1608, 1337, 816 cmꢂ1; HRMS (EI) m/z calcd
for C26H25N3O3 [M+] 427.1896 found 427.1892.
4.3.8 (E)-3-((4-(Dimethylamino)phenyl)((4-methoxyphenyl)
amino)-methylene)chromane-2,4-dione (4h). Rf ¼ 0.4 (25%
EtOAc/hexanes); yellow solid; yield 80%; mp 229–230 ꢀC; 1H
NMR (CDCl3, 400 MHz) d 14.81 (bs, 1H), 8.08 (d, J ¼ 8.0 Hz, 1H),
7.55 (t, J ¼ 8.0 Hz, 1H), 7.26–7.20 (m, 2H), 7.11 (d, J ¼ 8.4 Hz,
2H), 6.82 (d, J ¼ 8.8 Hz, 2H), 6.72 (d, J ¼ 8.8 Hz, 2H), 6.58 (d, J ¼
8.4 Hz, 2H), 3.76 (s, 3H), 3.00 (s, 6H); 13C NMR (CDCl3, 150 MHz)
d 181.1, 172.5, 162.5, 157.8, 154.1, 151.4, 133.8, 130.7, 130.3,
126.0, 126.0, 123.4, 120.8, 119.0, 116.6, 114.1, 111.1, 97.3, 55.3,
39.9; IR n (ATR) 3417, 2970, 1737, 1530, 1353, 1217, 829,
774 cmꢂ1; HRMS (EI) m/z calcd for C25H22N2O4 [M+] 414.1580
found 414.1583.
4.3.2 (E)-3-((4-Methoxyphenyl)(phenylamino)methylene)
chromane-2,4-dione (4b). Rf ¼ 0.5 (15% EtOAc/hexanes);
yellow solid; yield 88%; mp 200–201 ꢀC; 1H NMR (CDCl3,
400 MHz) d 15.49 (s, 1H), 8.11 (d, J ¼ 7.6 Hz, 1H), 7.57 (t, J ¼
7.6 Hz, 1H), 7.28–7.13 (m, 7H), 6.86 (d, J ¼ 7.2 Hz, 4H), 3.81 (s,
3H); 13C NMR (CDCl3, 150 MHz) d 182.4, 172.9, 161.3, 160.8,
154.3, 137.1, 134.3, 129.7, 129.0, 126.9, 126.0, 125.0, 124.8,
123.6, 120.3, 116.8, 114.0, 97.8, 55.2; IR n (ATR) 3398, 2922,
1715, 1466, 1341, 1021, 754 cmꢂ1; HRMS (EI) m/z calcd for
C
23H17NO4 [M+] 371.1158 found 371.1153.
4.3.3 (E)-3-(((4-Methoxyphenyl)amino)(phenyl)methylene)
chromane-2,4-dione (4c). Rf ¼ 0.5 (15% EtOAc/hexanes); yellow
solid; yield 83%; mp 184–185 ꢀC; 1H NMR (CDCl3, 400 MHz)
d 15.59 (s, 1H), 8.11 (d, J ¼ 7.6 Hz, 1H), 7.57 (t, J ¼ 7.6 Hz, 1H),
7.40–7.34 (m, 3H), 7.29–7.20 (m, 4H), 6.77 (d, J ¼ 8.8 Hz, 2H),
6.68 (d, J ¼ 8.8 Hz, 2H), 3.73 (s, 3H); 13C NMR (CDCl3, 150 MHz)
d 182.4, 172.9, 161.1, 158.2 (2C), 154.3, 134.3, 133.1, 129.6,
128.5, 127.5, 126.1, 126.0, 123.6, 120.3, 116.8, 114.1, 97.6, 55.3;
IR n (ATR) 3417, 2922, 1716, 1557, 1241, 831, 766 cmꢂ1; HRMS
(EI) m/z calcd for C23H17NO4 [M+] 371.1158 found 371.1156.
4.3.4 (E)-3-((4-Methoxyphenyl)((4-methoxyphenyl)amino)
methyl ene)chromane-2,4-dione (4d). Rf ¼ 0.3 (15% EtOAc/
hexanes); light orange solid; yield 86%; mp 159–160 ꢀC; 1H
NMR (CDCl3, 400 MHz) d 15.43 (s, 1H), 8.09 (d, J ¼ 8.8 Hz, 1H),
7.56 (td, J ¼ 8.8, 1.6 Hz, 1H), 7.28–7.20 (m, 2H), 7.16 (d, J ¼
8.8 Hz, 2H), 6.86 (d, J ¼ 8.8 Hz, 2H), 6.78 (d, J ¼ 8.8 Hz, 2H),
6.71 (d, J ¼ 8.8 Hz, 2H), 3.82 (s, 3H), 3.75 (s, 3H); 13C NMR
(CDCl3, 150 MHz) d 182.2, 172.5, 161.4, 160.7, 158.1, 154.3,
134.1, 129.9, 129.6, 126.2, 126.0, 125.0, 123.6, 120.4, 116.7,
114.2, 114.0, 97.6, 55.3, 55.2; IR n (ATR) 3419, 2970, 1715,
1462, 1235, 1029, 760 cmꢂ1; HRMS (EI) m/z calcd for
4.3.9 (E)-3-(((4-Bromophenyl)amino)(4-(dimethylamino)
phenyl)-methylene)chromane-2,4-dione (4i). Rf ¼ 0.5 (25%
1
ꢀ
EtOAc/hexanes); yellow solid; yield 82%; mp 258–259 C; H
NMR (CDCl3, 400 MHz) d 15.19 (bs, 1H), 8.07 (d, J ¼ 7.6 Hz,
1H), 7.56 (td, J ¼ 7.6, 1.2 Hz, 1H), 7.33 (d, J ¼ 8.4 Hz, 2H),
7.27–7.25 (m, 2H), 7.10 (d, J ¼ 8.4 Hz, 2H), 6.75 (d, J ¼ 8.4 Hz,
2H), 6.59 (d, J ¼ 8.4 Hz, 2H), 3.01 (s, 6H); 13C NMR (CDCl3,
150 MHz) d 182.4, 172.8, 161.3, 154.1, 151.6, 137.9, 133.9,
130.4, 128.9, 126.4, 126.0, 124.9, 123.4, 120.8, 118.8, 116.7,
111.1, 97.5, 39.9; IR n (ATR) 3422, 2970, 1727, 1530, 1338,
1065, 812, 753 cmꢂ1; HRMS (EI) m/z calcd for C24H19BrN2O3
[M+] 462.0579 found 462.0580.
C
24H19NO5 [M+] 401.1263 found 401.1269.
4.3.5 (E)-3-((4-(Dimethylamino)phenyl)(phenylamino)methy-
4.3.10 (E)-4-(((4-(Dimethylamino)phenyl)(2,4-dioxochroman-
3-ylid ene)-methyl)amino)benzonitrile (4j). Rf ¼ 0.5 (25% EtOAc/
hexanes); orange solid; yield 69%; mp 252–253 ꢀC; 1H NMR
(CDCl3, 400 MHz) d 14.92 (bs, 1H), 8.07 (d, J ¼ 7.6 Hz, 1H), 7.58 (td,
J ¼ 7.6, 1.6 Hz, 1H), 7.49 (d, J ¼ 8.8 Hz, 2H), 7.28–7.22 (m, 2H), 7.11
lene) chromane-2,4-dione (4e). Rf ¼ 0.6 (25% EtOAc/hexanes);
yellow solid; yield 77%; mp 222–223 ꢀC; 1H NMR (CDCl3, 400
MHz) d 14.84 (bs, 1H), 8.08 (dd, J ¼ 7.6, 1.6 Hz, 1H), 7.56 (td, J ¼
7.6, 1.6 Hz, 1H), 7.27–7.20 (m, 4H), 7.15–7.11 (m, 1H), 7.12 (d, J ¼
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(d, J ¼ 8.8 Hz, 2H), 6.94 (d, J ¼ 8.8 Hz, 2H), 6.60 (d, J ¼ 8.8 Hz, 2H), 154.2, 134.4, 132.8, 129.97, 129.89, 129.5, 127.3, 126.2,
3.03 (s, 6H); 13C NMR (CDCl3, 150 MHz) d 182.4, 172.5, 161.3, 126.1, 123.8, 120.5, 116.8, 114.3, 98.7, 55.4; IR nmax (KBr)
154.1, 152.0, 142.3, 134.4, 132.9, 130.6, 126.1, 125.1, 123.7, 120.4, 3454, 2929, 1714, 1608, 1546, 1365, 1228, 1032, 1653,
118.1, 117.8, 116.7, 111.1, 109.4, 98.3, 39.9; IR n (ATR) 3390, 2970, 727 cmꢂ1; HRMS (EI) m/z calcd for C21H15NO4S [M+]
1717, 1426, 1366, 1197, 770 cmꢂ1; HRMS (EI) m/z calcd for 377.0722, found 377.0725.
C25H19N3O3 [M+] 409.1426 found 409.1423.
4.3.16 ((E)-3-(((4-methoxyphenyl)amino)(3-methylthiophen-2-
4.3.11 (E)-3-((4-Bromophenyl)(phenylamino)methylene) yl) methylene)chromane-2,4-dione (4p). Rf ¼ 0.40 (30% EtOAc/
1
ꢀ
chromane 2,4-dione (4k). Rf ¼ 0.4 (15% EtOAc/hexanes); hexanes); yellow solid; yield 62%; mp 170–172 C; H NMR (400
yellow solid; yield 72%; mp 192–193 ꢀC; 1H NMR (CDCl3, MHz, CDCl3) d 15.60 (bs, 1H), 8.10 (bd, J ¼ 8.4 Hz, 1H), 7.57 (td, J ¼
400 MHz) d 15.65 (s, 1H), 8.12 (d, J ¼ 7.6 Hz, 1H), 7.60 (t, J ¼ 8.4, 1.6 Hz, 1H), 7.39 (d, J ¼ 4.8 Hz, 1H), 7.28–7.20 (m, 2H), 6.88 (d,
7.6 Hz, 1H), 7.48 (d, J ¼ 8.0 Hz, 2H), 7.28 (t, J ¼ 7.6 Hz, 1H), J ¼ 9.2 Hz, 2H), 6.80 (d, J ¼ 4.8 Hz, 1H), 6.75 (d, J ¼ 9.2 Hz, 2H),
7.24–7.18 (m, 4H), 7.12 (d, J ¼ 8.0 Hz, 2H), 6.86 (d, J ¼ 7.6 Hz, 3.77 (s, 3H), 2.03 (s, 3H); 13C NMR (100 MHz, CDCl3) d 182.0, 166.0,
2H); 13C NMR (CDCl3, 150 MHz) d 182.6, 172.1, 161.1, 154.3, 160.4, 158.5, 154.2, 137.6, 134.4, 130.0, 127.95, 127.79, 126.2, 125.6,
136.5, 134.6, 131.8, 129.3, 129.1, 127.4, 126.0, 125.4, 125.1, 125.3, 120.3, 116.8, 114.3, 114.0, 99.0, 55.4, 14.6; IR nmax (KBr) 3067,
124.2, 123.7, 120.1, 116.9, 97.7; IR n (ATR) 3407, 3102, 1709, 2968, 1711, 1608, 1558, 1463, 1339, 1247, 1028, 882 cmꢂ1; HRMS
1538, 1339, 758 cmꢂ1; HRMS (EI) m/z calcd for C22H14BrNO3 (EI) m/z calcd for C22H17NO4S [M+] 391.0878, found 391.0874.
[M+] 419.0157 found 419.0159.
4.3.17 5,5-Dimethyl-2-(phenyl(phenylamino)methylene)
4.3.12 (E)-3-((4-Nitrophenyl)(phenylamino)methylene)
cyclohexane-1,3-dione (4q). Rf ¼ 0.55 (30% EtOAc/hexanes);
chromane-2,4-dione (4l). Rf ¼ 0.4 (15% EtOAc/hexanes); pale yellow solid; yield 56%; mp 146–148 ꢀC; 1H NMR (400
orange solid; yield 54%; mp 227–228 ꢀC; 1H NMR (CDCl3, MHz, CDCl3) d 14.70 (bs, 1H), 7.34–7.27 (m, 3H), 7.14–7.05
400 MHz) d 15.75 (s, 1H), 8.21 (d, J ¼ 8.4 Hz, 2H), 8.14 (d, J ¼ (m, 5H), 6.76 (d, J ¼ 7.6 Hz, 2H), 2.57 (s, 2H), 2.33 (s, 2H), 1.12
7.6 Hz, 1H), 7.62 (t, J ¼ 7.6 Hz, 1H), 7.43–7.38 (m, 2H), 7.31 (s, 6H); 13C NMR (100 MHz, CDCl3) d 200.4, 195.3, 169.2,
(t, J ¼ 7.6 Hz, 1H), 7.24–7.21 (m, 4H), 6.88 (d, J ¼ 8.4 Hz, 2H); 137.2, 134.0, 129.0, 128.8, 128.3, 127.7, 126.4, 125.1, 108.5,
13C NMR (CDCl3, 100 MHz) d 182.9, 171.2, 161.2, 154.4, 53.3, 52.5, 30.3, 28.5; IR nmax (KBr) 2953, 1716, 1661, 1535,
148.1, 139.6, 136.1, 135.0, 129.4, 128.8, 127.9, 126.2, 125.4, 1434, 1335, 1219, 1210, 983, 776 cmꢂ1; HRMS (EI) m/z calcd
124.0, 123.7, 120.0, 117.0, 97.7; IR n (ATR) 3084, 1703, 1464, for C21H21NO2 [M+] 319.1572, found 319.1577.
1340, 767, 718 cmꢂ1; HRMS (EI) m/z calcd for C22H14N2O5
4.3.18 2-(((4-Methoxyphenyl)amino)(thiophen-2-yl)methylene)-
[M+] 386.0903 found 386.0899.
5,5 -dimethylcyclohexane-1,3-dione (4r). Rf ¼ 0.40 (30% EtOAc/
1
4.3.13 (E)-7-Methoxy-3-(phenyl(phenylamino)methylene) hexanes); brown solid; yield 55%; mp 138–140 ꢀC; H NMR (400
chromane-2,4-dione (4m). Rf ¼ 0.5 (15% EtOAc/hexanes); MHz, CDCl3) d 14.40 (bs, 1H), 7.41 (dd, J ¼ 5.2, 1.2 Hz, 1H), 6.93 (dd, J
light yellow solid; yield 85%; mp 205–206 ꢀC; 1H NMR ¼ 3.6, 1.2 Hz, 1H), 6.84–6.82 (m, 1H), 6.82 (d, J ¼ 8.8 Hz, 2H), 6.72 (d, J
(CDCl3, 400 MHz) d 15.65 (s, 1H), 8.03 (d, J ¼ 8.8 Hz, 1H), ¼ 8.8 Hz, 2H), 3.76 (s, 3H), 2.47 (s, 4H), 1.13 (s, 6H); 13C NMR (100
7.39–7.33 (m, 3H), 7.26–7.23 (m, 2H), 7.16–7.12 (m, 3H), 6.83 MHz, CDCl3) d 197.4 (2C), 162.1, 158.1, 134.3, 130.2, 129.2, 128.4,
(d, J ¼ 8.0 Hz, 3H), 6.66 (d, J ¼ 1.6 Hz, 1H), 3.88 (s, 3H); 13C 127.0, 126.1, 114.1, 109.7, 55.4, 52.8, 30.4, 28.5; IR nmax (KBr) 3078,
NMR (CDCl3, 150 MHz) d 182.1, 172.9, 164.8, 161.3, 156.1, 2836, 1652, 1578, 1547, 1407, 1247, 1031, 895, 825 cmꢂ1; HRMS (EI)
137.0, 133.1, 129.6, 128.8, 128.4, 127.6, 127.5, 126.9, 125.0, m/z calcd for C20H21NO3S [M+] 355.1242, found 355.1237.
113.6, 112.0, 100.1, 96.9, 55.7; IR n (ATR) 3065, 1719, 1532,
1333, 1104, 763, 704 cmꢂ1
23H17NO4 [M+] 371.1158 found 371.1159.
4.3.14 (E)-6-Chloro-3-(phenyl(phenylamino)methylene)
4.3.19 5,5-Dimethyl-2-((3-methylthiophen-2-yl)(phenylamino)
;
HRMS (EI) m/z calcd for methylene)cyclohexane-1,3-dione (4s). Rf ¼ 0.30 (30% EtOAc/
1
ꢀ
C
hexanes); light yellow solid; yield 52%; mp 142–144 C; H NMR
(400 MHz, CDCl3) d 14.62 (bs, 1H), 7.31 (d, J ¼ 4.8 Hz, 1H), 7.22 (t, J
chromane-2,4-dione (4n). Rf ¼ 0.5 (15% EtOAc/hexanes); ¼ 7.2 Hz, 2H), 7.15 (t, J ¼ 7.2 Hz, 1H), 6.89 (d, J ¼ 7.6 Hz, 2H), 6.74
light yellow solid; yield 52%; mp 188–189 ꢀC; 1H NMR (d, J ¼ 4.8 Hz, 1H), 2.61, 2.56 (ABq, J ¼ 17.2 Hz, 1H each), 2.46, 2.35
(CDCl3, 400 MHz) d 15.55 (s, 1H), 8.08 (s, 1H), 7.51 (d, J ¼ (ABq, J ¼ 16.4 Hz, 1H each), 1.97 (s, 3H), 1.15 (s, 3H), 1.12 (s, 3H);
8.4 Hz, 1H), 7.40–7.34 (m, 3H), 7.26–7.15 (m, 6H), 6.85 (d, J ¼ 13C NMR (100 MHz, CDCl3) d 200.0, 194.9, 161.8, 137.4, 136.9,
7.6 Hz, 2H); 13C NMR (CDCl3, 150 MHz) d 181.3, 173.5, 160.6, 129.8, 129.0, 128.9, 127.0, 126.6, 124.2, 110.0, 53.3, 52.4, 30.2, 28.6,
152.7, 136.6, 134.3, 132.7, 129.9, 129.2, 129.0, 128.5, 127.5, 28.3, 14.5; IR nmax (KBr) 2956, 2872, 1735, 1652, 1561, 1333, 1128,
127.3, 125.6, 125.1, 121.3, 118.5, 97.6; IR n (ATR) 3418, 3072, 982, 763 cmꢂ1; HRMS (EI) m/z calcd for C20H21NO2S [M+] 339.1293,
1959, 1719, 1543, 1334, 988 cmꢂ1; HRMS (EI) m/z calcd for found 339.1290.
C
22H14ClNO3 [M+] 375.0662 found 375.0667.
4.3.15 (E)-3-(((4-methoxyphenyl)amino)(thiophen-2-yl)
4.4 Photoirradiation of N-aryl-b-enaminone 4s
methylene)chromane-2,4-dio-ne (4o). Rf ¼ 0.50 (30% EtOAc/
hexanes); yellow solid; yield 65%; mp 166–168 C; 1H NMR The solution of compound 4s (50 mg) in acetonitrile (1000 mL)
(400 MHz, CDCl3) d 15.08 (bs, 1H), 8.08 (dd, J ¼ 7.6, 1.6 Hz, was irradiated under aerobic conditions using a photochemical
1H), 7.57 (td, J ¼ 7.2, 1.6 Hz, 1H), 7.50 (dd, J ¼ 4.0, 2.0 Hz, reactor (PR-2000, 352 nm ꢁ 10 lamps) for 30 min. The solution
1H), 7.28–7.24 (m, 1H), 7.22 (d, J ¼ 8.4 Hz, 1H), 7.00–6.99 (m, was then concentrated in vacuo and the crude product was
2H), 6.88 (d, J ¼ 8.8 Hz, 2H), 6.80 (d, J ¼ 8.8 Hz, 2H), 3.77 (s, puried by column chromatography (40% EtOAc/hexanes) to
3H); 13C NMR (100 MHz, CDCl3) d 181.4, 166.1, 161.8, 158.6, obtain the brown solid furopyridinone 5.
ꢀ
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4.4.1 2,2-Dimethyl-4-(7-methyl-2-oxo-4-phenyl-2,4-dihydrofuro
[3,2-b]pyridin-3-yl)-4-oxobutanal (5). Rf ¼ 0.20 (50% EtOAc/hexanes);
28 mg; yield 56%; mp charred @ 250 ꢀC; 1H NMR (400 MHz, CDCl3)
d 9.35 (s, 1H), 7.49–7.47 (m, 3H), 7.36 (d, J ¼ 7.2 Hz, 1H), 7.28–7.26
(m, 2H), 6.74 (d, J ¼ 7.2 Hz, 1H), 3.20 (s, 2H), 2.46 (s, 3H), 0.98 (s,
6H); 13C NMR (100 MHz, CDCl3) d 205.1, 190.8, 167.8, 145.2, 143.9,
143.0, 133.2, 129.5, 129.3, 125.5, 123.8, 116.2, 90.6, 49.5, 44.2, 22.1,
15.0; IR nmax (KBr) 2923, 2853, 1738, 1720, 1365, 1217, 1092,
757 cmꢂ1; HRMS (EI) m/z calcd for C20H19NO4 [M+] 337.1314, found
337.1309.
Conflicts of interest
There are no conicts to declare.
´
´
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8 E. H. Avdovic, D. Milenkovic, J. M. D. Markovic, J. Đorovic,
Acknowledgements
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´
´
N. Vukovic, M. D. Vukic, V. V. Jevtic, S. R. Trifunovic,
ˇˇ´
´
I. Potocnak and Z. Markovic, Spectrochim. Acta, Part A,
We thank the Ministry of Science and Technology of the
Republic of China, Taiwan, for nancially supporting this
research under Grant No. MOST 108-2113-M-029-001.
2018, 195, 31–40.
9 A. Saha, S. Payra, S. Akhtar and S. Banerjee, ChemistrySelect,
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12 Crystallographic data (excluding structure factors) for 4g, 4j,
4s, and 5 have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication
number CCDC-1913301, 1913302, 1953598, and 1953599
respectively.
Notes and references
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34094 | RSC Adv., 2019, 9, 34088–34094
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