Visible light-promoted synthesis of pyrrolidinone derivatives via Rose Bengal as a photoredox catalyst and their photophysical studies

Article abstract of DOI:10.1039/d1nj00343g

Herein, we report an intramolecular radical cyclization reaction towards the synthesis of pyrrolidinone derivatives via metal-free photoredox catalysis under irradiation from blue LEDs. Some of the remarkable features of this protocol include synthetic ef

Full text of DOI:10.1039/d1nj00343g

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Visible light-promoted synthesis of pyrrolidinone
derivatives via Rose Bengal as a photoredox
catalyst and their photophysical studies†
a
Cite this: New J. Chem., 2021,
45, 8136
Arup Dutta,a Mostofa A. Rohman,
Ridaphun Nongrum,b Aiborlang Thongni,a
a
a
Sivaprasad Mitra
and Rishanlang Nongkhlaw
*
Herein, we report an intramolecular radical cyclization reaction towards the synthesis of pyrrolidinone
derivatives via metal-free photoredox catalysis under irradiation from blue LEDs. Some of the remarkable
features of this protocol include synthetic efficiency, green reaction profile, easy isolation of products
and short reaction time. The photophysical properties of synthesized compounds were investigated via
steady state and time-resolved fluorescence spectroscopy in the solid state. Results showed the
promising opportunity for their spectral tuning together with large Stokes-shifted and highly active
fluorescence emission, thus indicating that these molecular scaffolds can be effective probes for the
biological applications and development of opto-electronic devices.
Received 21st January 2021,
Accepted 31st March 2021
DOI: 10.1039/d1nj00343g
rsc.li/njc
Five-membered nitrogen-containing heterocyclic compounds
such as polysubstituted 3-hydroxy-2-pyrrolidinones are important
Introduction
Over the last decade, visible light-induced reactions have emerged frameworks in many biologically active compounds and have found
as a powerful tool for initiating various organic transformations wide applications in the pharmaceutical and agricultural sectors.13
under mild conditions, and thus gained significance in the field of Several pyrazolone-based compounds have been successfully devel-
sustainable chemistry.1–5 Photoredox catalysis has been considered oped into commercial drugs such as pyrrolidinonequercetin14 and
a markable innovation that has provided an ideal way to generate pyrrolidinoneorhamnetin.15 More specifically, pyrazolone, as a
radical cyclization6 and path-breaking routes for the C–C/C–X bond constituent of doxapram,16 azaspirene,17 salinosporamide A18 and
formation in heterocyclic chemistry.7,8 It has also found several lactacystin,19 has proven to be a useful intermediate in biomedical
noteworthy applications in green synthesis9 and other areas such as research and natural product synthesis (Fig. 1).
radical chemistry and photochemistry.
Furthermore, low molecular weight N-containing heterocycles are
Photoredox catalysts utilize a renewable energy source to considered as promising candidates for developing optoelectronic
promote chemical reactions by absorbing visible light radiation devices due to their easy synthesis, functionalization, purification
and transferring it to low energy organic substrates through a and characterization. Five-membered nitrogen heterocycles with
single-electron transfer (SET) process.10 Heterogeneous semi- substituted diketopyrrolopyrrole20 and polypyrrole21 derivatives have
conductors such as mesoporous carbon nitride and various emerged as potential materials for optoelectronic devices in the
metal oxides have been widely used as photocatalysts in organic recent literature. Also, a recent review portrays the application
syntheses, which have been found to be complementary to of several pyrazine-functionalized p-conjugated materials for
iridium and ruthenium complexes as photoredox catalysts.11 optoelectronic applications.22 Although there are a few reports
Recently, the application of organic molecules as photocatalysts citing the use of substituted pyrrolidinone compounds for the
has attracted attention from many synthetic chemists given that development of optoelectronic materials,23,24 the detailed char-
this approach offers several advantages over the transition acterization of the fluorescence behaviour of a series of pyrro-
metal-mediated catalysis in terms of catalyst removal and lower lidinone derivatives, particularly in the solid state, is relatively
toxicity to various life forms.12 This method has also been found scarce (Scheme 1).
to be energetically sustainable and beneficial in the long term.
Considering the importance of substituted pyrrolidinones,
various methods for their synthesis have been reported with
enhanced procedures such as short reaction time, minimum side
reactions and the hassle-free isolation of desired products.25,26
A literature survey revealed that significant efforts have been
a Centre for Advanced Studies in Chemistry, Department of Chemistry, North
Eastern Hill University, Shillong 793022, India. E-mail: rlnongkhlaw@gmail.com
b Sankardev College, Bishnupur, Shillong, India
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1nj00343g made to synthesize pyrrolidinone derivatives by combining
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Based on the above-mentioned reports, herein, we present a
novel approach towards the synthesis of pyrrolidinone derivatives
via the visible light-initiated one-pot multicomponent reaction of
arylamines, aromatic aldehydes and acetylenedicarboxylate using
Rose Bengal as a photoredox catalyst. The reaction was carried out
in a CH3CN:H2O solvent mixture at room temperature, which
is environmentally harmless and non-toxic. The formation of
the products was confirmed using different characterization
1
techniques including FT-IR, H NMR, 13C NMR spectroscopy,
mass spectrometry and elementary analysis. Photophysical
studies of the synthesized compounds were carried out and a
detailed spectroscopic characterization of these compounds
is presented with the intention to rationalize the bright solid-
state photoluminescence behavior with the peripheral substi-
tuent pattern.
Fig. 1 Some biologically important structures containing pyrrolidinone
motifs.
Result and discussion
To test the feasibility of our protocol, aniline (1a), diethyl
acetylene dicarboxylate (DEAD) (2a) and benzaldehyde (3a) were
selected as model substrates for the designed product. Initially,
when we used thioxanthone as a catalyst under the irradiation
of blue LED light in CH3CN : H2O (1 : 1), pyrrolidinone 4a was
obtained in 77% yield (Table 1, entry 1). This result inspired us
to investigate the reaction conditions with several other photo-
Scheme 1 Synthesis of pyrrolidinone derivatives under irradiation from a
blue light-emitting diode (LED).
different structurally diverse motifs.27,28 Various protocols have redox catalysts including Eosin Y, methylene blue, rhodamine
been reported for the multicomponent synthesis of these moieties B, fluorescein, erythrosin B, xanthene, phenanthrenequinone,
using a range of catalysts such as [BBSI][HSO4],29 [Fe3O4@SiO2@ acenaphthenequinone, and acridinium-based photocatalyst
Propyl-ANDSA],30 [Cu(OAc)2],31 UiO-66-SO3H,32 and TiO2-np.33 One and the results are presented in Table 1. The model reaction
commonly employed route for the synthesis of pyrrolidinones was also carried out in the absence of catalyst, which gave only
involves the condensation of anilines, aromatic aldehydes and a trace amount of product 4a under the irradiation of blue LEDs
dialkylacetylenedicarboxylates using PTSA34 as a catalyst. However, (Table 1, entry 15). A satisfactory product yield of 94% was obtained
a substantial amount of catalyst is required in this reaction when Rose Bengal (15 mol%) was used as the photoredox catalyst.
because of the formation of a complex between the product and Therefore, Rose Bengal (15 mol%) was chosen as the most suitable
the acid catalyst, which results in the wastage of the catalyst. It also photocatalyst for our present study (Table 1, entry 13).
results in the production of acidic waste water during the post-
Encouraged by the aforementioned results, we screened
treatment process.35 Despite the advances in the synthesis of suitable solvents, and the results are summarized in Table 2.
pyrrolidinone derivatives, these methods still suffer from draw- Several polar and non-polar solvents such as toluene, DMF,
backs such as harsh reaction conditions, long reaction time, DCM, MeOH, EtOH, CH3CN and H2O were studied, and
complex synthetic pathways and limited structural diversity respectable yields of products were obtained (entries 1–13). In
and functional group tolerability. Accordingly, improved addition, neat condition was also screened, but the desired
methods for the synthesis of pyrrolidinone derivatives with product was not detected (Table 1, entry 1). Among the tested
high selectivity are still in demand and of utmost interest to solvents, CH3CN : H2O (1 : 1) was found to be the best choice for
the synthetic community.
the reaction (Table 2, entry 9).
Rose Bengal (RB) is one of the most versatile organic photo-
The model reaction with Rose Bengal (15 mol%) could also
sensitizers (PS) in diverse biological and medical applications, which be promoted by visible light of different intensities (LED 12 W,
also shows potential value in cancer therapy and diagnosis.36 In 18 W, 23 W and blue LEDs) (Table 3, entries 1–5), but blue LEDs
recent years, the use of RB as a photoredox catalyst has received (450 nm) were the most efficient (Table 3, entry 4). The control
considerable attention. Although it mostly works through SET experiments disclosed that no product was observed when the
processes, it is also known to function through energy transfer reaction was performed in the dark (Table 3, entry 5).
(EnT) processes, especially, as a singlet oxygen sensitizer. As a
After optimizing the reaction conditions, we investigated the
type II photosensitizer, RB converts triplet oxygen molecules substrate scope for the visible-light-mediated Rose Bengal-catalyzed
into singlet oxygen upon irradiation with blue light (450 nm) via synthesis of pyrrolidinone derivatives. A range of substituted
a photo-catalytic process. In addition, the singlet–triplet state anilines, substituted benzaldehydes and dialkylacetylenedi-
energy gap (DE) of RB is small (DE E 0.35 eV).37
carboxylates (alkyl = CH3 and C2H5) were studied and it was
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Table 1 Estimation of the reaction conditions with various catalysts
Table 1 (continued)
Entry
1
Photocatalyst
Time (min)
45
Yielda (%)
77
Entry
Photocatalyst
Time (min)
Yielda (%)
13
14
15
Rose Bengal (15 mol%)
Rose Bengal (20 mol%)
No catalyst
30
30
60
94
94
Trace
Reaction conditions: aniline (1 mmol), DEAD (1.2 mmol), benzaldehyde
(1 mmol), catalyst (10 mol%), CH3CN:H2O (3 mL), blue LED irradiation
a
under air atmosphere at rt. Isolated yield of product.
2
3
60
60
65
55
Table 2 Optimization of the solvent
4
5
6
60
60
60
76
69
45
Entry
Solvent
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
Neat
Toluene
DMF
DCM
MeOH
EtOH
CH3CN
H2O
CH3CN/H2O (1 : 1)
CH3CN/H2O (2 : 1)
CH3CN/H2O (3 : 1)
CH3CN/H2O (9 : 1)
THF
60
60
60
60
45
45
30
30
30
30
30
30
60
Trace
10
47
35
60
70
88
55
94
94
94
91
20
9
10
11
12
13
7
8
60
60
39
53
Reaction conditions: aniline (1 mmol), DEAD (1.2 mmol), benzaldehyde
(1 mmol), Rose Bengal (15 mol%), solvent (3 mL), blue LED irradiation
under air atmosphere at rt. Isolated yield of product.
a
Table 3 Evaluation of visible light source
9
60
45
57
73
Entry
Visible light source
Time (min)
Yielda (%)
10
1
2
3
4
5
White LEDs (12W)
White LEDs (18 W)
White LEDs (23 W)
Blue LEDs (450 nm)
Dark
60
45
45
30
90
83
81
88
94
Trace
11
45
30
77
88
Reaction conditions: aniline (1 mmol), DEAD (1.2 mmol), benzaldehyde
(1 mmol), Rose Bengal (15 mol%), CH3CN:H2O (3 mL), irradiation
under air atmosphere at rt in different reaction conditions. Isolated
a
yield of product.
found that both dimethylacetylenedicarboxylate (DMAD) and
diethylacetylenedicarboxylate (DEAD) proceeded without much
variation in the yield of the products (Table 4). The position and
12
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Table 4 Substrate scope of the reaction
expected, aromatic aldehydes with electron withdrawing groups
acted as better substrates compared to that with electron
donating groups. A comparative study between blue LEDs and
white LEDs as the irradiation source was performed to further
investigate the catalytic activity of Rose Bengal for the synthesis
of 4a and the results are presented in Table S1 (ESI†). The
results indicate the superiority of blue LEDs, which gave higher
product yields in shorter reaction times.
In addition, to demonstrate the scalability of this visible
light-initiated multicomponent process, we carried out the model
reaction on a large scale. When the reaction was conducted on a
10.0 mmol scale, the desired product 4a was obtained in 94%
yield, which is equivalent with the performance of the 1.0 mmol-
scale reaction.
To gain insight into the reaction mechanism of this visible
light-promoted three-component reaction, a series of control
experiments was performed. As shown in Scheme 2, the con-
densation of aniline with benzaldehyde was performed under the
standard conditions (Rose Bengal in water-acetonitrile under
blue LED) with the elimination of water to give the corresponding
imine D. When the reaction of diethyl acetylene dicarboxylate
(DEAD) with benzaldehyde was carried out under the same
reaction conditions, no product was detected.
However, the reaction of imine D and DEAD under standard
conditions generated the desired product 4a in 94% yield.
Furthermore, no corresponding product 4a was obtained when
the reaction was carried out in the absence of light.
After considering the outcome of this experimental study, a
plausible reaction pathway in the presence of Rose Bengal is
proposed in Scheme 3.
According to the literature,38 upon irradiation with visible
light, Rose Bengal (RB) accepts a photon to generate the excited
state RB* via intersystem crossing (ISC). This triplet state
converts aniline into radical-cation (A) by single-electron transfer
(SET). Then this radical cation (A) reacts with benzaldehyde to
form (B). Moreover, (B) is converted to (C) (by SET), which further
Reaction conditions: substituted aniline (1 mmol), DEAD/DMAD (1.2 mmol),
substituted benzaldehyde (1 mmol), Rose Bengal (15 mol%), CH3CN:H2O
(3 mL), blue LED irradiation under an air atmosphere at rt.
type of substituents on the aromatic ring (e.g., –NO2, –Cl, –Br,
–CH3, and –OMe) also did not have a significant effect on the
reaction and provided satisfactory yields (84–97%). However, as
Scheme 2 Control experiments relevant to the understanding of the
mechanistic course of the reaction of 1a (1 mmol), 2a (1 mmol) and 3a
(1 mmol).
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Scheme 3 Plausible mechanism.
undergoes dehydration to give (D). DEAD undergoes nucleophilic on the amine and aldehyde components used for synthesizing
addition reaction with water25,39,40 to form 1,3 dipolar intermedi- these derivatives (depicted as R1 and R3 in Table 4, respectively).
ate (E), which undergoes an SET reaction with RB* to give (F). The For example, the absorption peak position of compounds 9c
reaction between imine intermediate (D) and 1,3 dipolar radical (R1 = 4-CH3 and R3 = 4-Cl), 6d (R1 = 4-CH3 and R3 = H) and 5k
(F) followed by cyclisation leads to the formation of intermediate (R1 = H and R3 = 4-OCH3) appears at 320, 325 and 328 nm,
(G), which subsequently eliminates EtOH to give the target respectively. Therefore, it is evident that the electron donation
molecule 4a.
in the amine and aldehyde moieties shifts the UV-vis peak
Due to the limited solubility of the synthesized pyrrolidi- position to higher and lower energies in the spectrum, respectively.
none derivatives, the representative solution phase photo- Conversely, electron withdrawing substituents in the aldehyde
physical studies were performed in DMSO solvent. All the moiety make the absorption spectra very broad. For example, in
compounds show relatively broad absorption in the wavelength compounds such as 4f (R1 = H and R3 = 3-Cl), 5f (R1 = H
range of 290–350 nm with a peak position of 325 ꢀ 5 nm in and R3 = 3-OCH3) and 8b (R1 = 4-OCH3 and R3 = 3-Cl), it is
different systems. Some of the representative spectra are shown rather difficult to extract a definitive absorption peak position
in Fig. S2(a) (ESI†). Interestingly, the absorption spectral shape from the solution phase absorption profile [Fig. S2(a), ESI†]. In
and the peak position depend on the nature of the substituents this case, the absorption peak positions mentioned for the
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Table 5 Solution phase spectral data of some of the synthesized pyrrolidinone derivatives in DMSO
Steady-state measurements
Time-resolved fluorescence decay
P
Compounds
maxlabs/nm
maxlem/nm
Stokes shift/cmꢂ1
ff/10ꢂ2
tav/ns
kr/107 sꢂ1
k
nr/109 sꢂ1
5k
6a
6d
7b
8a
9c
326
334
325
301
325
321
435
442
427
480
462
459
7686
7316
7350
12389
9124
9366
0.26
0.39
0.31
0.27
0.29
0.25
0.85
1.21
0.59
0.28
0.91
0.58
0.31
0.32
0.53
0.96
0.31
0.44
1.17
0.83
1.69
3.56
1.10
1.72
different groups of compounds in Table 5 were obtained from 2.5 ns component. This ensures very fast decay of the excited
the excitation spectra.
state and may contribute to the very low fluorescence yield, as
P
Representative steady state fluorescence emission spectra of discussed above. The radiative (kr) and total non-radiative ( knr)
some of the investigated compounds in DMSO solvent are decay rate constants were calculated using the known value of
shown in Fig. S2(b) (ESI†) and the corresponding data is given fluorescence yield (ff) and average lifetime (tav) (Table 5) using
in Table 5. In general, the fluorescence spectra are very broad the following relations:
and cover the spectral range of 400–500 nm. Similar to that in
the absorption spectra, the fluorescence peak maxima also
depend on the nature of R1 and R2. For example, the fluorescence
X
ff
tav
ð1 ꢂ ff Þ
kr ¼
;
knr
¼
(1)
tav
peak for 9c (R1 = 4-CH3 and R3 = 4-Cl) with an electron-withdrawing It is evident from the calculated values that the non-radiative
substituent in the aldehyde component shows a bathochromic shift decay processes of all the investigated systems are about three orders
of B27 nm in comparison with 6d (R1 = 4-CH3 and R3 = H). of magnitude higher than the radiative part, justifying the proposi-
Therefore, both the absorption and photoluminescence behavior of tion discussed above for the significantly low luminescence yield.
the pyrrolidinone derivatives can be tuned over a broad spectral
Interestingly, some of the synthesized compounds showed
range with judicious choice of the substituents, giving a plethora of excellent bright light emission in the solid state (Fig. 4). Thus,
opportunities for synthetic manipulation towards the fabrication of to gain further insight into their PL behavior, both steady-state and
suitable probes for biophysical studies or optoelectronic devices.
time-resolved experiments were conducted for all the systems in
However, the major drawback of the synthesized systems for the solid phase. Fig. 3a shows some of the representative spectral
practical application is their extremely low fluorescence yield in profiles, and all the corresponding data is included in Table 6.
solution. For example, the quantum yield of fluorescence varies Typically, the fluorescence spectral peaks are distributed over three
in the range of (0.20–0.40) ꢁ 10ꢂ2 for the studied compounds in distinct regions, viz., 440, 460 and 480 nm (within ꢀ5 nm, as
DMSO. Thus, to understand more details about the dynamic shown by the shaded vertical lines) depending on the substitution
behavior of the excited states, the fluorescence lifetime of the pattern. Compounds 4g, 5a, 5f, and 5k having R1 = H and the
pyrrolidinone derivatives in DMSO solution was measured. electron-rich R3 component show a fluorescence peak at ca.
Simulation of the time-resolved decay traces with eqn (1) revealed 440 nm. However, with R1 = H or 4-CH3 and R3 = 3-Cl substitution,
the necessity of two components (Fig. 2a) to reproduce the systems 4f, 5h, 8b, etc. show mid-range fluorescence at B460 nm.
experimental data points with reliable statistical parameters.41 Conversely, strong electron donation at the R1 position through
However, as shown in Fig. 2b and Table S2 (ESI†), the major 4-OCH3 and electron-withdrawing substitution through a 3- or 4-Cl
component decay with a sub-nanosecond time constant was in group in 9b and 9d shifts the fluorescence peak in the extremely
the range of 0.14–0.36 ns with a very low contribution (o5%) of red end of the spectrum (ca. 460 nm). The time-resolved
Fig. 2 (a) Time-resolved fluorescence decay trace of 6d in DMSO solution required a two-exponential fitting model, as confirmed from the distribution
of weighted residuals and the magnitude of statistical parameters such as reduced chi-square (w2) values and Durbin–Watson (DW) parameter given in
inset. (b) Time-resolved fluorescence decay profiles of some representative synthesized pyrrolidinone derivatives in DMSO solution.
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Fig. 3 Photoluminescence spectral (a) and time-resolved decay (b) profiles of some of the synthesized pyrrolidinone derivatives in the solid state.
decay channels in the solid state (which are relevant in solution),
resulting quite strong PL intensity. Considering the inherent
complexity of measuring the fluorescence yield of the solid samples,
a qualitative measure of the PL intensity of the studied derivatives
was determined relative to 6a in DMSO (which shows highest
solution phase fluorescence yield of ff = 0.39 ꢁ 10ꢂ2), as reported
in the last column of Table 6. The results indicate systems 4f, 5h, 9b
and 9d show high PL intensity. Interestingly, all these compounds
are characterized by Cl substitution at either the 3- or 4-position of
the aldehyde fragment (R3) in the synthesis of pyrrolidinone
derivatives. Overall, the systematic pattern of the spectral response
and PL brightness with the electronic properties of peripheral
substitution in combination with the facile synthetic route discussed
Fig. 4 Images of fluorescence-active compounds in the solid state.
fluorescence decay traces of all the studied systems in the solid in this study opens a plethora of opportunities to design suitable
state still needed two-exponential fitting (Fig. 3b). However, the pyrrolidinone systems with significant biophysical responses and
component contribution of the fast decay component (found in new luminescent devices in the desired optical window.
the solution phase) decreases substantially with a concomitant
increase in the contribution from the time constant of the long
component. Thus, there is a substantial increase in the average
Experimental section
excited state lifetime (tav) in the range of 1.5–4.9 ns in comparison All chemicals were purchased from Alfa Aesar, Sigma-Aldrich and
with the solution phase (0.3–1.2 ns). This increase in fluorescence Merck and were used as received without further purification.
lifetime is possibly due to the arrest of several active non-radiative The purity of the synthesized compounds was confirmed by
Table 6 Photoluminescence data in the solid state of some of the synthesized pyrrolidinone derivatives
Steady statea
System
Time-resolved fluorescence decay
maxlabs/nm
maxlem/nm
Stokes shift/cmꢂ1
a1 (%)
t1/ns
a2 (%)
t2/ns
tav/ns
PL activityb
4f
375
375
357
357
380
365
368
390
352
353
362
375
409
364
397
462
453
439
439
466
444
449
461
460
474
465
467
489
468
478
5022
4592
5232
5232
4857
4875
4902
3949
6670
7232
6119
5253
4000
6105
4268
24.27
27.08
48.05
67.00
90.33
22.99
94.49
19.41
53.03
17.79
41.05
56.34
15.42
69.57
20.16
2.80
0.36
0.24
1.81
4.04
0.33
0.31
1.54
0.76
1.08
0.53
0.42
1.49
0.61
0.44
75.72
72.92
51.95
33.01
9.67
77.01
5.51
80.59
46.95
82.21
58.59
43.66
84.58
30.43
79.84
5.19
2.36
1.63
3.42
7.69
2.12
1.47
3.31
2.53
3.73
2.35
2.45
3.37
2.38
3.89
4.83
2.25
1.46
2.59
4.66
2.04
0.56
3.14
2.09
3.57
2.10
2.08
3.23
1.73
3.80
40
27
11
20
50
17
8
2
2
1
14
1
4g
5a
5f
5h
5k
6a
6d
7c
8a
8b
9a
9b
9c
9d
52
2
38
a
b
Absorption maxima for solid state was obtained from excitation spectra. Relative to the calculated fluorescence intensity of 6a in DMSO.
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FT-IR, 1H-NMR, 13C-NMR, mass spectrometry and Elementary (KBr): n 3309, 3072, 2980, 1716, 1497, 1096 cmꢂ1
NJC
.
1H NMR
analysis. An Aldrich blue LED micro photoreactor was purchased (DMSO-d6, 400 MHz): d 11.72 (s, 1H), 7.56 (d, 2H, J = 7.6 Hz),
from Sigma-Aldrich. All reactions were monitored by thin-layer 7.29–7.19 (m, 6H), 7.17–7.13 (m, 1H), 7.07 (t, 1H, J = 7.6 Hz),
chromatography (TLC) using precoated aluminum sheets (silica 6.06 (s, 1H), 4.02 (q, 2H, J = 7.0 Hz), 1.07 (t, 3H, J = 7.0 Hz) ppm;
gel 60 F 254 0.2 mm thickness) and developed in an iodine 13C NMR (DMSO-d6, 100 MHz): d 164.0, 161.9, 152.6, 136.5,
chamber. Melting points were recorded in capillary tubes using a 136.3, 128.7, 128.2, 127.9, 127.7, 125.3, 122.5, 112.2, 60.6. 59.7,
Thermo Scientific 9300 apparatus. FT-IR spectra were recorded 14.0 ppm. HRMS (ESI) m/z: [M + 1]+ calcd, 324.1236; found,
using KBr pellets on a Bruker Avance 400 (Model: ALPHA II) FT-IR 324.1237. Anal. calcd for C19H17NO4: C, 70.58; H, 5.30; N,
1
instrument and the frequencies are expressed in cmꢂ1. H-NMR 4.33%; found: C, 70.12; H, 5.21; N, 4.13%.
and 13C-NMR spectra were recorded on a Bruker Avance II-400
Ethyl 2-(4-chlorophenyl)-4-hydroxy-5-oxo-1-phenyl-2,5-dihydro-
spectrometer in DMSO-d6 (chemical shifts in d). Mass spectral data 1H-pyrrole-3-carboxylate (4b). White solid (yield: 93%); mp: 172–
of the representative compounds was recorded with a Waters 174 1C. IR (KBr): n 3307, 3068, 2982, 1718, 1495, 1092 cmꢂ1
.
ZQ-4000 (ESI) mass spectrometer. For the UV-visible absorption 1H NMR (DMSO-d6, 400 MHz): d 9.21 (s, 1H), 7.55 (d, 2H, J =
and fluorescence study, we selected spectroscopic-grade DMSO 7.6 Hz), 7.30–7.25 (m, 6H), 7.09 (t, 1H, J = 7.2 Hz), 6.10 (s, 1H),
(concentration ca. 50 mM), and the measurements were performed 4.02 (q, 2H, J = 7.2 Hz), 1.08 (t, 3H, J = 7.0 Hz) ppm; 13C NMR
using a PerkinElmer model Lambda25 and Quanta Master (QM-40) (DMSO-d6, 100 MHz): d 164.0, 162.3, 153.2, 136.5, 136.1, 132.8,
steady-state fluorescence apparatus supplied by Photon Technology 130.1, 129.1, 128.6, 125.8, 122.9, 112.1, 60.3, 60.2, 14.4 ppm.
International (PTI), respectively. Spectra were calibrated by ESI-MS: m/z 358 [M + 1]+.
subtracting the solvent as the blank control measured under
Ethyl 2-(4-bromophenyl)-2,5-dihydro-4-hydroxy-5-oxo-1-phenyl-
the same conditions. Photoluminescence spectra in the solid- 1H-pyrrole-3-carboxylate (4c). White crystalline solid (yield: 91%);
state were measured using a special solid-state sample holder mp: 188–190 1C. IR (KBr): n 3310, 3064, 2980, 1720, 1491,
1
(Part no. 557820058) supplied by PTI in the same instrument. 1089 cmꢂ1. H NMR (DMSO-d6, 400 MHz): d 11.83 (s, 1H), 7.56
Fluorescence lifetime measurements of the samples were per- (d, 2H, J = 7.6 Hz), 7.41 (d, 2H, J = 8.8 Hz), 7.29 (t, 2H, J = 7.8 Hz),
formed in a LED-based time-correlated single photon counting 7.23 (d, 2H, J = 8.0 Hz), 7.10 (t, 1H, J = 7.2 Hz), 6.09 (s, 1H), 4.04
(TCSPC) system (PM-3) supplied by PTI. The fluorescence decay (q, 2H, J = 7.2 Hz), 1.10 (t, 3H, J = 7.0 Hz) ppm; 13C NMR (DMSO-d6,
spectra of the samples were collected at magic angles to avoid 100 MHz): d 163.9, 161.9, 152.9, 136.2, 136.1, 131.2, 130.0, 128.7,
any anisotropic contribution. Details of the procedures for the 125.5, 122.5, 121.0, 111.7, 59.9, 59.8, 14.0 ppm. ESI-MS: m/z 401
calculation of relative fluorescence yield and analysis of time- [M]+, 403 [M + 2]+.
dependent fluorescence decay data are given in the ESI.†
Ethyl 2,5-dihydro-4-hydroxy-2-(4-hydroxyphenyl)-5-oxo-1-phenyl-
1H-pyrrole-3carboxylate (4d). White solid (yield: 84%); mp: 241–
243 1C. IR (KBr): n 3313, 3029, 2993, 1686, 1453, 1023 cmꢂ1
.
General procedure for the synthesis pyrrolidinone derivatives
To a 5 mL test tube equipped with a magnetic bar, a mixture of 1H NMR (DMSO-d6, 400 MHz): d 9.34 (s, 1H), 7.53 (d, 2H, J =
aniline (1 mmol, 0.9 mL), dialkylacetylenedicarboxylate (1.2 mmol, 8.0 Hz), 7.27 (t, 2H, J = 7.8 Hz), 7.07 (t, 3H, J = 7.2 Hz), 7.01 (d,
1.5 mL), benzaldehyde (1 mmol, 1 mL) and Rose Bengal (15 mol%) 2H, J = 8.4 Hz), 6.56 (d, 2H, J = 8.8 Hz), 5.91 (s, 1H), 4.01 (q, 2H,
in 3 mL of acetonitrile–water (1 : 1) solvent was taken and J = 7.2 Hz), 1.08 (t, 3H, J = 7.2 Hz) ppm; 13C NMR (DMSO-d6,
stirred at room temperature under the irradiation of blue LEDs 100 MHz): d 164.2, 162.2, 156.9, 153.0, 136.5, 128.8, 128.6,
for 30–45 minutes. Upon completion of the reaction (monitored 126.5, 125.2, 122.6, 115.0, 111.8, 60.3, 59.5, 14.1 ppm. ESI-MS:
by TLC), the mixture was filtered and washed many times with m/z 339 [M]+.
de-ionized water and the solid product obtained was purified by
recrystallization from hot ethanol.
Ethyl 2,5-dihydro-4-hydroxy-2-(4-nitrophenyl)-5-oxo-1-phenyl-
1H-pyrrole-3-carboxylate (4e). White solid (yield: 89%); mp: 181–
183 1C. IR (KBr): n 3449, 3219, 2980, 1679, 1497, 1020 cmꢂ1
.
1H NMR (DMSO-d6, 400 MHz): d 12.05 (s, 1H), 8.07 (d, 2H, J =
8.8 Hz), 7.59 (t, 4H, J = 7.0 Hz), 7.29 (t, 2H, J = 7.8 Hz), 7.09 (t, 1H,
General procedure for the synthesis pyrrolidinone derivatives
under irradiation from white LEDs (23 W)
In a 25 mL round-bottom flask, a mixture of aniline (1 mmol, J = 7.4 Hz), 6.28 (s, 1H), 4.02 (q, 2H, J = 6.8 Hz), 1.09 (t, 3H, J =
0.9 mL), dialkylacetylenedicarboxylate (1.2 mmol, 1.5 mL) and 7.2 Hz) ppm; 13C NMR (DMSO-d6, 100 MHz): d 164.0, 161.9,
benzaldehyde (1 mmol, 1 mL) was added to Rose Bengal 153.4, 147.2, 144.7, 136.0, 129.3, 128.9, 125.7, 123.4, 122.5,
(15 mol%) in 5 mL of acetonitrile–water (3 : 1) solvent and 111.3, 59.9, 59.7, 14.0 ppm. ESI-MS: m/z 368 [M]+.
stirred at room temperature for 40–50 minutes under the
irradiation of white LEDs (23 W). On completion of the reaction 1H-pyrrole-3-carboxylate (4f). White solid (yield: 90%); mp: 184–
(monitored by TLC), the mixture was filtered and washed many 187 1C. IR (KBr): n 3419, 3319, 2984, 1723, 1498, 1078 cmꢂ1
times with deionized water and the solid product obtained was 1H NMR (DMSO-d6, 400 MHz): d 11.87 (s, 1H), 7.58 (d, 2H, J =
Ethyl 2-(3-chlorophenyl)-2,5-dihydro-4-hydroxy-5-oxo-1-phenyl-
.
then purified by recrystallization from hot ethanol.
7.6 Hz), 7.41 (s, 1H), 7.30 (t, 2H, J = 7.8 Hz), 7.26–7.19 (m, 3H),
7.10 (t, 1H, J = 7.4 Hz), 6.12 (s, 1H), 4.10–3.97 (m, 2H), 1.10 (t, 3H,
J = 7.0 Hz) ppm; 13C NMR (DMSO-d6, 100 MHz): d 163.9, 161.9,
Analytical and spectroscopic data of the synthesized compounds
Ethyl 2,5-dihydro-4-hydroxy-5-oxo-1,2-diphenyl-1H-pyrrole-3- 153.0, 139.3, 136.0, 132.6, 130.1, 128.8, 128.2, 128.0, 126.1, 125.5,
carboxylate (4a). White solid (yield: 94%); mp: 178–180 1C. IR 122.4, 111.5, 59.8, 59.7, 14.0 ppm. ESI-MS: m/z 358 [M + 1]+.
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Ethyl 2,5-dihydro-4-hydroxy-5-oxo-1-phenyl-2-p-tolyl-1H-pyrrole- for C18H14N2O6: C, 61.02; H, 3.98; N, 7.91%; found: C, 60.88; H,
3-carboxylate (4g). White solid (yield: 86%); mp: 180–182 1C. IR 4.15; N, 7.60%.
(KBr): n 3448, 3301, 2984, 1716, 1477, 1031 cmꢂ1
.
1H NMR
Methyl 2-(4-bromophenyl)-2,5-dihydro-4-hydroxy-5-oxo-1-phenyl-
(DMSO-d6, 400 MHz): d 11.60 (s, 1H), 7.56 (d, 2H, J = 7.6 Hz), 1H-pyrrole-3-carboxylate (5d). White solid (yield: 89%); mp:
7.27 (t, 2H, J = 7.8 Hz), 7.12 (d, 2H, J = 7.6 Hz), 7.07 (t, 1H, J = 183–185 1C. IR (KBr): 3449, 3221, 2958, 1683, 1497,
7.4 Hz), 7.01 (d, 2H, J = 8.0 Hz), 6.01 (s, 1H), 4.02 (q, 2H, J = 1076 cmꢂ1 1H NMR (DMSO-d6, 400 MHz): d 11.87 (s, 1H),
n
.
7.2 Hz), 2.17 (s, 3H), 1.09 (t, 3H, J = 7.2 Hz) ppm; 13C NMR 7.55 (d, 2H, J = 8.4 Hz), 7.40 (d, 2H, J = 8.4 Hz), 7.29 (t, 2H, J =
(DMSO-d6, 100 MHz): d 163.9, 162.0, 152.4, 137.1, 136.3, 133.4, 7.4 Hz), 7.23 (d, 2H, J = 7.6 Hz), 7.10 (t, 1H, J = 7.4 Hz), 6.09
128.8, 128.6, 127.6, 125.3, 122.5, 112.2, 60.3, 59.7, 20.6, (s, 1H), 3.59 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz):
14.0 ppm. ESI-MS: m/z 337 [M]+.
d 163.9, 162.5, 152.8, 136.2, 136.0, 131.2, 130.0, 128.8, 125.5,
Ethyl 2,5-dihydro-4-hydroxy-2-(3-nitrophenyl)-5-oxo-1-phenyl- 122.5, 121.1, 111.5, 59.9, 51.2 ppm. ESI-MS: m/z 387 [M]+.
1H-pyrrole-3-carboxylate (4h). White solid (yield: 90%); mp: Methyl 2,5-dihydro-4-hydroxy-2-(3-hydroxyphenyl)-5-oxo-1-
225–227 1C. IR (KBr): 3323, 3088, 2985, 1723, 1499, phenyl-1H-pyrrole-3-carboxylate (5e). White solid (yield: 85%);
1023 cmꢂ1. H NMR (DMSO-d6, 400 MHz): d 12.00 (s, 1H), 8.25 mp: 224–225 1C. IR (KBr): n 3314, 2954, 1695, 1495, 1129 cmꢂ1
n
1
.
(s, 1H), 8.04 (d, 1H, J = 8.0 Hz), 7.71 (d, 1H, J = 7.6 Hz), 7.61 (d, 2H, 1H NMR (DMSO-d6, 400 MHz): d 9.31 (s, 1H), 7.54 (d, 2H, J =
J = 7.6 Hz), 7.51 (t, 1H, J = 8.0 Hz), 7.29 (t, 2H, J = 7.8 Hz), 7.09 7.6 Hz), 7.27 (t, 2H, J = 7.8 Hz), 7.07 (t, 1H, J = 7.6 Hz), 6.98
(t, 1H, J = 7.2 Hz), 6.33 (s, 1H), 4.02 (q, 2H, J = 7.2 Hz), 1.08 (t, 3H, (t, 1H, J = 7.8 Hz), 6.66 (d, 1H, J = 7.6 Hz), 6.57 (s, 1H),
J = 7.2 Hz) ppm; 13C NMR (DMSO-d6, 100 MHz): d 163.9, 161.8, 6.51(d, 1H, J = 8.0 Hz), 5.95 (s, 1H), 3.57 (s, 3H) ppm; 13C
153.4, 147.5, 139.4, 135.9, 134.0, 130.0, 128.9, 125.6, 123.2, 123.1, NMR (DMSO-d6, 100 MHz): d 164.0, 162.5, 157.1, 152.4, 137.9,
122.5, 111.2, 59.9, 59.6, 13.9 ppm. ESI-MS: m/z 369 [M + 1]+.
Ethyl 2,5-dihydro-4-hydroxy-2-(3-hydroxyphenyl)-5-oxo-1-phenyl- 51.1 ppm. ESI-MS: m/z 325 [M]+.
136.3, 129.2, 128.7, 125.3, 122.4, 118.5, 115.0, 114.0, 112.0, 60.5,
1H-pyrrole-3-carboxylate (4i). White sold (yield: 86%); mp: 198–
Methyl 2,5-dihydro-4-hydroxy-2-(3-methoxyphenyl)-5-oxo-1-
199 1C. IR (KBr): n 3283, 2984, 1707, 1499, 1077 cmꢂ1. 1H NMR phenyl-1H-pyrrole-3-carboxylate (5f). White solid (yield: 84%);
(DMSO-d6, 400 MHz): d 11.69 (s, 1H), 9.32 (s, 1H), 7.56 (d, 2H, mp: 168–170 1C. IR (KBr): n 3451, 2954, 1715, 1495, 1034 cmꢂ1
.
J = 7.6 Hz), 7.29 (t, 2H, J = 7.8 Hz), 7.09 (t, 1H, J = 8.0 Hz), 7.00 1H NMR (DMSO-d6, 400 MHz): d 9.31 (s, 1H), 7.54 (d, 2H, J =
(t, 1H, J = 7.6 Hz), 6.68 (d, 1H, J = 7.6 Hz), 6.59 (s, 1H), 6.53 (d, 7.6 Hz), 7.27 (t, 2H, J = 7.8 Hz), 7.07 (t, 1H, J = 7.6 Hz), 6.98 (t,
1H, J = 8.0 Hz), 5.97 (s, 1H), 4.04 (q, 2H, J = 7.0 Hz), 1.10 (t, 1H, J = 7.8 Hz), 6.66 (d, 1H, J = 7.6 Hz), 6.57 (s, 1H), 6.51(d, 1H,
3H, J = 7.2 Hz) ppm; 13C NMR (DMSO-d6, 100 MHz): d 164.0, J = 8.0 Hz), 5.95 (s, 1H), 3.57 (s, 3H) ppm; 13C NMR (DMSO-d6,
162.0, 157.1, 152.4, 137.9, 136.4, 129.2, 128.7, 125.3, 122.4, 100 MHz): d 164.0, 162.5, 157.1, 152.4, 137.9, 136.3, 129.2,
118.6, 115.0, 114.1, 112.3, 60.5, 59.7, 14.0 ppm. ESI-MS: m/z 128.7, 125.3, 122.4, 118.5, 115.0, 114.0, 112.0, 60.5, 51.1 ppm.
340 [M + 1]+.
ESI-MS: m/z 340 [M + 1]+.
Methyl 2,5-dihydro-4-hydroxy-5-oxo-1,2-diphenyl-1H-pyrrole-
Methyl 2,5-dihydro-4-hydroxy-2-(4-hydroxyphenyl)-5-oxo-1-
3-carboxylate (5a). White solid (yield: 92%); mp: 185–187 1C. IR phenyl-1H-pyrrole-3-carboxylate (5g). White solid (yield: 87%);
(KBr): n 3450, 3264, 2958, 1702, 1498, 1079 cmꢂ1 1H NMR mp: 214–216 1C. IR (KBr); n 3447, 3327, 2954, 1691, 1456, 1123,
.
(DMSO-d6, 400 MHz): d 11.67 (s, 1H), 7.56 (d, 2H, J = 7.6 Hz), 1005 cmꢂ1. 1H NMR (DMSO-d6, 400 MHz): d 11.65 (s, 1H), 9.35
7.29–7.19 (m, 6H), 7.14 (t, 1H, J = 6.8 Hz), 7.07 (t, 1H, J = 7.4 Hz), (s, 1H), 7.54 (d, 2H, J = 8.0 Hz), 7.28 (t, 2H, J = 7.8 Hz), 7.09
6.07 (s, 1H), 3.58 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d (t, 1H, J = 7.2 Hz), 7.02 (d, 2H, J = 8.0 Hz), 6.57 (d, 2H, J = 8.8 Hz),
163.8, 162.4, 152.8, 136.0, 135.7, 132.4, 129.6, 128.7, 128.3, 5.94 (s, 1H), 3.58 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d
125.5, 122.5, 111.5, 59.7, 51.1 ppm. ESI-MS: m/z 310 [M + 1]+.
Methyl 2-(4-chlorophenyl)-2,5-dihydro-4-hydroxy-5-oxo-1-phenyl- 122.6, 115.1, 112.1, 60.2, 51.1 ppm. ESI-MS: m/z 325 [M]+.
1H-pyrrole-3-carboxylate (5b). White solid (yield: 94%); mp: Methyl 2-(3-chlorophenyl)-2,5-dihydro-4-hydroxy-5-oxo-1-phenyl-
150–152 1C. IR (KBr): 3450, 3219, 2957, 1684, 1498, 1H-pyrrole-3-carboxylate (5h). White solid (yield: 92%); mp: 138–
1095 cmꢂ1 1H NMR (DMSO-d6, 400 MHz): d 11.89 (s, 1H), 139 1C. IR (KBr): n 3447, 2953, 1723, 1498, 1078 cmꢂ1. H NMR
163.9, 162.5, 156.9, 152.2, 136.3, 128.8, 128.6, 126.2, 125.3,
n
1
.
7.56 (d, 2H, J = 7.6 Hz), 7.31–7.25 (m, 6H), 7.09 (t, 1H, J = 7.4 (DMSO-d6, 400 MHz): d 12.10 (s, 1H), 7.57 (d, 2H, J = 8.0 Hz), 7.38 (s,
Hz), 6.11 (s, 1H), 3.59 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 1H), 7.30 (t, 2H, J = 7.8 Hz), 7.26–7.22 (m, 3H), 7.10 (t, 1H, J = 7.4 Hz),
MHz): d 163.8, 162.4, 152.8, 136.0, 135.7, 132.4, 129.6, 128.7, 6.12 (s, 1H), 3.60 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d
128.3, 125.5, 122.5, 111.5, 59.7, 51.1 ppm. ESI-MS: m/z 343 [M]+. 164.1, 162.6, 153.1, 139.4, 136.2, 132.9, 130.4, 129.0, 128.2, 128.1,
Methyl 2,5-dihydro-4-hydroxy-2-(4-nitrophenyl)-5-oxo-1-phenyl- 126.4, 125.7, 122.7, 111.5, 60.0, 51.4 ppm. ESI-MS: m/z 343 [M]+.
1H-pyrrole-3-carboxylate (5c). White solid (yield: 90%); mp:
135–137 1C. IR (KBr): n 3476, 2953, 1706, 1499, 1039 cmꢂ1
Methyl 2,5-dihydro-4-hydroxy-5-oxo-1-phenyl-2-p-tolyl-1H-pyrrole-
.
3-carboxylate (5i). White solid (yield: 88%); mp: 164–166 1C. IR (KBr):
1H NMR (DMSO-d6, 400 MHz): d 12.10 (s, 1H), 8.07 (d, 2H, J = n 3449, 3224, 2958, 1684, 1499, 1028 cmꢂ1. H NMR (DMSO-d6,
8.8 Hz), 7.59 (t, 4H, J = 7.0 Hz), 7.29 (t, 2H, J = 8.0 Hz), 7.10 400 MHz): d 11.62 (s, 1H), 7.55 (d, 2H, J = 8.0 Hz), 7.27 (t, 2H, J =
(t, 1H, J = 7.4 Hz), 6.30 (s, 1H), 3.59 (s, 3H) ppm; 13C NMR 7.8 Hz), 7.12 (d, 2H, J = 8.4 Hz), 7.07 (t, 1H, J = 7.4 Hz), 7.00 (d, 2H, J =
(DMSO-d6, 100 MHz): d 163.9, 162.4, 153.2, 147.1, 144.6, 135.9, 8.0 Hz), 6.02 (s, 1H), 3.57 (s, 3H), 2.16 (s, 3H) ppm; 13C NMR (DMSO-d6,
129.2, 128.8, 125.7, 123.4, 122.4, 111.0, 59.6, 51.2 ppm. HRMS 100 MHz): d 163.9, 162.5, 152.4, 137.1, 136.2, 133.4, 128.9, 128.7, 127.5,
(ESI) m/z: [M + 1]+ calcd, 355.0922; found, 355.0926. Anal. calcd 125.3, 122.5, 112.0, 60.3, 51.1, 20.6 ppm. ESI-MS: m/z 324 [M + 1]+.
1
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Methyl 2,5-dihydro-4-hydroxy-2-(3-nitrophenyl)-5-oxo-1-phenyl- 6.00 (s, 1H), 4.01 (q, 2H, J = 7.2 Hz), 2.18 (s, 3H), 1.06 (t, 3H, J =
1H-pyrrole-3-carboxylate (5j). White solid (yield: 89%); mp: 202– 7.0 Hz) ppm; 13C NMR (DMSO-d6, 100 MHz): d 163.8, 162.0,
204 1C. IR (KBr): n 3420, 3318, 2957, 1722, 1499, 1034 cmꢂ1
.
152.8, 138.6, 134.7, 133.8, 129.2, 128.2, 127.9, 127.7, 122.6,
1H NMR (DMSO-d6, 400 MHz): d 12.07 (s, 1H), 8.22 (s, 1H), 8.02 112.1, 60.7, 59.7, 20.4, 14.0 ppm. ESI-MS: m/z 337 [M]+.
(d, 1H, J = 7.6 Hz), 7.72 (d, 1H, J = 7.6 Hz), 7.59 (d, 2H, J = 8.0 Hz), Methyl 2,5-dihydro-4-hydroxy-1-(4-nitrophenyl)-5-oxo-2-phenyl-
7.51 (t, 1H, J = 8.0 Hz), 7.29 (t, 2H, J = 8.0 Hz), 7.09 (t, 1H, J = 1H-pyrrole-3-carboxylate (7a). White solid (yield: 88%); mp: 177–
7.2 Hz), 6.32 (s, 1H), 3.58 (s, 3H) ppm; 13C NMR (DMSO-d6, 178 1C. IR (KBr): n 3444, 3210, 2965, 1677, 1491, 1095 cmꢂ1
.
100 MHz): d 163.8, 162.3, 153.1, 147.4, 139.2, 135.7, 133.9, 1H NMR (DMSO-d6, 400 MHz): d 11.90 (s, 1H), 8.15 (d, 2H, J =
129.9, 128.8, 125.5, 123.0, 122.9, 122.4, 110.9, 59.4, 51.1 ppm. 9.2 Hz), 7.90 (d, 2H, J = 9.2 Hz), 7.32 (d, 2H, J = 7.2 Hz), 7.23 (t,
ESI-MS: m/z 354 [M]+.
2H, J = 7.4 Hz), 7.17 (t, 1H, J = 7.2 Hz), 6.19 (s, 1H), 3.59 (s, 3H) ppm;
Methyl 2,5-dihydro-4-hydroxy-2-(4-methoxyphenyl)-5-oxo-1- 13C NMR (DMSO-d6, 100 MHz): d 164.7, 162.3, 151.8, 143.5, 142.0,
phenyl-1H-pyrrole-3-carboxylate (5k). White solid (yield: 86%); 135.9, 128.5, 128.3, 127.7, 124.4, 121.7, 112.9, 60.3, 51.3 ppm. ESI-
mp: 239–240 1C. IR (KBr): n 3448, 3225, 2954, 1684, 1460, MS: m/z 354 [M]+.
1033 cmꢂ1
.
1H NMR (DMSO-d6, 400 MHz): d 11.68 (s, 1H),
Methyl 2,5-dihydro-4-hydroxy-5-oxo-2-phenyl-1-p-tolyl-1H-pyrrole-
7.55 (d, 2H, J = 8.0 Hz), 7.28 (t, 2H, J = 7.8 Hz), 7.16 (d, 2H, J = 3-carboxylate (7b). White solid (yield: 88%); mp: 284–286 1C. IR
8.8 Hz), 7.08 (t, 1H, J = 7.4 Hz), 6.75 (d, 2H, J = 8.8 Hz), 6.01 (s, 1H), (KBr): n 3442, 3230, 2950, 1679, 1465, 1078 1095 cmꢂ1. 1H NMR
3.64 (s, 3H), 3.58 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d (DMSO-d6, 400 MHz): d 11.80 (s, 1H), 7.43 (d, 2H, J = 8.4 Hz),
163.8, 162.5, 158.7, 152.3, 136.2, 128.8, 128.6, 128.0, 125.3, 122.5, 7.24–7.14 (m, 5H), 7.07 (d, 2H, J = 8.4 Hz), 6.02 (s, 1H), 3.57 (s,
113.6, 112.0, 60.0, 54.9, 51.1 ppm. HRMS (ESI) m/z: [M + 1]+ calcd, 3H), 2.18 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d 163.8,
340.1185; found, 340.1183. Anal. calcd for C19H17NO5: C, 67.25; H, 162.5, 152.6, 136.5, 134.7, 133.7, 129.1, 128.2, 127.9, 127.6,
5.05; N, 4.13%; found: C, 66.97; H, 4.79; N, 4.00%.
122.5, 111.7, 60.6, 51.1, 20.4 ppm. HRMS (ESI) m/z: [M + 1]+
Ethyl 1-(4-bromophenyl)-2,5-dihydro-4-hydroxy-5-oxo-2-phenyl- calcd, 324.1236; found, 324.1237. Anal. calcd for C19H17NO4: C,
1H-pyrrole-3-carboxylate (6a). White solid (yield: 88%); mp: 134– 70.58; H, 5.30; N, 4.33%; found: C, 69.91; H, 5.35; N, 4.13%.
136 1C. IR (KBr): n 3455, 3280, 2983, 1719, 1491, 1023 cmꢂ1
.
Methyl 1-(4-chlorophenyl)-2,5-dihydro-4-hydroxy-5-oxo-2-phenyl-
1H NMR (DMSO-d6, 400 MHz): d 11.80 (s, 1H), 7.55 (d, 2H, J = 1H-pyrrole-3-carboxylate (7c). White solid (yield: 91%); mp: 144–
8.8 Hz), 7.47 (d, 2H, J = 8.8 Hz), 7.26–7.17 (m, 5H), 6.07 (s, 1H), 4.01 146 1C. IR (KBr): n 3455, 2957, 1722, 1496, 1094 cmꢂ1. H NMR
1
(q, 2H, J = 7.0 Hz), 1.07 (t, 2H, J = 7.2 Hz) ppm; 13C NMR (DMSO-d6, (DMSO-d6, 400 MHz): d 11.85 (s, 1H), 7.60 (d, 2H, J = 8.4 Hz), 7.34 (d,
100 MHz): d 164.0, 161.8, 152.4, 136.2, 135.6, 131.5, 128.3, 128.0, 2H, J = 8.4 Hz), 7.26–7.16 (m, 5H), 6.08 (s, 1H), 3.57 (s, 3H) ppm; 13
C
127.7, 124.2, 117.6, 112.3, 60.4, 59.7, 13.9 ppm. ESI-MS: m/z 402 NMR (DMSO-d6, 100 MHz): d 164.0, 162.4, 152.3, 136.2, 135.1, 129.4,
[M]+, 404 [M + 2]+.
128.6, 128.3, 128.0, 127.6, 124.0, 112.1, 60.5, 51.1 ppm. HRMS
Ethyl 1-(4-chlorophenyl)-2,5-dihydro-4-hydroxy-5-oxo-2-phenyl- (ESI) m/z: [M + 1]+ calcd, 344.0691; found, 344.0692. Anal. calcd
1H-pyrrole-3-carboxylate (6b). White solid (yield: 90%); mp: 150– for C18H14ClNO4: C, 62.89; H, 4.10; N, 4.07%; found: C, 62.56; H,
152 1C. IR (KBr): n 3449, 3209, 2975, 1681, 1497, 1092 cmꢂ1
.
3.80; N, 3.93%.
1H NMR (DMSO-d6, 400 MHz): d 11.81 (s, 1H), 7.61 (d, 2H, J =
Ethyl 2-(4-chlorophenyl)-4-hydroxy-1-(4-methoxyphenyl)-5-oxo-
8.8 Hz), 7.34 (d, 2H, J = 8.8 Hz), 7.26–7.16 (m, 5H), 6.07 (s, 1H), 2,5-dihydro-1H-pyrrole-3-carboxylate (8a). White solid (yield:
4.01 (q, 2H, J = 7.2 Hz), 1.07 (t, 3H, J = 7.2 Hz) ppm; 13C NMR 88%); mp: 187–189 1C. IR (KBr): n 3425, 3235, 2940, 1650, 1468,
1
(DMSO-d6, 100 MHz): d 164.0, 161.9, 152.4, 136.3, 135.2, 129.4, 997 cmꢂ1. H NMR (DMSO-d6, 400 MHz): d 11.88 (s, 1H), 7.42 (d,
128.6, 128.3, 128.0, 127.7, 124.0, 112.3, 60.5, 59.7, 14.0 ppm. 2H, J = 9.2 Hz), 7.29–7.24 (m, 4H), 6.84 (d, 2H, J = 8.8 Hz), 6.02 (s,
ESI-MS: m/z 358 [M + 1]+.
1H), 4.02 (q, 2H, J = 6.8 Hz), 3.67 (s, 3H) ppm; 13C NMR (DMSO-d6,
Ethyl 4-hydroxy-1-(4-nitrophenyl)-5-oxo-2-phenyl-2,5-dihydro- 100 MHz): d 163.7, 162.0, 156.8, 153.2, 135.9, 132.3, 129.7, 128.9,
1H-pyrrole-3-carboxylate (6c). White solid (yield: 89%); mp: 128– 128.2, 124.5, 113.9, 60.3, 59.7, 55.1, 14.0 ppm. ESI-MS: m/z 387 [M]+.
130 1C. IR (KBr): n 3447, 3306, 2988, 1733, 1451, 1022 cmꢂ1
.
Ethyl 2-(3-chlorophenyl)-4-hydroxy-1-(4-methoxyphenyl)-5-
1H NMR (DMSO-d6, 400 MHz): d 9.80 (s, 1H), 8.16 (d, 2H, J = oxo-2,5-dihydro-1H-pyrrole-3-carboxylate (8b). White solid (yield:
9.2 Hz), 7.91 (d, 2H, J = 9.2 Hz), 7.32 (d, 2H, J = 7.6 Hz), 7.24 (t, 87%); mp: 125–127 1C. IR (KBr): n 3438, 3179, 2987, 1681, 1463,
2H, J = 7.2 Hz), 7.18 (t, 1H, J = 7.2 Hz), 6.19 (s, 1H), 4.03 (q, 2H, 1031 cmꢂ1. H NMR (DMSO-d6, 400 MHz): d 11.88 (s, 1H), 7.45
1
J = 7.2 Hz), 1.08 (t, 3H, J = 7.0 Hz) ppm; 13C NMR (DMSO-d6, (d, 2H, J = 9.2 Hz), 7.36 (s, 1H), 7.24–7.23 (m, 2H), 7.17–7.15
100 MHz): d 164.8, 161.8, 151.9, 143.5, 142.1, 136.0, 128.5, 128.3, (m, 1H), 6.85 (d, 2H, J = 8.8 Hz), 6.03 (s, 1H), 4.06–3.98 (m, 2H), 3.67
127.8, 124.4, 121.6, 113.2, 60.4, 60.0, 14.0 ppm. HRMS (ESI) m/z: (s, 3H), 1.08 (t, 3H, J = 7.2 Hz) ppm; 13C NMR (DMSO-d6, 100 MHz):
[M + 1]+ calcd, 369.1087; found, 369.1084. Anal. calcd for d 163.6, 161.9, 156.9, 153.3, 139.4, 132.6, 130.1, 128.9, 128.1, 127.9,
C19H16N2O6: C, 61.95; H, 4.38; N, 7.61%; Found: C, 61.60; H, 126.1, 124.4, 113.9, 60.3, 59.7, 55.1, 14.0 ppm. HRMS (ESI) m/z: [M +
4.17; N, 7.38%.
Ethyl 2,5-dihydro-4-hydroxy-5-oxo-2-phenyl-1-p-tolyl-1H-pyrrole- 61.94; H, 4.68; N, 3.61%; found: C, 61.92; H, 4.75; N, 3.15%.
3-carboxylate (6d). White solid (yield: 87%); mp: 185–187 1C. IR Methyl 4-hydroxy-5-oxo-1,2-di-p-tolyl-2,5-dihydro-1H-pyrrole-
(KBr): n 3306, 3106, 2981, 1689, 1495, 1091 cmꢂ1 1H NMR 3-carboxylate (9a). White solid (yield: 84%); mp: 131–132 1C. IR
(DMSO-d6, 400 MHz): d 11.58 (s, 1H), 7.42 (d, 2H, J = 8.4 Hz), (KBr): n 3437, 3229, 2932, 1667, 1461, 1087 cmꢂ1 1H NMR
7.22–7.20 (m, 4H), 7.16–7.13 (m, 1H), 7.07 (d, 2H, J = 8.0 Hz), (DMSO-d6, 400 MHz): d 11.57 (s, 1H), 7.41 (d, 2H, J = 8.4 Hz),
1]+ calcd, 388.0953; found, 388.0954. Anal. calcd for C20H18ClNO5: C,
.
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7.10–7.05 (m, 4H), 6.99 (d, 2H, J = 8.0 Hz), 5.97 (s, 1H), 3.56 8.06 (d, 2H, J = 8.4 Hz), 7.73 (d, 2H, J = 9.0 Hz), 7.23–7.17 (m,
(s, 3H), 2.18 (s, 3H), 2.16 (s, 3H) ppm; 13C NMR (DMSO-d6, 5H), 5.73 (s, 1H), 4.14 (q, 2H, J = 7.2 Hz), 1.21 (t, 3H, J = 7.0 Hz) ppm;
100 MHz): d 163.8, 162.5, 152.5, 137.1, 134.6, 133.7, 133.4, 13C NMR (CDCl3, 100 MHz): d 164.8, 163.2, 155.6, 144.0, 142.0,
129.1, 128.9, 127.5, 122.5, 111.8, 60.4, 51.1, 20.6, 20.4 ppm. 134.2, 129.0, 128.9, 127.2, 124.6, 120.5, 114.0, 61.6, 61.0, 13.8 ppm.
HRMS (ESI) m/z: [M + 1]+ calcd, 338.1392; found, 338.1389.
ESI-MS: m/z 358 [M]+.
Methyl 2-(3-chlorophenyl)-4-hydroxy-1-(4-methoxyphenyl)-5-
Ethyl 4-hydroxy-5-oxo-1-(2-oxo-2H-chromen-3-yl)-2-(p-tolyl)-
oxo-2,5-dihydro-1H-pyrrole-3-carboxylate (9b). White solid 2,5-dihydro-1H-pyrrole-3-carboxylate (10d). White solid (yield:
(yield: 89%); mp: 120–122 1C. IR (KBr): n 3414, 3183, 2954, 79%); mp: 197–199 1C. IR (KBr): n 3235, 2942, 1709, 1679, 1493,
1
1679, 1460, 1080 cmꢂ1. H NMR (DMSO-d6, 400 MHz): d 11.93 1239, 1091 cmꢂ1. 1H NMR (CDCl3, 400 MHz): d 9.13 (s, 1H), 7.51
(s, 1H), 7.44 (d, 2H, J = 9.2 Hz), 7.34 (s, 1H), 7.24–7.17 (m, 3H), (d, 2H, J = 7.6 Hz), 7.32–7.23 (m, 7H), 7.13 (t, 1H, J = 7.6 Hz),
6.85 (d, 2H, J = 8.8 Hz), 6.04 (s, 1H), 3.68 (s, 3H), 3.59 (s, 3H) ppm; 5.77 (s, 1H), 4.22 (q, 2H, J = 7.0 Hz), 2.21 (s, 3H), 1.22 (t, 3H,
13C NMR (DMSO-d6, 100 MHz): d 163.6, 162.5, 153.2, 139.4, 132.7, J = 7.0 Hz) ppm; 13C NMR (CDCl3, 100 MHz): d 165.0, 162.8,
130.2, 128.9, 128.0, 127.8, 126.2, 124.4, 113.9, 60.2, 55.1, 51.1 ppm. 158.4, 136.1, 134.9, 128.9, 128.5, 128.4, 127.4, 125.7, 122.2,
ESI-MS: m/z 373 [M]+.
113.1, 61.4, 61.2, 30.8, 13.8 ppm. ESI-MS: m/z 405 [M]+.
Methyl 4-hydroxy-5-oxo-1-(2-oxo-2H-chromen-3-yl)-2-phenyl-
Methyl 2-(4-chlorophenyl)-4-hydroxy-5-oxo-1-(p-tolyl)-2,5-dihydro-
1H-pyrrole-3-carboxylate (9c). White solid (yield: 91%); mp: 153– 2,5-dihydro-1H-pyrrole-3-carboxylate (10e). White solid (yield:
155 1C. IR (KBr): n 3444, 3226, 2922, 1674, 1469, 1093 cmꢂ1
77%); mp: 195–196 1C. IR (KBr): n 3227, 2949, 1718, 1675, 1498,
.
1H NMR (DMSO-d6, 400 MHz): d 11.90 (s, 1H), 7.42 (d, 2H, J = 1249, 1094 cmꢂ1. 1H NMR (CDCl3, 400 MHz): d 8.93 (s, 1H), 7.47
8.8 Hz), 7.27 (s, 4H), 7.08 (d, 2H, J = 8.4 Hz), 6.06 (s, 1H), 3.58 (d, 2H, J = 7.6 Hz), 7.29–7.21 (m, 7H), 7.10 (t, 1H, J = 7.6 Hz),
(s, 3H), 2.19 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d 163.1, 5.74 (s, 1H), 3.75 (s, 3Hz) ppm; 13C NMR (CDCl3, 100 MHz): d
161.8, 152.3, 135.1, 134.2, 132.9, 131.7, 129.0, 128.6, 127.7, 165.5, 163.1, 156.3, 136.3, 135.2, 129.2, 128.9, 128.8, 127.7,
121.9, 110.6, 59.2, 50.5, 19.8 ppm. HRMS (ESI) m/z: [M + 1]+ 126.2, 122.6, 113.1, 61.9, 52.3 ppm. ESI-MS: m/z 377 [M]+.
calcd, 358.0846; found, 358.0843. Anal. calcd for C19H16ClNO4:
Ethyl 2-(furan-2-yl)-4-hydroxy-5-oxo-1-phenyl-2,5-dihydro-1H-
C, 63.78; H, 4.51; N, 3.91%; found: C, 63.15; H, 4.91; N, 3.71%. pyrrole-3-carboxylate (11a). White solid (yield: 94%); mp: 155–
Methyl 2-(4-chlorophenyl)-2,5-dihydro-4-hydroxy 1-(4-methoxy- 156 1C. IR (KBr): n 3347, 2950, 1719, 1671, 1488, 1239, 1091
phenyl) 5-oxo-1H-pyrrole-3-carboxylate (9d). White solid (yield: cmꢂ1. 1H NMR (CDCl3, 400 MHz): d 9.09 (s, 1H), 7.47 (d, 2H, J =
87%); mp: 116–118 1C. IR (KBr): n 3448, 2955, 1679, 1461, 7.6 Hz), 7.32–7.25 (m, 3H), 7.22–7.19 (m, 2H), 7.15 (t, 1H, J =
1091 cmꢂ1. 1H NMR (DMSO-d6, 400 MHz): d 11.89 (s, 1H), 7.42 (d, 2H, 7.4 Hz), 7.11–7.09 (m, 1H), 5.71 (s, 1H), 4.21 (q, 2H, J = 7.0 Hz),
J = 8.8 Hz), 7.28–7.24 (m, 4H), 6.84 (d, 2H, J = 8.8 Hz), 6.02 (s, 1H), 3.67 1.22 (t, 3H, J = 7.0 Hz) ppm; 13C NMR (CDCl3, 100 MHz): d 165.2,
(s, 3H), 3.58 (s, 3H) ppm; 13C NMR (DMSO-d6, 100 MHz): d 163.6, 162.4, 162.9, 156.9, 137.6, 136.2, 134.6, 130.2, 129.4, 129.0, 128.1, 126.3,
156.8, 153.1, 135.8, 132.4, 129.6, 128.9, 128.3, 124.5, 113.9, 111.1, 60.2, 125.7, 122.4, 112.9, 61.7, 61.1, 14.2 ppm. ESI-MS: m/z 313 [M]+.
55.1, 51.1 ppm. HRMS (ESI) m/z: [M + 1]+ calcd, 374.0795; found,
374.0797. Anal. calcd for C19H16ClNO5: C, 61.05; H, 4.31; N, 3.75%; 1H-pyrrole-3-carboxylate (11b). White solid (yield: 93%); mp:
found: C, 61.09; H, 4.41; N, 3.62%. 150–151 1C. IR (KBr): n 3343, 2952, 1711, 1675, 1481, 1234,
Methyl 4-hydroxy-5-oxo-2-phenyl-1-(pyridin-4-yl)-2,5-dihydro- 1096 cmꢂ1 1H NMR (CDCl3, 400 MHz): d 9.03 (s, 1H), 7.48
1H-pyrrole-3-carboxylate (10a). White solid (yield: 89%); mp: (d, 2H, J = 7.6 Hz), 7.27 (t, 3H, J = 7.4 Hz), 7.10 (d, 3H, J = 7.6 Hz),
7.05 (d, 2H, J = 7.6 Hz), 5.71 (s, 1H), 4.19 (q, 2H, J = 7.0 Hz), 2.26
Ethyl 4-hydroxy-5-oxo-2-(thiophen-2-yl)-1-(p-tolyl)-2,5-dihydro-
.
170–172 1C. IR (KBr): n 3443, 2956, 1722, 1495, 1074 cmꢂ1
.
1H NMR (CDCl3, 400 MHz): d 8.93 (s, 1H), 7.36 (d, 2H, J = (s, 3H), 1.20 (t, 3H, J = 7.0 Hz) ppm; 13C NMR (CDCl3, 100 MHz): d
8.0 Hz), 7.23 (t, 2H, J = 7.8 Hz), 7.19 (s, 1H), 7.13 (s, 1H), 7.08– 164.6, 162.5, 156.9, 148.2, 137.7, 135.5, 132.9, 129.8, 129.3, 126.3,
7.03 (m, 3H), 5.63 (s, 1H), 3.70 (s, 3H) ppm; 13C NMR (CDCl3, 123.7, 123.1, 122.1, 112.2, 61.6, 60.5, 13.9 ppm. ESI-MS: m/z 344
100 MHz): d 164.8, 162.7, 156.0, 137.1, 135.7, 134.4, 129.9, 129.1, [M + 1]+.
128.8, 127.5, 126.1, 125.6, 122.3, 112.4, 60.9, 52.1 ppm. ESI-MS:
Methyl 4-hydroxy-5-oxo-1-phenyl-2-(pyridin-4-yl)-2,5-dihydro-
1H-pyrrole-3-carboxylate (11c). White solid (yield: 91%); mp:
m/z 310 [M]+.
Ethyl 4-hydroxy-5-oxo-1-(pyridin-4-yl)-2-(p-tolyl)-2,5-dihydro- 165–166 1C. IR (KBr): n 3353, 2972, 1721, 1676, 1489, 1238,
1
1H-pyrrole-3-carboxylate (10b). White solid (yield: 85%); mp: 1092 cmꢂ1. H NMR (CDCl3, 400 MHz): d 9.05 (s, 1H), 8.05 (d,
181–182 1C. IR (KBr): n 3305, 3101, 2980, 1685, 1492, 1090 cmꢂ1
.
2H, J = 7.6 Hz), 7.35 (d, 3H, J = 7.4 Hz), 7.24–7.19 (m, 3H), 7.06
1H NMR (CDCl3, 400 MHz): d 9.07 (s, 1H), 7.33 (d, 2H, J = (t, 1H, J = 7.6 Hz), 5.80 (s, 1H), 3.69 (s, 3H) ppm; 13C NMR
8.4 Hz), 7.27–7.20 (m, 4H), 7.06 (d, 2H, J = 8.0 Hz), 5.69 (s, 1H), (CDCl3, 100 MHz): d 164.4, 162.9, 155.9, 147.9, 142.6, 135.5,
4.18 (q, 2H, J = 7.2 Hz), 2.24 (s, 3H), 1.17 (t, 3H, J = 7.0 Hz) ppm; 129.3, 128.5, 126.5, 124.0, 122.2, 112.0, 60.8, 52.3 ppm. ESI-MS:
13C NMR (CDCl3, 100 MHz): d 165.1, 162.7, 156.7, 135.7, 135.1, m/z 311 [M + 1]+.
133.6, 129.5, 128.5, 128.4, 127.5, 122.3, 112.9, 61.6, 61.2, 30.9,
Ethyl 4-hydroxy-2-(1H-indol-3-yl)-5-oxo-1-phenyl-2,5-dihydro-
1H-pyrrole-3-carboxylate (11d). White solid (yield: 94%);
20.9, 13.9 ppm. ESI-MS: m/z 338 [M]+.
Ethyl 2-(4-chlorophenyl)-4-hydroxy-5-oxo-1-(pyridin-4-yl)-2,5- mp:178–179 1C. IR (KBr): n 3359, 2971, 1728, 1674, 1495,
1
dihydro-1H-pyrrole-3-carboxylate (10c). White solid (yield: 89%); 1246, 1096, cmꢂ1. H NMR (CDCl3, 400 MHz): d 9.05 (s, 1H),
mp: 177–179 1C. IR (KBr): n 3441, 3303, 2989, 1731, 1450, 7.44 (d, 2H, J = 7.6 Hz), 7.38 (d, 2H, J = 7.4 Hz), 7.29 (t, 3H, J =
1021 cmꢂ1 1H NMR (CDCl3, 400 MHz): d 9.09 (s, 1H), 7.6 Hz), 7.14–7.09 (m, 3H), 5.71 (s, 1H), 4.21 (q, 2H, J = 7.2 Hz),
.
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1.21 (t, 3H, J = 7.0 Hz) ppm; 13C NMR (CDCl3, 100 MHz): d 165.1,
162.9, 156.8, 136.2, 134.5, 132.1, 129.4, 129.3, 126.3, 122.7,
122.5, 113.0, 61.7, 61.1, 31.2, 14.2 ppm. ESI-MS: m/z 363 [M + 1]+.
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Conclusion
In conclusion, we developed a green, efficient and environmentally
benign protocol for the synthesis of pyrrolidinone derivatives from
aniline, dialkylacetylenedicarboxylate and benzaldehyde using
Rose Bengal as a metal-free photoredox catalyst under visible light
irradiation. The remarkable advantages of our present protocol are
avoidance of the use of any toxic catalyst and use of renewable
energy source together with mild reaction conditions, high yields
and broad substrate scope. Employing the merits and novelty of
this development including the reactivity and applicability of other
heterocyclic structures in the photoredox-catalyzed process is
ongoing in our laboratory. Furthermore, systematic variation in
the photo-physical response of these groups of systems with
peripheral substitution patterns may lead to the development of
potential candidates for optoelectronic applications in the desired
spectral window.
Conflicts of interest
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The authors declare no conflicts of interest.
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Acknowledgements
SAIF-NEHU, Department of Chemistry-NEHU, CSIR-NEIST Jorhat,
IIT Bombay and CDRI Lucknow are highly acknowledged for
providing various analytical assistances. We would like to thank
DST for financial support (sanctioned no.: EEQ/2016/000646).
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