Dimethyl sulfoxide participant iron-mediated cascade oxidation/α-formylation reaction of substituted 2,3-dihydropyrroles under air and protonic acid free condition

Article abstract of DOI:10.1021/jo501385w

An efficient and Bronsted acid free one-pot protocol to directly generate structurally sophisticated α-formylpyrrole derivatives in moderate to good yields has been demonstrated, involving an iron-mediated domino oxidation/formylation reaction of readily available 2,3-dihydro-1H-pyrroles in dimethyl sulfoxide and air atmosphere, in which dimethyl sulfoxide acts as the formyl donor. A possible mechanism is presented.

Full text of DOI:10.1021/jo501385w

Article
pubs.acs.org/joc
Dimethyl Sulfoxide Participant Iron-Mediated Cascade Oxidation/α-
Formylation Reaction of Substituted 2,3-Dihydropyrroles under Air
and Protonic Acid Free Condition
Zhiguo Zhang,* Qing Tian, Jingjing Qian, Qingfeng Liu, Tongxin Liu, Lei Shi, and Guisheng Zhang*
Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical
Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang,
Henan 453007, P. R. China
S
* Supporting Information
ABSTRACT: An efficient and Brønsted acid free one-pot protocol
to directly generate structurally sophisticated α-formylpyrrole
derivatives in moderate to good yields has been demonstrated,
involving an iron-mediated domino oxidation/formylation reaction
of readily available 2,3-dihydro-1H-pyrroles in dimethyl sulfoxide
and air atmosphere, in which dimethyl sulfoxide acts as the formyl
donor. A possible mechanism is presented.
of substrates is worthy of further exploration by using DMSO
as the carbonyl reagent.
INTRODUCTION
■
Dimethyl sulfoxide1 (DMSO) can act as an organic solvent,2
oxidant (Pfitzner−Moffatt oxidation, Pummerer rearrange-
ment),3,4 -SMe/-CH2SMe source,5,6 Me source,7,8 -CN source,9
and ligand.10,11 Besides, as a one-carbon source, it can also
transform to a formyl group (Scheme 1).12−14 In 2000, Suzuki
α-Formylpyrroles as one of the most important five-
membered heterocyclic synthons17−20 have been used for the
preparation of many biologically active compounds, including
some very important linked polycyclic systems18 (such as the
well-known compounds porphyrins20−23), fused-ring com-
pounds,19,24 and highly functional pyrrole derivatives.25−28
The Vilsmeier−Haack reaction is the most classical method for
the synthesis of α-formylpyrroles.25,29,30 However, it requires a
stoichiometric amount or even more of POCl3, which is not
environmentally benign. Oxidation of a methyl20,21,31 or
methylene alcohol18,19,21 at the 2-position or conversion an
α-ester group into the aldehyde group via a multistep process23
are also two powerful methods leading to α-formylated
pyrroles. However, these methods often require prepreparation
of α-functionalized pyrroles, which needs additional reaction
steps and thus affects the efficiency of the reactions. Overall, a
more facile route is the reaction of pyrroles with a one-carbon
donor undergoing an intermolecular reaction. Of course, in this
process, it would be better to consider a more moderate one-
carbon donor. Herein, we present a recent study of oxidative
dehydrogenation/α-formylation of 1H-pyrroles 1 in the
presence of FeCl3 and air atmosphere, where DMSO acts as
both the carbonyl source and solvent.
Scheme 1. Multipurpose DMSO
et al. obtained the 3-formyl derivatives of some nitroanilines via
nuclear formylation reaction in DMSO in the presence of a
12
t
strong base such as BuOK or NaH. Formylation and
dimerization of p-alkyl-substituted phenols also has been
achieved by Yu’s group in 2012 by using DCMT-activated
DMSO.13 Very recently, several valuable reactions that avoided
the use of too harsh one-carbon donors (such as the
Vilsmeier−Haack reagent) have been achieved by using
DMSO as a one-carbon source in the presence of transition
metal catalysts. Cheng’s group developed an NH4OAc-
promoted C3-formylation of indoles under nearly neutral
conditions with DMSO serving as a carbonyl reagent.15 A direct
C−H formylation of C(3) on indoles and C(2) on pyrrole (N-
phenyl-1H-pyrrole was the only example) was also developed
by Chiba’s group using DABCO as an additive in DMSO.14
Zhang et al. reported a Cu-catalyzed method for the synthesis
of quinazolines by using amidines and a sp3-carbon donor
DMSO in 2013.16 Critically reviewing the literatures, the highly
efficient transition-metal-catalyzed formylation of a wide range
RESULTS AND DISCUSSION
■
During the course of our studies on the transformation of easily
accessible acetoacetamide derivatives to highly functionalized
N-containing heterocyclic compounds,32−36 we found sub-
Received: June 21, 2014
Published: August 2, 2014
© 2014 American Chemical Society
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a
Table 1. Survey of Reaction Conditions
b
entry
catalyst (equiv)
FeCl3 (0)
temp, °C
time, h
yield 2a (4a), %
1
2
3
4
5
165
12
trace (38)
61 (11)
70 (4)
FeCl3 (0.2)
90 + 165
90 + 165
90 + 165
90 + 165
90 + 165
90 + 150
90 + 145
90 + 165
90 + 165
90 + 145
140 + 165
90 + 165
130 + 165
24 + 16
7 + 12
6 + 10
4 + 6
FeCl3 (0.4)
FeCl3 (0.6)
81 (trace)
30 (11)
25 (30)
61 (6)
FeCl3 (1.0)
c
6
FeCl3 (0.6)
2 + 4
7
FeCl3·6H2O (0.6)
Fe(OTf)3 (0.6)
7 + 13
7 + 4
8
25 (28)
40 (20)
35 (20)
64 (6)
9
Fe(NO3)3·9H2O (0.6)
Fe2(SO4)3·xH2O (0.6)
FeCl2·4H2O (0.6)
Fe(acac)2 (0.6)
4 + 8
10
11
12
13
14
6 + 11
10 + 8
5 + 10
55 + 6
6 + 10
20 (31)
30 (25)
37 (20)
FeSO4·7H2O (0.6)
Fe (0.6)
a
b
Unless otherwise indicated, all reactions were carried out with 1a (1.0 mmol) and DMSO 5.0 mL. The value in parentheses is the yield of
c
byproduct N-(4-chlorophenyl)acetamide 4a. The reaction was performed in O2.
stituted 2,3-dihydropyrroles can afford γ-amino ketones via a
ring-opening reaction.37 We are also interested in the further
functionalization of 2,3-dihydropyrroles, which can be readily
prepared in high yield by the reaction of doubly activated
cyclopropanes with amines.38 Meanwhile, we noted that Su et
al. reported a mild Ru-catalyzed C(3) formylation of indoles
using anilines as the carbonyl source in 2011.39 Cheng’s group
developed two methods of C(3) formylation of indoles
recently, and in the processes TMEDA40 and DMSO,15
respectively, served as a carbonyl reagent. Accordingly, we
postulated that it is possible to realize the α-formylation of 2,3-
dihydropyrroles in the presence of an effective, reusable,
operationally simple, and environmentally benign catalyst, such
as iron salts.41−44 Our investigation began with the reaction of
1-(4-chlorophenyl)-2-methyl-N-(p-tolyl)-4,5-dihydro-1H-pyr-
role-3-carboxamide (1a) and 100 mol % FeCl3 in DMSO at 90
°C for 6 h and then at 165 °C for 10 h. The desired 1-(4-
chlorophenyl)-5-formyl-2-methyl-N-(p-tolyl)-1H-pyrrole-3-car-
boxamide (2a) was obtained in 30% yield, and the intermediate
3a did not need to be isolated. Simultaneously, byproduct N-
(4-chlorophenyl)acetamide 4a was isolated in 11% yield from
the complex mixture45 (Table 1, entry 5). The result
encouraged us to further optimize the reaction conditions.
After a series of attempts, we were pleased to find that the yield
of 2a could be enhanced to 81% in the presence of 0.6 equiv of
FeCl3 (Table 1, entry 4). When the reaction was performed in
O2 atmosphere, some unidentified complex mixture was
obtained and the yield of 2a dropped to 25% (Table 1, entry
6). Subsequently, a series of other iron salts, including FeCl3·
6H2O, Fe(OTf)3, Fe(NO3)3·9H2O, Fe2(SO4)3·xH2O, FeCl2·
4H2O, Fe(acac)2, FeSO4·7H2O, and even Fe, were also tested
(entries 7−14) and also displayed catalytic efficiency for the
reaction but were inferior to anhydrous FeCl3.
the position and the electronic effect of the substituents on the
benzene ring of the N-phenyl and amide moiety. It was
disclosed that electron-donating groups (EDG) (Me, -OMe)
and electron-withdrawing groups (EWG) (-Cl, -CO2Et) on the
N-phenyl ring were tolerated in the transformation and gave
the compounds 2a−2k, in 40−81% yields, including the
products with no substituents on the N-phenyl ring
(compounds 2l and 2m, 75% and 71% yields, respectively).
2-Phenyl- or 3-carboxylate-substituted starting materials such as
1n−1s generally gave moderate yields (41−78%). N-Aliphatic-
substituted pyrroles such as N-(tert-butyl) pyrroles 1t and 1u
gave 2t and 2u in moderate yields together with some complex
decomposition products.46 In fact, all of the reactions produced
a black complex mixture due to the decomposition of 1 at the
high reaction temperatures, which should account for the low
yields of the reactions.37
In order to shed light on the reaction mechanism, several
control reactions were conducted. First, the reaction was
performed in N2 atmosphere, and as a result, only a trace
amount of 2a was observed along with an unidentified complex
mixture, which indicated that air is required for the trans-
formation (eq 1). Oxygen-involved reaction may proceed via a
radical mechanism.47−49 Two kinds of radical inhibitors such as
TEMPO and duroquinone were then added to the mixture to
test if one or both of the two steps of the reaction (from 1a to
3a and 3a to 2a) proceed through a free radical pathway, and it
was found that the reaction was completely inhibited (eqs
2−5). These results suggest that a radical process is involved in
this transformation.50 Furthermore, the experiment that was
carried out in deuterated d6-DMSO to obtain further insight
into the transformation clearly showed that there was
completely deuterated formyl at the α-position of pyrrole d-
2a (eq 6).
With these optimized conditions in hand, we next explored
the scope and generality of the process with respect to the
position of the different substituents on the benzene ring of the
N-phenyl and pyrrole rings of 1, and the results are summarized
in Table 2. Initial investigation mainly focused on the effect of
On the basis of all of the results described above together
with previous literature,15,39,40,51,52 especially several papers
concerning the variant of the Pummerer reaction,13,15,53
a
possible mechanism of this transformation is proposed in
Scheme 2. The reaction starts from a single electron-transfer
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a
Table 2. Reaction Extension
a
Unless otherwise indicated, all reactions were carried out with 1 (1.0 mmol), FeCl3 (0.6 equiv) in DMSO (5 mL). The value in parentheses is the
yield of byproducts 4.
oxidation of 2,3-dihydro-1H-pyrroles 1 by Fe3+ and O2 in air to
generate radical species A.54−56 Then, A leads to 1H-pyrroles 3
via the sequential loss of hydrogen radicals and protons.57,58
After a single electron-transfer oxidation, 3 gives intermediate
C.55 Radical coupling of C and methyl radical (formed from
DMSO in the presence of ferric salts and O2)7 leads to
methylated 1H-pyrrole derivatives 5. Subsequently, a single
electron-transfer oxidation of 5 generates intermediate D.59
Radical D is then trapped by dioxygen to provide peroxy radical
E, which is eventually converted into α-formylpyrroles 2.48 It is
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EXPERIMENTAL SECTION
■
General Information. Materials. Compounds 138 and 560 were
prepared according to the reported procedures. Anhydrous FeCl3 was
purchased from Aladdin. Unless otherwise indicated, DMSO were
purchased from commercial sources and used without purification.
Analytical Methods. All reagents were purchased from commercial
sources and used without further treatment. DMSO was distilled
under reduced pressure from CaH2 and stored over molecular sieves.
1
All reactions were carried out under air atmosphere. H NMR and
13C{1H} NMR spectra were recorded on a 400 MHz NMR
spectrometer (1H, 400 MHz; 13C{1H}, 100 MHz at 25 °C) with
TMS as internal standard. Data are represented as follows: chemical
shift, integration, multiplicity (br = broad, s = singlet, d = doublet, dd
= double doublet, t = triplet, q = quartet, m = multiplet), coupling
constants in Hz. All high-resolution mass spectra (HRMS) were
measured on a mass spectrometer (ESI-oa-TOF), and the purity of all
1
samples used for HRMS (>95%) was confirmed by H and 13C{1H}
NMR spectroscopic analysis. Melting points were measured on a
melting point apparatus equipped with a thermometer and are
uncorrected. All reactions were monitored by LC−MS. Flash
chromatography was carried out on SiO2 (silica gel 200−300 mesh).
Typical Experimental Procedure for the Synthesis of 2 (2a as
an Example). To a round-bottom flask (25 mL) equipped with a
drying tube (filled with calcium chloride) were added 1-(4-
chlorophenyl)-2-methyl-N-(p-tolyl)-4,5-dihydro-1H-pyrrole-3-carbox-
amide 1a (326 mg, 1 mmol) and anhydrous FeCl3 (97.5 mg, 0.6
mmol), the mixture was well stirred for 7 h in anhydrous DMSO (5
mL) at 90 °C, and then the reaction system was heated to 165 °C for 6
h. After cooling, 1 M HCl (10 mL) and water (5 mL) were added, the
mixture was extracted with CH2Cl2 (20 mL × 3), and the organic layer
was then dried over sodium sulfate and concentrated in vacuo. The
crude compound was purified via flash chromatography (eluent ethyl
acetate/petroleum ether = 1:3) to provide 1-(4-chlorophenyl)-5-
formyl-2-methyl-N-(p-tolyl)-1H-pyrrole-3-carboxamide 2a in 81%
yield (286 mg) as a white solid.
Scheme 2. Proposed Mechanism
1-(4-Chlorophenyl)-5-formyl-2-methyl-N-(p-tolyl)-1H-pyr-
role-3-carboxamide (2a). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
1
white solid (286 mg, 81%). Mp 232−235 °C. H NMR (400 MHz,
CDCl3) δ 9.36 (s, 1H), 7.81 (s, 1H), 7.50 (d, J = 8.4 Hz, 2H), 7.48 (d,
J = 8.4 Hz, 2H), 7.36 (s, 1H), 7.19 (d, J = 8.8 Hz, 2H), 7.15 (d, J = 8.0
Hz, 2H), 2.39 (s, 3H), 2.33 (s, 3H). 13C{1H} NMR (100 MHz,
CDCl3) δ 178.4, 162.4, 143.5, 135.5, 135.4, 134.8, 134.0, 132.1, 129.8,
129.6, 129.0, 120.3, 118.2, 20.9, 12.0, one carbon was not observed.
HRMS (ESI) m/z calcd for C20H17ClN2O2 [M + H]+ 353.1051, found
353.1077.
noteworthy that the formylpyrrole 2a could be isolated in 26%
yield when 1-(4-chlorophenyl)-2,5-dimethyl-N-(p-tolyl)-1H-
pyrrole-3-carboxamide 5a was used for the reaction in the
presence of FeCl3 (0.6 equiv) in DMSO at 165 °C after 9 h,
which further confirmed the rationality of processes of 5 →
2.14,48 Besides, at present, the Pummerer reaction mechanistic
pathway does not be excluded from 3 to 2. The DMSO was
polarized by iron, and then transferred to the pyrrole
intermediate, and the resulting sulfide hydrolyzed to the
CHO unit.15
1-(4-Chlorophenyl)-5-formyl-2-methyl-N-phenyl-1H-pyr-
role-3-carboxamide (2b). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
1
white solid (241 mg, 71%). Mp 193−196 °C. H NMR (400 MHz,
CDCl3) δ 9.40 (s, 1H), 7.74 (s, 1H), 7.61 (d, J = 7.6 Hz, 2H), 7.51 (d,
J = 8.4 Hz, 2H), 7.39−7.35 (m, 3H), 7.21 (d, J = 8.4 Hz, 2H), 7.14 (t,
J = 7.6 Hz, 1H), 2.41 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3) δ
178.5, 162.6, 143.7, 138.0, 135.7, 134.9, 132.3, 129.9, 129.2, 129.1,
124.5, 120.3, 118.8, 118.3, 12.1. HRMS (ESI), m/z calcd for
C19H15ClN2O2 [M + H]+ 339.0895, found 339.0870.
N,1-Bis(4-chlorophenyl)-5-formyl-2-methyl-1H-pyrrole-3-
carboxamide (2c). The product was isolated by flash chromatog-
raphy (eluent ethyl acetate/petroleum ether = 2:5) as a white solid
CONCLUSION
■
1
In conclusion, we have developed an efficient Fe-catalyzed
tandem oxidation/formylation reaction of readily available 1H-
pyrroles to give the corresponding α-formyled multisubstituted
pyrrole derivatives in moderate to good yields with DMSO
serving as the formyl donor. A wide range of substrates were
investigated to show the generality of the process. The
advantages of this new method are the ease of preparation of
substrates, operational simplicity, and use of inexpensive and
environmentally friendly FeCl3 as the catalyst and O2 as the
oxidant.
(302 mg, 81%). Mp 253−258 °C. H NMR (400 MHz, DMSO-d6) δ
10.03 (s, 1H), 9.38 (s, 1H), 7.85 (s, 1H), 7.79 (d, J = 8.8 Hz, 2H), 7.62
(d, J = 8.4 Hz, 2H), 7.45 (d, J = 8.4 Hz, 2H), 7.39 (d, J = 8.8 Hz, 2H),
2.32 (s, 3H). 13C{1H} NMR (100 MHz, DMSO-d6) δ 178.5, 162.4,
143.1, 138.2, 135.2, 133.7, 131.4, 129.7, 129.3, 128.4, 126.8, 121.6,
120.7, 117.4, 11.7. HRMS (ESI) m/z calcd for C19H14Cl2N2O2 [M +
H]+ 373.0505, found 373.0513.
Ethyl 4-(1-(4-Chlorophenyl)-5-formyl-2-methyl-1H-pyrrole-
3-carboxamido)benzoate (2d). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
1
white solid (164 mg, 40%). Mp 173−176 °C. H NMR (400 MHz,
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DMSO-d6) δ 10.22 (s, 1H), 9.38 (s, 1H), 7.94−7.90 (m, 5H), 7.62 (d,
J = 8.8 Hz, 2H), 7.46 (d, J = 8.4 Hz, 2H), 4.29 (q, J = 7.2 Hz, 2H),
2.33 (s, 3H), 1.31 (t, J = 7.2 Hz, 3H). 13C{1H} NMR (100 MHz,
DMSO-d6) δ 178.6, 165.4, 162.7, 143.8, 143.5, 135.2, 133.8, 131.4,
130.1, 129.8, 129.3, 124.2, 120.9, 119.3, 117.3, 60.4, 14.3, 11.8. HRMS
(ESI) m/z calcd for C22H19ClN2O4 [M + Na]+ 433.0926, found
433.0914.
117.3, 112.6, 55.8, 11.4, one carbon was not observed. HRMS (ESI)
m/z calcd for C20H17ClN2O3 [M + H]+ 369.1000, found 369.1018.
5-Formyl-2-methyl-N,1-di-p-tolyl-1H-pyrrole-3-carboxamide
(2k). The product was isolated by flash chromatography (eluent ethyl
acetateethyl acetate/petroleum ether = 1:4) as a white solid (242 mg,
73%). Mp 249−251 °C. 1H NMR (400 MHz, CDCl3) δ 9.35 (s, 1H),
7.73 (s, 1H), 7.49 (d, J = 8.4 Hz, 2H), 7.37 (s, 1H), 7.32 (d, J = 8.0
Hz, 2H), 7.15 (m, 4H), 2.45 (s, 3H), 2.41 (s, 3H), 2.33 (s, 3H).
13C{1H} NMR (100 MHz, CDCl3) δ 179.1, 162.8, 143.4, 139.8 135.6,
1-(3-Chlorophenyl)-N-(4-chlorophenyl)-5-formyl-2-methyl-
1H-pyrrole-3-carboxamide (2e). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
134.0, 133.6, 132.6, 130.3, 129.9, 129.7, 127.6, 120.4, 118.1, 21.4, 21.0,
12.2. HRMS (ESI) m/z calcd for C21H20N2O2 [M + Na]+ 355.1417,
found 355.1400.
1
white solid (291 mg, 78%). Mp 203−205 °C. H NMR (400 MHz,
DMSO-d6) δ 10.03 (s, 1H), 9.38 (s, 1H), 7.85 (s, 1H), 7.80 (d, J = 8.4
Hz, 2H), 7.64−7.55 (m, 3H), 7.41−7.38 (m, 3H), 2.33 (s, 3H).
13C{1H} NMR (100 MHz, DMSO-d6) δ 178.5, 162.4, 143.2, 138.3,
5-Formyl-N,1-bis(4-methoxyphenyl)-2-methyl-1H-pyrrole-3-
carboxamide (2l). The product was isolated by flash chromatography
(eluent ethyl acetate/petroleum ether = 1:2) as a white solid (222 mg,
137.7, 133.5, 131.4, 130.8, 129.3, 128.5, 128.0, 126.9, 126.8, 121.6,
117.4, 11.7, one carbon was not observed. HRMS (ESI) m/z calcd for
C19H14Cl2N2O2 [M + H]+ 373.0505, found 373.0505.
1
61%). Mp 116−120 °C. H NMR (400 MHz, DMSO-d6) δ 9.77 (s,
1H), 9.31 (s, 1H), 7.79 (s, 1H), 7.65 (d, J = 8.8 Hz, 2H), 7.33 (d, J =
8.8 Hz, 2H), 7.08 (d, J = 8.4 Hz, 2H), 6.91 (d, J = 8.8 Hz, 2H), 3.84 (s,
3H), 3.74 (s, 3H), 2.31 (s, 3H). 13C{1H} NMR (100 MHz, DMSO-
d6)δ 178.5, 162.2, 159.4, 155.3, 142.7, 132.4, 131.7, 129.0, 128.6,
121.7, 119.0, 117.5, 114.4, 113.7, 55.4, 55.2, 11.7. HRMS (ESI) m/z
calcd for C21H20N2O4 [M + H]+ 365.1496, found 365.1493.
1-(2-Chlorophenyl)-N-(4-chlorophenyl)-5-formyl-2-methyl-
1H-pyrrole-3-carboxamide (2f). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 2:5) as a
1
white solid (272 mg, 73%). Mp 171−175 °C. H NMR (400 MHz,
DMSO-d6) δ 10.04 (s, 1H), 9.38 (s, 1H), 7.85 (s, 1H), 7.80 (d, J = 8.8
Hz, 2H), 7.65−7.54 (m, 3H), 7.39 (m, 3H), 2.33 (s, 3H). 13C{1H}
NMR (100 MHz, DMSO-d6) δ 178.5, 162.4, 143.2, 138.2, 137.7,
133.4, 131.4, 130.8, 129.3, 128.5, 127.9, 126.9, 126.8, 121.6, 120.9,
117.4, 11.7. HRMS (ESI) m/z calcd for C19H14Cl2N2O2 [M + H]+
373.0505, found 373.0502.
5-Formyl-2-methyl-1-phenyl-N-(p-tolyl)-1H-pyrrole-3-car-
boxamide (2m). The product was isolated by flash chromatography
(eluent ethyl acetate/petroleum ether = 1:4) as a white solid (239 mg,
1
75%). Mp 161−163 °C. H NMR (400 MHz, DMSO-d6) δ 9.83 (s,
1H), 9.33 (s, 1H), 7.84 (s, 1H), 7.63 (d, J = 6.4 Hz, 2H), 7.55 (s, 3H),
7.41 (s, 2H), 7.13 (d, J = 6.8 Hz, 2H), 2.31 (s, 3H), 2.27 (s, 3H).
13C{1H} NMR (100 MHz, DMSO-d6) δ 178.5, 162.3, 142.7, 136.8,
Ethyl 4-(3-((4-Chlorophenyl)carbamoyl)-5-formyl-2-methyl-
1H-pyrrol-1-yl)benzoate (2g). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
136.2, 132.2, 131.5, 129.4, 129.1, 129.0, 127.9, 120.2, 119.8, 117.7,
20.5, 11.8. HRMS (ESI) m/z calcd for C20H18N2O2 [M + Na]+
341.1260, found 341.1239.
1
white solid (185 mg, 45%). Mp 200−202 °C. H NMR (400 MHz,
DMSO-d6) δ 10.07 (s, 1H), 9.39 (s, 1H), 8.10 (d, J = 8.4 Hz, 2H),
7.88 (s, 1H), 7.80 (d, J = 8.4 Hz, 2H), 7.56 (d, J = 8.4 Hz, 2H), 7.39
(d, J = 8.8 Hz, 2H), 4.36 (q, J = 7.2 Hz, 2H), 2.33 (s, 3H), 1.34 (t, J =
7.2 Hz, 3H). 13C{1H} NMR (100 MHz, DMSO-d6) δ 179.0, 165.5,
162.8, 143.5, 140.8, 138.7, 131.7, 130.8, 130.5, 128.9, 128.8, 127.3,
122.0, 121.6, 118.1, 61.6, 14.6, 12.2. HRMS (ESI) m/z calcd for
C22H19ClN2O4 [M + Na]+ 433.0926, found 433.0924.
N,1-Bis(4-chlorophenyl)-5-formyl-2-phenyl-1H-pyrrole-3-
carboxamide (2n). The product was isolated by flash chromatog-
raphy (eluent ethyl acetate/petroleum ether = 1:4) as a white solid
1
(339 mg, 78%). Mp 229−233 °C. H NMR (400 MHz, DMSO-d6) δ
10.07 (s, 1H), 9.50 (s, 1H), 7.87 (s, 1H), 7.67 (d, J = 8.8 Hz, 2H), 7.41
(d, J = 8.4 Hz, 2H), 7.32 (m, 4H), 7.28−7.18 (m, 5H). 13C{1H} NMR
(100 MHz, DMSO-d6) δ 179.4, 161.6, 143.4, 138.2, 135.3, 133.2,
132.0, 130.7, 130.4, 129.4, 128.7, 128.5, 128.4 127.6, 126.8, 121.3,
120.4, 119.6. HRMS (ESI) m/z calcd for C24H16Cl2N2O2 [M + H]+
435.0662, found 435.0682.
N-(4-Chlorophenyl)-5-formyl-1-(4-methoxyphenyl)-2-meth-
yl-1H-pyrrole-3-carboxamide (2h). The product was isolated by
flash chromatography (eluent ethyl acetate/petroleum ether = 1:3) as
1
a white solid (229 mg, 62%). Mp 203−204 °C. H NMR (400 MHz,
DMSO-d6) δ 10.00 (s, 1H), 9.32 (s, 1H), 7.81 (s, 1H), 7.80 (d, J = 9.2
Hz, 2H), 7.38 (d, J = 8.8 Hz, 2H), 7.34 (d, J = 8.8 Hz, 2H), 7.08 (d, J
= 9.2 Hz, 2H), 3.84 (s, 3H), 2.31 (s, 3H). 13C{1H} NMR (100 MHz,
DMSO-d6) δ 178.7, 162.6, 159.5, 143.1, 138.3, 131.8, 129.1, 128.5,
126.8, 121.6, 119.1, 117.1, 114.5, 55.5, 11.8, one carbon was not
observed. HRMS (ESI) m/z calcd for C20H17ClN2O3 [M + H]+
369.1000, found 369.1004.
Ethyl 4-(3-((4-Chlorophenyl)carbamoyl)-5-formyl-2-phenyl-
1H-pyrrol-1-yl)benzoate (2o). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
1
white solid (279 mg, 59%). Mp 223−226 °C. H NMR (400 MHz,
DMSO-d6) δ 10.11 (s, 1H), 9.51 (s, 1H), 7.90 (s, 1H), 7.89 (d, J = 6.8
Hz, 2H), 7.67 (d, J = 8.4 Hz, 2H), 7.40 (d, J = 8.4 Hz, 2H), 7.34 (d, J
= 8.4 Hz, 2H), 7.22 (s, 5H), 4.30 (q, J = 6.8 Hz, 2H), 1.30 (t, J = 6.8
Hz, 3H). 13C{1H} NMR (100 MHz, DMSO-d6) δ 179.5, 165.0, 161.6,
143.3, 140.6, 138.2, 131.9, 130.7, 129.9, 129.5, 129.3, 129.1, 128.6,
128.5, 127.6, 126.9, 121.4, 120.9, 119.8, 61.1, 14.1. HRMS (ESI) m/z
calcd for C27H21ClN2O4 [M + H]+ 473.1263, found 473.1260.
Ethyl 5-Formyl-2-phenyl-1-(p-tolyl)-1H-pyrrole-3-carboxy-
late (2p). The product was isolated by flash chromatography (eluent
ethyl acetate/petroleum ether = 1:4) as a white solid (160 mg, 48%).
N-(4-Chlorophenyl)-5-formyl-1-(3-methoxyphenyl)-2-meth-
yl-1H-pyrrole-3-carboxamide (2i). The product was isolated by
flash chromatography (eluent ethyl acetate/petroleum ether = 1:3) as
1
a white solid (177 mg, 48%). Mp 143−146 °C. H NMR (400 MHz,
DMSO-d6) δ 10.00 (s, 1H), 9.33 (s, 1H), 7.83 (s, 1H), 7.80 (d, J = 8.8
Hz, 2H), 7.47 (t, J = 8.0 Hz, 1H), 7.38 (d, J = 8.8 Hz, 2H), 7.13 (dd, J
= 8.0, 2.0 Hz, 1H), 7.02 (t, J = 2.0 Hz, 1H), 6.97 (d, J = 7.6 Hz, 1H),
3.81 (s, 3H), 2.34 (s, 3H). 13C{1H} NMR (100 MHz, DMSO-d6) δ
178.6, 162.5, 159.8, 142.7, 138.3, 137.0, 131.6, 130.1, 128.4, 126.8,
121.5, 120.0, 119.0, 117.2, 115.0, 113.7, 55.5, 11.8. HRMS (ESI) m/z
calcd for C20H17ClN2O3 [M + H]+ 369.1000, found 369.0981.
N-(4-Chlorophenyl)-5-formyl-1-(2-methoxyphenyl)-2-meth-
yl-1H-pyrrole-3-carboxamide (2j). The product was isolated by
flash chromatography (eluent ethyl acetate/petroleum ether = 1:3) as
1
Mp 165−167 °C. H NMR (400 MHz, DMSO-d6) δ 9.45 (s, 1H),
7.60 (s, 1H), 7.31−7.17 (m, 5H), 7.16−7.06 (m, 4H), 4.06 (q, J = 7.0
Hz, 2H), 2.26 (s, 3H), 1.06 (t, J = 7.0 Hz, 3H). 13C{1H} NMR (100
MHz, DMSO-d6) δ 179.6, 162.7, 144.7, 138.1, 133.7, 132.6, 130.8,
129.5, 129.2, 128.6, 128.2, 127.4, 121.9, 115.1, 59.6, 20.6, 13.9. HRMS
(ESI) m/z calcd for C21H19NO3 [M + Na]+ 356.1257, found 356.1236.
Ethyl 1-(4-Chlorophenyl)-5-formyl-2-phenyl-1H-pyrrole-3-
carboxylate (2q). The product was isolated by flash chromatography
(eluent ethyl acetate/petroleum ether = 1:4) as a white solid (209 mg,
1
a white solid (199 mg, 54%). Mp 141−145 °C. H NMR (400 MHz,
DMSO-d6) δ 10.00 (s, 1H), 9.29 (s, 1H),7.81−7.80 (m, 3H), 7.53 (td,
J = 7.6, 1.6 Hz, 1H), 7.39 (d, J = 8.8 Hz, 2H), 7.34 (dd, J = 7.6, 1.6 Hz,
1H), 7.26 (d, J = 8.4 Hz, 1H), 7.10 (t, J = 7.6, 1H), 3.74 (s, 3H), 2.24
(s, 3H). 13C{1H} NMR (100 MHz, DMSO-d6) δ 178.5, 162.6, 154.7,
143.0, 138.3, 131.3, 130.9, 129.2, 128.5, 126.8, 124.5, 121.6, 120.7,
1
59%). Mp 186−187 °C. H NMR (400 MHz, DMSO-d6) δ 9.52 (s,
1H), 7.66 (s, 1H), 7.38 (d, J = 8.4 Hz, 2H), 7.30−7.23 (m, 7H), 4.07
(q, J = 6.8 Hz, 2H), 1.06 (t, J = 6.8 Hz, 3H). 13C{1H} NMR (100
MHz, DMSO-d6) δ 179.7, 162.6, 145.0, 135.6, 133.2, 132.4, 130.8,
8186
dx.doi.org/10.1021/jo501385w | J. Org. Chem. 2014, 79, 8182−8188

The Journal of Organic Chemistry
Article
130.3, 129.2, 128.7, 128.6 127.5, 123.3, 115.3, 59.7, 13.9. HRMS (ESI)
m/z calcd for C20H16ClNO3 [M + H]+ 354.0891, found 354.0892.
Ethyl 1-(4-(Ethoxycarbonyl)phenyl)-5-formyl-2-phenyl-1H-
pyrrole-3-carboxylate (2r). The product was isolated by flash
chromatography (eluent ethyl acetate/petroleum ether = 1:3) as a
ACKNOWLEDGMENTS
■
We thank the NSFC (21002051, 21172056, 21272057, and
21372065), PCSIRT (IRT1061), China Postdoctoral Science
Foundation funded project (2012M521397, 2013T60701 and
2013M530339), and Key Project of Henan Educational
Committee (13A150546) for financial support of this research.
1
white solid (246 mg, 63%). Mp 112−115 °C. H NMR (400 MHz,
CDCl3) δ 9.54 (s, 1H), 7.96 (d, J = 8.4 Hz, 2H), 7.65 (s, 1H), 7.25−
7.13 (m, 7H), 4.34 (q, J = 7.2 Hz, 2H), 4.17 (q, J = 7.2 Hz, 2H), 1.36
(t, J = 7.2 Hz, 3H), 1.17 (t, J = 7.2 Hz, 3H). 13C{1H} NMR (100
MHz, CDCl3) δ 179.0, 165.5, 163.3, 145.4, 140.6, 132.4, 130.7, 130.7,
130.1, 129.2, 129.0, 128.3, 127.8, 124.1, 116.4, 61.4, 60.3, 14.3, 14.1.
HRMS (ESI) m/z calcd for C23H21NO5 [M + H]+ 392.1492, found
392.1495.
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1
41%). Mp 89−91 °C. H NMR (400 MHz, CDCl3) δ 9.41 (s, 1H),
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1
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white solid (169 mg, 53%). Mp 201−203 °C. H NMR (400 MHz,
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1
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AUTHOR INFORMATION
Corresponding Author
*E-mail: zhangzg@htu.edu.cn or zgs6668@yahoo.com.
■
Notes
The authors declare no competing financial interest.
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