Modular CeCl3·7H2O-catalyzed multi-component synthesis of 1,2,3,4-tetrasubstituted pyrroles under microwave irradiation and their further trichloroisocyanuric acid-mediated conversion into 5-sulfenylpyrrole derivatives

Article abstract of DOI:10.1016/j.tet.2013.08.035

A modular, multicomponent synthesis of 1,2,3,4-tetrasubstituted pyrroles promoted by the inexpensive CeCl₃·7H₂O, is reported. The reaction was carried out under microwave irradiation, affording good yields of products in short time. Scope and limitations were explored and a plausible reaction mechanism is discussed. The resulting heterocycles were smoothly and efficiently converted into their corresponding 5-arylsulfenyl derivatives by reaction with diaryl disulfides and trichloroisocyanuric acid in EtOAc.

Full text of DOI:10.1016/j.tet.2013.08.035

Tetrahedron 69 (2013) 9076e9085
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Modular CeCl3$7H2O-catalyzed multi-component synthesis of
1,2,3,4-tetrasubstituted pyrroles under microwave irradiation and
their further trichloroisocyanuric acid-mediated conversion into
5-sulfenylpyrrole derivatives
, ,
Claudio C. Silveira a y, Samuel R. Mendes b, Guilherme M. Martins a,
*
a
c,
*
€
Sheila C. Schlosser , Teodoro S. Kaufman
a Departamento de Química, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil
b GAPAM, Departamento de Química, Universidade do Estado de Santa Catarina, 89219-719 Joinville, SC, Brazil
c
ꢀ
Instituto de Química Rosario (IQUIR, CONICET-UNR) and Facultad de Ciencias Bioquímicas y Farmaceuticas-UNR, Suipacha 531, 2000 Rosario,
Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2013
Received in revised form 11 August 2013
Accepted 13 August 2013
Available online 22 August 2013
A modular, multicomponent synthesis of 1,2,3,4-tetrasubstituted pyrroles promoted by the inexpensive
CeCl3$7H2O, is reported. The reaction was carried out under microwave irradiation, affording good yields
of products in short time. Scope and limitations were explored and a plausible reaction mechanism is
discussed. The resulting heterocycles were smoothly and efficiently converted into their corresponding
5-arylsulfenyl derivatives by reaction with diaryl disulfides and trichloroisocyanuric acid in EtOAc.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Multicomponent reaction
Microwave-assisted transformation
Pyrrole synthesis
Cerium (III) chloride
Trichloroisocyanuric acid
1. Introduction
Paal-Knorr,11a,b and Clauson-Kaas11cee reactions and their modifi-
cations. In addition, these heterocycles have also been synthesized
The pyrrole nucleus is the characteristic structural motif of nu-
merous natural (storniamide A, lamellarin P, marinopyrrole B) and
synthetic products (Fig. 1).1 Many polyfunctionalized pyrroles are
known to display interesting biological activities, as antilipidemics
(atorvastatin, LipitorÒ),2 antioxidants,3a and anti-inflammatories.3b,c
They are also antibacterials,4a,b antitumorals,4c as well as anti-
fungal,5a antitubercular,5bed and central nervous system agents.6 In
addition, pyrroles were observed to inhibit cytokine-mediated dis-
eases7 and have alsofoundsomeapplications inmaterialschemistry.8
The growing importance and wide usefulness of polysubstituted
pyrroles have kept in focus the search of new methods for the ef-
ficient synthesis of these heterocycles.
by the Huisgen reaction, by transformations involving suitably
substituted alkynes and amines,12 cyclization of N-propargylic
derivatives,13a,b including propargyl aziridines,13c,d and through the
cyclocondensation of vinyl azides with 1,3-dicarbonyls,14 among
various other alternatives.
However, many of these transformations have important
drawbacks, including low yield, the need of multistep operations,
the requirement of precious metals or expensive reagents, difficult
availability of the starting materials, lack of regiospecificity and
narrow functional group compatibility.
Multicomponent reactions (MCRs) are a highly convergent al-
ternative towards complex molecules. Their advantages, in terms of
reaction times, yields, and reproducibility, have been repeatedly
exploited in various efficient syntheses of heterocyclic com-
pounds.15 Several MCR approaches towards pyrroles have been
described16 and the subject was repeatedly reviewed.17
Pyrroles have been prepared by several classical methods,9a
such as the BartoneZard,9b Hantzsch,9c,d Knorr,10a,b Trofimov,10c
Lanthanide salts are useful as catalysts and promoters in organic
synthesis.18 Many of them have recently attracted great scientific
interest because of their ready availability, low toxicity, and ease of
* Corresponding authors. E-mail addresses: silveira@quimica.ufsm.br (C.C. Silveira),
kaufman@iquir-conicet.gov.ar (T.S. Kaufman).
y
Fax: þ55 55 3220 8754.
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.035

C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
9077
HO
OH
OH
HO
OH
HO
O
OH
HO
N
Br
HO
H
H
H
Cl
i
N
Pr
N
OMe
O
N
N
N
N
F
Cl
O
O
O
O
Cl
O
HO
OH
OH
Cl
HO
N
H
OH
OH
HO2C
OH
Storniamide A
OMe
Lamellarin P
Marinopyrrole B
Atorvastatin
Fig. 1. Examples of relevant natural (storniamide A, lamellarin P, marinopyrrole B) and synthetic (atorvastatin) polysubstituted pyrroles.
handling, as well as for their air and water stability.19 Among them,
cerium compounds have found extensive use in organic
synthesis.20
Table 1
Process optimization. Microwave irradiation-assisted synthesis of polysubstituted
pyrrole 4a under different conditionsa
O
Over the past few years, cerium (III) chloride has emerged as
a suitable agent for achieving highly regio- and chemoselective
transformations.21 The salt is an inexpensive, non-toxic, and water-
tolerant catalyst, which has been used in its heptahydrate and
anhydrous forms, as well as in combination with NaI22 and as
a solid-supported reagent.23
Me
Ph
Me
O
O
Conditions
NH2
Ph
+
+
Ph
NO2
Me
N
Me
Ph
4a
Grob and Camenisch24a were the first to disclose that pyrroles
1a
2a
3a
Entry
Catalyst
Solvent
Temp/time (ꢀC/min)
Yield (%)b
can be obtained through the reaction of b-enamino carbonyls and
nitroalkenes, followed by intramolecular cyclization, but their
original protocol was seldom employed as such.24bed However,
several variations, including nitroalkane and aldehyde mixtures as
1
2
3
4
5
6
7
8
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
CeCl3$7H2O
Anhyd CeCl3
MeOH
MeCN
100/15
100/15
100/15
100/15
100/15
100/15
100/15
100/20
100/10
120/15
80/15
dc
dc
dc
48
75
50d
58e
75
63
65
68
75
47
45
60
Glycerol
Solvent-free
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
MeNO2
b
-nitroolefin precursors and reactions of nitroalkenes25 with
dicarbonyl compounds and amines, as
b-enamino carbonyl equiv-
alents,26 have been extensively explored.
In view of our interest in the development of new and cleaner
alternatives for classical reactions, promoted by CeIII species,27 and
taking advantage that the enamination of carbonyls mediated by
cerium salts,28 especially CeCl3 has been recently reported, we
decided to develop a modular CeIII-mediated MCR for the synthesis
of polysubstituted pyrroles.
9
10
11
12
13
14
15
100/15
100/15
100/15
100/15
Ce(NO3)3$6H2O
Ce(OTf)3
CAN
a
Conditions: Solvent (1 mL), catalyst (0.30 mmol), 1a (1.0 mmol), 2a (1.0 mmol),
3a (1.0 mmol), microwaves irradiation.
2. Results and discussion
b
After column chromatography.
No reaction.
Employing 0.15 mmol CeCl3$7H2O.
c
Therefore, in order to find the optimum reaction conditions
(Scheme 1), equimolar amounts of
tone (2a) and aniline (3a) were submitted to reaction in the pres-
ence of 0.3 equiv of CeCl3$7H2O.
d
b
-nitrostyrene (1a), acetylace-
e
Employing 0.50 mmol CeCl3$7H2O.
10 min gave only 63% of the product (entry 9). On the other hand,
carrying out the reaction at both, 120 ꢀC and 80 ꢀC resulted in
comparatively lower yields of the heterocycle (entries 10, 11),
whereas use of anhydrous CeCl3 did not improve the efficiency of
the transformation (entry 12).
O
R2
R1
4
R2
3
O
O
CeCl3.7H2O
NH2
R3
R1
+
+
2
NO2
Solvent, MW
Me
(100ºC, 15 min)
N1
The effects of adding different amounts of the promoter was also
tested using 0.15e0.50 equiv CeCl3$7H2O in MeNO2; however, the
best result was obtained with 0.30 equiv of the salt at 100 ꢀC (en-
tries 5e7). Other sources of CeIII (nitrate, triflate), as well as
(NH4)2Ce(NO3)6 (CAN, a CeIV derivative),28e were also examined as
promoters, observing that none of them surpassed the effective-
ness of CeCl3$7H2O (entries 13e15).
With the optimized conditions in hand (entry 5), and in order to
establish its scope, the transformation was next extended to the
synthesis of other pyrroles with various substituents (Table 2). It
R3
4
1
2
3
Scheme 1. Proposed MCR synthesis of 1,2,3,4-tetrasubstituted pyrroles.
At first, the effect of the solvent on the reaction outcome was
tested under microwave irradiation (100 ꢀC for 15 min). The results
(Table 1) revealed that no reaction was observed in MeOH, MeCN,
and glycerol (entries 1e3). On the other hand, running the cycli-
zation under solvent-free conditions (entry 4) gave moderate yields
of 4a, while MeNO2 afforded the best reaction performance (75%
yield, entry 5), confirming
a
solvent influence on the
was observed that electron-poor aromatics on the b-nitrostyrene
transformation.
side afforded comparatively lower reaction yields (entries 3, 6, 8,
and 12) than their counterparts carrying electron-richer aromatic
nuclei (entries 1, 2, 4, and 5).
Increasing the reaction time in MeNO2 to 20 min did not im-
prove the yields (entry 8), while performing the transformation for

9078
C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
Table 2
The microwaves-assisted and CeCl3-mediated MCR synthesis of polysubstituted pyrrolesa
R1
O
NH2
R2
Me
R1
O
O
R4
CeCl3.7H2O
+
+
R4
MeNO2, MW
(100ºC, 15 min)
R2
N
NO2
R3
3a-c
1a-d
2a-b
R3
4a-m
Entry no
b
-Nitrostyrene
1,3-Dicarbonyl
Amine
Product
Product no
Yield (%)b
O
Me
O
O
H
NO
1
4a
7529
NH2
Me
N
2a
1a
3a
Me
O
Me
O
O
H
Me
2
4b
80
NH2
NO
Me
N
2a
1b
3a
Cl
O
Cl
O
O
H
Me
Me
3
4c
59
NH2
NO
N
2a
1c
3a
O
Me
Me
O
O
H
Me
N
4
4d
77
NO
NH2
2a
1a
3b
Me
Me
O
Me
Me
Me
Me
O
O
H
5
4e
70
NH2
NO
N
2a
1b
3b
Me
Cl
O
Me
Me
Me
Cl
O
O
H
6
4f
55
NH2
NO
N
2a
1c
3b
Me

C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
9079
Table 2 (continued )
Entry no
b
-Nitrostyrene
1,3-Dicarbonyl
Amine
Product
Product no
Yield (%)b
O
Me
Me
MeO
O
O
H
NO
6029
N
7
4g
NH2
2a
1a
3c
OMe
O
Cl
Me
Me
MeO
Cl
O
O
H
8
4h
5829
NH2
NO
N
2a
1c
3c
OMe
O
Me
Br
O
O
H
Me
N
9
4i
61
NO
NH2
2a
1a
3c
Br
O
OEt
O
O
H
10
4j
64
NH2
OEt
NO
Me
N
2b
1a
3a
Me
O
Me
O
O
H
OEt
Me
11
4k
67
NH2
OEt
NO
N
2b
1b
3a
Cl
O
Cl
O
O
H
OEt
12
4l
46
NH2
OEt
NO
Me
N
2b
1c
3a
O
Me
Me
O
O
Me
NO
13
4m
4530
NH2
Me
N
2a
1d
3a
a
The reaction was performed under microwaves (100 W) in the presence of MeNO2 (1 mL), 1aec (1.0 mmol), 2a, b (1.0 mmol), 3aec (1.0 mmol), CeCl3$7H2O (0.30 mmol),
unless otherwise noted.
b
By column chromatography (Hexanes/EtOAc).
The use of a
b
-ketoester (2b) as the 1,3-dicarbonyl component
achieved, since only the products resulting from the cyclization of the
ketone carbonyl moiety were isolated (entries 10e12).
On the other hand, it was verified that cyclic 1,3-dicarbonyl
derivatives, such as dimedone, Meldrum’s acid and 1,3-cyclo-
furtherextended the scope of this method, demonstrating its tolerance
tothe introduction of various functional groups onpositions C-2 and C-
3. Despite observing slightly lower yields, good chemoselectivity was

9080
C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
hexanedione did not afford the expected reaction products, being
unsuitable as replacements of 2a, b. In addition, use of conventional
heating at 100 ꢀC afforded similar yields of the heterocyclic
products (4a, 73%; 4b, 75%; 4c, 56%), demonstrating that the
transformation can also be run under these conditions, albeit at the
expense of longer reaction times (2.5 h for 4a, b and 4 h for 4c).
The synthesis of 1,2,3,4,5-pentasubstituted pyrroles was also
attempted, employing (E)-(2-nitroprop-1-en-1-yl)benzene (1d).
included the use of aliphatic nitroolefin 1e31 and various primary
amines, such as methylamine (3d) benzylamine (3e), and -phe-
nethylamine (3f), with acetylacetone (2a) as the 1,3-dicarbonyl
b
component.
As shown in Table 3, when b-nitrostyrene 1a was subjected to
reaction with 2a and amines 3def, the yields of the resulting
cyclized products (4nep) were lower (23e31%) than those pre-
viously observed (entries 1e3).
Table 3
The microwaves-assisted and CeCl3-mediated MCR synthesis of polysubstituted pyrroles. Use of non-aromatic amines and nitroolefinsa
O
R1
Me
Me
O
O
CeCl3.7H2O
CHO
R1
NH2
R3
R1
or
+
+
NO2
MeNO2, MW
(100ºC, 15 min)
H
Me
Me
N
R3
4n-r
5a,b
1a,e
2a
3a,d-f
Entry no
b
-Nitrostyrene
Amine
Product
Yield (%)b
Entry no
Aldehyde
Amine
Product
Yield (%)b
O
NH2
H
NO
Me
1
40% MeNH2
3d (2.0 equiv)
2332
5
4p
23d,34c
CHO
Me
4n
N
Me
3f (1.2 equiv.)
5a (1.2 equiv.)
1a
O
Me
Me
H
NO
Me
O
3133
6
4q
No reaction
NH2
2
N
H
5b (1.2 equiv.)
1a
3a (1.2 equiv.)
4o
O
O
Me
Me
Me
Me
Me
H
NO
NH2
NH2
Me
O
H
N
N
3
25c,34c
7
46d
H
5b (1.2 equiv.)
3f (1.2 equiv.)
3f (1.2 equiv.)
1a
4p
4r
O
Me
Me
Me
NH2
Me
O
51d
8
4
48
4r
N
H
5b (1.5 equiv.)
3f (1.5 equiv.)
4q
a
The reaction was performed under microwaves (100 W) in the presence of MeNO2 (1 mL), to which the aldehyde or nitroolefin (1.0 mmol), 2a (1.0 mmol), amine 3a, def
(1.0 mmol), and CeCl3$7H2O (0.30 mmol) were added, unless otherwise noted.
b
By column chromatography (Hexanes/EtOAc).
Isolated yields of 4p were 23% when the mixture was irradiated for 30 min and 43% when 0.60 equiv CeCl3$7H2O were employed.
The reaction was performed under microwaves (100 W) for 30 min.
c
d
However, the
b
-nitrostyrene 1d was found to be less reactive than
Under the optimized conditions, compound 4n was obtained in
23% yield when 2.0 equiv of aqueous MeNH2 was employed and in
20% yield employing 5.0 equiv of the amine. In the case of 4p, which
was accessed in 25% yield, increasing the irradiation time to 30 min
had no effect on the reaction performance (23% yield), while
employing 0.60 mmol of the promoter afforded 43% of the het-
erocycle. These results compared favorably with conventional
conditions, which furnished only 13% of the expected pyrrole after
heating in an oil bath for 15 h.
its counterparts 1aec, and gave a comparatively lower product
yield (4m, 45%), probably as a result of steric hindrance.
Delightfully, it was also observed that heterocycle 4a could be
generated on a larger scale (5 mmol), under the optimized condi-
tions, without compromising the performance of the trans-
formation (79% isolated yield).
In order to further assess the scope and limitations of this MCR
transformation, other reactant combinations were tested. These

C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
9081
Table 4
Interestingly, comparison of the results consigned in entries 3 and
5 revealed that under an analogous load of promoter the isolated
yield of pyrrole 4p prepared from the preformed -nitrostyrene 1a
TCCA-mediated synthesis of 5-sulfenylpyrrolesa
O
O
b
R2
was similar to that observed when this olefinic component was
generated in situ from 1.2 equiv of benzaldehyde (5a).
Ph
R2
Ph
TCCA
4
3
2
+
ArS-SAr
Conditions
On the other side, when the nitroolefin 1e, derived from hexanal
(5b), was employed for the reaction with aniline as coupling part-
ner, 48% of pyrrole 4q was isolated (entry 4). Increasing the
amounts of the other reactants (2a and 3a) to 1.5 equiv did not
improve the performance of the MCR (45% yield of 4q), while
performing the irradiation for 30 min had a minor deleterious ef-
fect on the yield of product. Curiously, however, no reaction product
was observed even after irradiating for 60 min when aniline was
added as the amino coupling partner and the nitroolefin was pre-
pared in situ from hexanal (5b, entry 6).
ArS
Me
Me
5
N 1
Ph
7a-d
N
6a-c
Ph
4a
Entry Solvent TCCA (equiv) Ar
R2
Time (min) Prod. Yield (%)b
1
2
3
4
5
6
7
8
9
H2O
MeCN 1.2
THF 1.2
Acetone 1.2
EtOAc 1.2
EtOAc 0.5
EtOAc 1.2
EtOAc 1.2
EtOAc 1.2
1.2
Ph, 6a
6a
6a
6a
6a
6a
Me, 4a 60
7a
7a
7a
7a
7a
7a
7b
7c
7d
dc
45
57
82
94
dd
85
86
87
4a
4a
4a
4a
4a
4a
60
60
10
10
10
45
30
Contrastingly, using 5b as model aliphatic aldehyde in the
presence of 1.2 equiv of b-phenethylamine (3f) afforded 32% pyr-
p-ClPh, 6b
p-MeOPh, 6c 4a
6a
OEt, 4b 30
role 4r, which improved to 46% upon 30 min of irradiation time
(entry 7). Moreover, the yield of 4r increased to 51% when 1.5 equiv
of both, aliphatic aldehyde and amine, were employed (entry 8).
However, higher excesses of 5b and 3f (2.0 equiv each) gave no
further improvements (49% of 4r). These results confirmed that
nitroalkene 1e is being formed under the reaction conditions. They
also suggested that the different reaction outcomes should be, at
least in part, a result of the properties of the amino component of
the MCR.
Mechanisms for analogous transformations leading to pyrroles
and related heterocycles have been proposed.25c,26b,34 The re-
quirement of CeCl3$7H2O as a promoter is clear, since performing
the reaction without the salt, afforded only traces of 4a. Due to its
hardness, the CeIII cation is probably able to activate the carbonyl
functionalities of the 1,3-dicarbonyl reactant for a nucleophilic at-
a
The reaction was performed with a solution of the pyrrole 4a, b (1.0 mmol),
diaryl disulfides 6aec (0.60 mmol), and TCCA (1.2 equiv) in the given test solvent
(2 mL), at room temperature.
b
By column chromatography (Hexanes/EtOAc).
No reaction.
Only traces of 7a were detected.
c
d
also with ester 4b (entries 7e9), demonstrating its scope. The
progress of the reaction was monitored by GCeMS, which revealed
the quick formation of ArSCl and its subsequent consumption
during the reaction.
Therefore, it can be assumed that ArSCl is the actual active
electrophilic species responsible for the transformation. This find-
ing may also explain the stoichiometry of the reaction, because
1.0 mmol TCCA would be capable of forming 3.0 mmol of ArSCl.
Interestingly, arylsulfenyl moieties can act as protective groups of
the indole nucleus, being easily removed.41
tack, favoring the formation of initial imine and
bonyl intermediates.
b-enamino car-
The plausible role of CeIII in these key steps may also explain the
lack of product observed when p-nitroaniline was employed as the
amine component. This amine is a poor nucleophile and a weak
base (pKa¼1.02).35 Therefore, the initial nucleophilic attack to the
1,3-dicarbonyl compound is strongly disfavored.35a The results
observed when non-aromatic amines were employed as reaction
partners suggest that the outcome of the transformation is also
a result of the nucleophilic properties of the amino components of
the MCR.35e
3. Conclusion
In summary, we have developed an operationally simple,
modular, and atom-efficient MCR protocol for the chemoselective
synthesis 1,2,3,4-tetrasubstituted pyrroles, under microwave irra-
diation, which can be further extended to afford pentasubstituted
heterocycles.
This one-pot process, which exhibited wide generality, is me-
diated by CeCl3$7H2O and the substitution pattern on the different
positions of the pyrrole ring could be readily controlled through the
corresponding starting materials. The products are cleanly obtained
in good yields and after short reaction times, resulting in an ap-
pealing alternative for accessing highly functionalized pyrroles.
It was also demonstrated that the 1,2,3,4-tetrasubstituted het-
erocycles could be further efficiently converted into the corre-
sponding 5-arylsulfenyl pyrrole derivatives by treatment with
diaryl disulfides and TCCA in EtOAc at room temperature.
In view of the easy availability of the 1,2,3,4-tetrasubstituted
pyrroles and taking into account our recent experience36 on the
use of trichloroisocyanuric acid (TCCA) for the convenient prepa-
ration of 3-sulfenylindoles, the synthesis of their congener 5-
sulfanylpyrroles was explored, using TCCA as oxidant.
TCCA is a shelf-stable, inexpensive, and environmentally benign
solid, frequently found in commercial products for swimming-pool
disinfection,37 which has been widely used in organic synthesis.
Recent examples of its application include oxidation38 and halo-
genation39 reactions, as well as key steps during the total synthesis
of many complex structures.40
Following the previously described conditions,36 different al-
ternatives for the sulfenylation of pyrroles were tested (Table 4). It
was evidenced that the transformation did not proceed in water
(entry 1) and that the observed yields were moderate when it was
run in MeCN and THF (entries 2 and 3).
However, the efficiency of the transformation was higher in
acetone (entry 4), and EtOAc demonstrated to be the best reaction
solvent, furnishing 7a in 94% yield in a short reaction time (entry 5).
Interestingly, only traces of product were obtained when the
amount of TCCA was reduced from 1.2 equiv to 0.5 equiv (entry 6).
With the optimized conditions in hand (entry 5), the trans-
formation was also extended to examples with other disulfides and
4. Experimental section
4.1. General
The 1H (400 and 200 MHz) and 13C (100 and 50 MHz) NMR
spectra were recorded on Bruker DPX 400 and DPX 200 in-
struments, respectively, using CDCl3 as solvent. Chemical shifts (d)
are expressed in parts per million downfield from internal tetra-
methylsilane or CHCl3, and J values are given in Hertz. Elemental
analyses were carried out on a PerkineElmer 2400 instrument
(Central Analítica, IQeUSP, SP). Melting point (mp) determinations

9082
C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
were performed by using an MQAPF-301 instrument and are in-
formed uncorrected.
C19H16ClNO: C, 73.66; H, 5.21; N, 4.52. Found: C, 73.35; H, 5.17; N,
4.43.
The mass spectra were obtained in a Shimadzu GCeMS-QP2010
Plus gas chromatograph coupled to a mass detector. The molecular
ion and its fragments are described as the relations between their
atomic mass and corresponding charge (m/z), together with their
percent relative abundance (%). The gas chromatographies were
4.2.4. 1-(2-Methyl-4-phenyl-1-p-tolyl-1H-pyrrol-3-yl)ethanone
(4d). Yellow solid; mp 108e110 ꢀC. 1H NMR (200 MHz):
d
¼7.38e7.28 (m, 6H), 7.25e7.17 (m, 3H), 6.63 (s, 1H), 2.40 (s, 3H),
2.39 (s, 3H), and 2.07 (s, 3H). 13C NMR (50 MHz):
d
¼197.5, 138.0,
run on a 30.0 mꢁ0.25 mm RTX-5MS column (Thickness: 0.25
mm).
136.1, 136.0, 135.3, 129.8, 129.2, 128.2, 126.7, 126.0, 125.9, 122.3,
120.6, 31.0, 21.0, and 12.8. MS (EI): m/z (%)¼289 (Mþ, 56), 275 (21),
274 (100), 230 (11), 206 (10), 128 (14), 91 (17), 77 (7), and 65 (14).
Anal. Calcd (%) for C20H19NO: C, 83.01; H, 6.62; N, 4.84. Found: C,
82.95; H, 6.62; N, 4.82.
The running conditions were: time: 30 min; injector temperature:
280 ꢀC; initial column oven temperature: 30 ꢀC; linear gradient:
20 ꢀC/min up to 300 ꢀC. Helium (5.4 mL/min; linear velocity:
39.7 cm/s) was employed as carrier gas (Pressure: 68.2 KPa). The
high resolution mass spectrum was obtained with a Bruker
MicroTOF-Q II instrument (Bruker Daltonics, Billerica, MA). De-
tection of the ions was performed by electrospray ionization, in the
positive ion mode.
4.2.5. 1-(2-Methyl-1,4-di-p-tolyl-1H-pyrrol-3-yl)ethanone
(4e). Yellow solid; mp 94e96 ꢀC. 1H NMR (200 MHz):
d
¼7.27e7.13
(m, 8H), 6.59 (s, 1H), 2.39 (s, 3H), 2.37 (s, 3H), 2.35 (s, 3H), and 2.08
(s, 3H). 13C NMR (50 MHz):
Solvents were purified and dried before use, according to con-
ventional techniques.42 All reagents were used as obtained from
commercial sources. The reactions were performed in a CEM Dis-
cover microwave oven using a 10 mL Pyrex glass tube fitted with
a Teflon cap. All the reactions were monitored by thin layer chro-
matography (TLC) carried out on Whatman-AL SIL G/UV plates.
Column chromatography was carried out using silica gel 60
(Aldrich, 230e400 mesh).
d¼197.3, 137.8, 136.1, 136.0, 135.0, 132.8,
129.6, 129.0, 128.7, 125.9, 125.7, 122.2, 120.3, 30.8, 20.9, 20.8, and
12.6. MS (EI): m/z (%)¼303 (Mþ, 64), 289 (22), 288 (100), 253 (14),
244 (14), 208 (15), 207 (72), 133 (11), 128 (15), 115 (12), 96 (12), 91
(18), and 73 (25). Anal. Calcd (%) for C21H21NO: C, 83.13; H, 6.98; N,
4.62. Found: C, 83.18; H, 7.09; N, 4.61.
4.2.6. 1-(4-(4-Chlorophenyl)-2-methyl-1-p-tolyl-1H-pyrrol-3-yl)
ethanone (4f). White solid; mp 105e107 ꢀC. 1H NMR (200 MHz):
4.2. General procedure for the synthesis of polysubstituted
pyrroles 4
d
¼7.31e7.25 (m, 6H), 7.19e7.15 (m, 2H), 6.61 (s, 1H), 2.40e2.38 (m,
6H), and 2.09 (s, 3H). 13C NMR (50 MHz):
d
¼197.0, 138.1, 135.8,
135.6, 134.4,132.5, 130.3, 129.8, 128.2,125.8,124.7, 122.1, 120.7, 30.9,
20.9, and 12.7. MS (EI): m/z (%)¼323 (Mþ, 23), 310 (14), 308 (44),
281 (34), 253 (19), 209 (14), 208 (21), 207 (100), 191 (16), 133 (15),
96 (17), 91 (10), 77 (2), and 73 (35). Anal. Calcd (%) for C20H18ClNO:
C, 74.18; H, 5.60; N, 4.33. Found: C, 74.02; H, 5.77; N, 4.24.
The b-nitrostyrene (1.0 mmol) was added to a mixture of the
amine (1.0 mmol), acetylacetone (2a, 1.0 mmol) or ethyl acetoace-
tate (2b, 1.0 mmol) and CeCl3$7H2O (111 mg, 0.3 mmol) in MeNO2
(1 mL). The reaction mixture was stirred and heated at 100 ꢀC for
15 min in the microwave oven. The reaction progress was moni-
tored by GCeMS. After the specified reaction time, the reaction
mixture was extracted with EtOAc (3ꢁ10 mL). The organic phase
was washed with water and then brine, and dried over anhydrous
MgSO4. The solvent was removed under reduced pressure and the
residue was purified by silica gel flash chromatography (hexanes/
EtOAc, 95:5) to afford the pure products (4aer).
4.2.7. 1-(1-(4-Methoxyphenyl)-2-methyl-4-phenyl-1H-pyrrol-3-yl)
ethanone (4g). Yellow solid; mp 88e90 ꢀC (Lit.29 90e91 ꢀC). 1H
NMR (200 MHz):
d
¼7.37e7.27 (m, 5H), 7.21 (d, J¼8.8, 2H), 6.96 (d,
J¼8.8, 2H), 6.61 (s, 1H), 3.82 (s, 3H), 2.37 (s, 3H), and 2.07 (s, 3H). 13
C
NMR (50 MHz):
d¼197.3, 159.1, 135.9, 135.4, 131.3, 129.1, 128.1, 127.2,
126.6, 125.8, 122.0, 120.7, 114.2, 55.3, 30.9, and 12.6. MS (EI): m/z
(%)¼305 (Mþ, 70), 291 (21), 290 (100), 263 (8), 218 (8), 153 (5), 128
(8), and 77 (9).
4.2.1. 1-(2-Methyl-1,4-diphenyl-1H-pyrrol-3-yl)ethanone
(4a). White solid; mp 104e105 ꢀC (Lit.29 105e107 ꢀC). 1H NMR
(400 MHz):
d
¼7.50e7.27 (m,10H), 6.64 (s,1H), 2.40 (s, 3H), and 2.07
4.2.8. 1-(4-(4-Chlorophenyl)-1-(4-methoxyphenyl)-2-methyl-1H-
(s, 3H). 13C NMR (100 MHz):
d
¼197.4,138.5,135.8,135.1,129.2,129.1,
pyrrol-3-yl)ethanone (4h). Yellow solid; mp 116e118 ꢀC (Lit.29
128.9, 128.1, 127.9, 126.6, 126.0, 122.3, 120.4, 30.9, and 12.7. MS (EI):
m/z (%)¼275 (Mþ, 69), 261 (20), 260 (100), 230 (8), 217 (9), 138 (6),
128 (12), and 77 (20).
117e119 ꢀC). 1H NMR (200 MHz):
d
¼7.36e7.30 (m, 4H), 7.22 (d,
J¼8.9, 2H), 6.97 (d, J¼8.9, 2H), 6.61 (s, 1H), 3.84 (s, 3H), 2.36 (s, 3H),
and 2.09 (s, 3H). 13C NMR (50 MHz):
d
¼196.8, 159.1, 135.7, 134.4,
132.4, 131.1, 130.3, 128.2, 127.2, 124.5, 121.8, 120.8, 114.3, 55.3, 30.9,
and 12.6. MS (EI): m/z (%)¼339 (Mþ, 12), 324 (21), 281 (36), 253
(20), 209 (14), 208 (21), 207 (100), 191 (16), 133 (14), 96 (17), and 73
(35).
4.2.2. 1-(2-Methyl-1-phenyl-4-p-tolyl-1H-pyrrol-3-yl)ethanone
(4b). Yellow solid; mp 104e106 ꢀC. 1H NMR (400 MHz):
d
¼7.45e7.42 (m, 2H), 7.38e7.35 (m, 1H), 7.30e7.24 (m, 4H),
7.17e7.15 (m, 2H), 6.61 (s, 1H), 2.39 (s, 3H), 2.35 (s, 3H), and 2.07 (s,
3H). 13C NMR (100 MHz):
d
¼197.4, 138.5, 136.2, 134.9, 132.7, 129.1,
4.2.9. 1-(1-(4-Bromophenyl)-2-methyl-4-phenyl-1H-pyrrol-3-yl)
128.9, 128.8, 127.8, 126.0, 125.9, 122.3, 120.2, 30.8, 20.9, and 12.7.
MS (EI): m/z (%)¼274 (Mþ, 100), 230 (13), 207 (12) 145 (5), 137 (5),
128 (14), 115 (10), 104 (6), and 77 (26). Anal. Calcd (%) for
ethanone (4i). Yellow solid; mp 136e137 ꢀC. 1H NMR (200 MHz):
d
¼7.58 (d, J¼8.5, 2H), 7.36e7.34 (m, 5H), 7.18 (d, J¼8.5, 2H), 6.62 (s,
1H), 2.39 (s, 3H), and 2.06 (s, 3H). 13C NMR (50 MHz):
d
¼197.4,137.4,
C
20H19NO: C, 83.01; H, 6.62; N, 4.84. Found: C, 82.63; H, 6.57; N,
135.4,134.9,132.3,129.0,128.1,127.5,126.7,126.4,122.5,121.7,120.1,
30.8, and 12.7. MS (EI): m/z (%)¼355 (Mþ, 62), 340 (95), 338 (100),
258 (14), 230 (29), 202 (5), 137 (15), 128 (23), 115 (7), 77 (10), and 76
(13). Anal. Calcd (%) for C19H16BrNO: C, 64.42; H, 4.55; N, 3.95.
Found: C, 64.44; H, 4.63; N, 3.89.
4.81.
4.2.3. 1-(4-(4-Chlorophenyl)-2-methyl-1-phenyl-1H-pyrrol-3-yl)
ethanone (4c). Yellow solid; mp 99e101 ꢀC. 1H NMR (200 MHz):
d
¼7.52e7.40 (m, 3H), 7.36e7.28 (m, 6H), 6.64 (s, 1H), 2.39 (s, 3H),
and 2.09 (s, 3H). 13C NMR (50 MHz):
d
¼197.0, 138.4, 135.3, 134.3,
4.2.10. Ethyl 2-methyl-1,4-diphenyl-1H-pyrrole-3-carboxylate
132.6, 130.3, 129.2, 128.3, 128.1, 126.0, 124.8, 122.3, 120.6, 31.0, and
12.8. MS (EI): m/z (%)¼309 (Mþ, 62), 296 (34), 295 (20), 294 (100),
259 (10), 230 (16), 128 (10), and 77 (25). Anal. Calcd (%) for
(4j). Yellow oil. 1H NMR (200 MHz):
7.35e7.32 (m, 2H), 7.29e7.24 (m, 3H), 7.20e7.18 (m, 3H), 6.61 (s,
1H), 4.13 (q, J¼7.0, 2H), 2.41 (s, 3H), and 1.08 (t, J¼7.0, 3H). 13C NMR
d
¼7.41e7.39 (m, 2H),

C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
9083
(50 MHz):
d
¼165.2, 138.5, 136.0, 135.3, 129.0, 128.9, 128.9, 127.5,
14.0, 13.6. MS (EI): m/z (%)¼269 (Mþ, 62), 254 (26), 213 (100), 197
(40), 103 (19), and 77 (35). HRMS Found m/z 292.1672; C18H23NNaO
[(MþNa)þ] requires m/z 292.1672.
127.1, 126.4,125.8,120.4,111.5, 58.8, 13.6, and 12.1. MS (EI): m/z (%)¼
305 (Mþ, 100), 276 (42), 260 (37), 258 (31), 230 (26), 217 (10), 128
(13), and 77 (28). Anal. Calcd (%) for C20H19NO2: C, 78.66; H, 6.27; N,
4.59. Found: C, 78.41; H, 6.27; N, 4.27.
4.2.18. 1-(2-Methyl-4-pentyl-1-phenethyl-1H-pyrrol-3-yl)ethanone
(4r). Yellow oil. 1H NMR (400 MHz):
d
¼7.29e7.20 (m, 3H), 7.04 (d,
4.2.11. Ethyl 2-methyl-1-phenyl-4-p-tolyl-1H-pyrrole-3-carboxy late
J¼6.6, 2H), 6.22 (s, 1H), 3.97 (t, J¼7.2, 2H), 2.94 (t, J¼7.3, 2H), 2.62 (t,
J¼7.4, 2H), 2.39 (s, 3H), 2.30 (s, 3H),1.57e1.50 (m, 2H),1.35e1.32 (m,
(4k). Yellow oil. 1H NMR (200 MHz):
d
¼7.44e7.24 (m, 7H),
7.14e7.10 (m, 2H), 6.65 (s, 1H), 4.18 (q, J¼7.1, 2H), 2.43 (s, 3H), 2.34
4H), and 0.90 (t, J¼6.8, 3H). 13C NMR (100 MHz):
¼195.6, 137.8,
d
(s, 3H), and 1.15 (t, J¼7.1, 3H). 13C NMR (50 MHz):
d
¼165.6, 138.7,
135.1, 128.7, 128.6, 126.8, 124.8, 121.2, 118.4, 47.9, 37.5, 31.8, 30.9,
30.1, 27.5, 22.5, 14.0, and 12.0. MS (EI): m/z (%)¼297 (Mþ, 83), 254
(39), 241 (96), 150 (96), 105 (100), and 76 (28). HRMS Found m/z
320.1982; C20H27NNaO [(MþNa)þ] requires m/z 320.1985.
136.1, 135.5, 132.3, 129.1, 128.9, 128.1, 127.8, 126.4, 126.0, 120.4,111.5,
59.2, 20.9, 14.0, and 12.5. MS (EI): m/z (%)¼319 (Mþ, 100), 290 (36),
274 (29), 244 (16), 230 (15), 141 (4), 128 (9), and 77 (17). Anal.
Calcd (%) for C21H21NO2: C, 78.97; H, 6.63; N, 4.39. Found: C, 78.85;
H, 6.58; N, 4.27.
4.3. General procedure for the synthesis of 5-sulfenylpyrroles
7
4.2.12. Ethyl 4-(4-chlorophenyl)-2-methyl-1-phenyl-1H-pyrrole-3-
carboxylate (4l). White solid; mp 84e86 ꢀC. 1H NMR (200 MHz):
A solution of the diaryl disulfide (6, 0.6 mmol) in EtOAc (2 mL)
was treated with TCCA (0.4 mmol, 1.2 equiv) and the reaction was
stirred at room temperature until it became colorless. Then, the
1,2,3,4-tetrasubstituted pyrrole (4, 1.0 mmol) was added. The
mixture was further stirred at room temperature for the specified
time while being monitored by TLC and GCeMS. When all the
starting material had disappeared, the reaction was diluted with
EtOAc (3ꢁ10 mL) and brine (1 mL); the organic phase was sepa-
rated and successively washed with water (20 mL) and saturated
brine (20 mL), and dried over anhydrous MgSO4. The solvent was
removed under reduced pressure and the residue was purified by
silica gel flash chromatography (hexanes/EtOAc, 95:5) to afford
pure products (7aed).
d
¼7.49e7.36 (m, 3H), 7.33e7.26 (m, 6H), 6.68 (s, 1H), 4.19 (q, J¼7.1,
2H), 2.44 (s, 3H), and 1.16 (t, J¼7.1, 3H). 13C NMR (50 MHz):
¼165.5,
d
138.7, 136.8, 134.0, 132.0, 130.5, 129.3, 128.1, 127.6, 126.2, 125.3,
120.8,111.4, 59.5,14.1, and 12.6. MS (EI): m/z (%)¼339 (Mþ, 100), 310
(40), 294 (41), 267 (9), 258 (8), 229 (31), 128 (9), and 77 (30). Anal.
Calcd (%) for C20H18ClNO2: C, 70.69; H, 5.34; N, 4.12. Found: C,
70.64; H, 5.35; N, 4.05.
4.2.13. 1-(2,5-Dimethyl-1,4-diphenyl-1H-pyrrol-3-yl)ethanone
(4m). Reddish solid; mp 113e116 ꢀC (Lit.30 114e115 ꢀC). 1H NMR
(200 MHz):
d
¼7.56e7.44 (m, 3H), 7.42e7.23 (m, 7H), 2.29 (s, 3H),
1.95 (s, 3H), and 1.85 (s, 3H). 13C NMR (50 MHz):
d
¼197.4, 137.4,
136.7, 134.9, 130.4, 129.4, 128.5, 128.1, 128.1, 126.6, 126.5, 122.0,
121.7, 30.9, 13.0, and 11.1. MS (EI): m/z (%)¼289 (Mþ, 72), 274 (100),
230 (16), 144 (9), 128 (10), 102 (3), and 77 (30).
4.3.1. 1-(2-Methyl-1,4-diphenyl-5-(phenylthio)-1H-pyrrol-3-yl)etha-
none (7a). White solid; mp 145e147 ꢀC. 1H NMR (200 MHz):
d
¼7.24e7.14 (m, 8H), 6.97e6.89 (m, 5H), 6.66e6.61 (m, 2H), 2.22 (s,
4.2.14. 1-(1,2-Dimethyl-4-phenyl-1H-pyrrol-3-yl)ethanone
3), and 1.86 (s, 3H). 13C NMR (50 MHz):
d
¼197.2, 139.2, 138.0, 136.8,
(4n). Yellow oil.31 1H NMR (400 MHz):
d
¼7.32e7.30 (m, 2H),
7.29e7.26 (m, 2H), 7.21e7.20 (dd, J¼7.4 and 1.5, 1H), 6.43 (s, 1H),
3.51 (s, 3H), 2.45 (s, 3H), 1.99 (s, 3H). 13C NMR (100 MHz):
135.4, 134.2, 130.3, 129.3, 128.7, 128.5, 128.4, 128.1, 127.4, 126.6,
125.4, 123.0, 118.4, 31.0, and 13.7. MS (EI): m/z (%)¼383 (Mþ, 29),
382 (100), 340 (49), 289 (8), 258 (33),188 (3),152 (13), 128 (20), and
77 (45). Anal. Calcd (%) for C25H21NOS: C, 78.30; H, 5.52; N, 3.65.
Found: C, 78.11; H, 5.59; N, 3.74.
d
¼195.7,
139.2, 135.5, 129.2, 127.9, 126.4, 125.5, 122.4, 120.0, 31.9, 31.0, 30.0,
27.4, 22.6, 14.0, and 13.6. MS (EI): m/z (%)¼213 (Mþ, 73), 198 (100),
128 (18), 98 (12), and 77 (6). HRMS Found m/z 214.1223; C14H16NO
[(MþH)þ] requires m/z 214.1226.
4.3.2. 1-(5-((4-Chlorophenyl)thio)-2-methyl-1,4-diphenyl-1H-pyr-
rol-3-yl)ethanone (7b). White solid; mp 167e168 ꢀC. 1H NMR
4.2.15. 1-(1-Benzyl-2-methyl-4-phenyl-1H-pyrrol-3-yl)ethanone
(200 MHz):
d
¼7.37e7.26 (m, 8H), 7.07e7.03 (m, 4H), 6.66 (d, J¼8.4,
(4o). Brown solid, mp: 51e54 ꢀC (Lit.32 52e54 ꢀC). 1H NMR
2H), 2.33 (s, 3H), and 1.96 (s, 3H). 13C NMR (50 MHz):
d
¼197.1, 139.4,
(400 MHz):
2H), 6.52 (s, 1H), 5.03 (s, 2H), 2.42 (s, 3H), and 2.02 (s, 3H); 13C NMR
(100 MHz):
d¼7.35e7.30 (m, 6H), 7.28e7.23 (m, 2H), 7.07 (d, J¼7.3,
136.6, 136.6, 135.2, 134.4, 131.3, 130.2, 129.2, 128.9, 128.7, 128.3,
128.1, 127.7, 127.6, 123.1, 117.8, 31.0, and 13.7. MS (EI): m/z (%)¼417
(Mþ, 100), 401 (27), 376 (24), 374 (62), 289 (10), 261 (12), 258 (33),
152 (17), 128 (26), and 77 (41). Anal. Calcd (%) for C25H20ClNOS: C,
71.84; H, 4.82; N, 3.35. Found: C, 71.74; H, 4.97; N, 3.43.
d
¼197.4, 136.5, 136.3, 135.1, 129.3, 128.9, 128.1, 127.8,
126.6, 126.6, 125.9, 122.0, 120.0, 50.2, 31.0, and 11.5; MS (EI): m/z
(%)¼289 (Mþ, 58), 274 (61), 153 (2), 91 (100), and 77 (2).
4.2.16. 1-(2-Methyl-1-phenethyl-4-phenyl-1H-pyrrol-3-yl)ethanone
4.3.3. 1-(5-((4-Methoxyphenyl)thio)-2-methyl-1,4-diphenyl-1H-pyr-
(4p). White solid; mp: 86e88 ꢀC.34c 1H NMR (400 MHz):
rol-3-yl)ethanone (7c). White solid; mp 100e102 ꢀC. 1H NMR
d
¼7.35e7.23 (m, 8H), 7.09 (d, J¼6.6, 2H), 6.39 (s, 1H), 4.05 (t, J¼7.5,
(200 MHz):
d
¼7.44e7.31 (m, 8H), 7.04e7.00 (m, 2H), 6.65e6.54 (m,
2H), 3.00 (t, J¼7.2, 2H), 2.38 (s, 3H),1.99 (s, 3H). 13C NMR (100 MHz):
4H), 3.71 (s, 3H), 2.30 (s, 3H), and 1.96 (s, 3H). 13C NMR (50 MHz):
d¼197.4, 137.6, 136.4, 134.8, 129.4, 128.7 (2C), 128.1, 126.9, 126.6,
d¼197.2, 158.3, 138.7, 136.9, 135.7, 133.3, 130.6, 129.8, 129.4, 128.7,
125.8, 121.6, 119.4, 48.0, 37.5, 30.9, and 11.3; MS (EI): m/z (%)¼303
(Mþ,100), 288 (76),198 (58),105 (46), and 77 (19). HRMS Found m/z
304.1708; C21H22NO [(MþH)þ] requires m/z 304.1696.
128.6, 128.1, 127.9, 127.3, 122.9, 120.2, 114.2, 55.2, 30.9, and 13.6. MS
(EI): m/z (%)¼413 (Mþ, 100), 371 (82), 290 (18), 229 (10), 128 (16),
102 (5), and 77 (28). Anal. Calcd (%) for C26H23NO2S: C, 75.52; H,
5.61; N, 3.39. Found: C, 75.39; H, 5.75; N, 3.43.
4.2.17. 1-(2-Methyl-4-pentyl-1-phenyl-1H-pyrrol-3-yl)ethanone
(4q). Yellow oil. 1H NMR (400 MHz):
d
¼7.46e7.43 (m, 2H),
4.3.4. Ethyl 2-methyl-1,4-diphenyl-5-(phenylthio)-1H-pyrrole-3-car-
7.40e7.36 (m,1H), 7.26e7.23 (m, 2H), 6.48 (s,1H), 2.71 (t, J¼7.2, 2H),
2.47 (s, 3H) 2.37 (s, 3H), 1.62 (quintet, J¼7.2, 2H), 1.43e1.31 (m, 4H),
boxylate (7d). Yellow oil. 1H NMR (200 MHz):
d
¼7.35e7.26 (m, 8H),
7.09e6.98 (m, 5H), 6.79e6.75 (m, 2H), 4.10 (q, J¼7.1, 2H), 2.36 (s,
0.92e0.88 (t, J¼7.2, 3H). 13C NMR (100 MHz):
d
¼195.7, 139.2, 135.5,
3H), and 1.01 (t, J¼7.1, 3H). 13C NMR (50 MHz):
¼165.1, 139.9, 138.2,
d
129.2, 127.9, 126.4, 125.5, 122.4, 120.0, 31.9, 31.0, 30.0, 27.4, 22.6,
136.8, 135.0, 134.6, 130.1, 128.59, 128.6, 128.4, 128.4, 127.1, 126.6,

9084
C.C. Silveira et al. / Tetrahedron 69 (2013) 9076e9085
50, 3959; (j) Yavari, I.; Kowsari, E. Mol. Diversity 2009, 13, 519; (k) Lu, Y.;
Arndtsen, B. A. Angew. Chem., Int. Ed. 2008, 47, 5430; (l) St. Cyr, D. J.; Arndtsen,
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126.3, 125.2, 118.2, 112.6, 59.4, 13.8, and 13.3. MS (EI): m/z (%)¼413
(Mþ, 100), 384 (5), 340 (26), 287 (5), 230 (13), 128 (14), and 77 (31).
HRMS Found m/z 436.1323; C26H23NNaO2S [(MþNa)þ] requires m/z
436.1342.
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The authors gratefully thank FAPERGS, CAPES, MCT/CNPq for the
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