The fast and efficient KI/H2O2 mediated 2-sulfonylation of indoles and N-methylpyrrole in water

Article abstract of DOI:10.1039/c8ra09367a

The rapid and efficient KI/H₂O₂-mediated 2-sulfonylation of substituted indoles and N-methylpyrrole was established. The corresponding 2-sulfonylation products are synthesized from readily available sulfur sources, namely arylsulfonyl hydrazides, 4-methylbenzenesulfinic acid and sodium 4-methylbenzenesulfinate in good to excellent yields in only 5 min. Moreover, the aqueous solution of hydrogen peroxide is used as both oxidant and solvent. Mechanistic studies demonstrated that 2,3-diiodoindoline was the main sulfonylation intermediate.

Full text of DOI:10.1039/c8ra09367a

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The fast and efficient KI/H2O2 mediated 2-
sulfonylation of indoles and N-methylpyrrole in
water†
Cite this: RSC Adv., 2018, 8, 41651
*
*
and Bin Dai
Jun Zhang, Zhong Wang, Lingjuan Chen, Yan Liu, Ping Liu
The rapid and efficient KI/H2O2-mediated 2-sulfonylation of substituted indoles and N-methylpyrrole was
established. The corresponding 2-sulfonylation products are synthesized from readily available sulfur
sources, namely arylsulfonyl hydrazides, 4-methylbenzenesulfinic acid and sodium 4-
methylbenzenesulfinate in good to excellent yields in only 5 min. Moreover, the aqueous solution of
hydrogen peroxide is used as both oxidant and solvent. Mechanistic studies demonstrated that 2,3-
diiodoindoline was the main sulfonylation intermediate.
Received 13th November 2018
Accepted 7th December 2018
DOI: 10.1039/c8ra09367a
rsc.li/rsc-advances
times, the use of organic solvents and large amounts of acid,
non-green oxidant, and a relatively expensive iodine source.
Introduction
Therefore, a more environmentally benign protocol for the
synthesis of 2-sulfonylindoles is highly desirable. Herein, we
report a rapid and efficient KI-mediated 2-sulfonylation of
substituted indoles and N-methylpyrrole using 30% H2O2
solution as both oxidant and solvent. Importantly, this trans-
formation can be completed within 5 min and features a broad
substrate scope.
Indole is a widely used building block and is found in many
natural products, pharmaceuticals and ne chemicals.1 2-Sul-
fonylindoles are an important class of indole derivatives due to
the sulfonyl moiety which can enhance bioactivity2 and acts as
a useful vehicle for the development of new strategies for
synthesis.3 Generally, 2-sulfonylindoles are synthesized via the
oxidation of the corresponding arylthioindoles.4 In recent years,
a series of simple, efficient and direct 2-sulfonylations of
indoles with sodium sulnates have been reported for the
synthesis of 2-arylsulfonyl indoles. For example, Deng and co-
workers developed the I2-catalyzed 2-sulfonylation of indoles
using sodium sulnates, with TBHP as the oxidant and HOAc as
the solvent.5 Around the same time Kuhakarn and co-workers
Results and discussion
As our model reaction for the optimization study 1H-indole (1a,
0.5 mmol) and p-toluenesulfonyl hydrazide (TsNHNH2, 2a, 1.0
mmol) were used (Table 1). When the reaction was rst con-
ducted using 10% KI and 1 equiv. of H2O2 in HOAc at 60 ꢀC for
2 h, 2-tosyl-1H-indole 3a was obtained in only 15% yield (entry
1). With the addition of EtOH as the solvent product 3a was
isolated in 20% yield (entry 2). However, by increasing the KI
content to 20%, and with the slow addition of 30% H2O2 solu-
tion to the reaction, we found that the 2-sulfonylation of indole
can occur rapidly resulting in 53% yield of product 3a in only
5 min (entry 3). The main reason for the increase in yield may be
that a large amount of heat is released due to the addition of
hydrogen peroxide to the mixture of 1H-indole and TsNHNH2 in
absence of any other solvent, and the high temperature gener-
ated promotes the progress of the 2-sulfonylation. Moreover, by
increasing the amount of KI, the reaction yield rose signicantly
(entries 4 and 5). In the case of altering the substrate ratio of
compounds 1a and 2a, no signicant change in the reaction
yield was observed (entries 6 and 7). When 70% TBHP was used
as the oxidant product 3a was produced in 65% yield (entry 8). A
similar yield was observed when NH4I was employed as the
iodine source, furnishing product 3a in 69% yield (entry 9).
Since KI is substantially greener and has lower-cost, it was
proposed
a similar catalytic process in the absence of
oxidants.6 This provoked the development of numerous cata-
lytic systems, such as NH4I–TBHP in HOAc7 and KI-oxones
(2KHSO5–KHSO4–K2SO4) in H2O.8 Recently, Yu and co-workers
presented the electrochemical-sulfonylation of 1H-indoles
using sodium sulnates under chemical oxidant-free condi-
tions with TBAI as the catalyst.9 In addition, sulfonyl hydrazides
are environmentally friendly sulfur sources, and have been
extensively employed in organic reaction because they are
stable, readily accessible, odor-free.10 Barman and co-workers
reported the elegant sulfonylation of sulfonyl hydrazides and
indoles using TBHP/I2 as the catalyst and DCE as solvent.11
However, drawbacks still remain, such as prolonged reaction
School of Chemistry and Chemical Engineering, The Key Laboratory for Green
Processing of Chemical Engineering of Xinjiang Bingtuan, Shihezi University, Shihezi
City, 832004, China. E-mail: liuyan1979810@aliyun.com; liuping1979112@aliyun.
com; Fax: +86 0993 2057270; Tel: +86 0993 2057213
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra09367a
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Table 1 Optimization of the reaction conditionsa
Entry
Catalyst
Oxidation/solvent
Time (min)
Yieldb (%)
1c
2c
3
KI (10%)
KI (10%)
KI (20%)
KI (40%)
KI (60%)
KI (60%)
KI (60%)
KI (60%)
NH4I (60%)
KI (100%)
KI (120%)
KI (100%)
H2O2 (1 equiv.)/HOAc(1 mL)
H2O2 (2 equiv.)/EtOH(1 mL)
H2O2 (1 mL)/—
H2O2 (1 mL)/—
H2O2 (1 mL)/—
H2O2 (1 mL)/—
H2O2 (1 mL)/—
TBHP (1 mL)/—
H2O2 (1 mL)/—
120
120
5
5
5
5
5
5
5
15
20
53
58
71
60
48
65
69
81
83
63
4
5
6d
7e
8
9
10
11
12
H2O2 (1 mL)/—
H2O2 (1 mL)/—
H2O2 (1 mL)/EtOH(1 mL)
5
5
5
a
Reaction conditions: 1H-indole (1a, 0.5 mmol), TsNHNH2 (2a, 1 mmol). b Isolated yield. c 60 ꢀC. d 0.50 mmol of 2a was used. e 0.75 mmol of 1a was
used.
selected as the iodine source and H2O2 as the oxidant. Finally, extended to 2-naphthylsulfonyl hydrazide, producing product
by using excess KI, 1.0 and 1.2 equiv. of KI, the reaction yield 3w in 81% yield.
reached 81% and 83% of compound 3a, respectively (entries 10
In our scope studies, 4-methylbenzenesulnic acid and
and 11). Meanwhile, we also tried the reaction at room sodium 4-methylbenzenesulnate were also examined under
temperature using ethanol as a solvent, but only to give a yield the optimized conditions, as shown in Table 4. Weather
of 63% (entry 12). On the basis of the above experiments, the
optimized reaction conditions are as follows: 1H-indole (1a, 0.5
mmol), TsNHNH2 (2a, 1 mmol), KI (1.0 equiv.), H2O2 (1 mL), for
5 min under air.
Table 2 KI/H2O2-mediated 2-sulfonylation of substituted indoles and
TsNHNH2
a
With the optimized reaction conditions in hand, we next
investigated the scope of the reaction with a series of indoles,
which are summarized in Table 2. The electronic nature of the
substituents on the indole was found to have a considerable
effect on the reaction yield. Electron-donating substituents (1-
Me, 3-Me, 5-Me, 7-Me, 4-MeO, 5-MeO, and 7-MeO) gave better
reactivity and provided the corresponding 2-sulfonylated prod-
ucts 3a, 3b, and 3e–j in 78–89% yields. In addition, 4-(benzy-
loxy)-1H-indole furnished product 3k in 60% yield. Whereas, 6-
bromo- and 7-bromoindoles gave products 3l and 3m in 78%
and 52% yield, respectively. To our delight, 2-methyl-1H-indole
showed good reactivity and C-3 regioselectivity, providing
product 3n in 88% yield. Unfortunately, when 1-ethyl or 1-
benzyl-substituted indole was used as the reactant, the desired
product 3c or 3d was obtained in a low yield.
Encouraged by the above results, we further explored our
sulfonylation method using a variety of arylsulfonyl hydrazides
with 1H-indole 1a under optimum conditions (Table 3). The
reaction of benzenesulfonyl hydrazide with 1H-indole gave
product 3o in only 55% yield. A similar result was obtained for
the substituted benzenesulfonyl hydrazide bearing electron-
withdrawing groups 4-F, 4-Br, 4-CF3. However, 4-Cl or 4-NO2
substituted substrates were converted into 2-sulfonylated
products 3q and 3t in good yields. Electron-donating substrates
4-tBu, and 4-OMe gave 2-sulfonylated products 3u and 3v in 76%
and 51% yield, respectively. Furthermore, the method was also
a
Reaction conditions: 1 (0.5 mmol), 2a (1.0 mmol), KI (1 equiv.), H2O2 (1
mL), reaction time 5 min. The yields of isolated products are given.
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Table 3 KI/H2O2-mediated 2-sulfonylation of 1H-indole and arylsul- Table 5 KI/H2O2-mediated 2-sulfonylation of N-methylpyrrolea
fonyl hydrazidesa
a
Reaction conditions: 1a (0.5 mmol), 2 (1.0 mmol), KI (1 equiv.), H2O2 (1
mL), reaction time 5 min. The yields of isolated products are given.
electron-donating or withdrawing groups were employed the
reactions performed well, giving the desired products in high
yields. In this case, the electronic nature of the substituent had
a
Reaction conditions: N-methylpyrrole (0.5 mmol), 2 (1.0 mmol), KI (1
equiv.) in H2O2 (1 mL), reaction time 5 min. The yields of isolated
products are given. b 4-Methylbenzenesulnic acid as sulfur source.
no signicant inuence on the reactivity. Compared with the
reported methods,5–9 operational simplicity, short reaction time
and good yield are the key advantages of this protocol.
methylbenzenesulnic acid was used as the sulfur source, the
reaction yield (5b) signicantly improved. In addition, 1H-
pyrrole as a substrate reacted with p-toluenesulfonyl hydrazide
to afford the desired product 5b0 in only 18% yield.
To the best of our knowledge, the 2-sulfonylation of N-
methylpyrrole has rarely been reported, with unstable sulfur
sources and complex reaction conditions oen required.12,13
Gratifyingly, various arylsulfonyl hydrazides showed good
results with N-methylpyrrole, giving the desired products 5a–i in
42–57% yields (Table 5). We also found that when 4-
A series of experiments were conducted to uncover the
reaction mechanism. In order to conrm that the reaction was
radical, a radical scavenger, 1.2 equiv. of hydroquinone, was
added into the reaction mixture. Dichloroethane was also
added to aid in solubility of the scavenger. We found that the
reaction did not proceed; hence, the reaction was radical
(Scheme 1a). In the absence of 1H-indole, p-toluenesulfonyl
hydrazide underwent a self-coupling reaction to form S-p-tolyl
4-methylbenzenesulfonothioate (Scheme 1b). However, when
S-p-tolyl 4-methylbenzenesulfonothioate was used as the
sulfur source, the 2-sulfonylation reaction did not proceed.
Table 4 2-Sulfonylation of 4-methylbenzenesulfinic acid or sodium
4-methylbenzenesulfinate as sulfur sourcesa
This
result
indicates
that
S-p-tolyl
4-methyl-
benzenesulfonothioate is not an intermediate of the reaction.
Subsequently, we tested other sulfur sources, such as sodium
4-methylbenzenesulnate and thiophenol, giving the 2-sulfo-
nylated product under standard conditions in 88% and 11%
yield, respectively (Scheme 1c). 1H-Indole underwent iodin-
ation to form 3-iodo-1H-indole in the absence of p-toluene-
sulfonyl hydrazide in 62% yield, and 3-iodo-1H-indole reacted
with p-toluenesulfonyl hydrazide to give 3a in 71% yield under
standard conditions (Scheme 1d). In addition, we found an
important experimental fact that benzenesulfonyl hydrazide
reacted with 1H-indole to afford C2- and C3-sulfonylation
1
a
products, which were detected by H NMR in a ratio of 10 : 3
Reaction conditions: 1a (0.5 mmol), 4-methylbenzenesulnic acid or
sodium 4-methylbenzenesulnate (1.0 mmol), KI (1 equiv.), H2O2 (1
mL), reaction time 5 min (0.5 mL HOAc was added, when sodium 4-
methylbenzenesulnate is used as sulfur source). The yields of
isolated products are given.
(80% conversion, Scheme 1e).
According to the above results, as well as support from
previous reports,5–9,11
a
plausible radical mechanism is
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Conclusions
In summary, we have developed a simple KI-mediated 2-sulfo-
nylation of substituted indoles and N-methylpyrrole using 30%
H2O2 solution as the oxidant and the solvent in presence of
various sulfur sources. This method provides a fast and efficient
approach to produce diversied 2-sulfonylation products in
good to excellent yields within 5 min. This protocol has great
advantages including short reaction time, green oxidant and
solvent, cheap iodine source, avoiding the use of acid, and
broad substrate scope. Notably, 2,3-diiodoindoline maybe the
main sulfonylation intermediates in this transformation.
Studies to further investigate this catalytic system to other
related reactions are currently underway in our laboratory.
Experimental
Materials and instruments
Chemicals were obtained commercially and used as received.
All products were isolated by short chromatography on a silica
ꢀ
gel (200–300 mesh) column using petroleum ether (60–90 C)
and ethyl acetate. 1H NMR and 13C NMR spectra were recorded
on a Bruker Avance III HD 400 MHz spectrometer in CDCl3
solution. All chemical shis were reported in ppm (d) relative to
the internal standard TMS (0 ppm). ESI-mass spectrum was
measured on an Agilent 6210 ESI/TOF MS.
Scheme 1 Control experiments.
General procedure for a KI/H2O2 mediated 2-sulfonylation of
indoles and N-methylpyrrole in water
A mixture of substituted indole or N-methylpyrrole (0.5 mmol),
sulfur source (1.0 mmol, arylsulfonyl hydrazides or 4-methyl-
benzenesulnic acid or sodium 4-methylbenzenesulnate +
0.5 mL HOAc) and KI (0.5 mmol) was stirred at room temper-
ature under air. Subsequently, 30% H2O2 solution (1 mL) was
slowly added to the above system (note: a large amount of heat
is generated during this process) and the reaction stirred for an
additional 5 min. The solution was quenched the saturated
solution of sodium thiosulfate (5 mL) and extracted with EtOAc
(3 ꢁ 10 mL). The combined EtOAc extracts were dried over
anhydrous MgSO4, ltered and concentrated under reduced
pressure. The crude residue was puried by ash column
chromatography on silica gel using PE/EtOAc as the eluent.
Scheme 2 Proposed mechanism.
proposed (Scheme 2). KI is rst oxidized by H2O2 to form
molecular iodine, which reacts quickly with p-toluenesulfonyl
hydrazide to produce the active sulfonyl radical. Meanwhile, the
addition of molecular iodine to indole occurs and generates
a key intermediate I (2,3-diiodoindoline). Subsequently, inter-
mediate I reacts with the sulfonyl radical to produce interme-
diate II, II0, and iodine radical. Then, HI elimination takes place
to provide 2- or 3-sulfonylindole. Meanwhile, the molecular
iodine can be re-generated via the coupling of two iodine radi-
cals or the oxidation of HI by H2O2. This mechanism provides
a reasonable explanation for the generation of C2- and/or C3-
sulfonylation products (Scheme 1e), and even product 3n
(Table 2).
The characterization data of products
4-Methoxy-2-tosyl-1H-indole (3h). White solid, 123 mg, 82%
yield, mp 155–158 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.90 (s, 1H),
7.87 (d, J ¼ 8.4 Hz, 2H), 7.28 (d, J ¼ 7.1 Hz, 3H), 7.23 (d, J ¼
8.0 Hz, 1H), 6.99 (d, J ¼ 8.4 Hz, 1H), 6.52 (d, J ¼ 7.8 Hz, 1H), 3.92
(s, 3H), 2.38 (s, 3H); 13C NMR (101 MHz, CDCl3) d 154.65, 144.52,
130.06, 127.45, 127.20, 106.80, 105.11, 100.55, 55.52, 21.72;
HRMS(ESI): m/z calcd for C16H15NO3S (M)+: 301.0767, found:
301.0763.
7-Methoxy-2-tosyl-1H-indole (3j). White solid, 123 mg, 82%
yield, mp 149–151 ꢀC; 1H NMR (400 MHz, CDCl3) d 9.00 (s, 1H),
7.86 (d, J ¼ 8.3 Hz, 2H), 7.28 (s, 2H), 7.23 (d, J ¼ 8.2 Hz, 1H),
7.16–7.03 (m, 3H), 6.73 (d, J ¼ 7.7 Hz, 1H), 3.95 (s, 3H), 2.38 (s,
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3H); 13C NMR (101 MHz, CDCl3) d 146.65, 144.52, 138.77, 124.63, 121.92, 119.92, 108.94, 35.87; HRMS(ESI): m/z calcd for
134.40, 130.04, 127.47, 122.15, 114.85, 109.09, 104.80, 55.60,
21.71; HRMS(ESI): m/z calcd for C16H15NO3S (M)+: 301.0767,
found: 301.0769.
C
12H11F3NO2S (M + H)+: 290.0457, found: 290.0457.
2-((3-Bromophenyl)sulfonyl)-1-methyl-1H-pyrrole (5h). Pale
yellow solid, 79 mg, 53% yield, mp 55–58 ꢀC; 1H NMR (400 MHz,
4-(Benzyloxy)-2-tosyl-1H-indole (3k). White solid, 113 mg, CDCl3) d 8.01 (t, J ¼ 1.8 Hz, 1H), 7.81 (d, J ¼ 7.9 Hz, 1H), 7.68 (d, J
60% yield, mp 136–139 ꢀC; 1H NMR (400 MHz, CDCl3) d 8.97 (s, ¼ 8.0 Hz, 1H), 7.38 (t, J ¼ 7.9 Hz, 1H), 7.05 (dd, J ¼ 4.1, 1.9 Hz,
1H), 7.87 (d, J ¼ 8.3 Hz, 2H), 7.47 (d, J ¼ 7.2 Hz, 2H), 7.37 (dt, J ¼ 1H), 6.80 (t, J ¼ 2.2 Hz, 1H), 6.20 (dd, J ¼ 4.1, 2.6 Hz, 1H), 3.72 (s,
24.0, 7.0 Hz, 4H), 7.28 (s, 1H), 7.22 (t, J ¼ 8.1 Hz, 1H), 6.58 (d, J ¼ 3H); 13C NMR (101 MHz, CDCl3) d 144.26, 136.02, 130.86,
7.8 Hz, 1H), 5.18 (s, 2H), 2.38 (s, 3H); 13C NMR (101 MHz, CDCl3) 130.36, 130.09, 127.11, 125.78, 123.25, 119.62, 108.77, 35.85;
d 153.74, 138.79, 138.54, 136.92, 133.16, 130.07, 128.72, 128.15, HRMS(ESI): m/z calcd for C11H10BrNO2S (M)+: 298.9688, found:
127.44, 107.00, 105.38, 101.85, 70.11, 21.72; HRMS(ESI): m/z 298.9690.
calcd for C22H19NO3S (M)+: 377.1080, found: 377.1075.
1-Methyl-2-(naphthalen-2-ylsulfonyl)-1H-pyrrole (5i). Pale
6-Bromo-2-tosyl-1H-indole (3l). Brown solid, 136 mg, 78% yellow solid, 60 mg, 45% yield, mp 60–63 ꢀC; 1H NMR (400 MHz,
yield, mp 181–182 ꢀC; 1H NMR (400 MHz, CDCl3) d 9.25 (s, 1H), CDCl3) d 8.50 (s, 1H), 7.93 (td, J ¼ 17.0, 16.6, 7.8 Hz, 3H), 7.80
7.88 (d, J ¼ 8.3 Hz, 2H), 7.61–7.48 (m, 2H), 7.33–7.27 (m, 3H), (dd, J ¼ 8.7, 1.9 Hz, 1H), 7.66–7.57 (m, 2H), 7.10 (dd, J ¼ 4.0,
2.39 (s, 3H); 13C NMR (101 MHz, CDCl3) d 144.99, 138.28, 1.9 Hz, 1H), 6.75 (t, J ¼ 2.2 Hz, 1H), 6.19 (dd, J ¼ 4.0, 2.6 Hz, 1H),
137.75, 135.32, 130.24, 127.50, 126.01, 125.30, 123.96, 119.78, 3.72 (s, 3H); 13C NMR (101 MHz, CDCl3) d 139.13, 135.02,
115.35, 108.91, 21.77; HRMS(ESI): m/z calcd for C15H12
-
132.30, 129.85, 129.73, 129.47, 129.15, 128.33, 128.06, 127.72,
BrNNaO2S (M + Na)+: 371.9664, found: 371.9653.
122.71, 119.14, 108.54, 35.81; HRMS(ESI): m/z calcd for
7-Bromo-2-tosyl-1H-indole (3m). Dark red solid, 91 mg, 52%
yield, mp 155–158 ꢀC. 1H NMR (400 MHz, CDCl3) d 8.86 (s, 1H),
7.91 (d, J ¼ 8.3 Hz, 2H), 7.60 (d, J ¼ 8.1 Hz, 1H), 7.51–7.47 (m,
1H), 7.33 (d, J ¼ 8.1 Hz, 2H), 7.22 (d, J ¼ 2.2 Hz, 1H), 7.06 (t, J ¼
C
15H14NO2S (M + H)+: 272.0740, found: 272.0745.
Conflicts of interest
7.8 Hz, 1H), 2.41 (s, 3H). 13C NMR (101 MHz, CDCl3) d 144.87, There are no conicts to declare.
138.14, 135.77, 135.57, 130.10, 128.20, 128.02, 127.51, 122.67,
121.87, 109.60, 105.32, 21.64; HRMS(ESI): m/z calcd for C15
-
Acknowledgements
H12BrNNaO2S (M + Na)+: 371.9664, found: 371.9661.
2-Methyl-3-tosyl-1H-indole (3n). White solid, 125 mg, 88% We gratefully acknowledge nancial support of this work by the
yield; mp 179–181 ꢀC. 1H NMR (400 MHz, CDCl3) d 9.26 (s, 1H), National Natural Science Foundation of China (No. 21563025),
7.97 (d, J ¼ 8.5 Hz, 1H), 7.83 (d, J ¼ 8.3 Hz, 2H), 7.24–7.10 (m, and the Program for Changjiang Scholars and Innovative
5H), 2.64 (s, 3H), 2.32 (s, 3H). 13C NMR (101 MHz, CDCl3) Research Team in University (No. IRT_15R46), and Yangtze
d 143.38, 141.52, 141.19, 134.54, 129.75, 126.15, 125.40, 123.10, River scholar research project of Shihezi University (No.
122.17, 119.28, 111.42, 111.27, 21.57, 13.04. HRMS(ESI): m/z CJXZ201601).
calcd for C16H16NO2S (M + H)+: 286.0896, found: 286.0900.
2-((4-Nitrophenyl)sulfonyl)-1H-indole (3t). Light yellow solid,
Notes and references
102 mg, 68% yield, mp 129–132 ꢀC; 1H NMR (400 MHz, CDCl3)
d 8.90 (s, 1H), 8.36–8.34 (m, 1H), 8.33 (d, J ¼ 2.1 Hz, 1H), 8.20–
8.15 (m, 2H), 7.69 (d, J ¼ 8.1 Hz, 1H), 7.46–7.42 (m, 1H), 7.41–
7.37 (m, 1H), 7.29 (dd, J ¼ 2.1, 0.8 Hz, 1H), 7.22 (ddd, J ¼ 8.0, 6.8,
1.1 Hz, 1H); 13C NMR (101 MHz, CDCl3) d 150.40, 147.18, 137.49,
132.20, 129.24, 128.58, 127.15, 126.92, 124.61, 124.46, 122.97,
122.12, 112.35, 110.85. HRMS(ESI): m/z calcd for C14H10N2-
NaO4S (M + Na)+: 325.0253, found: 325.0251.
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2-((4-(tert-Butyl)phenyl)sulfonyl)-1-methyl-1H-pyrrole (5c).
Pale yellow solid, 58 mg, 42% yield, mp 59–61 ꢀC; 1H NMR (400
MHz, CDCl3) d 7.80 (d, J ¼ 8.7 Hz, 2H), 7.50 (d, J ¼ 8.7 Hz, 2H),
7.02 (dd, J ¼ 4.0, 1.9 Hz, 1H), 6.75 (t, J ¼ 2.2 Hz, 1H), 6.16 (dd, J ¼
4.0, 2.6 Hz, 1H), 3.72 (s, 3H), 1.32 (s, 9H); 13C NMR (101 MHz,
CDCl3) d 156.84, 139.25, 129.56, 128.43, 127.16, 126.33, 118.64,
108.33, 35.79, 35.30, 31.18; HRMS(ESI): m/z calcd for
C
15H20NO2S (M + H)+: 278.1209, found: 278.1208.
1-Methyl-2-((4-(triuoromethyl)phenyl)sulfonyl)-1H-pyrrole
(5g). Pale yellow solid, 62 mg, 43% yield, mp 66–68 ꢀC; 1H NMR
(400 MHz, CDCl3) d 8.01 (d, J ¼ 8.2 Hz, 2H), 7.77 (d, J ¼ 8.3 Hz,
2H), 7.09 (dd, J ¼ 4.1, 1.9 Hz, 1H), 6.81 (t, J ¼ 2.2 Hz, 1H), 6.21
(dd, J ¼ 4.1, 2.6 Hz, 1H), 3.73 (s, 3H); 13C NMR (101 MHz, CDCl3)
d 145.96, 134.76, 134.43, 130.61, 127.77, 126.85, 126.53, 126.50,
2 (a) N. S. Simpkins, in Sulfones in Organic Synthesis, ed. J. E.
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B. M. Trost, Comprehensive Organic Chemistry, Pergamon
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