2-Bromo-N-(p-toluenesulfonyl)pyrrole: A Robust Derivative of 2-Bromopyrrole

Article abstract of DOI:10.1055/s-2003-42036

2-Bromo-AL(p-toluenesulfonyl)pyrrole (2), a crystalline stable derivative of 2-bromopyrrole (1) has been prepared in 80% yield by bromination of pyrrole, followed by conversion to the N-(p-toluenesulfonyl) derivative. This compound is stable indefinitely at ambient temperature. Compound 2 is an excellent substrate for Suzuki coupling with arylboronic acids.

Full text of DOI:10.1055/s-2003-42036

LETTER
1993
2-Bromo-N-(p-toluenesulfonyl)pyrrole: A Robust Derivative of
2-Bromopyrrole
2
-Bromo-
N
-(
p
-t
e
oluenesulf
o
a
nyl)pyrrole:
A
R
W
r
.
omopyrroleKnight, John W. Huffman,* Matthew L. Isherwood
H. L. Hunter Laboratory, Clemson University, Clemson, SC 29634-0973, USA
Fax +1(864)6566613; E-mail: huffman@clemson.edu
Received 7 March 2003
parallel synthesis, because they require that each starting
2-arylpyrrole must be prepared individually.
Abstract: 2-Bromo-N-(p-toluenesulfonyl)pyrrole (2), a crystalline
stable derivative of 2-bromopyrrole (1) has been prepared in 80%
yield by bromination of pyrrole, followed by conversion to the N-
(p-toluenesulfonyl) derivative. This compound is stable indefinitely
at ambient temperature. Compound 2 is an excellent substrate for
Suzuki coupling with arylboronic acids.
Previous workers have employed Suzuki chemistry to
prepare 2-arylpyrroles, employing either N-BOC-pyrrole-
2-boronic acid14 or N-BOC protected 2-bromopyrrole.15
Although N-BOC-pyrrole-2-boronic acid is reported to be
be readily available by the procedure of Martina et al.,16 in
which initial lithiation followed by quenching with trime-
thyl borate, and hydrolysis provides the boronic acid, this
approach did not appear appealing due to reported insta-
bility of N-BOC-pyrrole-2-boronic acid.17 Also, the re-
ported yields for the Suzuki reactions of this boronic acid
are variable (16–98%) and in the case of several simple
aryl halides with electron releasing or weakly electron
withdrawing groups the yields are at the lower end of this
range.14 N-Phenylsulfonyl-pyrrole-2-boronic acid has
also been employed in Suzuki couplings, however the re-
ported yield for the preparation of the boronic acid is less
than 10%.17
Key words: 2-arylpyrroles, radical reactions, Suzuki coupling,
palladium catalysis, p-toluenesulfonyl protecting group
Several years ago our group described the synthesis and
pharmacology of a series of N-alkyl-3-(1-naphthoyl)pyr-
roles which are ligands for the cannabinoid central
nervous system (CB1) receptor.1 Relative to similarly sub-
stituted cannabimimetic indoles, these compounds show
at best modest affinity for the CB1 receptor and have cor-
responding diminished potency in vivo.1,2 Both these in-
doles and pyrroles were designed on the basis of a
hypothesis that the 3-acyl group which is present in these
compounds is involved in a hydrogen bonding interaction
with the receptor.1,2 However, subsequent experiments
have provided convincing evidence that the 3-acyl group
is not essential for binding to the CB1 receptor and suggest
that cannabimimetic indoles and indenes interact with the
receptor primarily by aromatic stacking.3 This hypothesis
suggested that N-alkyl-2-aryl-4-(1-naphthoyl)pyrroles
should have greater receptor affinity than the N-alkyl-3-
(1-naphthoyl)pyrroles reported previously due to the
presence of an additional aromatic ring.
An alternative route employing N-BOC protected 2-bro-
mopyrrole is reported to give excellent yields (90–99%) in
Suzuki couplings with four simple arylboronic acids.15
However, N-BOC-2-bromopyrrole as previously de-
scribed by Cava, et al.18 is a quite sensitive compound
which is best stored as a 20–25% solution in hexane at –
10 °C, under which conditions it is stable for several
months. In order to obtain a more robust derivative of 2-
bromopyrrole, an N-p-toluenesulfonyl group was investi-
gated as an alternative to N-BOC, since the toluenesulfo-
nyl group should prove to be considerably less sensitive to
subsequent conversions.19
The synthesis of the target N-alkyl-2-aryl-4-(1-naph-
thoyl)pyrroles requires a convenient source of 2-arylpyr-
roles. Substituted pyrroles are frequently tedious to
prepare, and many of the syntheses are plagued by low
yields and difficult purification of the final product. Most
of the reported methods center around either ring expan-
sion of a suitably substituted precursor4–6 or addition to
conjugated systems followed by ring closure.7–9 Arylke-
toximes have been alkylated then cyclized to a 2-arylpyr-
role under basic conditions.10–12 Cycloaddition of 2,3-
butadienoates and dimethyl acetylenedicarboxylate with
imines can also be used to form substituted pyrrolidines
that can be oxidized to the pyrrole using DDQ or TBAF.13
However, these linear methods are ill-suited to a rapid
Two groups have previously reported the preparation of 2-
bromo-N-arylsulfonylpyrroles.20,21 Groenendaal et al. em-
ployed the stannylation of 2-lithio-N-benzenesulfonylpyr-
role using trimethyltin chloride.20 This procedure is not
attractive for the preparation of gram quantities of 2-bro-
mo-N-p-toluenesulfonylpyrrole due to the toxicity and
cost of trimethyltin chloride. In an initial approach to the
preparation of N-tosyl-2-bromopyrrolehe the direct bro-
mination of pyrrole with NBS, followed by in situ protec-
tion of nitrogen was attempted. This procedure gave
complex mixtures of products of variable composition
and although the desired product could be detected spec-
troscopically, pure material could not be isolated. Subse-
quently, Koike et al. reported the preparation of N-tosyl-
2-bromopyrrole by a route similar to that which we had
explored.21 Repetition of the experimental procedure re-
SYNLETT 2003, No. 13, pp 1993–1996
1
6
.1
0
.2
0
0
3
Advanced online publication: 08.10.2003
DOI: 10.1055/s-2003-42036; Art ID: S02203ST
© Georg Thieme Verlag Stuttgart · New York

1994
L. W. Knight et al.
LETTER
ported by these workers gave a complex mixture. Chro- gives moderate to good yields of the corresponding N-to-
matography of this mixture gave a major fraction, analysis syl-2-arylpyrrole, except with 3-nitrophenylboronic acid,
of which by GC/MS indicated that it contained an approx- which provides only a 24% yield (entry 7). All Suzuki
imately eqimolar mixture of N-tosyl-2-bromopyrrole and products have 1H and 13C NMR spectra, which are consis-
a dibrominated compound, plus several other compounds. tent with the assigned structures, and all gave satisfactory
analytical data. In order to determine the feasability of
removing the N-p-toluenesulfonyl group, the base hydrol-
ysis of N-tosyl-2-(4-methoxyphenyl)pyrrole was carried
out to provide the 2-arylpyrrole (4, Ar = 4-methoxy-
phenyl) in excellent yield.26
(ii, iii)
(i)
Br
Br
N
H
N
H
N
Ts
Scheme 1 Reagents: (i) 1,3-Dibromo-5,5-dimethylhydantoin, THF,
–78 °C, AIBN or ambient light; (ii) n-Bu3N, Et2O; (iii) TsCl, NaH.
(i)
(ii)
Br
Ar
Ar
N
N
N
H
Ts
Ts
N-Tosyl-2-bromopyrrole was finally prepared reproduc-
ibly by a modification of Cava’s procedure in which pyr-
role was treated with 1,3-dibromo-5,5-dimethylhydantoin
in the presence of AIBN at –78 °C to effect regioselective
bromination at the 2-position (Scheme 1).18 Treatment of
the cold mixture with ether and Bu3N precipitated the re-
sidual hydantoin and its reduction products. Subsequent Entry
addition of p-toluenesulfonyl chloride and sodium hy-
dride initially gave a low yield of 2. GC-MS analysis of
the crude mixture showed the presence of a significant
quantity of unprotected 2-bromopyrrole (1). This unpro-
tected compound turns black within minutes upon con-
centration from solution. Increasing the equivalents of p-
toluenesulfonyl chloride from 1.1 to 2.0 and the equiva-
lents of sodium hydride from 1.5 to 3.0 gives 2 in a repro-
ducible yield of 80% as a gray crystalline solid of
sufficient purity for use in subsequent reactions. This ma-
terial is stable to light and air for several months at ambi-
ent temperature. Recrystallization from isopropyl alcohol
provides the pure material as white crystals, mp 105–
106 °C. The 1H and 13C NMR spectra of 2 are consistent
with the assigned structure (see Experimental) and the
structure was confirmed by X-ray crystallography.22,23
Scheme 2 Reagents: (i) ArB(OH)2, Pd(PPh3)4, Na2CO3, toluene,
EtOH, H2O, reflux; (ii) NaOH, EtOH, reflux.
Table 1 Suzuki Reactions of N-p-Toluenesulfonyl-2-bromopyr-
rolea
3
Yieldb
68
1
Ar = 4-MeC6H4
Ar = 3-ClC6H4
Ar = 4-ClC6H4
Ar = 4-MeOC6H4
Ar = 1-Naphthyl
Ar = Phenyl
2
3
4
5
6
7
76
60
80
52
75
Ar = 3-NO2C6H4
24
a For the general experimental procedure and characterization data see
ref.25,
b Isolated yield.
In summary, N-tosyl-2-bromopyrrole provides a robust
derivative of 2-bromopyrrole, which promises to be a ver-
satile precursor for substituted pyrroles. This compound is
an excellent substrate for Suzuki reactions, and should
also prove useful in other metal-mediated coupling reac-
tions.
A study of the bromination step was carried out in order
to determine if the reaction proceeds via a free radical or
ionic mechanism. Removal of the AIBN catalyst had no
effect on the overall yield of 2, however, exclusion of light
resulted in a mixture of 2 and N-tosylpyrrole. One minute
of irradiation by shortwave (254 nm) UV light followed
by exclusion of all light for the duration of the bromina-
tion step resulted in moderate yields of 2. These results in-
Acknowledgment
dicate that the reaction is best catalyzed by the continual This work was supported by grants DA03590, K05-DA15340
(JWH) and F31-DA15579 (LWK) all from the National Institute on
Drug Abuse.
exposure to ambient light, and is thus probably radical-
mediated. The addition of Bu3N minimizes the extent of
dibromination and the amount of unbrominated N-p-tolu-
enesulfonylpyrrole. Also, polymeric materials are ob-
tained if the reaction temperature is allowed to increase
above –50 °C.
References
(1) Lainton, J. A. H.; Huffman, J. W.; Martin, B. R.; Compton,
D. R. Tetrahedron Lett. 1995, 36, 1401.
N-Tosyl-2-bromopyrrole (2) was employed in Suzuki
coupling reactions (Scheme 2) and is an excellent sub-
strate for this reaction. Table 1 provides examples of
Suzuki coupling products (3) synthesized utilizing this
synthon under standard Suzuki conditions using commer-
cially available arylboronic acids.24,25 This procedure
(2) (a) Huffman, J. W.; Dai, D.; Martin, B. R.; Compton, D. R.
Bioorg. Med. Chem. Lett. 1994, 4, 563. (b) Wiley, J. L.;
Compton, D. R.; Dai, D.; Lainton, J. A. H.; Phillips, M.;
Huffman, J. W.; Martin, B. R. J. Pharmacol. Exp. Ther.
1998, 278, 995. (c) Huffman, J. W. Curr. Med. Chem. 1999,
6, 705.
Synlett 2003, No. 13, 1993–1996 © Thieme Stuttgart · New York

LETTER
2-Bromo-N-(p-toluenesulfonyl)pyrrole: A Robust Derivative of 2-Bromopyrrole
1995
(3) (a) Reggio, P. H.; Basu-Dutt, S.; Barnett-Norris, J.; Castro,
M. T.; Hurst, D. P.; Seltzman, J. J.; Roche, M. J.; Gilliam, A.
F.; Thomas, B. F.; Stevenson, L. A.; Pertwee, R. G.; Abood,
M. E. J. Med. Chem. 1998, 41, 5177. (b) Huffman, J. W.;
Mabon, R.; Wu, M.-J.; Lu, J.; Hart, R.; Hurst, D. P.; Reggio,
P. H.; Wiley, J. L.; Martin, B. R. Bioorg. Med. Chem. 2003,
11, 539.
(4) Apsimon, J. W.; Durham, D. G.; Rees, A. H. J. Chem. Soc.,
Perkin Trans. 1 1978, 1588.
(5) Thompson, T. W. J. Chem. Soc., Chem. Commun. 1968, 532.
(6) Sukawa, H.; Seshimoto, O.; Tezuka, T.; Mukai, T. J. Chem.
Soc., Chem. Commun. 1974, 696.
layer was dried (MgSO4) and concentrated in vacuo to give
a light brown solid. Recrystallization from isopropyl alcohol
gave 10.73 g (80%) of 2-bromo-1-(p-toluenesulfonyl)pyr-
role as a white crystalline solid: mp 105–106 °C. 1H NMR
(300 MHz, CDCl3): d = 2.43 (s, 3 H), 6.23–6.29 (m, 2 H),
7.32 (d, J = 8.3 Hz, 2 H), 7.46 (dd, J = 2.0, 3.5 Hz, 1 H), 7.81
(d, J = 8.4 Hz, 2 H). 13C NMR (75.5 MHz, CDCl3): d =
145.5, 135.1, 129.9, 127.8, 124.2, 117.9, 113.5, 112.5,
100.0, 21.7. MS (EI): m/z (%) = 301 (27), 299 (28), 155 (56),
91 (100). Anal. Calcd for C11H10BrNO2S: C, 44.02; H, 3.36;
N, 4.67. Found: C, 44.65; H, 3.36; N, 4.67. Although this
compound is homogeneous to TLC, GC/MS, 1H and 13
NMR, aceptable analytical data could not be obtained.
C
(7) Boukou-Poba, J. P.; Farnier, M.; Guilard, R. Tetrahedron
Lett. 1979, 19, 1717.
(24) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981,
11, 513.
(8) Katritzky, A. R.; Li, J.; Gordeev, M. F. Synthesis 1994, 93.
(9) Severin, T.; Poehlmann, H. Chem. Ber. 1977, 110, 491.
(10) Ellames, G. J.; Hewkin, C. T.; Jackson, R. F. W.; Smith, D.
I.; Standen, S. P. Tetrahedron Lett. 1989, 26, 3471.
(11) Dhanak, D.; Reese, C. B.; Romana, S.; Zappia, G. J. Chem.
Soc., Chem. Commun. 1986, 903.
(12) Korostova, S. E.; Mikhaleva, A. I.; Sobenina, L. N.;
Shevchenko, S. G.; Polovnikova, R. I. J. Org. Chem. USSR
1986, 436.
(13) Xu, Z.; Lu, X. J. Org. Chem. 1999, 63, 5031.
(14) Johnson, C. N.; Stemp, G.; Anand, N.; Stephen, S. C.;
Gallagher, T. Synlett 1998, 1025.
(15) Thoresen, L. H.; Kim, H.; Welch, M. B.; Burghart, A.;
Burgess, K. Synlett 1998, 1276.
(16) Martina, S.; Enkelmann, V.; Wegner, G.; Schluter, A.-D.
Synthesis 1991, 613.
(17) Grieb, J. G.; Ketcha, D. M. Synth. Commun. 1995, 25, 2145.
(18) Chen, W.; Stephenson, E. K.; Cava, M. P.; Jackson, Y. A.
Org. Synth. 1991, 70, 151.
(19) Rokach, J.; Hamel, P.; Kakushima, M.; Smith, G. M.
Tetrahedron Lett. 1981, 22, 4901.
(20) Groenendaal, L.; Van Loo, J. A. J. M.; Meijer, E. W. Synth.
Commun. 1995, 25, 1589.
(25) Experimental Procedure for the Preparation of 4
(Ar = 4-Methoxyphenyl). A mixture of 0.020 g (0.02
mmol) of Pd(PPh3)4 and 4.4 mL of distilled toluene was
stirred under an inert atmosphere for 5 min at ambient
temperature, and 0.470 g (1.6 mmol) of 2-bromo-N-p-
toluenesulfonylpyrrole was added as a solid, followed by
0.256 g (2.4 mmol) of Na2CO3 in 2.2 ml of H2O. To this
mixture was added 0.250 g (1.6 mmol) of 4-methoxy-
phenylboronic acid in 3 mL of 95% EtOH. The mixture was
heated at reflux for 6 h, cooled to ambient temperature, and
extracted into EtOAc. The combined organic extracts were
washed with brine, dried (MgSO4), and concentrated in
vacuo to give a brown solid. Recrystallization from 2-
propanol gave 0.412 g (80%) of 2-(4-methoxyphenyl)-N-
tosylpyrrole as a white crystalline solid: mp 120–121 °C. 1H
NMR (300 MHz, CDCl3): d = 2.34 (s, 3 H), 3.84 (s, 3 H),
6.10 (dd, J = 1.8, 3.0 Hz, 1 H), 6.28 (t, J = 3.4 Hz, 1 H),
6.81–6.86 (m, 2 H), 7.09–7.17 (m, 4 H), 7.25–7.26 (m, 2 H),
7.41 (dd, J = 1.8, 3.1 Hz, 1 H). 13C NMR (75.5 MHz,
CDCl3): d = 21.5, 55.2, 111.9, 112.7, 115.3, 123.7, 127.1,
129.3, 132.2. MS (EI): m/z (%) = 327 (17), 172 (100). Anal.
Calcd for C18H17NO3S: C, 66.03; H, 5.23; N, 4.28. Found: C,
66.27; H, 5.31; N, 4.31.
(21) (a) Koike, T.; Shinohara, Y.; Nishimura, T.; Hagiwara, M.;
Tobinaga, S.; Takeuchi, N. Heterocycles 2000, 53, 1351.
(b) Although the 1H NMR data reported by these authors
agree with ours, these authors report a mp of 122–123 °C,
while in several preparations of 2, we find a mp of 105–
106 °C (see ref.23).
Compound 3 (Ar = Phenyl): mp 123–124 °C. 1H NMR
(300 MHz, CDCl3): d = 2.35 (s, 3 H), 6.15 (dd, J = 1.7, 3.2
Hz, 1 H), 6.30 (t, J = 3.3 Hz, 1 H), 7.09 (d, J = 8.3 Hz, 2 H),
7.21–7.38 (m, 7 H), 7.44 (dd, J = 1.7, 3.3 Hz, 1 H). 13C NMR
(75.5 MHz, CDCl3): d = 21.6, 112.0, 115.7, 124.1, 127.1,
127.3, 128.2, 129.3, 130.9, 131.4, 135.6, 136.0, 144.6. MS
(EI): m/z (%) = 297 (38), 142 (100). Anal. Calcd for
C17H15NO2S: C, 68.66; H, 5.08, N, 4.71. Found: C, 68.39; H,
5.03, N, 4.56.
(22) Knight, L. W.; Padgett, C. W.; Huffman, J. W.; Pennington,
W. T. Acta Crystallogr., Sect. E 2003, 59, 762.
(23) Experimental Procedure for the Preparation of 2. To a
solution of 3.1 mL of 1 (44.7 mmol) in 120 mL of freshly
distilled THF in a flame-dried flask under N2 at –78 °C was
added 6.53 g (22.4 mmol) of 1,3-dibromo-5,5-dimethyl-
hydantoin. The mixture was stirred for 30 min and allowed
to stand for an additional 3.5 h under ambient room light at
–78 °C. To this solution were added 4 mL of Bu3N and 180
mL of freshly distilled Et2O and the mixture was stirred for
10 min at –78 °C. The resulting gray precipitate was
removed by filtration(vacuum) and the solution was
concentrated in vacuo to remove the Et2O. To this solution
was added 17.04 g (89.4 mmol) of p-toluenesulfonyl
chloride and the inert atmosphere was reestablished. The
solution was cooled to 0 °C and 5.36 g (134.0 mmol) of NaH
(60% in mineral oil) was added cautiously. The mixture was
stirred for 18 h at ambient temperature and 60 mL of H2O
were added. The mixture was extracted with Et2O and the
ether extracts were washed with successive portions of 1 M
HCl and sat. aq NaHCO3. This mixture was combined with
an equal volume of 2 M NaOH and was stirred for 2 h at r.t.
The layers were separated and the organic extract was
washed repeatedly with H2O and 2 M NaOH. The organic
Compound 3 (Ar = 4-Methylphenyl): mp 120–121 °C. 1H
NMR (300 MHz, CDCl3): d = 2.34 (s, 3 H), 2.39 (s, 3 H),
6.11 (dd, J = 1.7, 3.2 Hz, 1 H), 6.28 (t, J = 3.3 Hz, 1 H),
7.06–7.12 (m, 6 H), 7.24–7.16 (m, 2 H), 7.41 (dd, J = 1.8,
3.3 Hz, 1 H). 13C NMR (75.5 MHz, CDCl3): d = 21.3, 21.5,
112.0, 115.5, 123.9, 127.0, 128.0, 128.5, 129.3, 130.7,
135.7, 136.1, 138.0, 144.5. MS (EI): m/z (%) = 311 (40), 156
(100). Anal. Calcd for C18H17NO2S: C, 69.43; H, 5.50, N,
4.50. Found: C, 69.69; H, 5.51, N, 4.42.
Compound 3 (Ar = 3-Chlorophenyl): mp 91–92 °C. 1H
NMR (300 MHz, CDCl3): d = 2.37 (s, 3 H), 6.16–6.17 (m, 1
H), 6.30 (t, J = 3.2 Hz, 1 H), 7.04–7.34 (m, 8 H), 7.45–7.46
(m, 1 H). 13C NMR (75.5 MHz, CDCl3): d = 21.5, 111.9,
116.1, 124.4, 127.0, 128.2, 128.7, 129.2, 129.4, 130.6,
133.1, 134.1, 135.4, 145.0. MS (EI): m/z (%) = 331 (37), 176
(100). Anal. Calcd for C17H14ClNO2S: C, 61.53; H, 4.25; N,
4.22. Found: C, 61.25; H, 4.34; N, 4.25.
Compound 3 (Ar = 1-Naphthyl): mp 146–147 °C. 1H
NMR (300 MHz, CDCl3): d = 2.18 (s, 3 H), 6.26 (dd, J = 1.7,
2.2 Hz, 1 H), 6.41 (t, J = 3.3 Hz, 1 H), 6.79 (d, J = 8, 2 Hz, 2
Synlett 2003, No. 13, 1993–1996 © Thieme Stuttgart · New York

1996
L. W. Knight et al.
LETTER
H), 7.03 (d, J = 8.3 Hz, 2 H), 7.09–7.26 (m, 2 H), 7.33–7.44
(m, 3 H), 7.59 (dd, J = 1.7, 3.3 Hz, 1 H), 7.77 (d, J = 8.2 Hz,
1 H), 7.86 (d, J = 8.2 Hz, 1 H). 13C NMR (75.5 MHz,
CDCl3): d = 21.3, 111.0, 116.5, 122.8, 124.4, 125.3, 125.8,
127.2, 127.6, 128.6, 129.0, 129.1, 130.5, 131.9, 132.9,
133.7, 135.0, 144.4. MS (EI): m/z (%) = 347(34), 192(100);
Anal. Calcd for C21H17NO2S: C, 72.60; H, 4.93; N, 4.03.
Found: C, 72.36; H, 4.96; N, 3.99.
(26) A mixture of 0.050 g (0.15 mmol) of 2-(4-methoxyphenyl)-
N-tosylpyrrole in 0.6 mL of EtOH and 0.2 mL of 15%
ethanolic NaOH was stirred at reflux temperature for 3 h.
The solution was concentrated in vacuo; the residue was
dissolved in CH2Cl2 and washed with H2O. The organic
layer was dried (MgSO4) and concentrated in vacuo to give
0.025 g (97%) of 2-(4-methoxyphenyl)pyrrole as a white
solid: mp 143–144 °C (lit. mp 147 °C27). 1H NMR (300
MHz, CDCl3): d = 3.81 (s, 3 H), 6.27 (dd, J = 2.8, 5.7 Hz, 1
H), 6.40 (t, J = 3.5 Hz, 1 H), 6.79 (dd, J = 2.4, 3.9 Hz, 1 H),
Compound 3 (Ar = 3-Nitrophenyl): pale pink gum. 1H
NMR (300 MHz, CDCl3): d = 2.36 (s, 3 H), 6.27 (dd, J = 1.7,
3.1 Hz, 1 H), 6.36 (t, J = 3.3 Hz, 1 H), 7.14 (d, J = 8.3 Hz, 2
H), 7.25 (d, J = 8.4 Hz, 2 H), 7.49 (dd, J = 1.6, 3.9 Hz, 1 H),
7.53 (d, J = 7.9 Hz, 1 H), 7.68 (dt, J = 1.3, 7.7 Hz, 1 H), 7.94
(t, J = 1.9 Hz, 1 H), 8.18–8.22 (m, 1 H). 13C NMR (75.5
MHz, CDCl3): d = 21.5, 112.4, 117.1, 122.9, 125.0, 125.1,
126.8, 128.3, 129.6, 133.0, 135.3, 136.9, 145.3, 147.3. MS
(EI): m/z (%) = 342 (100), 203 (26). HRMS calcd for
C17H14N2O4S: 342.0674. Found: 342.0670.
6.88–6.91 (m, 2 H), 7.36–7.39 (m, 2 H), 8.32 (br s, 1 H). 13
C
NMR (75.5 MHz, CDCl3): d = 55.3, 104.8, 109.9, 114.3,
118.1, 125.2, 125.9, 132.1, 158.2. MS (EI): m/z (%) = 245
(7), 173 (70), 158 (100). The spectroscopic data agree with
those reported previously.27
(27) Laatsch, H.; Pudleiner, H. Liebigs Ann. Chem. 1989, 863.
Synlett 2003, No. 13, 1993–1996 © Thieme Stuttgart · New York