Synthesis of N, N′-bis(2-thiazolinyl)-, N, N′-bis(2-thiazolyl)- , and N, N′-bis (2-pyrimidinyl)-benzene dicarboxamides

Article abstract of DOI:10.1081/SCC-200028517

New heteroaromatic benzene dicarboxamides have been synthesized in moderate to good yields by the reactions of 2-aminothiazoline, 2-aminothiazole, and 2-aminopyrimidine with phthaloyl dichloride, isophthaloyl dichloride, and terephthaloyl dichloride in the presence of an organic base. The amides are sparingly soluble in common organic solvents but dissolve readily in dimethyl sulfoxide. Reactions of 2-aminothiazoline and 2-aminopyrimidine with phthaloyl dichloride yield a tricyclic compound and an imide, respectively, instead of the expected products.

Full text of DOI:10.1081/SCC-200028517

w
SYNTHETIC COMMUNICATIONS
Vol. 34, No. 17, pp. 3061–3072, 2004
0
Synthesis of N, N -bis(2-Thiazolinyl)-,
0
0
N, N -bis(2-Thiazolyl)-, and N, N -bis
2-Pyrimidinyl)-Benzene Dicarboxamides
(
*
Sudershan R. Gondi and David Y. Son
Department of Chemistry, Southern Methodist University,
Dallas, Texas, USA
ABSTRACT
New heteroaromatic benzene dicarboxamides have been synthesized
in moderate to good yields by the reactions of 2-aminothiazoline,
2-aminothiazole, and 2-aminopyrimidine with phthaloyl dichloride, iso-
phthaloyl dichloride, and terephthaloyl dichloride in the presence of an
organic base. The amides are sparingly soluble in common organic
solvents but dissolve readily in dimethyl sulfoxide. Reactions of
2-aminothiazoline and 2-aminopyrimidine with phthaloyl dichloride
yield a tricyclic compound and an imide, respectively, instead of the
expected products.
Key Words: Amide; Heterocycle; Pyrimidine; Thiazole; Thiazoldine.
*
Correspondence: David Y. Son, Department of Chemistry, Southern Methodist Uni-
versity, P.O. Box 750314, Dallas, TX 75275-0314, USA; E-mail: dson@mail.smu.edu.
3
061
DOI: 10.1081/SCC-200028517
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3
062
Gondi and Son
INTRODUCTION
Heteroaromatic benzene dicarboxamides have been used extensively for
[
1–9]
the self-assembly of supramolecular structures.
amides have received the most attention due to the well-known coordination
In particular, pyridyl
[
10–12]
chemistry of pyridine and its derivatives.
Unlike the pyridyl derivatives,
benzene dicarboxamides of thiazoline, thiazole, and pyrimidine are unknown.
These heteroaromatic amides would contain an extra nitrogen atom in the ring
or sulfur, which can also serve as a donor atom. In this report, we describe the
synthesis and characterization of these new materials.
RESULTS AND DISCUSSION
We prepared the benzene dicarboxamides by the reactions of 2-amino-
thiazoline, 2-aminothiazole, and 2-aminopyrimidine with phthaloyl dichloride,
isophthaloyl dichloride, and terephthaloyl dichloride in the presence of an orga-
nic base (Sch. 1). All products were obtained as high melting, white to tan solids
that were stable to both air and moisture. All new compounds were characteri-
1
13
zed fully using H and C nuclear magnetic resonance (NMR) spectroscopy
and elemental analysis.
For the thiazoline amides, it was necessary for us to use the 2-amino-
thiazoline hydrochloride salt, since 2-aminothiazoline was not commercially
Scheme 1.

Synthesis of Heteroaromatic Benzene Dicarboxamides
3063
available. Attempts at deprotonating the salt and isolating the free amine were
not successful, primarily due to the high solubility of the amine in water. As a
result, we performed an in situ deprotonation of the salt with triethylamine in
the presence of the aromatic dichlorides. The results of these reactions are
listed in Table 1 (entries 1–4). Reactions with phthaloyl and isophthaloyl
dichloride were straightforward and gave the expected products 1p and 1m
in high yields, respectively. Reaction with phthaloyl dichloride, however,
gave a complex mixture of products. Treatment of this mixture with a hot
5
0/50 EtOAc/MeOH solution followed by filtration resulted in the crystal-
lization of the monoester 1o-ester (Sch. 2). By switching the base used in
this synthesis from triethylamine to pyridine, we obtained an unexpected tri-
cyclic product (1o), the formation of which we believe to proceed as shown in
Sch. 2. The structure of 1o was confirmed by spectroscopic analysis, elemental
analysis, and x-ray single crystal diffraction.
Reactions of 2-aminothiazole with terephthaloyl, isophthaloyl, and phtha-
loyl dichloride proceeded smoothly to give the corresponding benzene dicar-
boxamides 2p, 2m, and 2o in good yields (Table 1, entries 5–7). As with the
Table 1. Products from the reactions of heteroaromatic amines with aromatic acyl
dichlorides.
Yield
(%)
Mp
(8C)
Entry
Product
Solubility
1
2
3
1p
1m
88
64
35
306
227
227
dil aq HCl, DMSO (sl)
dil aq HCl, DMSO
a
1o
EtOAc, DCM, CHCl
HCl, pyridine, MeOH, EtOH,
iPrOH, CH CN, DMSO
3
, ether, dil aq
3
4
1o-ester
34
165
dil aq HCl, DMSO; sparingly soluble
in MeOH, EtOH, iPrOH, AcCN
dil aq HCl, DMSO
5
6
7
8
9
2p
2m
73
64
71
344
311
212
184
271
253
dil aq HCl, DMSO
dil aq HCl, DMSO
2o
b
2o-ester
3p
3m
5
dil aq HCl, DMSO, hot MeOH
dil aq HCl, DMSO, MeOH
36
53
1
0
dil aq HCl, DCM, CHCl
MeOH
3
, DMSO,
c
3o
1
1
65
220
dil aq HCl, DCM, CHCl
MeOH
3
, DMSO,
a
Tricyclic compound.
b
Yield from crude 2o.
Imide compound.
c

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064
Gondi and Son
Scheme 2.
thiazolinyl amides, the crude products were suspended in hot EtOAc/MeOH
and filtered to separate soluble impurities. The monoesterification of 2o
occurred to a small extent under these conditions to give 2o-ester (Sch. 3).
0
We next turned our attention to the N,N -bis(2-pyrimidinyl)benzene dicar-
boxamides. A review of the literature revealed that 3p had already been
prepared from the reaction of 2-aminopyrimidine with terephthaloyl dichlor-
[13]
ide in the presence of 1-methyl-2-pyrrolidone (NMP) and lithium chloride.
On repeating this procedure, we did not obtain the desired product but only the
singly substituted monoacid after aqueous workup (Sch. 4). Utilizing our
standard procedure with pyridine as the base, we obtained 3p in 36%
yield (Table 1, entry 9). Reaction of 2-aminopyrimidine with isophthaloyl
dichloride under similar conditions gave 3m in 53% yield after purification
(Table 1, entry 10). Unlike the corresponding thiazolinyl and thiazoyl
amides, compounds 3p and 3m were soluble in organic solvents other
than dimethyl sulfoxide (DMSO) and dilute aqueous HCl. The reaction of
Scheme 3.

Synthesis of Heteroaromatic Benzene Dicarboxamides
3065
Scheme 4.
2-aminopyrimidine with phthaloyl dichloride did not give the expected struc-
ture for 3o but rather the imide resulting from intramolecular cyclization of the
monosubstituted product (Sch. 5). Using triethylamine as the organic base in
this reaction gave the same product.
In conclusion, we have synthesized a variety of nitrogen-containing
heteroaromatic benzene dicarboxamides via straightforward procedures. The
products were obtained in moderate to good yields as stable solids. Attempted
syntheses of the 1,2-thiazolinyl and pyrimidinyl amides were not successful
Scheme 5.

3
066
Gondi and Son
and instead gave products resulting from intramolecular cyclization. On the
basis of solubility properties, pyrimidine derivatives 3p and 3m appear to
be the most ideal candidates for metal complexation studies.
EXPERIMENTAL SECTION
All reactions were carried out under a nitrogen atmosphere unless other-
wise noted. All reagents were obtained from either Aldrich (Milwaukee, WI,
USA) or Acros (Morris Plains, NJ, USA) and used without further purification.
1
13
29
H, C, and Si NMR spectra were recorded using a 400-MHz Bruker
AVANCE DRX multinuclear NMR spectrometer. All chemical shifts are
reported in parts per million. Melting points were collected on a TA Instru-
ments DSC 2010 Differential Scanning Calorimeter using a heating rate of
108C/min and nitrogen as a purge gas. Infrared spectra were obtained on a
Nicolet Magna-IR 560 spectrometer E.S.P. Elemental analyses were obtained
using a CE Elantech Flash 1112 CHN elemental analyzer.
Synthesis of 1p
2
-Aminothiazoline hydrochloride salt (3.41 g, 0.024 mol) was suspended
in 70 mL of chloroform. The flask was cooled in a water/ice bath, and triethyl-
amine (18 mL, 0.12 mol) was added. After an additional 1 hour of stirring,
terephthaloyl dichloride (2.5 g, 0.012 mol) was added portion-wise to the
suspension via spatula. The reaction mixture was stirred overnight at room
temperature to give a pale yellow suspension. The reaction mixture was
then poured into a beaker containing saturated aqueous sodium bicarbonate
solution and stirred for 30 min. Effervescence was observed. The suspension
was filtered and the solid was washed with saturated aqueous sodium bicar-
bonate solution (250 mL) and water (250 mL) and air-dried for 24 hours
to give crude 1p (3.8 g). A small amount of crude 1p (2 g) was added to
1
sion was filtered hot and dried under vacuum to give 1.9 g of pure 1p (88%).
00 mL of 50/50 EtOAc/MeOH and heated at reflux for 15 min. The suspen-
1
mp 3068C. H-NMR (DMSO-d ): 8.10 (s, 4H), 3.65–3.61 (t, 2H, J ¼ 7.4 Hz),
6
3.27–3.24 (t, 2H, J ¼ 7.7 Hz). Elemental Analysis: Calcd: C, 50.28; H, 4.22;
N, 16.75. Found: C, 50.20; H, 4.23; N, 16.61.
Synthesis of 1m
Compound 1m was prepared in the same manner as 1p from 2-aminothia-
zoline hydrochloride (3.41 g, 0.024 mol), triethylamine (18 mL, 0.12 mol), and

Synthesis of Heteroaromatic Benzene Dicarboxamides
3067
isophthaloyl dichloride (2.5 g, 0.012 mol). After workup, compound 1m was
1
obtained in 64% yield. mp 2278C. H-NMR (DMSO-d ): 9.54 (s, 2H, NH),
6
8
.82 (s, 1H), 8.20–8.18 (dd, 2H, J ¼ 1.6 and 7.7 Hz), 7.54–7.51 (t, 1H,
J ¼ 7.7 Hz), 3.65–3.61 (t, 2H, J ¼ 7.7 Hz), 3.27–3.23 (t, 2H, J ¼ 7.9 Hz).
13
C-NMR (DMSO-d ): 175.9, 174.7, 137.5, 132.7, 130.4, 129.0, 44.8, 30.1.
6
Elemental Analysis: Calcd: C, 50.28; H, 4.22; N, 16.75. Found: C, 50.26;
H, 4.20; N, 16.45.
Synthesis of 1o
2
-Aminothiazoline hydrochloride (3.41 g, 0.024 mol) was suspended in
chloroform (60 mL). The mixture was cooled in a water/ice bath and pyridine
15 mL, 0.12 mol) was added. After stirring in the cold bath for 1 hour, a sus-
(
pension was still present. Phthaloyl dichloride (2.5 g, 0.012 mol) was added
portion-wise with a spatula, and the mixture was stirred overnight for 24
hours. The pale yellow suspension was poured into an aqueous saturated
sodium bicarbonate solution and stirred for 15 min. Effervescence was
observed. The mixture was filtered and the solid washed with aqueous satu-
rated sodium bicarbonate (250 mL), water (250 mL), and then air-dried for
24 hours. After vacuum drying for 6 hours, crude 1o was obtained (1.5 g).
This crude material was added to 50/50 EtOAc/MeOH (50 mL) and heated
at reflux for 15 min. The suspension was filtered hot to give 0.8 g of purified
1
1
o. After cooling the filtrate for 12 hours at 58C, an additional amount of
o crystallized (0.6 g, 35% total). mp 2278C. NMR data were obtained in
1
both DMSO-d6 and CDCl3. H-NMR (DMSO-d ): 8.01–7.99 (d, 1H,
J ¼ 7.5 Hz), 7.84–7.77 (m, 2H), 7.72–7.70 (d, 1H, J ¼ 7.2 Hz), 4.54–4.51
6
1
3
(
t, 2H, J ¼ 6.9 Hz), 3.44–3.40 (t, 2H, J ¼ 6.9 Hz). C-NMR (DMSO-d ):
6
1
1
72.6, 164.9, 163.4, 136.7, 134.8, 133.2, 131.6, 130.3, 129.7, 53.2, 28.0.
H-NMR (CDCl ): 8.14–8.12 (d, 1H, J ¼ 7.3 Hz), 7.87–7.85 (d, 1H,
3
J ¼ 6.5 Hz), 7.77–7.29 (m, 2H), 4.70–4.66 (m, 2H), 3.39–3.35 (m, 2H).
1
3
C-NMR (CDCl ): 173.0, 164.8, 162.1, 136.6, 134.6, 132.7, 131.6, 130.1,
3
129.4, 52.2, 27.9. Elemental Analysis: Calcd: C, 54.53; H, 4.58; N, 10.60.
Found: C, 54.54; H, 4.53; N, 10.42.
Synthesis of 1o-Ester
Compound 1o-ester was prepared in the same manner as 1p from
-aminothiazoline hydrochloride (3.41 g, 0.024 mol), triethylamine (18 mL,
2
0
.12 mol), and phthaloyl dichloride (2.5 g, 0.012 mol). After the initial
1
workup, a crude solid product was obtained (1.6 g). A H-NMR spectrum of

3
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Gondi and Son
this product indicated a complex product mixture. This product was added to
0/50 EtOAc/MeOH (100 mL) and heated at reflux for 15 min to give a clear
5
solution. The solution was filtered hot and the filtrate was stored at 58C for 12
hours. The resulting crystals that formed were separated from the solution by
filtration and dried under high vacuum (1o-ester, 1.4 g, 34%). mp 1658C.
1
H-NMR (DMSO-d ): 9.65 (s, 1H, NH), 7.82–7.80 (d, 1H, J ¼ 5.9 Hz),
6
7
.54 (s, 3H), 3.75 (s, 3H), 3.66–3.62 (t, 2H, J ¼ 7.6 Hz), 3.27–3.23 (t, 2H,
1
3
J ¼ 7.7 Hz). C-NMR (DMSO-d ): 174.9, 173.6, 169.7, 138.2, 133.4,
6
1
5
31.3, 131.1, 129.6, 128.7, 53.0, 46.3, 30.4. Elemental Analysis: Calcd: C,
4.53; H, 4.58; N, 10.60. Found: C, 54.54; H, 4.53; N, 10.42.
Synthesis of 2p
2
-Aminothiazole (2.46 g, 0.024 mol) was dissolved in dichloromethane
70 mL) to make a clear solution. The solution was cooled in a water/ice
bath and then pyridine (10 mL, 0.12 mol) was added. Terephthaloyl dichloride
2.5 g, 0.012 mol) was added portion-wise with a spatula, causing the immedi-
(
(
ate formation of a yellow suspension. The mixture was stirred at room temp-
erature overnight. The pale yellow suspension was then poured into a beaker
containing saturated aqueous sodium bicarbonate solution and stirred for
3
0 min. Effervescence was observed. The suspension was filtered and
washed with saturated aqueous sodium bicarbonate solution (250 mL) and
water (250 mL). The solid was air-dried for 24 hours and dried under high
vacuum for 6 hours to give crude 2p (3.7 g). A small amount of crude 2p
(
2.0 g) was added to 2 : 1 EtOAc/MeOH (150 mL) and heated at reflux for
5 min. The suspension was filtered hot and the solid residue was dried
1
in high vacuum to obtain pure 2p (1.5 g). After cooling the filtrate at 58C
for 12 hours, an additional small amount of 2p crystallized (100 mg, 73%
total). An alternate method of purifying crude 2p is to dissolve the product
in DMSO, filter the resulting solution, and add water to the filtrate to precipi-
1
tate 2p. mp 3448C. H-NMR (DMSO-d ): 12.82 (s, 2H, NH), 8.23–8.21
6
(
d, 4H, J ¼ 7.4 Hz), 7.59–7.58 (d, 2H, J ¼ 3.6 Hz), 7.31–7.30 (d, 2H,
1
3
J ¼ 3.6 Hz). C-NMR (DMSO-d ): 165.5, 159.8, 138.2, 136.5, 129.1,
6
1
5
14.8. Elemental Analysis: Calcd: C, 50.89; H, 3.05; N, 16.96. Found: C,
0.60; H, 3.07; N, 16.42.
Synthesis of 2m
Compound 2m was prepared in the same manner as 2p from 2-amino-
thiazole (2.46 g, 0.024 mol), pyridine (10 mL, 0.12 mol), and isophthaloyl

Synthesis of Heteroaromatic Benzene Dicarboxamides
3069
dichloride (2.5 g, 0.012 mol). After workup and purification using 50/50
EtOAc/MeOH, compound 2m was obtained in 64% yield. mp 3118C.
1
H-NMR (DMSO-d ): 12.68 (s, 2H, NH), 8.82 (s, 1H), 8.30–8.28 (d, 2H,
J ¼ 7.4 Hz), 7.71–7.69 (t, 1H, J ¼ 7.6 Hz), 7.58–7.57 (d, 2H, J ¼ 3.2 Hz),
6
1
3
7
.29 (d, 2H, J ¼ 3.0 Hz). C-NMR (DMSO-d ): 165.4, 159.6, 138.3, 133.5,
6
132.8, 130.0, 129.0, 114.9. Elemental Analysis: Calcd: C, 50.89; H, 3.05;
N, 16.96. Found: C, 50.88; H, 3.07; N, 16.90.
Synthesis of 2o and 2o-Ester
Compound 2o was prepared in the same manner as 2p from 2-aminothia-
zole (2.46 g, 0.024 mol), pyridine (10 mL, 0.12 mol), and phthaloyl dichloride
(
2.5 g, 0.012 mol). After workup and purification of crude 2o (2.0 g) using 50/
1
5
0 EtOAc/MeOH, pure 2o was obtained (1.8 g, 71%). mp 2128C. H-NMR
(
(
DMSO-d ): 12.74 (s, 2H, NH), 7.81–7.79 (d, 2H, J ¼ 3.2 Hz), 7.67–7.66
6
d, 2H, J ¼ 3.1 Hz), 7.52–7.51 (d, 2H, J ¼ 3.3 Hz), 7.26–7.25 (d, 2H,
1
3
J ¼ 3.3 Hz). C-NMR (DMSO-d ): 167.1, 159.3, 138.5, 135.1, 131.5,
6
1
29.4, 114.6. Elemental Analysis: Calcd: C, 50.89; H, 3.05; N, 16.96.
Found: C, 50.95; H, 3.05; N, 16.93. After cooling the filtrate at 58C for 12
1
hours, compound 2o-ester crystallized (100 mg, 5%). mp 1848C. H-NMR
(
DMSO-d ): 12.59 (s, 1H, NH), 7.91 (d, 1H, J ¼ 7.4 Hz), 7.71–7.69 (t, 1H,
6
J ¼ 6.0 Hz), 7.66–7.63 (m, 2H), 7.52–7.51 (d, 1H, J ¼ 3.6 Hz), 7.29–7.28
1
3
(
d, 1H, J ¼ 3.6 Hz), 3.75 (s, 3H). C-NMR (DMSO-d ): 167.7, 167.1,
6
1
59.1, 138.5, 137.1, 133.0, 131.2, 130.3, 130.0, 129.1, 114.6, 53.3. Elemental
Analysis: Calcd: C, 54.95; H, 3.84; N, 10.68. Found: C, 54.73; H, 3.86;
N, 10.70.
Synthesis of 3p
2
-Aminopyrimidine (2.34 g, 0.024 mol) was dissolved in dichloromethane
50 mL) to make a clear solution. The solution was cooled in a water/ice bath
and pyridine (10 mL, 0.12 mol) was added. Terephthaloyl dichloride (2.5 g,
.012 mol) was added portion-wise with a spatula, resulting in the immediate
(
0
formation of a yellow suspension. The reaction mixture was then stirred over-
night at room temperature. The pale yellow suspension was poured into a
beaker containing saturated aqueous sodium bicarbonate solution and stirred
for 30 min. Effervescence was observed. The suspension was filtered and
the solid washed with saturated aqueous sodium bicarbonate solution
(250 mL) and water (250 mL). After air-drying for 24 hours, crude 3p was
obtained (2.4 g). The crude material was added to 50/50 EtOAc/MeOH

3
070
Gondi and Son
(
100 mL) and heated at reflux for 15 min. The suspension was filtered hot to
1
give purified 3p (1.4 g, 36%). mp 2718C. H-NMR (DMSO-d ): 11.17
6
(
s, 2H, NH), 8.75–8.74 (d, 4H, J ¼ 4.8 Hz), 8.05 (s, 4H), 7.29–7.26 (t, 2H,
J ¼ 4.7 Hz). Elemental Analysis: Calcd: C, 60.00; H, 3.78; N, 26.24.
Found: C, 59.65; H, 3.87; N, 26.01. After cooling the filtrate at 58C for
1
2 hours, a small amount of dimethyl terephthalate crystallized (100 mg).
1
mp 1428C [lit. (Aldrich) mp 140–28C]. H-NMR (DMSO-d ): 8.09 (s, 4H),
6
1
.90 (s, 6H). C-NMR (DMSO-d ): 166.3, 134.4, 130.3, 53.3.
3
3
6
Synthesis of 3m
2
-Aminopyrimidine (2.34 g, 0.024 mol) was dissolved in dichloromethane
50 mL) to make a clear solution. The mixture was cooled in a water/ice bath
and pyridine (10 mL, 0.12 mol) was added. Isophthaloyl dichloride (2.5 g,
.012 mol) was added portion-wise with a spatula. The mixture was stirred
(
0
overnight at room temperature. The mixture remained clear for 16 hours, at
which point a suspension slowly formed. After a total of 24 hours, the pale
yellow suspension was poured into a beaker containing aqueous saturated
sodium bicarbonate solution and stirred for 15 min. Effervescence was
observed. The suspension was filtered and the solid was washed with
aqueous saturated sodium bicarbonate solution (250 mL) and water (250 mL)
to give crude 3m (2.5 g). The crude material was suspended in ethyl acetate
(50 mL) and heated at reflux for 15 min. The suspension was filtered hot
and the solid was dried under vacuum to give purified 3m (2.2 g, 53%).
1
mp 2538C. H-NMR (DMSO-d ): 11.05 (s, 2H, NH), 8.75 (s, 4H), 8.56
(
6
1
3
s, 1H), 8.14 (s, 2H), 7.67 (s, 1H), 7.27 (s, 2H). C-NMR (DMSO-d6):
65.6, 159.3, 158.9, 135.1, 132.6, 129.6, 128.7, 118.3. Elemental Analysis:
Calcd: C, 60.00; H, 3.78; N, 26.24. Found: C, 59.60; H, 3.78; N, 25.70.
1
Synthesis of 3o
2
-Aminopyrimidine (2.34 g, 0.024 mol) was dissolved in dichloro-
methane (50 mL) to make a clear solution. The solution was cooled in a
water/ice bath and pyridine (10 mL, 0.12 mol) was added. Phthaloyl dichlor-
ide (2.5 g, 0.012 mol) was added portion-wise with a spatula, resulting in the
immediate formation of a reddish suspension. The mixture was stirred 24
hours at room temperature, after which it was poured into a beaker containing
aqueous saturated sodium bicarbonate solution and stirred for 30 min. Effer-
vescence was observed. The mixture was extracted with dichloromethane

Synthesis of Heteroaromatic Benzene Dicarboxamides
3071
(
2 ꢀ 100 mL), water (250 mL), and brine (100 mL); dried over anhydrous
magnesium sulfate; and filtered. Concentration under reduced pressure gave
crude 3o (2.1 g). The crude material was added to ethyl acetate (50 mL) and
heated at reflux for 15 min. The suspension was filtered hot to give purified
3o as a tan solid (1.0 g) After cooling the filtrate at 58C for 12 hours, an
additional amount of pure 3o crystallized (800 mg, 65% total). Repeating
this experiment using triethylamine as the base gave similar results. mp
1
2
208C [lit mp 2268C(14)]. H-NMR (DMSO-d ): 8.94–8.93 (d, 2H,
6
J ¼ 4.8 Hz), 8.00–7.98 (t, 2H, J ¼ 3.0 Hz), 7.83–7.82 (d, 2H, J ¼ 3.0 Hz),
1
3
7
.41–7.39 (t, 1H, J ¼ 4.7 Hz). C-NMR (DMSO-d ): 166.2, 159.5, 153.9,
6
1
35.2, 132.0, 124.5, 120.8. Elemental Analysis: Calcd: C, 64.00; H, 3.13;
N, 18.66. Found: C, 64.30; H, 3.17; N, 18.66.
ACKNOWLEDGMENTS
The authors thank the National Science Foundation and the Welch
Foundation for financial support.
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Received in the USA May 24, 2004