Carboxylate derivatives of oligopyridines

Article abstract of DOI:10.1055/s-2000-6331

The key compound ethyl 2,6-dibromopyridine-4-carboxylate was prepared in two steps starting from the commercially available citrazinic acid. By using the Stille coupling reaction ethyl 2,6- dibromopyridine-4-carboxylate was converted to 2,2'-bipyridines, 2,2':6',2''-terpyridines and 2,2':6',2'':6'',2''':6''',2''''- quinquepyridines which bear a carboxylate functional group directly attached to the central pyridine ring.

Full text of DOI:10.1055/s-2000-6331

1138
PAPER
Carboxylate Derivatives of Oligopyridines
Reza-Ali Fallahpour
Institut für Anorganische Chemie, Universität Basel, Spitalstrasse 51, CH-4056 Basel, Switzerland
E-mail: Reza.Fallahpour@unibas.ch
Received 21 March 2000; revised 15 April 2000
By oxidation of 4,4',4''-trimethyl-2,2':6',2''-terpyridine,
which is accessible by Kröhnke method,3 with chromium
trioxide in sulfuric acid a 2,2':6',2''-terpyridine-4,4',4''-tri-
carboxylic acid was obtained.13 A selective oxidation of
Abstract: The key compound ethyl 2,6-dibromopyridine-4-carbox-
ylate was prepared in two steps starting from the commercially
available citrazinic acid. By using the Stille coupling reaction ethyl
2,6-dibromopyridine-4-carboxylate was converted to 2,2'-bipy-
ridines, 2,2':6',2''-terpyridines and 2,2':6',2'':6'',2''':6''',2''''-quin- the methyl groups is not possible and any other functional
quepyridines which bear a carboxylate functional group directly
attached to the central pyridine ring.
group sensitive to oxidation or hydrolysis should be
avoided. In addition, yields are low and the oxidation and
Key words: terpyridine, bipyridine, carboxylates, Stille coupling
reaction, palladium
workup of such reactions are not easy. The synthesis of
4''-cyano-2,2':6',2'':6'',2''':6''',2''''-quinquepyridine using
another method has been reported.14 We report here a fac-
ile synthesis of oligopyridines bearing directly attached
carboxylates in good yields.
Due to their versatile reactions with transition metals to
form complexes, oligopyridines have received consider-
able attention in supramolecular chemistry.1 The
2,2’:6’,2’’-terpyridine (tpy) and 2,2’-bipyridine (bpy) met-
al-binding motif is commonly incorporated in multinucle-
ating systems using 4’-chloro- or 4’-hydroxy-
functionalized2 derivatives.
Oligopyridines have been synthesized by the following
methods: i. Ullman coupling of bromopyridines;15 ii. cross
coupling methods such as Stille reaction,16 Suzuki
reaction17 and nickel mediated reactions;18 iii. a-oxo-
ketene dithioacetal method;5 iv. Kröhnke method;3 and
v. Jameson method.19
Particular interest rests in 4’-substituted tpy-ligands;
4-substituted bpy ligands and many substituents can be di-
rectly inserted by the Kröhnke methodology.3 Some func-
tional groups, such as hydroxy,2 chloro,2 bromo,4
methylthio,5 methanesulfonyl,5 and dimethylamine6 have
already been attached directly to C(4') tpy ligand. We also
become interested in the functionalization of C(4') of the
tpy ligand and have inserted hydroxy,7,8 nitro,9,10 amino9,10
and azido11 at C(4'). By the latter methods the terminal py-
ridine rings may or may not bear functionalities (substitu-
ents).
We have already applied the Stille coupling reaction for
the synthesis of functionalized oligopyridines.9-11 The
Stille coupling, which consists of reacting stannyl and
bromo compounds in the presence of a catalytic amount of
palladium(0) and palladium(II), respectively, has found
wide application in the synthesis of aromatic and hetero-
cyclic compounds. The advantage of this method is that
many functionalities such as nitro, nitrilo or carboxylate
groups do not react under the reaction conditions.
The key compound of the Stille coupling reaction was eth-
yl 2,6-dibromo-4-pyridinecarboxylate (3) (Scheme 1).
Though several derivatives of 2,6-dihydroxypyridine-4-
carboxylic acid (citrazinic acid, 1) have been synthesized,
only just recently it has, to the best of our knowledge, been
used as a starting material for the synthesis of oligopy-
ridines.20 The presence of a functionality in a position des-
tined to become C(4') of a 2,2':6',2''-terpyridine and C(4)
The syntheses of butyl 2,2':6',2''-terpyridine-4'-carboxy-
late and some other pyridine derivatives have recently
been reported.12 Some of the starting materials are not so
easily accessible. Furthermore, this method does not al-
low any other functional groups, especially at the tpy
ligand.
CO2H
CO2H
CO2Et
b)
a)
HO
N
OH
Br
N
Br
Br
N
Br
1
2
3
Reagents and conditions: a) 1/POBr3, 175 °C, 5 h, 57%; b) 2/EtOH/concd H2SO4, 78 °C, 4 h, 91%
Scheme 1
Synthesis 2000, No. 8, 1138–1142 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Carboxylate Derivatives of Oligopyridines
1139
CO2R1
N
N
N
R2
R2
R1=H, R2= H
R1=Et, R2= H
8
9
R2
R2
R1=H, R2= Me 10
R1=Et, R2= Me 11
N
SnBu3
a)
N
Br
R2=H
4
6
7
R2=Me 5
CO2R
b)
3
N
Br
N
R=H
R=Et
12
13
c)
N
N
SnBu3
CO2R
N
14
N
N
N
N
R=H
R=Et
15
16
Reagents and conditions: a) 3/6 (2 equiv)/Pd(PPh3)4 (0.02 equiv)/toluene, 110 °C, 16 h; 8 (54%), 9 (34%). 3/7 (2 equiv)/Pd(PPh3)4
(0.02 equiv)/toluene, 110 °C, 16 h; 10 (24%), 11 (37%); b) 3/6 (1 equiv)/Pd(PPh3)4 (0.01 equiv)/toluene, 110 °C, 16 h; 12 (20%), 13 (38%);
c) 3/14 (2 equiv)/Pd(PPh3)4 (0.02 equiv)/toluene, 110°C, 16 h; 15 (22%), 16 (24%)
Scheme 2
of 2,2’-bipyridine (bpy) makes it an attractive starting terpyridine-4’-carboxylic acid (8) and ethyl 2,2’:6’,2’’-
point.
terpyridine-4’-carboxylate (9) in 54% and 34% yields,
respectively, both as colorless crystalline solids.
Commercially available citrazinic acid (1) was converted
to 2,6-dibromopyridine-4-carboxylic acid (2) upon reac- A major consideration in working up reaction mixtures
tion with phosphorus oxybromide in 55% yield.21 Subse- from the Stille cross coupling is the removal of tin byprod-
quent esterification with sulfuric acid and ethanol ucts. While trimethyltin chloride is water soluble and rath-
produced ethyl 2,6-dibromo-4-pyridinecarboxylate (3) as er volatile, tributyltin chloride has a low volatility and is
a yellow microcrystalline compound in 95% yield soluble in most organic solvents. Separation on silica gel
(Scheme 1).22
is difficult due to the tendency of tributyltin chloride to
elute under nonpolar conditions, and to streak on the col-
umn.
The syntheses of bi-, ter- and quinquepyridines are illus-
trated in Scheme 2. 2-Bromopyridine (4) was converted to
tributyl(pyridin-2-yl)stannane (6) by reacting with butyl- However, with basic compounds, e.g. oligopyridines, the
lithium and tributyltin chloride in tetrahydrofuran.23 Com- workup of the reaction mixture is made very easy. While
pound 3 was coupled with 2 equivalents of 6 in the oligopyridines are soluble in concentrated hydrochloric
presence of 0.02 equivalent of (Ph3P)4Pd to give 2,2’:6’,2’’- acid, the tin byproducts can be removed by extraction with
Synthesis 2000, No. 8, 1138–1142 ISSN 0039-7881 © Thieme Stuttgart · New York

1140
R.-A. Fallahpour
PAPER
dichloromethane. Neutralization of the acidic aqueous spectra of the esters the carbonyl band was observed at ca.
phase with an inorganic base, usually sodium carbonate or 1730 cm-1. The 1H, 13C NMR and the mass spectral data
sodium hydroxide, gives the free oligopyridine ligands. are in accord with the proposed formulations and struc-
The organic compound which contains no trace of tin tures.
byproducts can be extracted with dichloromethane and
In conclusion, this method has established the direct at-
easily purified by chromatography. If some sensitive
tachment of carboxylates to oligopyridines which are of
groups, such as carboxylates, are present the neutraliza-
high interest in supramolecular chemistry. The starting
tion should be carried out with sodium carbonate rather
materials are either commercially available or readily ac-
than sodium hydroxide.
cessible. This method allows the insertion of other func-
If interest in both carboxylic acid and ester exists, the neu- tional groups into oligopyridines, e.g. bromo or methyl
tralization was carried out with sodium hydroxide. Part of groups. Furthermore, the ester groups are of interest due
ester was hydrolyzed under the reaction conditions. The to their conversion to other functional groups and this
carboxylic acid which is not soluble either in dichlo- work is currently under investigation.
romethane or in water was easily collected by filtration.
Pure carboxylic acids were obtained by further purifica-
tion on silica gel using gradient solvent dichloromethane/
ethyl acetate (1:1) changed to methanol. The esters were
extracted with dichloromethane and purified on silica gel
using dichloromethane/hexane (2:1) followed by recrys-
tallization from ethanol.
All reagents were used as supplied. Silica gel (0.060-0.200 mm)
was obtained from Chemie Uetikon and aluminum oxide (type 507
C neutral; 100-125 mesh) from Fluka. Melting points were mea-
sured on Büchi 535 and are not corrected. IR spectra were recorded
on a Mattson Genesis Fourier-transform spectrophotometer with
samples in compressed KBr discs; abbreviations used are:
1
br = broad, s = strong, m = middle. H and 13C NMR spectra were
When the reaction mixtures were neutralized with solid
sodium carbonate no carboxylic acid was observed and
only esters were isolated. Alternatively, the esters can be
subsequently hydrolyzed to carboxylic acids, or carboxy-
lic acids can be esterified with a catalytic amount of sul-
furic acid in alcohol.
recorded on Bruker AM 250 spectrometer and referenced against
TMS. Time of flight (Maldi) spectra were recorded using a PerPe-
spective Biosystems Voyagers-RP Biospectrometry Workstation.
2,6-Dibromopyridine-4-carboxylic Acid (2)
Citrazinic acid (1; 25.0 g, 0.16 mol) and POBr3 (73.0 g, 0.25 mol)
were heated at 175 °C in an autoclave for 5 h. The autoclave was
cooled down over a period of 20 h. H2O (300 mL) was cautiously
added to the black product and filtered. The brown aqueous phase
2-Bromo-5-methylpyridine (5)24 was converted to tribu-
tyl(5-methylpyridin-2-yl)stannane (7) in the same man-
ner. When 3 was reacted under the same conditions with 2 was extracted with CH2Cl2 (5 × 40 mL). The black residue was con-
tinually extracted in a Soxhlet extractor with CH2Cl2 for 12 h and
the brown solution obtained was combined with previous organic
extracts. The organic phase was dried (MgSO4) and solvent was re-
moved. The brown residue was recrystallized from H2O to obtain a
equivalents of 7, 5,5’’-dimethyl-2,2’:6’,2’’-terpyridine-4’-
carboxylic acid (10) and ethyl 5,5’’-dimethyl-2,2’:6’,2’’-
terpyridine-4’-carboxylate (11) were obtained as colorless
microcrystalline solids in 24% and 37% yields, respec-
colorless solid; yield: 26 g (57%); mp 184-185 °C.
tively (Scheme 2).
IR (KBr): n = 3074m, 2950br, 1732s, 1536s, 1413m, 1356s, 1237m,
1221m, 1162m, 995m, 760m, 671s cm-1.
1H NMR (CDCl3): d = 8.05 (s, 2 H).
However, if 3 was reacted with only one equivalent of 6
in the presence of the catalyst under the same conditions,
6-bromo-2,2’-bipyridine-4’-carboxylic acid (12) and ethyl
6-bromo-2,2’-bipyridine-4’-carboxylate (13) were ob-
tained as colorless microcrystalline solids in 20% and
38% yields, respectively (Scheme 2). These compounds
are also of interest because they can be coupled together
with a Ni(0)-catalyst25 to obtain 2,2’:6’,2’’:6’’,2’’’-quater-
pyridines with two carboxylate functions, one at each of
the central pyridine rings.
13C NMR (CDCl3): d = 167.25, 141.76, 140.53, 127.03.
MS (Maldi-TOF): m/z = 281.
Anal. calcd for C6H3Br2NO2: C, 25.65; H, 1.08; N, 4.99. Found: C,
25.64; H, 1.25; N, 4.97.
Ethyl 2,6-Dibromopyridine-4-carboxylate (3)
A mixture of 2,6-dibromopyridine-4-carboxylic acid (2; 4.0 g,
0.014 mol) and concd H2SO4 (1 mL) in EtOH (30 mL) was heated
at 78 °C for 4 h. EtOH was removed by evaporation and to the res-
idue H2O (30 mL) was added. The aqueous phase was extracted
with CH2Cl2 (3 × 30 mL). The combined organic phases were dried
(MgSO4) and the solvent was removed. Chromatographic separa-
tion (silica gel, CH2Cl2/hexane, 1:2) followed by recrystallization
from EtOH gave a yellow solid; yield: 4.0 g (91%); mp 79 °C.
These reactions were extended to synthesize higher oli-
gopyridines. Compound 3 was reacted with 2 equivalents
of 1426 in the presence of 0.02 equivalent of Pd(PPh3)4 to
give 2,2’:6’,2’’:6’’,2’’’:6’’’,2’’’’-quinquepyridine-4’’-carboxyl-
ic acid (15) and ethyl 2,2’:6’,2’’:6’’,2’’’:6’’’,2’’’’-quinquepyri-
dine-4’’-carboxylate (16) as colorless microcrystalline
solids in 22% and 24% yields, respectively (Scheme 2).
IR (KBr): n = 3084m, 1730s, 1536m, 1352m, 1277s, 1160m,
1016m, 897m, 764m cm-1.
All these compounds have been characterized by spectro-
scopic methods, elemental analyses and conversion of ac-
ids/esters to esters/acids, respectively. The carboxylic
acids contain water of crystallizaztion and in the IR spec-
tra a broad band at ca. 3400 cm-1 was observed. In the IR
1H NMR (CDCl3): d = 7.99 (s, 2 H), 4.42 (q, J = 7.10 Hz, CH2, 2 H),
1.41 (t, J = 7.10 Hz, CH3, 3 H).
13C NMR (CDCl3): d = 160.60, 141.88, 141.48, 126.69, 62.67,
14.12.
MS (Maldi-TOF): m/z = 309.
Synthesis 2000, No. 8, 1138–1142 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Carboxylate Derivatives of Oligopyridines
MS (Maldi-TOF): m/z = 305.
1141
Anal. calcd for C8H7Br2NO2: C, 31.10; H, 2.28; N, 4.53. Found: C,
30.99; H, 2.43; N, 4.42.
Anal. calcd for C18H15N3O2•H2O: C, 66.86; H, 5.30; N, 12.99.
Found: C, 67.11; H, 5.55; N, 13.11.
Stille Coupling Reactions; General Procedure
Ethyl 5,5’’-Dimethyl-2,2’:6’,2’’-terpyridine-4’-carboxylate (11)
Dibromo compound 3 (1 mol), stannyl compounds 6, 7 and 14, re-
spectively, (1 or 2 equiv) and (Ph3Ph)4Pd (0.01 or 0.02 equiv) were
heated under N2 in toluene (50 mL) for 16 h. Upon cooling to r.t. aq
sat. NH4Cl solution (20 mL) was added. The mixture was stirred for
further 30 min and then filtered over Celite. The precipitate was
washed with CH2Cl2 (50 mL) and the organic phase was separated.
The aqueous phase was extracted with toluene (3 × 25 mL). The
combined organic phases were dried (MgSO4) and the solvent was
removed. Concd HCl (30 mL) was added to the residue and extract-
ed with CH2Cl2 (3 × 30 mL). The aqueous phase was cautiously
neutralized by solid NaOH. The oligopyridines were then extracted
with CH2Cl2 (3 ¥ 30 mL) and dried (MgSO4). The solvent was re-
moved and the product purified by chromatography on silica gel
with CH2Cl2/hexane (1:2) as eluent. Oligopyrindine carboxylic ac-
ids which are not soluble in CH2Cl2 were filtered and purified by
chromatography on silica gel with MeOH.
Mp 169-170 °C.
IR (KBr): n = 1721s, 1562m, 1480m, 1374m, 1261s, 1234m, 849m,
777m cm-1.
1H NMR (CDCl3): d = 8.92 (s, H-3’, 2 H), 8.58 (d, J = 1.95 Hz,
H-6, 2 H), 8.53 (d, J = 7.80 Hz, H-3, 2 H), 7.87 (dd, J = 7.80, 1.95
Hz, H-4, 2 H), 4.47 (q, J = 6.90 Hz, CH2, 2 H), 2.44 (s, CH3, 6 H),
1.54 (t, J = 6.90 Hz, CH3, 3 H).
13C NMR (CDCl3): d = 165.42, 156.43, 152.95, 149.61, 139.85,
137.28, 133.71, 120.73, 119.58, 61.59, 18.39, 14.27.
MS (Maldi-TOF): m/z = 333.
Anal. calcd for C20H19N3O2•1.5H2O: C, 70.16; H, 5.89; N, 12.27.
Found: C, 70.64; H, 6.01; N, 12.26.
Ethyl 2,6-dibromopyridine-4-carboxylate (3; 0.40 g, 1.29 mmol) re-
acted with 6 (1 equiv) to give 0.075 g (20%) 12 and 0.15 g (38%) 13.
Ethyl 2,6-dibromopyridine-4-carboxylate (3; 0.50 g, 1.62 mmol) re-
acted with 6 (2 equiv) to give 0.21 g (54%) of 8 and 0.17 g (34%)
of 9.
6-Bromo-2,2’-bipyridine-4-carboxylic Acid (12)
Mp 203-204 °C.
IR (KBr): n = 3386br, 1609m, 1588m, 1540s, 1397s, 1366m, 780m,
2,2’:6’,2’’-Terpyridine-4’-carboxylic Acid (8)
Mp 280-282 °C.
733m cm-1.
1H NMR (CD3OD): d = 8.76 (s, H-3, 1 H), 8.65 (d, J = 7.80 Hz,
H-6’, 1 H), 8.33 (d, J = 7.80 Hz, H-3’, 1 H), 7.96 (s, H-5, 1 H), 7.94
(ddd, J = 8.30, 7.80, 1.95 Hz, H-4’, 1 H), 7.45 (ddd, J = 8.30,
7.80, 1.95 Hz, H-5’, 1 H).
13C NMR (CD3OD): d = 170.96, 158.57, 155.92, 151.21, 150.41,
142.79, 138.59, 128.77, 125.61, 122.64, 120.90.
IR (KBr): n = 3400br, 1625m, 1592m, 1555m, 1473m, 1401s, 777m
cm-1.
1H NMR (CD3OD): d = 8.82 (s, H-3’, 2 H), 8.68 (d, J = 7.80 Hz, H-
6, 2 H), 8.57 (d, J = 7.80 Hz, H-3, 2 H), 7.98 (ddd, J = 8.30, 7.80,
1.95 Hz, H-4, 2 H), 7.46 (ddd, J = 8.30, 7.80, 1.95 Hz, H-5, 2 H).
13C NMR (CD3OD): d = 173.01, 157.46, 157.14, 150.26, 149.72,
138.62, 125.26, 122.84, 121.87.
MS (Maldi-TOF): m/z = 279.
Anal. calcd for C11H7BrN2O2•2.75H2O: C, 40.20; H, 3.83; N, 8.52.
Found: C, 40.06; H, 3.06; N, 8.22.
MS (Maldi-TOF): m/z = 277.
Anal. calcd for C16H11N3O2•H2O: C, 65.08; H, 4.44; N, 14.23.
Found: C, 65.61; H, 4.65; N, 14.02.
Ethyl 6-Bromo-2,2’-bipyridine-4-carboxylate (13)
Mp 169-170 °C.
Ethyl 2,2’:6’,2’’-Terpyridine-4’-carboxylate (9)
IR (KBr): n = 2980m, 1731s, 1585s, 1543s, 1480m, 1387s, 1364m,
Mp 133.5 °C.
1300m, 1260s, 1225s, 1147m, 1112m, 1021m, 766m cm-1.
IR (KBr): n = 2991m, 1725s, 1584m, 1536m, 1466m, 1396s,
1H NMR (CDCl3): d = 8.86 (s, H-3, 1 H), 8.68 (d, J = 7.80 Hz,
H-6’, 1 H), 8.38 (d, J = 7.80 Hz, H-3’, 1 H), 8.02 (s, H-5, 1 H), 7.81
(ddd, J = 8.30, 7.80, 1.95 Hz, H-4’, 1 H), 7.33 (ddd, J = 8.30, 7.80,
1.95 Hz, H-5’, 1 H), 4.43 (q, J = 6.90 Hz, CH2, 2 H), 1.40 (t,
J = 6.90 Hz, CH3, 3 H).
13C NMR (CDCl3): d = 163.82, 153.75, 149.30, 141.96, 141.13,
137.02, 130.83, 127.38, 124.58, 121.58, 119.18, 62.16, 14.21.
1370m, 1259s, 1237s, 1024m, 764m, 732m cm-1.
1H NMR (CDCl3): d = 8.97 (s, H-3’, 2 H), 8.74 (d, J = 7.80 Hz,
H-6, 2 H), 8.61 (d, J = 7.80 Hz, H-3, 2 H), 7.87 (ddd, J = 8.30, 7.80,
1.95 Hz, H-4, 2 H), 7.36 (ddd, J = 8.30, 7.80, 1.95 Hz, H-5, 2 H),
4.47 (q, J = 6.90 Hz, CH2, 2 H), 1.54 (t, J = 6.90 Hz, CH3, 3 H).
13C NMR (CDCl3): d = 165.36, 156.49, 155.49, 149.30, 140.13,
136.91, 124.09, 121.30, 120.35, 61.76, 14.35.
MS (Maldi-TOF): m/z = 307.
MS (Maldi-TOF): m/z = 305.
Anal. calcd for C13H11BrN2O2: C, 50.84; H, 3.61; N, 9.12. Found:
C, 51.21; H, 3.58; N, 9.19.
Anal. calcd for C18H15N3O2: C, 70.81; H, 4.95; N, 13.76. Found: C,
70.58; H, 5.23; N, 13.69.
Ethyl 2,6-dibromopyridine-4-carboxylate (3; 0.50 g, 1.62 mmol) re-
acted with 14 (2 equiv) to give 0.145 g (22%) 15 and 0.17 g (24%)
16.
Ethyl 2,6-dibromopyridine-4-carboxylate (3; 0.50 g, 1.62 mmol) re-
acted with 7 (2 equiv) to give 0.12 mg (24%) 10 and 0.20 g (37%)
11.
2,2’:6’,2’’:6’’,2’’’:6’’’,2’’’’-Quinquepyridine-4’’-carboxylic Acid
(15)
Mp 250-252 °C.
5,5’’-Dimethyl-2,2’:6’,2’’-terpyridine-4’-carboxylic Acid (10)
Mp 245-246 °C.
IR (KBr): n = 3360br, 1648m, 1616s, 1537s, 1488m, 1404s, 1378s,
IR (KBr): n = 3370br, 1627m, 1581m, 1538s, 1401s, 1364m, 779s,
794m, 730s cm-1.
751m cm-1.
1H NMR (CD3OD): d = 8.74 (s, H-3’, 2 H), 8.51 (br s, H-6, 2 H),
8.46 (d, J = 7.80 Hz, H-3, 2 H), 7.78 (d, J = 7.80 Hz, H-4, 2 H), 2.43
(s, CH3, 6 H).
13C NMR (CD3OD): d = 171.04, 157.06, 150.72, 138.99, 135.37,
128.37, 122.41, 122.24, 121.27, 18.26.
1H NMR (CD3OD): d = 9.05 (s, H-3’’, 2 H), 8.85 (d, J = 7.80 Hz,
2 H), 8.76 (t, J = 7.80 Hz, H-4’, 2 H), 8.66 (m, 2 H), 8.41 (d,
J = 7.80 Hz, 2 H), 8.05 (ddd, J = 8.30, 7.80, 1.95 Hz, H-4, 2 H), 8.02
(d, J = 7.80 Hz, 2 H), 7.47 (ddd, J = 8.30, 7.80, 1.95 Hz, H-5, 2 H).
Synthesis 2000, No. 8, 1138–1142 ISSN 0039-7881 © Thieme Stuttgart · New York

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R.-A. Fallahpour
PAPER
13C NMR (CD3OD): d = 170.99, 158.54, 157.00, 156.57, 150.04,
142.70, 139.31, 138.68, 128.86, 125.38, 122.89, 122.44, 122.27,
120.75.
(5) Potts, K. Bull. Soc. Chim. Belg. 1990, 99, 741.
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Daniels, M. A. M. New J. Chem. 1992, 16, 855.
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Trans. 1 1997, 2263.
(8) Fallahpour, R.-A.; Neuburger, M.; Zehnder, M. Polyhedron
1999, 18, 2445.
MS (Maldi-TOF): m/z = 431.
Anal. calcd for C26H17N5O2•H2O: C, 69.48; H, 4.26; N, 15.58.
Found: C, 69.11; H, 4.65; N, 15.66.
(9) Fallahpour, R.-A. Eur. J. Inorg. Chem,. 1998, 1205.
(10) Fallahpour, R.-A.; Neuburger, M.; Zehnder, M. New J. Chem.
1999, 23, 53.
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1999, 1051.
(12) El-ghayoury, A.; Ziessel, R. Tetrahedron Lett. 1998, 39, 4473.
(13) Zakeeruddin, S. M.; Nazeeruddin, M. K.; Rotzinger, F. P.;
Humphry-Baker, R.; Kalynasundaram, K.; Grätzel, M.;
Shklover, V.; Haibach, T. Inorg. Chem. 1997, 36, 5937.
(14) Pabst, G. R.; Sauer, J. Tetrahedron Lett. 1998, 39, 6687.
(15) Morgan, G. T.; Burstall, F. H. J. Chem. Soc. 1932, 20.
Burstall, F. H. J. Chem. Soc. 1938, 1662.
Ethyl 2,2’:6’,2’’:6’’,2’’’:6’’’,2’’’’-Quinquepyridine-4’’-carboxy-
late (16)
Mp 118-119 °C.
IR (KBr): n = 1735s, 1580m, 1562m, 1545m, 1392m, 1318m,
1289m, 1270m, 1254m, 765s cm-1.
1H NMR (CDCl3): d = 9.07 (s, H-3’’, 2 H), 8.72 (m, 2 H), 8.64 (d,
J = 7.80 Hz, 2 H), 8.53 (d, J = 7.80 Hz, 2 H), 8.47 (d, J = 7.80 Hz,
2 H), 8.76 (t, J = 7.80 Hz, H-4’, 2 H), 7.90 (ddd, J = 8.30, 7.80, 1.95
Hz, H-4, 2 H), 7.36 (ddd, J = 8.30, 7.80, 1.95 Hz, H-5, 2 H), 4.48
(q, J = 6.90 Hz, CH2, 2 H), 1.47 (t, J = 6.90 Hz, CH3, 3 H).
13C NMR (CDCl3): d = 170.64, 161.20, 158.34, 155.60, 153.03,
149.10, 138.05, 137.02, 127.29, 123.98, 121.95, 121.58, 121.27,
119.38, 62.24, 14.21.
(16) Farina, V.; Krishnamurthy, V.; Scott, W. J. Org. React. 1997,
50, 1.
(17) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(18) Kalinin, V. N. Synthesis 1992, 413.
MS (Maldi-TOF): m/z = 459.
(19) Jameson, D. L.; Guise, L. E. Tetrahedron Lett. 1991, 32, 1999.
(20) Lehmann, U.; Henze, O.; Schlüter, A. D. Chem. Eur. J. 1999,
5, 854.
Anal. calcd for C28H21N5O2: C, 69.85; H, 5.52; N, 19.16. Found: C,
69.71; H, 5.65; N, 19.19.
(21) Levelt, W. H.; Wibaut, J. P. Recl. Trav. Pay-Bas. 1929, 38,
466.
(22) Beilstein, Springer Verlag: Heidelberg, 1990, 5. Supplement,
22/2, 305.
(23) Bolm, C.; Ewald, M.; Felder, M.; Schlingloff, G. Chem. Ber.
1992, 125, 1169.
(24) Windscheif, P.-M.; Vögtle, F. Synthesis 1994, 87.
(25) Constable, E. C.; Ward, M. D. J. Chem. Soc., Dalton Trans.
1990, 1405.
Acknowledgement
I would like to thank Prof. Edwin C. Constable for his generous sup-
port and Prof. Catherine Housecroft for critical reading of the ma-
nuscript.
I would also like to thank the Schweizerischer
Nationalfonds zur Förderung der wissenschaftlichen Forschung and
the University of Basel for support.
(26) Hanan, G. S.; Schubert, U. S.; Volkmer, D.; Rivière, E.; Lehn,
J.-M.; Kyritsakas, N.; Fischer, J. Can. J. Chem. 1997, 75, 169.
References
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(3) Kröhnke, F. Synthesis 1976, 1.
Article Identifier:
1437-210X,E;2000,0,08,1138,1142,ftx,en;Z01700SS.pdf
(4) Grosshenny, V. ; Ziessel, R., J. Organomet. Chem. 1993B,
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Synthesis 2000, No. 8, 1138–1142 ISSN 0039-7881 © Thieme Stuttgart · New York