Facile synthesis of 6-aryl-3-pyridyl-1,2,4-triazines as a key step toward highly fluorescent 5-substituted bipyridines and their Zn(II) and Ru(II) complexes

Article abstract of DOI:10.1016/j.tet.2008.06.040

A wide series of substituted bipyridines were obtained through the synthesis of 1,2,4-triazines and their aza Diels-Alder reactions. The reported method facilitates the synthesis of functionally diverse bipyridines that provides fine-tuning of photophysical properties of new ligands and their Zn(II) and Ru(II) complexes. Some of substituted bipyridines exhibit 'off-on' fluorescence response toward Zn²⁺ cations.

Full text of DOI:10.1016/j.tet.2008.06.040

Tetrahedron 64 (2008) 8963–8973
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Facile synthesis of 6-aryl-3-pyridyl-1,2,4-triazines as a key step toward highly
fluorescent 5-substituted bipyridines and their Zn(II) and Ru(II) complexes
,
a
a
a
Valery N. Kozhevnikov b , Olga V. Shabunina , Dmitry S. Kopchuk , Maria M. Ustinova ,
*
Burkhard Ko¨nig c, Dmitry N. Kozhevnikov a
,b,
*
a Urals State Technical University, Mira 19, Ekaterinburg 620002, Russia
b I. Postovsky Institute of Organic Synthesis, Ural Branch of Russian Academy of Sciences, Kovalevskoy 22, Ekaterinburg 620219, Russia
c Institut fu¨r Organische Chemie, Universita¨t Regensburg, D-93040 Regensburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
A wide series of substituted bipyridines were obtained through the synthesis of 1,2,4-triazines and their
aza Diels–Alder reactions. The reported method facilitates the synthesis of functionally diverse bipyr-
idines that provides fine-tuning of photophysical properties of new ligands and their Zn(II) and Ru(II)
complexes. Some of substituted bipyridines exhibit ‘off–on’ fluorescence response toward Zn2þ cations.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 4 February 2008
Received in revised form 26 May 2008
Accepted 12 June 2008
Available online 14 June 2008
Keywords:
2,20-Bipyridines
1,2,4-Triazines
Luminescence
1. Introduction
2,20-bipyridine skeleton is polarized along the 5,50 positions,9 the 5
position of bipyridines is considered the best for introduction of
2,20-Bipyridines (bpy) are undoubtedly among the most widely
used ligands in coordination and supramolecular chemistry.1 The
photophysical properties of their metal complexes are of special
interest. In particular, electroluminescent chelate complexes have
been shown to be useful in organic light emitting diodes (OLEDs).2
Ruthenium complexes of functionalized bipyridines are presently
the most effective sensitizers for dye-sensitized solar cells (DSSCs).3
A critical element in designing and fabricating materials for
OLEDs is the control of their emission wavelength.4 One of the
approaches for controlling the emitted color of organic materials is
to append fluorescent chromophores to a polymeric backbone or to
blend such dyes into inert polymeric matrices.5,20 Ideally, one would
like to utilize one family of modular chromophores and tune their
photophysical characteristics as required.6 The parent oligopyr-
idines (2,20-bipyridine, 2,20:60,200-terpyridine, and 1,10-phenan-
throline) possess extremely low fluorescence quantum yields and
undesirable short emissionwavelengths. Introduction of conjugated
electron donor moieties, e.g., pyrrolylethenyl,7 phenylethynyl,11c
aminophenyl,8 or manisyl (4-methoxy-2,6-dimethylphenyl)9 leads
to an increase in quantum yields and a shift in emission wavelength
in the visible area. Since the most intense electronic transition of the
aromatic substituents. As an example 5-manisyl-2,20-bipyridines
have been previously shown to exhibit higher emission quantum
yields compared with the 2- and 4-manisyl analogs.9 In addition, an
aryl moiety at the b-position does not affect the coordination be-
havior of the ligand. DSSCs are in principle the opposite of OLEDs,
producing electrical energy from photonic energy. However, since
a sensitizer in DSSC must effectively absorb sunlight, conjugated
aromatic substituents in bipyridine are desirable at position 4 or 5.
The position 5 is more preferable due to the reasons mentioned
above. Although existing methods for the synthesis of symmetri-
cally functionalized 2,2-bipyridines permit the elaboration of many
different derivatives, the synthesis of bipyridines with differently
functionalized pyridine subunits is still not common. Onlyavery few
examples of the synthesis of unsymmetrically substituted 5-aryl-
bipyridines are known.9,10 They involve a sequence of the cross-
coupling reactions and/or require not easily accessible starting
materials. Therefore, it is of no surprise that most researchers focus
their intereston the use of more readilyaccessible 4,40-disubstituted
2,20-bipyridines.
2. Results and discussion
One of the most promising pathways toward unsymmetrically
substituted bipyridines is the [4þ2] cycloaddition of tailor-made
1,2,4-triazines.11 Based on this strategy, we report here an efficient
* Corresponding authors. Tel.: þ7 343 3623341; fax: þ7 343 3693058.
E-mail address: dnk@ios.uran.ru (D.N. Kozhevnikov).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.06.040

8964
V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
Ar
N
NH2
N
+
N
N
OH
3
Ar
N
N
Ar
N
N
Ar
O
Ar
O
N
N
R
R
N
Ar
N
1
NH2
2
OH
O
+
N
N
OH
3
R
Scheme 1. Retrosynthetic analysis of arylbipyridines 1.
method for the synthesis of 5-(hetero)aryl-2,20-bipyridines 1. The
key idea is as follows: if suitable 2-pyridyl-substituted 1,2,4-tri-
azines were readily accessible starting materials, the cycloaddition
reaction with 2,5-norbornadiene would accomplish two goals. First,
the triazine ring could be transformed into the desired pyridine
core. Secondly, the position of an aryl substituent in the pyridine
ring can be controlled by the structure of the 1,2,4-triazine starting
material. The synthesis of bipyridine 1 was planned as shown in
Scheme 1.
A potential problem arises for 1,2,4-triazines bearing a pyridine
residue at the position 3, a (hetero)aromatic substituent at position
6, but no substituent at position 5. Double condensation of the
appropriate carbamidrazones with 1,2-dicarbonyl compounds
provides one of the most straightforward syntheses of 1,2,4-
The suggested [5þ1] cycloaddition was found to be more
effective. Condensation of oximinohydrazones 3 with pyridine-2-
carboxaldehyde gave 1-aryl-2-oximino-1-(2-pyridylmethylene-
hydrazono)ethanes 8 in excellent yields. Open-chain hydrazones 8
exist in solutions in equilibrium with the cyclic 6-aryl-4-hydroxy-
3-(2-pyridyl)-3,4-dihydro-1,2,4-triazines
9 (according to NMR
spectroscopic data), which is typical for 4-hydroxy-3,4-dihydro-
1,2,4-triazines.15 In spite of the ratio of open-chain and cyclic iso-
mers in the mixture, dehydration of 9 should lead to the desired
triazines 2.
Indeed, heating the mixture of isomers in acetic acid for a short
time gave pyridyltriazines 2 in good yields (Scheme 3). Isolation of
the intermediates 8 and 9 from the reaction mixtures can be
omitted to make the synthetic procedure easier. Keeping in mind
that acetylarenes are quite accessible starting materials one can
realize that the approach allows an easy synthesis of a series of
pyridyltriazines with a variety of aromatic substituents. The same
procedure was applied to the reaction of hydrazones 3 with pyri-
dine-4-carboxaldehyde to give 3-(4-pyridyl)-1,2,4-triazines 7 in
good yields (Scheme 3).
It should be noted that oxidative aromatization of dihydro-
triazines like 9 is a useful method for the synthesis of 3,6-susbti-
tuted 1,2,4-triazine 4-oxides,15 while the dehydration of 9 has not
been previously observed. Indeed, we found that prolonged heating
of 3-aryl-4-hydroxy-3,4-dihydro-1,2,4-triazines 10 in acetic acid
did not result in aromatic 1,2,4-triazines 11, only starting materials
were isolated. Furthermore, when the product of condensation of
hydrazone 3 with pyridine-3-carboxaldehydeddihydrotriazine 12
was heated in acetic acid, 3-(3-pyridyl)-1,2,4-triazine 6 did not
triazines. In this procedure,
a-ketoaldehydes normally give
5-substituted 1,2,4-triazines.12 The obvious reason for such regio-
selectivity is that the first condensation of the amino group of
the amidrazone proceeds on the more reactive aldehyde group of
the a-ketoaldehyde followed by the second condensation on the
ketone carbonyl. To change this regioselectivity one can substitute
the formyl group with a less active substituent. Recently a method
for the synthesis of 6-phenyl-3-(2-pyridyl)-1,2,4-triazine has been
reported, where
a-hydroxyacetophenone was used for the con-
densation with the pyridylamidrazone.13 In this case, the formyl
group was formed by the oxidation of the hydroxyl group after the
first condensation. Earlier we communicated an alternative strat-
egy for the synthesis of 3-pyridyl-6-aryl-1,2,4-triazines.14 We de-
cided to use 1-aryl-1-hydrazono-2-oximinoethanes as the starting
material. The oximinohydrazones were obtained from readily
i
available acyl(hetero)arenes through nitrosation with PrONO and
reaction of the oximinoketones with hydrazine hydrate. This
sequence of reactions determines unambiguously the position of
the aromatic substituent in the assembled 1,2,4-triazine.
i
ii
HN
N
N
NC
OMe
4
Herein we describe two methods for the synthesis of triazines 2
starting from oximinohydrazones 3: [4þ2] cycloaddition with
cyanopyridines (four atoms of the triazine ring, N-2, N-1, C-6, C-5
fragments, are introduced with the oximinohydrazone and two
atoms, C-3, N-4 fragmentsdwith the nitrile group of the cyano-
pyridine) and [5þ1] cycloaddition with pyridinecarboxaldehydes
(five atoms of the triazine ring, N-2, N-1, C-6, C-5, N-4 fragments,
are introduced with the oximinohydrazone and one atom,
C-3dwith the aldehyde group of the pyridinecarboxaldehyde).
However, 2-cyanopyridine itself did not react with the oximino-
hydrazones 3. Thus we decided to use methoxyimidate 4 obtained
in situ from 2-cyanopyridine in MeOH in the presence of MeONa.
Addition of the oximinohydrazones 3 to the mixture obtained
resulted in an open-chain product 5. The latter was used without
purification and gave after refluxing in AcOH the desired aryl-
triazines 2a,b in moderate yields. By following an identical pro-
cedure with 3- and 4-cyanopyridine the triazines 6a,b and 7a,b
were obtained in 27–50% yields (Scheme 2).
Ar
N
N
Ar
N
iii
N
N
(30-40%)
N
OH
H2N
N
N
2a,b
5
NC
Ar
N
N
i, ii, iii
(27-45%)
N
N
6a,b
N
CN
Ar
N
N
N
i, ii, iii
(45-50%)
N
N
7a,b
Ar = Ph (a), Tol (b)
Scheme 2. Reagents and conditions: (i) MeONa/MeOH, 23 ꢀC, 1 h; (ii) hydrazone 3,
MeOH, 23 ꢀC, 1 h; (iii) AcOH, refluxing, 0.5 h.

V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
8965
Ar
Ar
N
N
Ar
N
N
OH
8
Ar
NNH2
N
Ar
N
N
iii
ii
N
N
i
N
H
N
(85-95%)
(60-85%)
N
(93-98%)
H
N
N
OH
OH
N
1a-k
2a-k
3a-k
9
v
iv
Ph
N
N
Ar
Ar
N
N
Ph
Ph
N
N
N
ii
N
vi
H
N
OH
7a,b,e
N
N
R
11
10
R
(80-95%)
iii
R = H, Me, Cl, NO2
N
Ph
N
N
ii
N
N
N
OH
N
H
N
N
15b,e
6
12
Ar = Ph (a), 4-Me-C6H4 (b), 4-MeO-C6H4 (c), 4-Cl-C6H4 (d), 4-Br-C6H4 (e), 3,4-Cl2-C6H3 (f), 4-NO2-C6H4 (g),
2-pyridyl (h), 4-pyridyl (i), thienyl-2 (j), naphthyl-2 (k)
Scheme 3. Reagents and conditions: (i) pyridyl-2-carboxaldehyde, EtOH; (ii) AcOH, 90 ꢀC, 1 h; (iii) 2,5-norbornadiene, o-xylene, reflux, 24 h; (iv) pyridyl-4-carboxaldehyde, AcOH,
rt, 1 h then 90 ꢀC, 1 h; (v) R–C6H4–CHO, EtOH; (vi) pyridyl-3-carboxaldehyde, EtOH.
form. Thus aromatization of 4-hydroxy-3,4-dihydro-1,2,4-triazines
via dehydration is possible under the following conditions: (1) the
pyridine residue is at position 3 of the triazine ring; (2) a nitrogen
formation of intermediate 6-aryl-3-(50-methoxycarbonyl-2-pyr-
idyl)-1,2,4-triazines 17a–l (Scheme 5). The key reagent in this case
is 5-methoxycarbonylpyridine-2-carboxaldehyde 18, which was
obtained from pyridine-2,5-dicarboxylic acid by esterification,
atom is in a- and g-position of the pyridyl group. Such selectivity in
the dehydration step can be explained by the formation of en-
amine 13 from dihydrotriazine 9 as the first step of the reaction. The
en-amine 13 can be represented as Zwitterion 14, which under
acidic conditions loses the hydroxyl group to give aromatic triazine
2. This process can be considered as an E1cb elimination of water
(2-pyridyl as an internal base) (Scheme 4).
mono reduction of
a
-carboxylate and oxidation using SeO2.
COOMe
i,ii, iii, iv
COOMe
v
(50-80%)
MeOOC
N
OHC
N
18
Ar
N
Ar
N
vi
Ar
N
N
H
N
N
N
N
(55-70%)
COOMe
N
N
COOMe
17a-l
16a-l
OH
13
Ar
N
N
N
Ar = Ph (a), 4-Me-C6H4(b), 4-MeO-C6H4(c), 4-Cl-C6H4(d),
4-Br-C6H4(e), 4-pyridyl (i), 2-naphthyl (k), 1-naphthyl (l)
9
-HOH
Ar
N
N
N
N
C
H
N
Scheme 5. Reagents and conditions: (i) SOCl2; (ii) MeOH, reflux; (iii) NaBH4, MeOH/
THF, 0 ꢀC; (iv) MnO2, CHCl3, reflux, 3–4 h; (v) hydrazone 3, AcOH, 23 ꢀC, 1 h then 90 ꢀC,
1 h; (vi) 2,5-norbornadiene, o-xylene, reflux, 20 h.
-
+
2
OH
14
Unsymmetrically substituted quinoline analogs of bipyridines
can be obtained by the reported method. In this case, quinoline-2-
carboxaldehyde 19 (available from quinaldine) was used as the
starting material. The reaction of 19 with oximinohydrazones 3
afforded 3-quinolyl-1,2,4-triazines 20a–c (Scheme 6). Refluxing
triazines 20a–c with norbornadiene in xylene gave 2-(5-aryl-2-
pyridyl)quinolines 21a–c in 50–70% total yield. However, it was
interesting to apply the described method to the synthesis of an-
alogs of the widely used ligand 8-hydroxyquinoline. Starting from
8-hydroxyquinoline-2-carboxaldehyde, 21 was obtained by allylic
oxidation of the accessible 8-hydroxy-2-methylquinoline using
SeO2.17 The cyclization reactions of 21 with hydrazones 3 gave
hydroxyquinolyltriazines 23 in high yields. The following aza Diels–
Alder reactions of triazine 23a with 2,5-norbornadiene afforded the
desired 2-(5-aryl-2-pyridyl)-8-hydroxyquinoline 24a (Scheme 6).
Table 1 summarizes the photophysical data of new bipyridines
in acetonitrile solutions. Lowest energy absorption maxima of
2,20-bipyridines 1, 16 are not affected by the nature of the aryl
Scheme 4. Mechanism of the cyclization of 1,2,4-triazines.
With the desired 1,2,4-triazines now readily available, the aza
Diels–Alder reactions planned with 2,5-norbornadiene were car-
ried out under forcing conditions (8–15 h reflux in o-xylene) to give
the desired 2,20-bipyridines 1 and 2,40-bipyridines 15 in 80–95%
yields (Scheme 3). It is noteworthy that the reactions are easily
scaled up to produce multi-gram quantities of bipyridines 1 (we
obtained 5 g of bipyridine 1b from a single operation). The forcing
conditions did not affect the yields or purities of bipyridines 1.
Encouraged by these results, we investigated the synthesis of
unsymmetrically substituted 2,20-bipyridines by the method. Using
substituted pyridinecarboxaldehydes is an additional means of
providing diverse arylbipyridines. We decided to explore this by the
synthesis of arylbipyridines bearing a carboxylate group, because of
the importance of bipyridinecarboxylic acids as building blocks
for supramolecular chemistry.16 5-Aryl-50-methoxycarbonyl-2,20-
bipyridines 16a–l were synthesized by the same route through

8966
V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
R
R
H3C
N
OHC
N
i
ii
(76-81%)
19 (R = H)
22 (R =OH)
Ar
N
Ar
R
N
R
iii
N
N
N
(64-76%)
N
20a-c, e (R = H)
23a-c (R =OH)
25c (R =OMe)
21a-c, e (R = H)
24a (R =OH)
26c (R =OMe)
iii
Ar = Ph (a), 4-Me-C6H4 (b), 4-MeO-C6H4 (c)
Scheme 6. i) SeO2, dioxane, 80 ꢀC, 16–20 h; (ii) hydrazone 3, AcOH, 23 ꢀC, 1 h, then
90 ꢀC, 1 h; (iii) 2,5-norbornadiene, o-xylene, reflux, 20 h.
Figure 1. Quantum yields of new aryl-2,20-bipyridines.
substituents and lie in the interval of wavelength of 298–326 nm.
On the other hand, the substituents control the emission maxima
(298–438 nm) and quantum yields (0.002–0.90) (Table 1). All new
bipyridines can be divided into two groups: exhibiting weak fluo-
delocalized over the whole conjugated system and can be denoted
as
p and p , respectively (Fig. 2). Apparently, lone pairs of nitrogen
*
atoms substantially contribute to the second HOMO (HOMO-1),
which can be denoted as n-orbital. This shows competition be-
tween n–p and
*
p
–
p excited states, and there is no ICT from
*
rescence (
emitting (
F
F<0.20) with short Stoke’s shifts (50–60 nm) and bright
F>0.30) with large Stoke’s shifts (80–130 nm) (Fig. 1).
F
HOMO to LUMO. Contrary to that, excitation of 16b leads to the ICT
from the HOMO localized on the aryl substituent and the central
pyridine to the LUMO localized on the pyridine and ester group
(Fig. 2).
The lowest energy absorbance maxima of bipyridines of both
groups display a very small red shift upon increasing solvent po-
larity. Solvent polarity has little influence on the emission maxima
of bipyridines of the first group. For example, 1a and 21a exhibit
a very weak emission. Fluorescence maxima of phenyl derivatives
1a and 21a undergo slight red shifts upon increasing solvent po-
larity (8–12 nm on comparing emission maxima in toluene and
methanol). This behavior can be explained by close proximity of the
Increasing polarization along 5,50-axis of the bipyridine moiety
(introduction of electron-donating aryl substituents at the position
5 and/or electron-withdrawing ester group at the position 50) re-
sults in red shifts of emission maxima and increasing fluorescence
quantum efficiency. Observing difference in luminescence means
that a difference in the nature of the excited states of these two
groups of bipyridines is observed. It was considered to be n–
p
*
, p–
p
*
, and intraligand charge transfer (ICT) excited states. DFT calcu-
lation (B3LYP/6-31G**) was carried out on bipyridine 1b (from the
first group) and 16b (from the second group). The results for 1b
show that both HOMO and LUMO having
p character are
Table 1
Photophysical data for new arylbipyridines
lmax (Zn2þ
)
d [nm]
lem (Zn2þ
)
e [nm]
a
c
Compound
Ar
lmax [nm]
lemb [nm]
(FF
)
1a
1b
1c
1d
1e
1f
1g
1h
Ph
Tol
298
302
309
301
299
300
320
305
298
322
312
312
317
326
313
313
308
322
306
357
360
399
354
355
357
377
365
385
375
378
380
395, 430sh.
438, 510sh.
376
378
350
435
438
370
377, 429sh.
432
367
377
434
0.032
0.17
0.89
0.050
0.008
0.036
0.025
0.006
0.002
0.22
322
326
339
326
322
320
322
319
378, 430sh.
403, 423sh.
460, 512sh
401
397
380
396, 435
371
354
4-MeO–C6H4
4-Cl–C6H4
4-Br–C6H4
3,4-Cl2–C6H3
4-NO2–C6H4
2-Pyridyl
4-Pyridyl
2-Thienyl
2-Naphthyl
Ph
1i
1j
1k
316
344
326
328
339
355
333
332
324
335
344
359
360
367
358
312, 358
375
437
0.90
0.045
0.68
467, 517
410, 430
438
520
434
432
352, 364
520
16a
16b
16c
16d
16e
16i
16k
16l
21a
21b
21c
21e
24a
26c
Tol
4-MeO–C6H4
4-Cl–C6H4
4-Br–C6H4
4-Pyridyl
2-Naphthyl
1-Naphthyl
Ph
0.49
0.061
0.062
0.072
0.52
0.30
530
315sh., 324, 340sh.
315sh., 326, 342sh.
318sh., 328, 342sh.
315sh., 326, 340sh.
295, 326
0.012
0.051
0.65
0.010
0.030
0.35
400, 430
436, 510sh.
520
434
d
Tol
4-MeO–C6H4
4-Br–C6H4
Ph
4-MeO–C6H4
335
525
a
Absorption maxima in MeCN.
Emission maxima in MeCN.
b
c
Fluorescence quantum yields were measured using anthracene as the standard (
Absorption maxima in MeCN after addition of excess Zn(ClO4)2.
Emission maxima in MeCN after addition of excess Zn(ClO4)2.
F
¼0.27 in EtOH20).
d
e

V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
8967
Figure 4. ORTEP view of [Zn(1b)Cl2]. Selected bond lengths, (Å): Zn(1)–N(1) 2.093,
Zn(1)–N(2) 2.078, Zn(1)–Cl(1) 2.243, Zn(1)–Cl(2) 2.232.
Zn(ClO4)2 into solutions of bipyridines of the second group resulted
in larger red shifts of the emission maxima (60–100 nm) and
somewhat decreasing fluorescence intensity (Table 1).
We isolated complex [Zn(1b)Cl2] from the reaction of 1b with
ZnCl2. Single crystals of [Zn(1b)Cl2] suitable for X-ray diffraction
were grown from acetonitrile. The molecular structure of the
complex [Zn(1b)Cl2] is shown in Figure 4, and selected bond dis-
tances are given in the caption. The bipyridine fragment is planar
(torsion angle is 5.26ꢀ), the torsion angle between the pyridine ring
and the aromatic substituent is 10.43ꢀ. The Zn atom adopts a tet-
Figure 2. Pictorial presentation of HOMO and LUMO of 1b (left) and 16b (right) cal-
culated at the B3LYP/6-31G**
.
n–
excited state in fluorescence leads to low emission quantum yield,
since the n– excited state often decays through nonradiative
p
*
and
p
–
p
*
excited states. Greater contribution of the n–
p
*
p
*
pathways. In contrast, emission maxima of bipyridines of the sec-
ond group are affected considerably by solvent polarity. For ex-
ample, large red shifts were observed for bright fluorescence of 16b
upon increasing solvent polarity (60 nm on comparing emission
maxima in benzene and methanol) (Fig. 3). This indicates great
contribution of the ICT excited state to emission of 16b. Fluorescent
spectra of 16b recorded in different solvents can be split into two
overlapping components: the short-wavelength band of emission
rahedral coordination geometry. Complex face-to-face
p–p stack-
ing interactions between the phenylbipyridine ligands are also
evident, the interplanar separations are in the range 3.5 Å, and the
glide-related complexes are linked in a head-to-tail fashion to
generate a supramolecular architecture of infinite chains (see
Supplementary data).
Many of the bipyridines of the first group can be assumed as
potential ‘off–on’ fluorescent probes for Zn(II) ions. For example,
titrating Zn(ClO4)2 into a 1 mM solution of pyridylquinoline 21a in
from the
p
–
p excited state, and the long-wavelength band of
*
emission from ICT excited state. The latter increases with increasing
solvent polarity (Fig. 3).
Co-ordination metal ion, e.g., Zn2þ, involves the lone pairs of the
acetonitrile shows increasing emission intensity by a factor 200
(excitation at the isobestic point 333 nm) measured at the complex
emission maximum (430 nm) (Fig. 5). Other transition metal ions
(Ni2þ, Cu2þ, Co2þ) quench the emission of 21a and any other new
bipyridines.
Reactions of new bipyridines 1, 16 with Ru(bpy)2Cl2 followed by
treatment of the reaction mixtures with NH4PF6 resulted in the
formation of the corresponding complexes [Ru(bpy)2(1a–e,i)](PF6)2
and [Ru(bpy)2(16a–c)](PF6)2. These complexes exhibit typical for
polypyridine-Ru(II) complexes photophysical properties (Table 1).
Lowest energy absorption bands for the complexes are centered
around 450 nm that is very similar to absorption of parent [Ru(b-
py)3](PF6)2.19 Fluorescence maxima of new complexes are red
shifted in comparison with those of [Ru(bpy)3](PF6)2. The presence
of the electron-withdrawing ester group in bipyridines 16a–c sta-
bilizes MLCT excited states and causes larger red shifts (56–60 nm).
nitrogen atoms of bipyridines and excludes n–
resulting in intensive fluorescence from
deed, addition of excess Zn(ClO4)2 to the solutions of bipyridines of
the first group leads to moderate red shifts of the emission maxima
(20–60 nm) and significant enhanced emission intensity. Titrating
p
*
transitions,
p–
p
*
excited states.18 In-
3. Conclusions
The relatively simple synthesis and availability of numerous
precursors enable the preparation of 5-aryl-2,20-bipyridines.
Structural diversity leads to fine-tunable chromophores with di-
verse photophysical properties, where changes in the substitution
patterns, solvation, and co-ordination are translated into dramatic
spectral changes. Unique selective responses allow new ligands to
be considered as sensitive probes for zinc(II).
Figure 3. Fluorescence spectra of 16b recorded in different solvents.

8968
V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
Figure 5. (A) Fluorescence enhancement of 21a as a function of Zn2þ concentration. Spectra were acquired in MeCN solutions. Compound 21a (1
aliquots of Zn(ClO4)2 (0–0.5 M). (B) Fluorescence as a function of added Zn(II) monitored at 430 nm (molar ratio plot).
mM) was titrated with 0.05 mM
m
4. Experimental section
4.1. General
diffraction. Crystal data for [Zn(1b)Cl2] were measured with an
Xcalibur 3 CCD (graphite monochromator, Mo K ): C17H14Cl2N2Zn,
a
FW¼382.57, needle, a¼20.978(6), b¼8.436(2), c¼9.792(3) Å,
a
¼90.00ꢀ,
b
¼96.24(2)ꢀ,
g
¼90.00ꢀ, V¼1722.7(8) Å3, T¼295(2) K,
All solvents were purified by standard methods prior to use.
Melting points are uncorrected. NMR spectra were recorded on a
400 MHz Bruker Avance DRX spectrometer. Electronic absorption
spectra were recorded on a Varian Cary 50 Bio UV–visible spec-
trophotometer and the emission spectra were measured on a
Varian Cary Eclipse fluorescence spectrophotometer. Fluorescence
quantum yields were determined in EtOH using optically matching
solutions of anthracene (Fstd 0.27 in EtOH)20 for new bipyridines or
[Ru(bpy)3]Cl2$6H2O (Fstd 0.042 in deaerated water)21 for new Ru
complexes as the standard and the quantum yields were calculated
using Eq. 1.
space group-P2ybc, Z¼4, 3427 reflections were used in all calcula-
tions. R¼0.0402. Crystallographic data (excluding structure factors)
for the structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publi-
cation number CCDC 668968. Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [fax: þ44(0) 1223 336033 or e-mail: deposit@
ccdc.cam.ac.uk].
4.3. Typical procedure for the synthesis of hydrazones 3
ꢀ
ꢁ.ꢀ
ꢁ
Corresponding acetophenone (0.5 mol) was added to the solu-
tion prepared by dissolving Na (11.5 g) in EtOH (200 mL) at 10 ꢀC.
After 2 min iso-propylnitrite was added, and the resulting mixture
was stirred at 10–15 ꢀC for 2 h and kept at room temperature
overnight. The precipitate of the sodium salt of iso-nitro-
soacetophenone was filtered off, dried in vacuo, and dissolved in
water (100–200 mL) at room temperature. Acetic acid (21 mL,
0.35 mol) was added to the solution, mixture was cooled by adding
of ice (50 g), the crystals of the iso-nitrosoacetophenone were
filtered off, and dried under reduced pressure. The latter was dis-
solved in the mixture of EtOH (100 mL) and hydrazone hydrate
(25 mL, 0.5 mol) at 40–50 ꢀC and the mixture was kept for 1 h at
room temperature. Water (300–500 mL) was added, appeared
crystals were filtered off and dried. The crude hydrazone 3 was used
directly in the next step.
FF
¼
Fstd
A
stdFh2
AFstdh2std
(1)
where, A and Astd are the absorbance of the sample and standard
solutions, respectively, at the excitation wavelength, F and Fstd are
relative integrated fluorescence intensities of the sample and
standard solutions correspondingly,
indexes of the corresponding solutions (pure solvents were
assumed).
All reagents were obtained from commercial suppliers and used
without further purification. Solvents were dried by standard
methods and distilled under nitrogen before use. The C, H, and N
analyses were carried out with a Perkin–Elmer PE 2400 micro-
analyzer. Mass spectra were determined with a Varian CH-5 mass
spectrometer. NMR spectra were recorded on a Bruker DPX-300
instrument at 300 MHz (1H) or 75.4 MHz (13C), using SiMe4 (1H and
13C NMR) as standard.
h and hstd are the refractive
4.4. Typical procedure for the synthesis of 1,2,4-triazines 2
and 7 starting from pyridinecarboxaldehydes
4.2. X-ray crystallography for complex [Zn(1b)Cl2]
To solution of 1-hydrazono-2-oximino-1-arylethanes 3a–k
(8.4 mmol) in EtOH (50 mL) was added 2-pyridinecarboxaldehyde
or 4-pyridinecarboxaldehyde (8.4 mmol). The mixture was stirred
at 23 ꢀC for 12 h. Appeared crystals were filtered off, then dissolved
in AcOH at 90 ꢀC, heated at this temperature for 1 h, allowed to cool
A solution of bipyridine 1b (50 mg, 0.13 mmol) in acetonitrile
(30 mL) was added to a solution of ZnCl2 (19 mg, 0.13 mmol) in
acetonitrile (30 mL). The resulting colorless solution was kept for 13
days at rt for slow evaporation to yield crystals suitable for X-ray

V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
8969
to room temperature, and then diluted with water (10 mL). The
resulting precipitate was filtered off, washed with water and eth-
anol. The crude triazine was used directly in the next step.
4.4.11. 6-(2-Naphthyl)-3-(2-pyridyl)-1,2,4-triazine (2k)
Yield 1.69 g, 71%, mp 143–145 ꢀC. 1H NMR (DMSO-d6)
3H), 7.9–8.1 (m, 4H), 8.41 (dd, 1H, J 7.8, 1.0 Hz), 8.52 (ddd, 1H, J 7.9,
1.2, 0.7 Hz, H-30), 8.82 (m, 2H), 9.62 (s, 1H, H-5).
d: 7.55 (m,
4.4.1. 6-Phenyl-3-(2-pyridyl)-1,2,4-triazine (2a)
Yield 1.36 g, 69%, mp 148–150 ꢀC. 1H NMR (DMSO-d6)
d
: 7.58 (m,
4.4.12. 6-Phenyl-3-(4-pyridyl)-1,2,4-triazine (7a)
4H, PhþH-50), 8.03 (ddd, 1H, J 7.8, 7.8, 1.2 Hz, H-40), 8.31 (m, 2H, Ph),
8.54 (d, 1H, J 7.8 Hz, H-30), 8.83 (dd, 1H, J 4.7, 1.2 Hz, H-60), 9.50 (s,
1H, H-5).
Yield 1.48 g, 75%, mp 166–168 ꢀC. 1H NMR (DMSO-d6)
d: 7.64 (m,
3H), 8.32 (m, 4H), 8.86 (m, 2H, H-30,50), 9.52 (s, 1H, H-6). EIMS m/z
(I (%)): 234 (4) [Mþ], 206 (2) [MꢁN2], 102 (100).
4.4.2. 6-Tolyl-3-(2-pyridyl)-1,2,4-triazine (2b)
4.4.13. 6-(4-Methylphenyl)-3-(4-pyridyl)-1,2,4-triazine (7b)
Yield 1.50 g, 72%, mp 164–166 ꢀC. 1H NMR (DMSO-d6)
d
: 2.50 (s,
Yield 1.75 g, 84%, mp 192–194 ꢀC. 1H NMR (DMSO-d6)
d: 2.51 (s,
3H, CH3), 7.41 (d, 2H, J 8.2 Hz, Tol), 7.57 (ddd, 1H, J 7.8, 4.7, 1.2 Hz, H-
50), 8.02 (ddd, 1H, J 7.8, 7.8, 1.2 Hz, H-40), 8.18 (d, 2H, J 8.2 Hz, Tol),
8.50 (d, 1H, J 7.8 Hz, H-30), 8.81 (dd, 1H, J 4.7, 1.2 Hz, H-60), 9.43 (s,
1H, H-5). EIMS m/z (I (%)) 248 (5) [Mþ], 220 (10) [MꢁN2], 116 (100).
3H), 7.44 (m, 2H, HAr), 8.20 (m, 2H, HAr), 8.35 (m, 2H, H-20,60), 8.85
(m, 2H, H-30,50), 9.43 (s, 1H, H-6). EIMS m/z (I (%)): 248 (6) [Mþ], 220
(8) [MꢁN2], 116 (100).
4.4.14. 6-(4-Bromophenyl)-3-(4-pyridyl)-1,2,4-triazine (7e)
4.4.3. 6-(4-Methoxyphenyl)-3-(2-pyridyl)-1,2,4-triazine (2c)
Yield 2.10 g, 80%, mp 208–210 ꢀC. 1H NMR (DMSO-d6)
d: 7.84 (m,
Yield 1.24 g, 56%, mp 184–186 ꢀC. 1H NMR (DMSO-d6)
d: 3.88 (c,
2H, HAr), 8.30 (m, 4H), 8.84 (m, 2H, H-30,50), 9.57 (s, 1H, H-6).
3H, OCH3), 7.12 (d, 2H), 7.55 (ddd, 1H, J 7.8, 4.7, 1.2 Hz, H-50), 7.99
(ddd, 1H, J 7.8, 7.8, 1.2 Hz, H-40), 8.25 (d, 2H), 8.47 (dd, 1H, J 4.7,
0.7 Hz, H-30), 8.80 (dd, 1H, J 4.7, 1.2 Hz, H-60), 9.42 (s, 1H, H-5). MS
m/z (I (%)) 264 (8) [Mþ], 236 (8) [MꢁN2], 132 (100).
4.5. Typical procedure for the synthesis of triazines 6
3-Cyanopyridine (0.06 mol) was dissolved in the solution of
sodium methoxide obtained from sodium (20 mg) and MeOH
(20 mL). The resulting solution was stirred at 23 ꢀC for 1 h and
corresponding hydrazone 3 (0.06 mol) was added, and the mixture
was stirred at room temperature for additional 1 h. The solvent was
removed under reduced pressure, and the residue (oil) was
refluxed in acetic acid (20 mL) for 0.5 h. The resulting mixture was
diluted with water (40 mL), crystals appeared were filtered off, and
recrystallized from ethanol.
4.4.4. 6-(4-Chlorophenyl)-3-(2-pyridyl)-1,2,4-triazine (2d)
Yield 1.92 g, 85%, mp 187–189 ꢀC. 1H NMR (DMSO-d6)
d: 7.59 (m,
2H), 7.68 (ddd, 1H, J 7.80, 4.75, 1.25 Hz), 8.05 (ddd, 1H, J 7.80, 7.80,
1.25 Hz), 8.34 (d, 2H), 8.50 (dd, 1H, J 4.25, 1.5 Hz), 8.83 (ddd, 1H, J
4.75, 0.75 Hz), 9.54 (s, 1H). EIMS m/z (I (%)): 270 (2) [Mþ], 268 (5)
[Mþ], 136 (100).
4.4.5. 6-(4-Bromophenyl)-3-(2-pyridyl)-1,2,4-triazine (2e)
Yield 1.92 g, 73%, mp 118–120 ꢀC. 1H NMR (DMSO-d6)
2H), 7.65 (ddd, 1H, J 7.80, 4.75, 1.25 Hz), 8.00 (ddd, 1H, J 7.80, 7.80,
1.25 Hz), 8.31 (d, 2H), 8.48 (dd, 1H, J 4.25, 1.5 Hz), 8.79 (ddd, 1H, J
4.75, 0.75 Hz), 9.52 (s, 1H).
d: 7.48 (m,
4.5.1. 3-(3-Pyridyl)-6-phenyl-1,2,4-triazine (6a)
Yield: 45%, mp 155–156 ꢀC. 1H NMR (DMSO-d6)
d: 7.58 (m, 4H),
8.28 (m, 2H, C6H5), 8.76 (m, 2H), 9.47 (s, 1H), 9.60 (m, 1H). Found, %:
C, 71.86; H, 4.14; N, 24.08. C14H10N4. Calculated, %: C, 71.78; H, 4.30;
N, 23.92.
4.4.6. 6-(3,4-Dichlorophenyl)-3-(2-pyridyl)-1,2,4-triazine (2f)
Yield 2.06 g, 81%, mp 215–216 ꢀC. 1H NMR (DMSO-d6)
d: 7.60
4.5.2. 6-(4-Methylphenyl)-3-(3-pyridyl)-1,2,4-triazine (6b)
(ddd, 1H, J 7.9, 4.7, 1.2 Hz, H-50), 7.85 (d, 1H, J 8.5 Hz, H-500), 8.05
(ddd, 1H, J 7.9, 7.9, 1.7 Hz, H-40), 8.30 (dd, 1H, J 8.5, 2.0 Hz, H-600),
8.52 (ddd, 1H, J 7.9, 1.2, 0.7 Hz, H-30), 8.54 (d,1H, J 2.0 Hz, H-200), 8.83
(ddd, 1H, J 4.7, 1.2, 0.7 Hz, H-60), 9.60 (s, 1H, H-5).
Yield 27%, mp 159–160 ꢀC. 1H NMR (DMSO-d6)
d: 2.48 (m, 3H),
7.40 (m, 2H), 7.57 (m, 1H), 8.17 (m, 2H), 8.78 (m, 2H), 9.42 (s, 1H, H-
5), 9.57 (m, 1H). Found, %: C, 72.62; H, 4.78; N, 22.54. C15H12N4.
Calculated, %: C, 72.56; H, 4.87; N, 22.57 for C15H12N4 (248.29).
4.4.7. 6-(4-Nitrophenyl)-3-(2-pyridyl)-1,2,4-triazine (2g)
4.6. Typical procedure for the synthesis of bipyridines
(1) and (15)
Yield 1.92 g, 82%, mp>220 ꢀC. 1H NMR (DMSO-d6)
d: 7.61 (m,
1H), 8.05 (ddd, 1H, J 7.80, 4.75, 1.25 Hz), 8.45 (ddd, 2H, J 7.80, 7.80,
1.25 Hz), 8.60 (m, 3H), 8.85 (dd, 1H, J 4.25, 1.5 Hz), 9.65 (s, 1H).
Triazines 2a–l (3.1 mmol), bicyclo[2.2.1]hepta-2,5-diene
(1.58 mL, 15.5 mmol), and o-xylene (30 mL) were refluxed for 24 h
and cooled to room temperature. The solvent was removed under
reduced pressure, residue was purified by column chromatography
(silica gel, CH2Cl2) to give arylbipyridines 1a–l. Analytical sample of
1 was recrystallized from ethanol.
4.4.8. 3,6-Bis(2-pyridyl)-1,2,4-triazine (2h)
Yield 1.32 g, 67%, mp 155–157 ꢀC. 1H NMR (DMSO-d6)
d: 7.58
(ddd, 2H, J 7.6, 4.7, 1.2 Hz), 8.05 (ddd, 2H, J 7.6, 7.6, 1.8 Hz), 8.61 (ddd,
2H, J 7.9, 1.0, 1.0 Hz), 8.78 (ddd, 1H, J 4.7, 1.6, 1.0 Hz), 8.81 (m, 1H),
9.69 (s, 1H).
4.6.1. 5-Phenyl-2,20-bipyridine (1a)
4.4.9. 3-(2-Pyridyl)-6-(4-pyridyl)-1,2,4-triazine (2i)
Yield 0.53 g, 73%, mp 83–85 ꢀC. 1H NMR (DMSO-d6)
d: 7.33–7.53
Yield 1.74 g, 88%, mp 193–194 ꢀC. 1H NMR (DMSO-d6)
d: 7.64
(m, 4H, PhþH-50), 7.72 (m, 2H, Ph), 7.89 (ddd, 1H, J 7.6, 7.6, 1.7 Hz, H-
40), 8.11 (dd, 1H, J 7.6, 2.5 Hz, H-4), 8.48 (m, 2H, H-3,30), 8.64 (ddd,
1H, J 7.6, 1.7, 1.2 Hz, H-60), 8.90 (d, 1H, J 2.5 Hz, H-6). Found, %: C,
82.77; H, 5.16; N, 11.98. Calculated, %: C, 82.73; H, 5.21; N, 12.06 for
(ddd, 1H, J 7.5, 4.7, 1.1 Hz), 8.09 (ddd, 1H, J 7.8, 7.8, 1.8 Hz), 8.26 (m,
2H), 8.52 (d, 1H, J 7.9 Hz), 8.85 (m, 3H), 9.65 (s, 1H).
4.4.10. 6-Thienyl-3-(2-pyridyl)-1,2,4-triazine (2j)
C16H12N2 (232.29).
Yield 1.31 g, 65%, mp 189–190 ꢀC. 1H NMR (DMSO-d6)
d: 7.28 (dd,
1H, J 5.0, 3.7 Hz), 7.56 (m, 1H), 7.82 (dd, 1H, J 5.0, 1.0 Hz), 8.00 (ddd,
1H, J 7.80, 7.80, 1.25 Hz), 8.14 (dd, 1H, J 3.7, 1.0 Hz), 8.47 (dd, 1H, J
4.25, 1.5 Hz), 8.8 (dd, 1H, J 4.75, 0.75 Hz), 9.48 (s, 1H). EIMS m/z
(I (%)): 240 (7) [Mþ], 212 (8) [MꢁN2], 108 (100).
4.6.2. 5-(4-Methylphenyl)-2,20-bipyridine (1b)
Yield 0.63 g, 82%, mp 90–92 ꢀC. 1H NMR (DMSO-d6)
d: 2.49 (s,
3H), 7.28 (m, 2H), 7.37 (ddd, 1H, J 7.6, 4.9, 1.2 Hz, H-50), 7.57 (m, 2H),
7.85 (ddd, 1H, J 7.6, 7.6, 1.7 Hz, H-40), 8.07 (dd, 1H, J 7.6, 2.5 Hz, H-4),

8970
V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
8.48 (m, 2H, H-3,30), 8.63 (ddd,1H, J 7.6,1.7,1.2 Hz, H-60), 8.85 (d,1H,
J 2.5 Hz, H-6). EIMS m/z (I (%)): 246 (100) [M]þ. Found, %: C, 82.87;
H, 5.76; N, 11.42. Calculated, %: C, 82.90; H, 5.73; N, 11.37 for
4.6.11. 5-(2-Naphthyl)-2,20-bipyridine (1k)
Yield 0.73 g, 84%, mp 130–132 ꢀC. 1H NMR (DMSO-d6)
d: 7.38
(ddd, 1H, J 7.8, 5.0, 1.2 Hz, H-50), 7.52 (m, 2H), 7.8–8.0 (m, 5H), 8.27
(m, 2H), 8.48 (ddd, 1H, J 7.8, 1.2, 0.7 Hz, H-30), 8.52 (dd, 1H, J 8.5,
1.0 Hz), 8.64 (ddd, 1H, J 4.8, 1.7, 1.2 Hz, H-60), 9.06 (d, 1H, J 2.3 Hz, H-
6). Found, %: C, 70.48; H, 4.19; N, 11.86. Calculated, %: C, 85.08; H,
5.00; N, 9.92 for C20H14N2 (282.35).
C
17H14N2 (246.31).
4.6.3. 5-(4-Methoxyphenyl)-2,20-bipyridine (1c)
Yield 0.69 g, 85%, mp 124–126 ꢀC. 1H NMR (DMSO-d6)
d: 3.84 (s,
3H), 7.02 (m, 2H), 7.35 (ddd, 1H, J 7.6, 4.9, 1.2 Hz, H-50), 7.65 (m, 2H),
7.86 (ddd, 1H, J 7.6, 7.6, 1.7 Hz, H-40), 8.05 (dd, 1H, J 7.6, 2.5 Hz, H-4),
8.42 (m, 2H, H-3,30), 8.62 (ddd,1H, J 7.6,1.7,1.2 Hz, H-60), 8.81 (d,1H,
J 2.5 Hz, H-6). Found, %: C, 77.91; H, 5.42; N, 10.57. Calculated, %: C,
77.84; H, 5.38; N, 10.68 for C17H14N2O (262.31).
4.6.12. 5-(4-Methylphenyl)-2,40-bipyridine (15b)
Yield 0.64 g, 84%, mp 156–158 ꢀC. 1H NMR (DMSO-d6)
d: 2.39 (s,
3H, CH3), 7.29 (m, 2H, HAr), 7.61 (m, 2H, HAr), 8.00–8.21 (m, 4H, H-
20,60,3,4), 8.66 (m, 2H, H-30,50), 8.95 (dd,1H, J 2.1,1.1 Hz, H-6). Found,
%: C, 82.75; H, 5.71; N, 11.21. Calculated, %: C, 82.90; H, 5.73; N, 11.37
for C17H14N2 (246.31).
4.6.4. 5-(4-Chlorophenyl)-2,20-bipyridine (1d)
Yield 0.79 g, 95%, mp 143–145 ꢀC. 1H NMR (DMSO-d6)
d: 7.38 (m,
1H), 7.51 (m, 2H), 7.75 (m, 2H), 7.88 (ddd, 1H, J 7.6, 7.6, 1.75 Hz), 8.13
(dd, 1H, J 8.25, 2.5 Hz), 8.46 (m, 2H), 8.65 (m, 1H), 8.90 (dd, 1H, J 2.5,
1.0 Hz). EIMS m/z (I (%)): 266 (100) and 268 (33) [M]þ. Found, %: C,
72.11; H, 4.10; N, 10.54. Calculated, %: C, 72.05; H, 4.16; N, 10.50 for
4.6.13. 5-(4-Bromophenyl)-2,40-bipyridine (15e)
Yield 0.73 g, 76%, mp 160–161 ꢀC. 1H NMR (DMSO-d6)
d: 7.60–
7.75 (m, 4H, HAr), 8.04 (m, 2H, H-20,60), 8.10 (dd, 1H, J 8.2, 0.9 Hz, H-
3), 8.16 (dd, 1H, J 8.2, 2.1 Hz, H-4), 8.67 (m, 2H, H-30,50), 8.99 (dd, 1H,
J 2.1, 0.9 Hz, H-6). Found, %: C, 61.85; H, 3.69; N, 8.81. Calculated, %:
C, 61.76; H, 3.56; N, 9.00 for C16H11BrN2 (311.18).
C
16H11ClN2 (266.73).
4.6.5. 5-(4-Bromophenyl)-2,20-bipyridine (1e)
Yield 0.77 g, 89%, mp 215–217 ꢀC. 1H NMR (DMSO-d6)
d: 7.38
(ddd, 1H, J 7.6, 4.75, 1.25 Hz), 7.67 (m, 4H), 7.88 (ddd, 1H, J 7.6, 7.6,
1.75 Hz), 8.13 (dd, 1H, J 8.25, 2.5 Hz), 8.47 (m, 2H), 8.65 (m, 1H), 8.90
4.7. 5-Methoxycarbonylpyridine-2-carboxaldehyde (18)
(dd, 1H, J 2.5, 1.0 Hz). 1H NMR (CDCl3),
d: 121.0, 121.1, 122.6, 123.9,
To the stirring mixture of dimethyl pyridine-2,5-dicarboxylate
(20 g, 102.4 mmol), ethanol (200 mL), and THF (70 mL) was added
NaBH4 (7.8 g, 204 mmol) at 0 ꢀC. The mixture was stirred at this
temperature for 8 h. Then, ice (100 g) and water (300 mL) were
added and resulting mixture was extracted with DCM (4ꢂ200 mL).
Combined organic extracts were dried over Na2SO4, the solvent
was removed under reduced pressure. So obtained crude methyl
2-hydroxymethylpyridine-2-carboxylate (10 g, 60 mmol) was dis-
solved in 1,4-dioxane (80 mL), SeO2 (5 g, 43 mmol) was added,
and the mixture was refluxed for 2 h. Solids were filtered off
and the solvent was removed under reduced pressure. The residue
was extracted with hot hexane (6ꢂ100 mL). Removing the solvent
from combined extracts gave crude aldehyde 18, which was
used on the next step without additional purification. Yield 7.2 g,
43%.
128.7, 132.3, 135.0, 135.4, 136.5, 137.0, 147.4, 149.3, 155.3, 155.7. EIMS
m/z (I (%)): 310 (99) and 312 (100) [M]þ. Found, %: C, 61.91; H, 3.50; N,
9.18. Calculated, %: C, 61.76; H, 3.56; N, 9.00 for C16H11BrN2 (311.18).
4.6.6. 5-(3,4-Dichlorophenyl)-2,20-bipyridine (1f)
Yield 0.85 g, 91%, mp 192–194 ꢀC. 1H NMR (DMSO-d6)
d: 7.40
(ddd, 1H, J 7.8, 5.0, 1.2 Hz, H-50), 7.64 (d, 1H, J 8.5 Hz, H-500), 7.72 (dd,
1H, J 8.5, 2.0 Hz, H-600), 7.89 (ddd, 1H, J 7.8, 7.8, 1.7 Hz, H-40), 7.97 (d,
1H, J 2.0 Hz, H-200), 8.19 (dd, 1H, J 7.6, 2.5 Hz, H-4), 8.44 (ddd, 1H, J
7.9, 1.2, 0.7 Hz, H-30), 8.49 (d, 1H, J 8.5 Hz), 8.65 (ddd, 1H, J 5.0, 1.2,
0.7 Hz, H-60), 8.94 (d, 1H, J 2.5 Hz, H-6). Found, %: C, 63.67; H, 3.30;
N, 9.17. Calculated, %: C, 63.81; H, 3.35; N, 9.30 for C16H10Cl2N2
(301.18).
4.6.7. 5-(4-Nitrophenyl)-2,20-bipyridine (1g)
Yield 0.75 g, 87%, mp 218–220 ꢀC. 1H NMR (DMSO-d6)
d: 7.48
(ddd, 1H, J 7.6, 4.75, 1.25 Hz), 7.97 (ddd, 1H, J 7.6, 7.6, 1.75 Hz), 8.12
(d, 2H), 8.38 (m, 2H), 8.50 (m, 2H), 8.72 (m, 1H), 9.13 (dd, 1H, J 2.5,
1.0 Hz). Found, %: C, 69.27; H, 3.90; N, 15.01. Calculated, %: C, 69.31;
H, 4.00; N, 15.15 for C16H11N3O2 (277.28).
4.8. Typical procedure for the synthesis of 5-methoxy-
carbonylpyridyltriazines (17a–l)
Mixture of aldehyde 18 (1.83 g, 12 mmol), hydrazones 3a–l
(12 mmol) and acetic acid (50 mL) was stirred at 23 ꢀC for 1 h.
Resulting mixture was heated at 90 ꢀC for 1 h, then cooled to room
temperature. Crystals of triazine 17 were filtered off and washed
with ethanol. The crude triazine 17 was used directly in the next
step.
4.6.8. 2,20:50,200-Terpyridine (1h)
Yield 0.62 g, 86%, mp 182–184 ꢀC. 1H NMR (DMSO-d6)
d: 7.33–
7.42 (m, 2H), 7.90 (m, 2H), 8.03 (m, 1H), 8.45–8.56 (m, 3H), 8.64–
8.71 (m, 2H), 9.30 (m, 1H). Found, %: C, 77.20; H, 4.61; N, 18.06.
Calculated, %: C, 77.23; H, 4.75; N, 18.01 for C15H11N3 (233.28).
4.6.9. 2,20:50,400-Terpyridine (1i)
4.8.1. 3-(5-Methoxycarbonyl-2-pyridyl)-6-phenyl-1,2,4-
Yield 0.64 g, 88%, mp 183–185 ꢀC. 1H NMR (DMSO-d6)
d: 7.31 (m,
triazine (17a)
1H), 7.62 (d, 2H, J 7.6 Hz), 7.95 (m, 1H), 8.14 (dd, 1H, J 2.25, 8.25 Hz),
8.37 (dd, 1H, J 2.25, 2.25 Hz), 8.55 (m, 3H), 8.92 (s, 1H). Found, %: C,
77.25; H, 4.68; N, 17.96. Calculated, %: C, 77.23; H, 4.75; N, 18.01 for
Yield 48%, mp>250 ꢀC. 1H NMR (DMSO-d6)
d: 3.97 (s, 3H, OCH3),
7.58–7.66 (m, 3H, Ph), 8.32 (m, 2H, Ph), 8.54 (dd, 1H, J 8.3, 2.1 Hz, H-
40), 8.66 (d, 1H, J 8.3 Hz, H-30), 9.31 (d, 1H, J 0.9 Hz, H-60), 9.54 (c, 1H,
H-5).
C
15H11N3 (233.28).
4.6.10. 5-(2-Thienyl)-2,20-bipyridine (1j)
4.8.2. 3-(5-Methoxycarbonyl-2-pyridyl)-6-(4-methylphenyl)-1,2,4-
Yield 0.64 g, 87%, mp 96–98 ꢀC. 1H NMR (DMSO-d6)
d: 7.16 (m,
triazine (17b)
1H), 7.35 (m,1H), 7.51 (dd,1H, J 5.2,1.2 Hz), 7.60 (dd,1H, J 5.2,1.2 Hz),
7.88 (ddd, 1H, J 7.9, 7.9, 1.8 Hz), 8.10 (dd, 1H, J 8.5, 2.44 Hz), 8.42 (m,
2H), 8.63 (m, 1H), 8.92 (m, 1H). Found, %: C, 70.48; H, 4.19; N, 11.86.
Calculated, %: C, 70.56; H, 4.23; N, 11.75 for C14H10N2S (238.31).
Yield 43%, mp 240–242 ꢀC. 1H NMR (DMSO-d6)
d: 2.49 (s, 3H,
CH3), 3.97 (s, 3H, OCH3), 7.42 (m, 2H, HAr), 8.21 (m, 2H, HAr), 8.52
(dd, 1H, J 8.3, 2.3 Hz, H-40), 8.64 (d, 1H, J 8.3 Hz, H-30), 9.30 (dd, 1H, J
2.3 Hz, H-60), 9.50 (s, 1H, H-5).

V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
8971
4.8.3. 3-(5-Methoxycarbonyl-2-pyridyl)-6-(4-methoxyphenyl)-
121.8, 125.5, 127.0, 129.9, 134.4, 135.0, 137.2, 138.0, 138.5, 147.7,
150.6, 153.5, 159.3, 165.9. Found, %: C, 74.98; H, 5.39; N, 9.31.
C19H16N2O2. Calculated, %: C, 74.98; H, 5.30; N, 9.20.
1,2,4-triazine (17c)
Yield 40%, mp 254–256 ꢀC. 1H NMR (DMSO-d6)
d
: 3.90 (s, 3H,
OCH3), 3.98 (s, 3H, COOMe), 7.15 (m, 2H, HAr), 8.27 (m, 2H, HAr), 8.49
(dd, 1H, J 8.1, 2.4 Hz, H-40), 8.63 (d, 1H, J 8.1 Hz, H-30), 9.30 (d, 1H, J
2.4 Hz, H-60), 9.49 (c, 1H, H-5).
4.9.3. 50-Methoxycarbonyl-5-(4-methoxyphenyl)-2,20-
bipyridine (16c)
Yield 84%, mp 208–210 ꢀC. 1H NMR (DMSO-d6)
d: 3.85 (s, 3H,
4.8.4. 6-(4-Chlorophenyl)-3-(5-methoxycarbonyl-2-pyridyl)-1,2,4-
OCH3), 3.95 (s, 3H, COOMe), 7.04 (m, 2H, HAr), 7.68 (m, 2H, HAr), 8.11
(dd, 1H, J 8.3, 2.0 Hz, H-4), 8.38 (dd, 1H, J 8.5, 2.0 Hz, H-40), 8.51 (d,
1H, J 8.3 Hz, H-3), 8.54 (d, 1H, J 8.5 Hz, H-30), 8.92 (d, 1H, J 2.0 Hz,
triazine (17d)
Yield 55%, mp>250 ꢀC. 1H NMR (DMSO-d6)
d: 3.97 (s, 3H,
COOMe), 7.66 (m, 2H, HAr), 8.35 (m, 2H, HAr), 8.53 (dd, 1H, J 8.1,
1.9 Hz, H-40), 8.66 (d, 1H, J 8.1 Hz, H-30), 9.31 (d, 1H, J 1.9 Hz, H-60),
9.58 (s, 1H, H-5).
H-6), 9.16 (d, 1H, J 2.0 Hz, H-60). 13C NMR (CDCl3)
d: 31.0, 52.4, 55.4,
114.7, 120.4, 121.9, 125.6, 128.3, 129.7, 134.7, 138.0,147.5, 150.6, 160.1,
165.9. EIMS m/z (I (%)): 320 [M]þ. Found, %: C, 71.16; H, 4.86; N, 8.89.
C19H16N2O3. Calculated, %: C, 71.24; H, 5.03; N, 8.74.
4.8.5. 6-(4-Bromophenyl)-3-(5-methoxycarbonyl-2-pyridyl)-1,2,4-
triazine (17e)
4.9.4. 5-(4-Chlorophenyl)-50-methoxycarbonyl-2,20-
bipyridine (16d)
Yield 51%, mp>250 ꢀC. 1H NMR (CF3COOD)
d: 4.28 (s, 3H,
COOMe), 7.89 (m, 2H, HAr), 8.06 (m, 2H, HAr), 9.46 (d, 1H, J 8.6 Hz, H-
30), 9.51 (dd, 1H, J 8.6, 1.6 Hz, H-40), 9.56 (s, 1H, H-5), 9.74 (d, 1H, J
1.6 Hz, H-60).
Yield 75%, mp 209–211 ꢀC. 1H NMR (DMSO-d6)
d: 3.94 (s, 3H,
COOMe), 7.53 (m, 2H, HAr), 7.82 (m, 2H, HAr), 8.23 (dd, 1H, J 8.5,
2.0 Hz, H-4), 8.41 (dd, 1H, J 8.3, 1.8 Hz, H-40), 8.54 (d, 1H, J 8.5 Hz,
H-3), 8.57 (d, 1H, J 8.3 Hz, H-30), 9.00 (d, 1H, J 2.0 Hz, H-6), 9.17 (d,
1H, J 1.8 Hz, H-60). Found, %: C, 66.58; H, 3.84; N, 8.55. C18H13N2O2Cl.
Calculated, %: C, 66.57; H, 4.03; N, 8.63.
4.8.6. 3-(5-Methoxycarbonyl-2-pyridyl)-6-(4-pyridyl)-1,2,4-
triazine (17i)
Yield 36%, mp>250 ꢀC. 1H NMR (DMSO-d6)
d: 3.97 (s, 3H,
COOMe), 8.26 (m, 2H, H-200,600), 8.55 (dd,1H, J 8.8, 2.0 Hz, H-40), 8.68
(d, 1H, J 8.8 Hz, H-30), 8.84 (m, 2H, H-300,500), 9.32 (d, 1H, J 2.0 Hz,
H-60), 9.68 (s, 1H, H-5).
4.9.5. 5-(4-Bromophenyl)-50-methoxycarbonyl-2,20-
bipyridine (16e)
Yield 63%, mp 206–208 ꢀC. 1H NMR (DMSO-d6)
d: 3.95 (s, 3H,
COOMe), 7.66 (m, 2H, HAr), 7.72 (m, 2H, HAr), 8.19 (dd, 1H, J 8.4,
2.1 Hz, H-4), 8.40 (dd, 1H, J 8.3, 2.0 Hz, H-40), 8.54 (d, 1H, J 8.4 Hz, H-
3), 8.57 (d, 1H, J 8.3 Hz, H-30), 8.97 (d, 1H, J 2.1 Hz, H-6), 9.17 (d, 1H, J
2.0 Hz, H-60). Found, %: C, 58.50; H, 3.29; N, 7.63. C18H13N2O2Br.
Calculated, %: C, 58.56; H, 3.55; N, 7.59.
4.8.7. 3-(5-Methoxycarbonyl-2-pyridyl)-6-(2-naphthyl)-1,2,4-
triazine (17k)
Yield 22%, mp>250 ꢀC. 1H NMR (DMSO-d6)
d: 3.97 (s, 3H,
COOMe), 7.63 (m, 2H, HAr), 8.07 (m, 3H, HAr), 8.45 (m, 1H, HAr), 8.55
(dd, 1H, J 8.1, 2.1 Hz, H-40), 8.67 (d, 1H, J 8.1 Hz, H-30), 8.93 (m, 1H,
H
Ar), 9.33 (d, 1H, J 2.1 Hz, H-60), 9.73 (s, 1H, H-5).
4.9.6. 5-Methoxycarbonyl-2,20:50,400-terpyridine (16i)
Yield 74%, mp 210–212 ꢀC. 1H NMR (DMSO-d6)
d: 3.95 (s, 3H,
4.8.8. 3-(5-Methoxycarbonyl-2-pyridyl)-6-(1-naphthyl)-1,2,4-
COOMe), 7.76 (m, 2H, H-300,500), 8.30 (dd, 1H, J 8.5, 1.8 Hz, H-40), 8.39
(dd, 1H, J 8.5, 1.8 Hz, H-4), 8.57 (d, 1H, J 8.5 Hz, H-30), 8.58 (d, 1H, J
8.5 Hz, H-3), 8.67 (m, 2H, H-200,600), 9.07 (d, 1H, J 1.8 Hz, H-60), 9.17
(d, 1H, J 1.8 Hz, H-6). Found, %: C, 70.22; H, 4.60; N, 14.23.
triazine (17l)
Yield 33%, mp 207–209 ꢀC. 1H NMR (DMSO-d6)
d: 3.99 (s, 3H,
COOMe), 7.57–7.74 (m, 3H, HAr), 7.88 (m, 1H, HAr), 8.02–8.21 (m, 3H,
H
Ar), 8.54 (dd, 1H, J 8.1, 2.1 Hz, H-40), 8.72 (d, 1H, J 8.1 Hz, H-30), 9.26
C17H13N3O2. Calculated, %: C, 70.09; H, 4.50; N, 14.42.
(s, 1H, H-5), 9.34 (d, 1H, J 2.1 Hz, H-60).
4.9.7. 50-Methoxycarbonyl-5-(2-naphthyl)-2,20-bipyridine (16k)
Yield 71%, mp 211–213 ꢀC. 1H NMR (DMSO-d6)
: 3.95 (s, 3H,
4.9. Typical procedure for the synthesis of 50-methoxy-
carbonyl-2,20-bipyridines (16)
d
COOMe), 7.54 (m, 2H, HAr), 7.88–8.05 (m, 4H, HAr), 8.32–8.44 (m,
3H, HAr, H-4,40), 8.59 (d, 2H, J 8.5 Hz, H-3,30), 9.14 (d, 1H, J 1.5 Hz,
H-6), 9.18 (d, 1H, J 1.3 Hz, H-60). Found, %: C, 77.48; H, 4.80; N, 8.17.
Suspension of the triazine 17 (5 mmol) and 2,5-norbornadiene
(1.5 mL, 15 mmol) in o-xylene (60 mL) were refluxed 16 h. Hexane
(40 mL) was added and the resulting mixture was kept for 0.5 h at
room temperature. Appeared crystals were filtered off and washed
with hexane.
C22H16N2O2. Calculated, %: C, 77.63; H, 4.74; N, 8.23.
4.9.8. 50-Methoxycarbonyl-5-(1-naphthyl)-2,20-bipyridine (16l)
Yield 71%, mp 151–153 ꢀC. 1H NMR (DMSO-d6)
: 3.96 (s, 3H,
d
COOMe), 7.45–7.65 (m, 4H, HAr), 7.84 (m, 1H, HAr), 7.98 (m, 2H, HAr),
8.05 (dd, 1H, J 7.9, 2.4 Hz, H-4), 8.43 (dd, 1H, J 8.4, 2.1 Hz, H-40), 8.62
(m, 2H, H-3,30), 8.79 (d, 1H, J 2.4 Hz, H-6), 9.20 (d, 1H, J 2.1 Hz, H-60).
Found, %: 77.77; H, 4.81; N, 7.99. C22H16N2O2. Calculated, %: C,
77.63; H, 4.74; N, 8.23.
4.9.1. 50-Methoxycarbonyl-5-phenyl-2,20-bipyridine (16a)
Yield 82%, mp 183–185 ꢀC. 1H NMR (DMSO-d6)
d: 3.94 (s, 3H,
OCH3), 7.20–7.60 (m, 3H, Ph), 7.72 (m, 2H, Ph), 8.15 (dd, 1H, J 8.2,
2.4 Hz, H-4), 8.38 (dd, 1H, J 8.2, 2.1 Hz, H-40), 8.55 (d, 1H, J 8.1 Hz, H-
3), 8.58 (d, 1H, J 8.2 Hz, H-30), 8.94 (d, 1H, J 2.þ4 Hz, H-6), 9.16 (d, 1H, J
2.1 Hz, H-60). EIMS m/z (I (%)): 290 (100) [M] . Found, %: C, 74.29; H,
4.58; N, 9.53. C18H14N2O2. Calculated, %: C, 74.47; H, 4.86; N, 9.65.
4.10. Typical procedure for the synthesis of quino-
linyltriazines (20)
4.9.2. 50-Methoxycarbonyl-5-(4-methylphenyl)-2,20-
To solution of hydrazone 3 (10 mmol) in AcOH (10 mL) was
added 2-quinolinecarboxaldehyde 22 (1.57 g, 10 mmol). The mix-
ture was stirred at room temperature for 1 h, heated at 90 ꢀC for
1 h, allowed to cool to room temperature, and then diluted with
water (10 mL). The resulting precipitate was filtered off, washed
with water and ethanol. The crude triazines 20a–c were used di-
rectly in the next step.
bipyridine (16b)
Yield 84%, mp 187–189 ꢀC. 1H NMR (DMSO-d6)
d: 2.40 (s, 3H,
CH3), 3.94 (s, 3H, OCH3), 7.31 (m, 2H, HAr), 7.64 (m, 2H, HAr), 8.17
(dd, 1H, J 8.3, 2.5 Hz, H-4), 8.40 (dd, 1H, J 8.4, 2.1 Hz, H-40), 8.51 (d,
1H, J 8.3 Hz, H-3), 8.55 (d, 1H, J 8.4 Hz, H-30), 8.94 (d, 1H, J 2.5 Hz,
H-6), 9.16 (d, 1H, J 2.1 Hz, H-60). 13C NMR (CDCl3)
d: 21.2, 52.4, 120.4,

8972
V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
4.10.1. 6-Phenyl-3-(20-quinolyl)-1,2,4-triazine (20a)
Yield 2.30 g, 81%, 1H NMR (DMSO-d6)
8.20 (d, 1H, J 8.2 Hz, H-80), 8.31 (d, 1H, J 8.5 Hz, H-40), 8.60 (d, 1H, J
8.5 Hz, H-30), 8.73 (dd, 1H, J 8.2, 0.8 Hz, H-3), 8.93 (dd, 1H, J 2.5, 0.8
d
: 7.73–7.62 (m, 4H, PhþH-
70), 7.86 (ddd, 1H, J 8.2, 7.9, 1.5 Hz, H-60), 8.08 (dd,1H, J 7.9, 1.5 Hz, H-
50), 8.22 (dd, 1H, J 7.9, 1.5 Hz, H-80), 8.33 (m, 2H, Ph), 8.58 (d, 1H, J
8.7 Hz, H-40), 8.64 (d, 1H, J 8.7 Hz, H-30), 9.58 (s, 1H, H-5).
Hz, H-6). 13C NMR (CDCl3)
d: 118.9, 121.9, 122.7, 126.9, 127.7, 128.3,
128.7, 129.7, 129.8, 132.3, 135.1, 135.7, 136.5, 136.9, 147.4, 148.0,
155.5, 155.7. EIMS m/z (I (%)): 360 (100) and 362 (99) [M]þ. Found,
%: C, 66.67; H, 3.58; N, 7.70. C20H13BrN2. Calculated, %: C, 66.50; H,
3.63; N, 7.75.
4.10.2. 6-Tolyl-3-(20-quinolyl)-1,2,4-triazine (20b)
Yield 2.55 g, 86%, 1H NMR (DMSO-d6)
d: 2.49 (s, 3H, Me), 7.38 (m,
2H), 7.64 (ddd, 1H, J 8.2, 7.9, 1.2 Hz, H-70), 7.80 (ddd, 1H, J 8.2, 7.9,
1.5 Hz, H-60), 7.99 (dd, 1H, J 7.9, 1.5 Hz, H-50), 8.21 (m, 3H, TolþH-80),
8.48 (d,1H, J 8.5 Hz, H-4), 8.62 (d,1H, J 8.5 Hz, H-3), 9.45 (s,1H, H-5).
4.12. Typical procedure for the synthesis of hydroxy-
quinolinyl-1,2,4-triazines (23a–c)
To solution of 1-hydrazono-2-oximino-1-arylethanes 3a–c
(13 mmol) in EtOH (30 mL) was added 8-hydroxyquinolin-2-car-
boxaldehyde 25 (2.28 g, 13.2 mmol) in EtOH (20 mL). The mixture
was kept at room temperature overnight. Appeared crystals were
filtered off, dried, and dissolved in AcOH (40 mL). The mixture was
heated at 80 ꢀC for 30 min and allowed to cool to room tempera-
ture. The resulting precipitate was filtered off and washed with
ethanol. The crude triazine was used directly in the next step.
4.10.3. 6-(400-Methoxyphenyl)-3-(20-quinolyl)-1,2,4-triazine (20c)
Yield 2.42 g, 77%, 1H NMR (DMSO-d6)
d: 3.89 (s, 3H, OMe), 7.14
(m, 2H), 7.67 (ddd, 1H, J 8.2, 7.9, 1.2 Hz, H-70), 7.83 (ddd, 1H, J 8.2, 7.9,
1.5 Hz, H-60), 8.04 (d, 1H, J 7.9 Hz, H-50), 8.21 (d, 1H, J 7.9 Hz, H-80),
8.28 (m, 2H), 8.57 (d, 1H, J 8.5 Hz, H-40), 8.62 (dd, 1H, J 8.5 Hz, H-30),
9.48 (s, 1H, H-5).
4.10.4. 6-(400-Bromophenyl)-3-(20-quinolyl)-1,2,4-triazine (20e)
Yield 2.35 g, 65%, 1H NMR (CDCl3)
d
: 7.62 (ddd, 1H, J 8.2, 7.9,
4.12.1. 3-(8-Hydroxyquinolin-2-yl)-6-phenyl-1,2,4-triazine (23a)
1.2 Hz, H-70), 7.73 (m, 2H, HAr), 7.80 (ddd, 1H, J 8.2, 7.9, 1.2 Hz, H-60),
7.93 (dd, 1H, J 7.9, 1.2 Hz, H-50), 8.09 (m, 2H, HAr), 8.41 (m, 2H, H-40,
H-80), 8.82 (dd, 1H, J 8.5 Hz, H-30), 9.25 (s, 1H, H-5).
Yield 2.25 g (63%), mp 187–190 ꢀC. 1H NMR (DMSO-d6)
d: 7.22
(dd, 1H, J 7.6, 1.2 Hz, H-70), 7.52 (dd, 2H, J 7.6, 1.2 Hz, H-50), 7.56 (dd,
2H, J 7.6, 7.6 Hz, H-60), 7.67 (m, 3H, Ph), 8.34 (m, 2H, Ph), 8.56 (d, 1H,
J 8.4 Hz, H-30), 8.60 (d,1H, J 8.4 Hz, H-40), 9.63 (s, 1H, H-5), 9.95 (br s,
1H, OH).
4.11. Typical procedure for the synthesis of pyridyl-
quinolines (21)
4.12.2. 3-(8-Hydroxyquinolin-2-yl)-6-(4-methylphenyl)-1,2,4-
Quinolinyltriazine 20 (3.1 mmol), bicyclo[2.2.1]hepta-2,5-diene
(1.58 mL, 15.5 mmol), and o-xylene (30 mL) were refluxed for 6–
12 h and cooled to room temperature. The solvent was removed
under reduced pressure, residue was recrystallized from ethanol to
give title arylpyridylquinolines 7a–c.
triazine (23b)
Yield 2.37 g (58%), mp 155–157 ꢀC. 1H NMR (DMSO-d6)
d: 2.44 (s,
3H, CH3), 7.21 (dd, 1H, J 7.6, 1.4 Hz, H-70), 7.47 (d, 2H, Tol), 7.50 (dd,
2H, J 7.6, 1.4 Hz, H-50), 7.54 (dd, 2H, J 7.6, 7.6 Hz, H-60), 8.25 (m, 2H,
Tol), 8.56 (d, 1H, J 8.6 Hz, H-30), 8.59 (d, 1H, J 8.6 Hz, H-40), 9.61 (s,
1H, H-5), 9.98 (br s, 1H, OH).
4.11.1. 2-(5-Phenyl-2-pyridyl)quinoline (21a)
Yield 612 mg, 70%, mp 145–146 ꢀC. 1H NMR (DMSO-d6)
d
: 7.4–
4.12.3. 3-(8-Hydroxyquinolin-2-yl)-6-(4-methoxyphenyl)-1,2,4-
7.6 (m, 4H), 7.7–7.8 (m, 3H), 7.95 (dd, 1H, J 8.2, 1.5 Hz, H-8), 8.09
(ddd, 1H, J 8.2, 1.2, 0.9 Hz, H-5), 8.19 (dd, 1H, J 8.2, 2.4 Hz, H-40), 8.40
(dd, 1H, J 8.5, 0.6 Hz, H-30), 8.62 (d, 1H, J 8.5 Hz, H-3), 8.72 (dd, 1H, J
8.2, 0.9 Hz, H-4), 8.98 (dd, 1H, J 2.4, 0.6 Hz, H-60). Found, %: C, 85.19;
H, 4.88; N, 9.99. C20H14N2. Calculated, %: C, 85.08; H, 5.00; N, 9.92.
triazine (23c)
Yield 2.45 g (57%), mp 158–160 ꢀC. 1H NMR (DMSO-d6)
d: 3.89 (s,
3H, OCH3), 7.21 (m, 3H, H-70, H-300), 7.52 (dd, 2H, J 7.6, 1.2 Hz, H-50),
7.56 (dd, 2H, J 7.6, 7.6 Hz, H-60), 8.32 (m, 2H), 8.55 (d, 1H, J 8.4 Hz, H-
30), 8.58 (d, 1H, J 8.4 Hz, H-40), 9.58 (s, 1H, H-5), 9.97 (br s, 1H, OH).
4.11.2. 2-(5-Tolyl-2-pyridyl)quinoline (21b)
4.13. 2-(8-Hydroxyquinolin-2-yl)-5-phenylpyridine (24a)
Yield 698 mg, 76%, mp 157–158 ꢀC. 1H NMR (DMSO-d6)
d: 2.41 (s,
3H, Me), 7.32 (m, 2H), 7.58 (ddd, 1H, J 8.2, 7.0, 1.2 Hz, H-7), 7.62 (m,
2H), 7.77 (ddd, 1H, J 8.2, 7.0, 1.5 Hz, H-6), 7.96 (dd, 1H, J 8.2, 1.5 Hz,
H-8), 8.09 (ddd, 1H, J 8.2, 1.2, 0.9 Hz, H-5), 8.17 (dd, 1H, J 8.2, 2.4 Hz,
H-40), 8.42 (dd,1H, J 8.5, 0.6 Hz, H-30), 8.61 (d,1H, J 8.5 Hz, H-3), 8.69
(dd, 1H, J 8.2, 0.9 Hz, H-4), 8.96 (dd, 1H, J 2.4, 0.6 Hz, H-60). Found, %:
C, 85.22; H, 5.38; N, 9.51. C21H16N2. Calculated, %: C, 85.11; H, 5.44;
N, 9.45.
Triazine 23a (1.5 g, 5 mmol), bicyclo[2.2.1]hepta-2,5-diene
(2.52 mL, 25 mmol), and o-xylene (50 mL) were refluxed for 24 h
and cooled to room temperature. The solvent was removed under
reduced pressure, residue was purified by column chromatography
(silica gel, CH2Cl2). Analytical sample of 24a–c was recrystallized
from ethanol. Yield 1.06 g (71%), mp 197–200 ꢀC. 1H NMR (DMSO-
d6) d
: 7.16 (dd, 1H, J 7.2, 1.6 Hz, H-70), 7.4–7.6 (m, 5H, Ph, H-50 H-60),
7.88 (m, 2H, Ph), 8.31 (dd, 1H, J 8.4, 2.4 Hz, H-4), 8.46 (d, 1H, J 8.6 Hz,
H-40), 8.63 (d,1H, J 8.6 Hz, H-30), 9.07 (dd,1H, J 2.4, 0.8 Hz, H-6), 9.21
(dd, 1H, J 8.4, 0.8 Hz, H-3), 9.88 (br s, 1H, OH). Found, %: C, 80.50; H,
4.84; N, 9.30. C20H14N2O. Calculated, %: C, 80.52; H, 4.73; N, 9.39.
4.11.3. 2-[5-(4-Methoxyphenyl)-2-pyridyl]quinoline (21c)
Yield 620 mg, 64%, mp 181–182 ꢀC. 1H NMR (DMSO-d6)
d: 3.85
(s, 3H, OMe), 7.04 (m, 2H), 7.57 (ddd, 1H, J 8.2, 7.0, 1.2 Hz, H-7), 7.69
(m, 2H), 7.75 (ddd, 1H, J 8.2, 7.0, 1.5 Hz, H-6), 7.94 (dd, 1H, J 8.2,
1.5 Hz, H-8), 8.09 (ddd, 1H, J 8.2, 1.2, 0.9 Hz, H-5), 8.12 (dd, 1H, J 8.2,
2.4 Hz, H-40), 8.38 (dd,1H, J 8.5, 0.6 Hz, H-30), 8.61 (d,1H, J 8.5 Hz, H-
3), 8.69 (dd, 1H, J 8.2, 0.9 Hz, H-4), 8.93 (dd, 1H, J 2.4, 0.6 Hz, H-60).
Found, %: C, 80.77; H, 5.08; N, 9.02. C21H16N2O. Calculated, %: C,
80.75; H, 5.16; N, 8.97.
4.14. 6-(4-Methoxyphenyl)-3-(8-methoxyquinolin-2-yl)-1,2,4-
triazine (25c)
Mixture of hydroxyquinolinyltriazine 26c (660 mg, 2 mmol),
K2CO3 (2.02 g, 20 mmol), and MeI (0.14 mL, 2.2 mmol) in DMF
(30 mL) was stirred overnight at room temperature, then diluted
with water (80 mL), and appeared crystals were filtered off. The
crude triazine was used directly in the next step. Yield 520 mg
4.11.4. 2-[5-(4-Bromophenyl)-2-pyridyl]quinoline (21e)
Yield 940 mg, 84%, mp 187–189 ꢀC. 1H NMR (CDCl3)
d: 7.5–7.6
(m, 3H, H-70, HAr), 7.65 (m, 2H, HAr), 7.74 (ddd, 1H, J 8.2, 7.8, 1.5 Hz,
H-60), 7.87 (dd,1H, J 7.8,1.5 Hz, H-50), 8.04 (dd,1H, J 8.2, 2.5 Hz, H-4),
(73%), mp 150–153 ꢀC. 1H NMR (DMSO-d6)
4.05 (s, 3H, OCH3), 7.21 (m, 2H), 7.31 (dd, 1H, J 6.5, 2.2 Hz, H-70), 7.62
d: 3.89 (s, 3H, OCH3),

V.N. Kozhevnikov et al. / Tetrahedron 64 (2008) 8963–8973
8973
(m, 2H, H-50, H-60), 8.32 (m, 2H, H-200), 8.56 (d, 1H, J 8.4 Hz, H-40),
8.61 (d, 1H, J 8.4 Hz, H-30), 9.58 (c, 1H, H-5). Found, %: C, 69.81; H,
4.16.7. [Ru(16b)(bpy)2](PF6)2
Yield 76%. 1H NMR (CD3CN)
d
: 2.33 (s, 3H), 3.78 (s, 3H, COOCH3),
4.69; N, 16.09. C20H16N4O2. Calculated, %: C, 69.76; H, 4.68; N, 16.27.
7.2–7.3 (m, 4H, HAr), 7.35–7.45 (m, 4H), 7.71–7.83 (m, 5H), 8.00–8.12
(m, 5H), 8.29 (dd, 1H, J 8.5, 1.9 Hz, H-4), 8.44–8.62 (m, 6H), 8.58 (d,
1H, J 8.5 Hz, H-3).
4.15. 5-(4-Methoxyphenyl)-2-(8-methoxyquinolin-2-yl)-
pyridine (26c)
4.16.8. [Ru(16c)(bpy)2](PF6)2
Yield 69%. 1H NMR (CD3CN)
d: 3.79 (s, 6H, COOCH3), 3.81 (s, 3H,
Triazine 25c (500 mg, 1.4 mmol), bicyclo[2.2.1]hepta-2,5-diene
(0.73 mL, 7 mmol), and o-xylene (20 mL) were refluxed for 24 h and
cooled to room temperature. The solvent was removed under re-
duced pressure, residue was purified by column chromatography
(silica gel, CH2Cl2). Analytical sample of 29c was recrystallized from
OCH3), 6.98 (m, 2H, HAr), 7.33 (m, 2H, HAr), 7.38–7.48 (m, 5H), 7.79
(m, 4H), 7.84 (ddd,1H, J 5.0,1.1, 0.7 Hz, H-60), 8.00–8.09 (m, 4H), 8.11
(ddd,1H, J 7.8, 7.8,1.7 Hz, H-40), 8.29 (dd,1H, J 8.5,1.9 Hz, H-4), 8.45–
8.60 (m, 7H).
ethanol. Yield 343 mg (71%), mp 185–190 ꢀC. 1H NMR (DMSO-d6)
d:
Acknowledgements
3.83 (s, 3H, OCH3), 4.06 (s, 3H, OCH3), 7.12 (m, 2H, H-300, H-500), 7.25
(m, 1H, H-70), 7.56 (m, 2H, H-50, H-60), 7.79 (m, 2H), 8.26 (dd, 1H,
J 8.2, 2.2 Hz, H-4), 8.45 (d, 1H, J 8.4 Hz, H-30), 8.59 (d, 1H, J 8.4 Hz,
H-30), 8.65 (d, 1H, J 8.4 Hz, H-3), 9.03 (d, 1H, J 2.2 Hz, H-6). Found, %:
C, 77.05; H, 5.50; N, 7.91. C22H18N2O2. Calculated, %: C, 77.17; H, 5.30;
N, 8.18.
We thank the RFBR, the DAAD (M.M.U.) and the CRDF (O.V.S.) for
funding. We thank Dr. Pavel A. Slepukhin for collecting X-ray
crystallography data.
Supplementary data
Supplementary data contain changes in the absorbance and
emission spectra of 21a as a function of Zn2þ concentration and
crystal packing of the complex [Zn(1b)Cl2]. Supplementary data
associated with this article can be found in the online version, at
doi:10.1016/j.tet.2008.06.040.
4.16. Typical procedure for the synthesis of complexes
[Ru(L)(bpy)2](PF6)2
Arylbipyridine 1 or 19 (0.11 mmol) and Ru(bpy)2Cl2$2H2O
(0.052 g, 0.1 mmol) were refluxed 10 h in 10 mL of methanol/water
(2:1) mixture. Water (20 mL) was added and the mixture was
treated with CH2Cl2 (2ꢂ30 mL). Water solution of NH4PF6 (10%,
2 mL) was added to the water layer and resulting mixture was
extracted with CH2Cl2 (3ꢂ30 mL). Organic layer was dried over
Na2SO4, the solvent was removed under reduced pressure, the
residue was treated with methanol, and crystals were filtered off.
References and notes
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4.16.1. [Ru(1a)(bpy)2](PF6)2
Yield 75%. 1H NMR (CD3CN)
d: 7.37–7.46 (m, 10H), 7.73–7.81 (m,
5H), 7.83 (ddd, 1H, J 5.0, 1.2, 0.7 Hz, H-60), 8.02–8.10 (m, 5H), 8.30
(dd, 1H, J 8.5, 2.1 Hz, H-4), 8.50 (m, 5H), 8.55 (d, 1H, J 8.5 Hz, H-3).
4.16.2. [Ru(1b)(bpy)2](PF6)2
Yield 84%. 1H NMR (CD3CN)
d: 2.35 (s, 3H, CH3), 7.28 (m, 4H, HAr),
7.40 (m, 5H), 7.70–7.80 (m, 5H), 7.84 (ddd,1H, J 5.0,1.2, 0.7 Hz, H-60),
8.05 (m, 5H), 8.27 (dd, 1H, J 8.5, 2.2 Hz, H-4), 8.50 (m, 5H), 8.55 (d,
1H, J 8.5 Hz, H-3).
4.16.3. [Ru(1c)(bpy)2](PF6)2
11. (a) Pabst, G. R.; Pfu¨ ller, O. C.; Sauer, J. Tetrahedron 1999, 55, 8045–8064; (b)
Sauer, J.; Heldmann, D. K.; Pabst, G. R. Eur. J. Org. Chem. 1999, 313–321; (c) Raw,
S. A.; Taylor, R. J. K. Chem. Commun. 2004, 508–509; (d) Kozhevnikov, V. N.;
Kozhevnikov, D. N.; Nikitina, T. V.; Rusinov, V. L.; Chupakhin, O. N.; Zabel, M.;
Koenig, B. J. Org. Chem. 2003, 68, 2882–2888.
Yield 73%. 1H NMR (CD3CN)
d: 3.80 (s, 3H, OCH3), 6.97 (m, 2H,
H
Ar), 7.32 (m, 2H, HAr), 7.35–7.45 (m, 6H), 7.70–7.80 (m, 5H), 7.84
(ddd, 1H, J 5.0, 1.1, 0.7 Hz, H-60), 8.00–8.10 (m, 5H), 8.23 (dd, 1H, J
8.5, 2.2 Hz, H-4), 8.45–8.54 (m, 6H).
12. For review see Neunhoeffer, H. In Comprehensive Heterocyclic Chemistry II;
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Tetrahedron Lett. 2006, 47, 3865–3870.
4.16.4. [Ru(1d)(bpy)2](PF6)2
Yield 80%. 1H NMR (CD3CN)
d: 7.36–7.48 (m, 9H), 7.68–7.80 (m,
5H), 7.84 (ddd, 1H, J 5.0, 1.2, 0.7 Hz, H-60), 8.06 (m, 5H), 8.27 (dd, 1H,
J 8.5, 2.2 Hz, H-4), 8.48–8.52 (m, 5H), 8.56 (d, 1H, J 8.5 Hz, H-3).
14. Kozhevnikov, V. N.; Kozhevnikov, D. N.; Shabunina, O. V.; Rusinov, V. L.;
Chupakhin, O. N. Tetrahedron Lett. 2005, 46, 1521–1523.
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Sidorov, E. O.; Klyuev, N. A. Russ. J. Org. Chem. (Engl. Transl.) 1998, 34, 393–399.
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4.16.5. [Ru(1e)(bpy)2](PF6)2
Yield 70%. 1H NMR (CD3CN)
d: 7.30 (m, 2H, HAr), 7.40 (m, 5H),
7.60 (m, 2H, HAr), 7.70–7.80 (m, 5H), 7.85 (ddd, 1H, J 5.0, 1.1, 0.7 Hz,
H-60), 8.05 (m, 5H), 8.27 (dd, 1H, J 8.5, 1.9 Hz, H-4), 8.50 (m, 5H),
8.55 (d, 1H, J 8.5 Hz, H-3).
17. Hassani, M.; Cai, W.; Holley, D. C.; Lineswala, J. P.; Maharjan, B. R.; Ebrahimian,
G. R.; Seradj, H.; Stocksdale, M. G.; Mohammadi, F.; Marvin, C. C.; Gerdes, J. M.;
Beall, H. D.; Behforouz, M. J. Med. Chem. 2005, 48, 7733–7749.
4.16.6. [Ru(16a)(bpy)2](PF6)2
Yield 64%. 1H NMR (CD3CN)
d: 3.81 (s, 3H, COOCH3), 7.38–7.48
18. Kotlicka, J.; Grabowski, Z. R. J. Photochem. 1979, 413–418.
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21. Van Houten, J.; Watts, R. J. J. Am. Chem. Soc. 1976, 98, 4853–4858.
(m, 9H), 7.72–7.88 (m, 5H), 8.0–8.15 (m, 5H), 8.33 (dd, 1H, J 8.5,
1.9 Hz, H-4), 8.43–8.57 (m, 6H), 8.62 (d, 1H, J 8.5 Hz, H-3).