Synthesis of new polyaza heterocycles. Part 42: Diazines

Article abstract of DOI:10.1016/j.tet.2005.01.059

Using Pd-catalyzed Stille cross-coupling reactions, we report here the synthesis of various mono- or bis(tri-n-butylstannyl)diazines which were reacted with various halogenated diazines to access to various polyaza heterocyclic derivatives.

Full text of DOI:10.1016/j.tet.2005.01.059

Tetrahedron 61 (2005) 2897–2905
Synthesis of new polyaza heterocycles. Part 42: Diazines
a
Mircea Darabantu, Ludovic Boully, Alain Turck and Nelly Ple
b
b
b,
*
´
aDepartment of Organic Chemistry, ‘Babes-Bolyai’ University 11 Aranyi Janos Str., 400028 Cluj-Napoca, Romania
´ ´
Laboratoire de Chimie Organique Fine et Heterocyclique, UMR 6014, IRCOF-INSA, B.P. 08, 76131 Mont St Aignan Cedex, France
b
Received 8 November 2004; revised 6 January 2005; accepted 13 January 2005
Abstract—Using Pd-catalyzed Stille cross-coupling reactions, we report here the synthesis of various mono- or bis(tri-n-
butylstannyl)diazines which were reacted with various halogenated diazines to access to various polyaza heterocyclic derivatives.
q 2005 Elsevier Ltd. All rights reserved.
Polyaromatic compounds containing N-heterocyclic sub-
units have received considerable attention due to their wide
use in various fields such as molecular recognition, metal
cryptates, supramolecular devices and self-assembly.
Among them, oligopyridines have been extensively studied
during the last two decades and many well-defined
supramolecular architectures with 2,20-bipyridines (bpy)
and 2,2060,200-terpyridines (tpy) units as building blocks
have found applications in catalysis,1 electrochemistry,2
photochemistry3 or new materials.4
Scheme 1.
The Suzuki reaction involves the palladium-catalyzed cross-
More recently, synthesis of polydentate nitrogen ligands
based on pyridine and 1,3-pyrimidine5 or 3,6 pyridazine6
units have been reported. Interest in this class of molecules
incorporating several coordination sites is mostly due to
their use in supramolecular chemistry, and as building
blocks for self-assembled polynuclear coordination arrays.7
coupling of heteroarylboronic acids with heteroaryl halides
(or triflates). It is remarkable that whereas halopyridines
have often been employed in Suzuki reactions there are only
few examples in the literature of use of pyridylboronic acids
or esters.11 In diazine series only the 5-pyrimidylboronic
acids or esters have been described12 while to our knowl-
edge, they are unknown with pyrazine or pyridazine rings
probably because of their unstability.
We report here the synthesis of a new family of
polyaromatic compounds containing a pyridine or pyrimi-
dine ring as central unit substituted by two pyrazinyl groups
(type I) and symmetrical structures with a pyrazine central
unit substituted at the 2 and 6 positions by p-deficient
heterocycles such as pyridine, quinoline, diazine or
benzodiazine (type II) (Scheme 1).
Some Negishi reactions have been achieved with organo-
zinc derivatives of diazines to give cross-coupling reactions
with iodo or bromo aromatics leading to diazine-aryl or
(heteroaryl) bound.13
Stille-type coupling provides another efficient way for the
formation of aryl–aryl bonds in particular between
p-deficient N-heterocycles. This process has been used to
prepare a wide variety of functionalized 2,20-bipyridines and
2,2060,200-terpyridines.14
Synthetic approaches to such polyaza heterocyclic com-
pounds are based either on palladium-catalyzed cross-
coupling procedures: Suzuki,8 Negishi9 and Stille10
coupling reactions or by generation of the aza-heterocyclic
rings with the help of ring-closure reactions.
Using a synthetic strategy based on Stille coupling reaction,
we report here the synthesis of mono- or bis(tri-n-
butylstannyl) diazines which were reacted with various
halogenated diazines to obtain polyaza heterocyclic
derivatives.
Keywords: Stille cross-coupling reaction; Diazines; Polyaza heterocycles.
* Corresponding author. Tel.: C33 2 35 52 29 02; fax: C33 2 35 52 29 62;
e-mail: nelly.ple@insa-rouen.fr
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.01.059

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M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
1. Results
were obtained for chloropyrazine (entry 5) and 2,6-
dichloropyrazine (entry 6). For this last compound, mono
or distannylation has been achieved in good and moderate
yield (entries 6 and 7). The nucleophilic substitution was
performed successfully with good yield with 2-chloro-4-
methoxypyrimidine (entry 4) whereas the yield was low
with 2,4-dichloropyrimidine (entry 3). Such a result could
suggest that the presence of a methoxy group makes the
substitution reaction more easy, however, it can be noticed
that stannylation failed with 3-chloro-6-methoxypyridazine
(entry 2). In benzodiazine series good yields with mono-
chloro-quinazoline (entry 8) or quinoxaline (entry 9) were
observed. With 2,3-dichloroquinoxaline, a disubstitution
can be obtained with a very good yield (entry 10) despite the
steric hindrance of the tri-n-butylstannyl group.
The synthesis of diazinylstannanes could be performed
either using the lithiation reaction of diazine followed by a
transmetalation step with tributyltin chloride15 or by use of
the nucleophilic substitution of a chlorine atom by the
stannyl anion.16
We have investigated this last procedure to synthesize the
tri-(n-butyl)organostannanes (1–9) with a diazine moiety
(Scheme 2) the results of which are given in Table 1.
One can observe a monosubstitution with very low yields
for dichloro-pyridazine and pyrimidine (entries 1 and 3).
These low yields could be explained by competitive radical
reactions, since some dimers and bistributyltin were
observed besides the expected compounds. Good results
Coupling reactions of the stannyl derivatives 3, 7–9 were
Scheme 2.
Table 1. Synthesis of tri-n-butyl-N-heteroarylstannanes
Entry
1
Het-Cl
Product
n (equiv)
t (h)
Compound
Yield (%)
9
1.1
5
1
2
3
1.1
1.1
5
6
—
—
4
2
4
5
6
7
1.1
1.1
1.1
2.1
1
3
4
5
6
70
85a
95
56
8
21
24
8
1.1
1
7
97
9
1.1
2.1
1
1
8
9
54
98
10
a Hydrolysis was performed at K40 8C.

M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
2899
Scheme 3.
Table 2. Cross-coupling reaction of HetSnBu3 with iodobenzene
Entry
HetSnBu3
Product
Compounda
Yield (%)
78
1
1017
2
1118
67
3
4
1218
64
39
1319
a All products 10–13 have been characterized and comparison with already published data are in agreement.
Scheme 4.
Table 3. Cross-coupling reaction of tri-(n-butyl)stannylpyrazine 4 with halogeno-N-heteroaryl compounds
Entry
N-HetX2
Product
t (h)
Compound
Yield (%)
66
1
15
14
2
27
15
64
3
4
26
27
16
17
75
61
5
48
18
70

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M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
Scheme 5.
Table 4. Cross-coupling reaction of the 2,6-distannylpyrazine 6 with halogenoaromatics
Entry
ArX
Product
Compound
Yield (%)
82
1
19
2
20
51
3
4
21
22
76
30
5
23
60
6
7
16
24
65
21
8
25
59
9
26
27
91
65
10
11
28
71

M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
2901
tested with iodobenzene according to the general procedure
3. Experimental
for Stille reaction in toluene with Pd(PPh3)4 as catalyst.
Under these conditions, the expected phenyl or diphenyl
compounds 10–13 were obtained in moderate yields
(Scheme 3, Table 2).
Melting points were determined on a Kofler hot-stage. The
1H, and 13C spectra were recorded on a Bruker AC 300
(300 MHz 1H, 75 MHz 13C) instrument. Microanalyses were
performed on a Carlo Erba CHNOS 1160 apparatus. The IR
spectra were obtained as potassium bromide pellets with a
Perkin–Elmer Paragon 500 spectrophotometer. Mass spectra
were recorded on an ATI-Unicam Automassw apparatus.
We then extended this procedure to the coupling reaction of
2-tri-n-butylstannylpyrazine 4 with various mono or
dihalogeno N-heteroaryl compounds leading to various
p-deficient heterocycles appended to a pyrazinyl group
(Scheme 4, Table 3).
3.1. General procedure A for the nucleophilic
substitution of a chlorine atom by the tributylstannyl
anion
Compounds 14–18 were obtained in fairly good yields and
present a bi- or tridentate binding system which make them
potential metal cryptands. Compounds 15 and 18 may be
viewed as aza-analogues of bipyridine (bpy), 17 as aza-
analogue of two bpys and 14 and 16 as aza-analogues of
terpyridine (tpy). Compounds 16 and 17 belong to a
family of symmetrical tridiazines, whereas 14 and 15 are
di-pyrazinylpyridines.
A solution of n-butyllithium (1.6 or 2.5 M in hexane) was
added to cold (0 8C), stirred and anhydrous mixture of
THF (50 mL) and diisopropylamine (DIPAH) under an
atmosphere of dry nitrogen. After 15 min, tributyltinhydride
was introduced, the yellow pale solution was stirred at 0 8C
for 15 min and the temperature was decreased to at K78 8C.
Then a solution of chloro- or dichlorodiazine in THF at
K78 8C was added, after t hours of stirring, mixture was
warmed to 0 8C. Hydrolysis was then carried out at this
temperature, using a saturated aqueous solution of
potassium fluoride. The aqueous layer was extracted with
dichoromethane or ethylacetate (3!20 mL), the combined
organic extracts were then dried over magnesium sulfate,
filtered and evaporated in vacuo. The crude product was
purified by column chromatography on silica gel.
In the aim to synthesize symmetrical polydentates with a
pyrazine moiety as central unit, the cross-coupling reaction
of the 2,6-bis-tri-n-butylstannylpyrazine 6 was performed
with various monohalogenoaryl compounds. Pyrazine
linked to various aromatic rings (benzene, naphthalene,
thiophene or p-deficient N-heterocycles) were obtained
(Scheme 5, Table 4).
This general methodology allowed us to access to a
wide range of compounds which constitute a new
family of triaromatic strands with a diazine as central
unit, most of them (16, 22–28) are tri-p-deficient
N-heterocycles linked by direct aryl–aryl bounds and
could be seen as aza-analogues of terpyridines. These
structures are potential trinucleating ligands due to the
presence of coordinating atoms such as nitrogen, oxygene or
sulfur.
3.2. Procedure B for cross-coupling of heteroaryl halides
with tributylstannylheteroarene under Stille conditions
A solution of tributylstannylheteroarene, arylhalide and
Pd(PPh3)4 (0.05 equiv) in degassed toluene (15 mL) was
heated under reflux under nitrogen atmosphere for a time t.
After cooling, water (20 mL) was added. The aqueous phase
was extracted with dichloromethane (3!20 mL). The
combined organic extracts were then dried over magnesium
sulfate, filtered and evaporated in vacuo. The crude product
was purified by column chromatography on silica gel.
Compounds 19 and 20 have two phenyl or naphthyl ring,
ortho substituted by a methoxy group which could allow
complexation, whereas for the compound 21, the sulfur of
the thiophene ring could play this role. All the other
compounds 16, 22–28 are obtained in moderate to good
yields. One can notice an exception observed with a
pyridazine unit as lateral rings (24).
3.3. Procedure C for cross-coupling of heteroaryl halides
with 2,6-bis(tributylstannyl)pyrazine under Stille
conditions
A mixture of 2,6-bis(tributylstannyl)pyrazine used as crude
product (constitutedwith77% of6 and 21% ofhexabutylditin)
(1.010 g, 1.17 mmol of 6), heteroaryl halide (2–3 mmol), and
Pd(PPh3)4 (0.10 equiv) in degassed toluene (25 mL) was
heated under reflux under nitrogen atmosphere for a time t.
After cooling, dichloromethane (150 mL) was added and the
mixture was filtered. The organic phase was washed with
aqueous ammonia (2!25 mL). The combined organic
extracts were then dried over magnesium sulfate, filtered
and evaporated in vacuo. The crude product was purified by
column chromatography on silica gel.
2. Conclusion
In conclusion, a simple general procedure for the synthesis
of new polyaza heterocycles has been developed on the
basis of palladium-mediated coupling of mono- or bis-
tribuylstannanes of diazines. Among the compounds
prepared here some are aza-analogues of terpyridines (tpy)
and will be new potential ligands for metal chelation and
new building blocks for synthesis of supramolecular arrays.
Further studies on this new family of polyaza heterocycles
are underway and will include a careful assessment of metal
coordination, photo- and electrochemical properties.
Variation of functionalization of lateral units will be
performed to access new ligand-bridged supramolecular
structures.
3.3.1. 3-Chloro-6-tri-n-butylstannylpyridazine (1). Sub-
stitution of 3,6-dichloropyridazine (2.0 g, 13.02 mmol) by
Bu3SnLi according to the general procedure A with n-BuLi
2.5 M (14.7 mmol, 5.88 mL), DIPAH (14.1 mmol,
2.00 mL), tributyltinhydride (14.4 mmol, 4.00 mL), tZ5 h,

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M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
gave after purification by column chromatography (silica,
eluent petroleum ether/ethyl acetate (9/1)) 480 mg of 1
1.6 M (10.60 mmol, 6.60 mL), DIPAH (10.60 mmol,
1.50 mL), tributyltinhydride (10.60 mmol, 2.95 mL), tZ
4 h. gave 2.7 g as a yellow oil which contains 77% of 6 and
21% of hexabutylditin. The product was not purified by
column chromatography because its unstability on silica gel.
1
(9.2%) as a pale yellow oil; H NMR (CDCl3): d 0.63 (m,
9H), 0.93 (m, 6H), 1.04 (m, 6H), 133 (m, 6H), 7.07 (dd, JZ
8.67, 2.64 Hz, 1H), 7.22 (dd, JZ8.67, 2.64 Hz, 1H); 13C
NMR (CDCl3): d 10.63, 13.70, 27.60, 29.24, 126.0, 136.6,
156.7, 174.4. MS (CI) m/z 403 (MC, 40), 347 (MKBu, 10),
269 (MK2Bu, 10), 235 (MK3Bu, 5).
1
It will be used as crude product for further reactions; H
NMR (CDCl3): d 0.85–1.70 (m 76H, (HBu of 6 and
(SnBu3)2), 8.07 (s, 2H); 13C NMR (CDCl3): d 10.3, 14.1,
27.7, 29.4, 149.0, 171.7. MS (CI) m/z 658 (MC, 100).
3.3.2. 4-Chloro-2-tri-n-butylstannylpyrimidine (2). Sub-
stitution of 2,4-dichloropyrimidine (1.0 g, 6.7 mmol) by
Bu3SnLi according to the general procedure A with n-BuLi
1.6 M (14.1 mmol, 8.80 mL), DIPAH (14.1 mmol,
1.99 mL), tributyltinhydride (14.1 mmol, 3.91 mL), tZ6 h,
gave after purification by column chromatography (silica,
eluent petroleum ether/ethyl acetate (25/1)) 120 mg of 2
(4%) as a pale yellow oil; 1H NMR (CDCl3): d 0.80 (t, JZ
7.1 Hz, 9H), 1.11 (m, 6H), 1.26 (m, 6H), 1.51 (m, 6H), 7.09
(d, JZ5.65 Hz, 1H), 8.46 (d, JZ5.65 Hz, 1H); 13C NMR
(CDCl3): d 10.8, 14.0, 27.6, 29.2, 120.1, 155.9, 159.9, 191.3.
3.3.7. 2-Phenyl-4-tri-n-butylquinazoline (7). Substitution
of 2-phenyl-4-chloroquinazoline (1.08 g, 4.5 mmol) by
Bu3SnLi according to the general procedure A with
n-BuLi 1.6 M (4.5 mmol, 2.81 mL), DIPAH (4.5 mmol,
0.64 mL), tributyltinhydride (4.5 mmol, 1.25 mL), tZ1 h,
gave after purification by column chromatography (silica,
eluent cyclohexane) 2.15 g of 7 (97%) as a pale yellow oil;
1H NMR (CDCl3): d 0.91 (m, 9H), 1.16 (m 6H), 1.32 (m,
6H), 1.47 (m, 6H), 7.77 (m, 3H), 7.92 (t, JZ8.3 Hz, 1H),
8.19 (t, JZ8.3 Hz, 1H), 8.35 (d, JZ8.3 Hz, 1H), 8.51 (d,
JZ8.3 Hz, 1H), 8.85 (m, 2H); 13C NMR (CDCl3): d 11.7,
14.1, 27.8, 29.6, 127.0, 128.9, 129.1, 129.6, 130.0, 130.6,
131.4, 133.4, 139.1, 148.6, 159.0, 193.0. MS (EI) m/z 455
(90, MKBu).
3.3.3. 4-Methoxy-2-tri-n-butylstannylpyrimidine (3).
Substitution of 2-chloro,4-methoxypyrimidine (0.650 g,
4.5 mmol) by Bu3SnLi according to the general procedure
A with n-BuLi 1.6 M (5 mmol, 3.12 mL), DIPAH (5 mmol,
0.71 mL), tributyltinhydride (5 mmol, 1.35 mL), tZ1 h,
gave after purification by column chromatography (silica,
eluent petroleum ether/ethyl acetate (25/1)) 1.20 g of 3
3.3.8. 2-Tri-n-butylquinoxaline (8). Substitution of
2-chloroquinoxaline (0.740 g, 4.5 mmol) by Bu3SnLi
according to the general procedure A with n-BuLi 1.6 M
(4.5 mmol, 2.81 mL), DIPAH (4.5 mmol, 0.64 mL),
tributyltinhydride (4.5 mmol, 1.25 mL), tZ1 h, gave after
purification by column chromatography (silica, eluent
1
(70%) as a colorless oil; H NMR (CDCl3): d 0.80 (t, JZ
7.1 Hz, 9H), 1.11 (m, 6H), 1.26 (m, 6H), 1.51 (m, 6H), 3.73
(s, 3H), 6.32 (d, JZ6.0 Hz, 1H), 8.15 (d, JZ6.0 Hz, 1H);
13C NMR (CDCl3): d 10.3, 14.0, 27.8, 31.0, 54.8, 117.1,
153.9, 158.9, 188.6. MS (EI) m/z 343 (MKBu, 100).
1
cyclohexane) 1.01 g of 8 (54%) as a pale yellow oil; H
NMR (CDCl3): d 0.82 (m, 9H), 1.17 (m 6H), 1.30 (m, 6H),
1.55 (m, 6H), 7.63 (m, 2H), 7.96 (m, 1H), 8.06 (m, 1H), 8.52
(s, 1H). MS (EI) m/z 363 (10, MKBu).
3.3.4. Tri-n-butylstannylpyrazine (4). Substitution of
chloropyrazine (1.50 g, 12.8 mmol) by Bu3SnLi according
to the general procedure A with n-BuLi 1.6 M (13.5 mmol,
8.5 mL), DIPAH (13.47 mmol, 1.90 mL), tributyltinhydride
(13.5 mmol, 3.75 mL), tZ8 h. Hydrolysis was carried out at
K40 8C. Purification by column chromatography (silica,
eluent petroleum ether/ethyl acetate (10/1)) gave 4.05 g of 4
3.3.9. 2,6-Bis(tri-n-butylstannyl)quinoxaline (9). Substi-
tution of 2,3-dichloroquinoxaline (0.445 g, 4.5 mmol) by
Bu3SnLi according to the general procedure A with n-BuLi
1.6 M (4.5 mmol, 2.81 mL), DIPAH (4.5 mmol, 0.64 mL),
tributyltinhydride (4.5 mmol, 1.25 mL), tZ1 h, gave after
purification by column chromatography (silica, eluent
1
(85%) as a yellow oil; H NMR (CDCl3): d 0.80 (t, JZ
1
7.5 Hz, 9H), 1.10 (m, 6H), 1.25 (m, 6H), 1.48 (m, 6H), 8.29
(d, JZ2.64 Hz, 1H), 8.48 (d, JZ1.86 Hz, 1H), 8.63 (dd, JZ
2.64, 1.88 Hz); 13C NMR (CDCl3): d 10.2, 14.0, 27.6, 29.3,
143.3, 147.1, 151.7, 170.2. MS (CI) m/z 371 (MC, 100).
cyclohexane) 3.12 g of 9 (98%) as a pale yellow oil; H
NMR (CDCl3): d 0.86 (m, 18H), 1.10 (m 12H), 1.27 (m,
12H), 1.55 (m, 12H), 7.59 (dd, JZ6.4 Hz, 3.3 Hz, 2H), 7.82
(dd, JZ6.4 Hz, 3.3 Hz, 2H); 13C NMR (CDCl3): d 11.2,
13.7, 27.4, 29.2, 128.4, 129.7, 142.0, 179.2. MS (EI) m/z 708
(MC, 1), 651 (MKBu, 5), 413 (MKSnBu3, 90).
3.3.5. 6-Chloro-2-tri-n-butylstannylpyrazine (5). Substi-
tution of 2,6-dichloropyrazine (0.75 g, 5.0 mmol) by Bu3-
SnLi according to the general procedure A with n-BuLi
1.6 M (5.30 mmol, 3.30 mL), DIPAH (5.30 mmol,
0.75 mL), tributyltinhydride (5.30 mmol, 1.47 mL), tZ
21 h, gave after purification by column chromatography
(silica, eluent petroleum ether/ethyl acetate (30/1)) 456 mg
of 5 (56%) as a pale yellow oil; 1H NMR (CDCl3): d 0.85 (t,
JZ7.1 Hz, 9H), 1.16 (m, 6H), 1.31 (m, 6H), 1.54 (m, 6H),
8.34 (s, 1H), 8.41 (s, 1H); 13C NMR (CDCl3): d 10.5, 14.0,
27.6, 29.3, 143.2, 149.2, 151.6, 170.7. HRMS (FAB) calcd
for C16H29ClN2Sn 403.58394; found 403.57764).
3.3.10. 2-Phenyl-4-methoxypyrimidine (10). Cross-
coupling reaction of iodobenzenze (408 mg, 225 mL,
2 mmol) with 3 (400 mg, 1 mmol) according to the general
procedure B (tZ48 h) gave after purification by column
chromatography (silica, eluent: dichloromethane) 145 mg
(76%) of 10 as a colorless solid, mp 44–45 8C (lit.16 45 8C);
1H NMR (CDCl3): d 4.05 (s, 3H, HOMe); 6.80 (d, JZ6.0 Hz,
0
1H, H5 ) 7.51 (m, 3H, HPh0); 8.40 (m, 2H, HPh); 8.60 (d, JZ
0
70.95; N, 15.04; H, 5.41. Found: C, 71.02; N, 15.15; H, 5.35.
6.0 Hz, 1H, H6 )). Anal. Calcd for C11H10N2O (186.21): C,
MS (EI) m/z 186 (MC, 100).
3.3.6. 2,6-Bis(tri-n-butylstannyl)pyrazine (6). Substi-
tution of 2,6-dichloropyrazine (0.75 g, 5.0 mmol) by Bu3-
SnLi according to the general procedure A with n-BuLi
3.3.11. 2,4-Diphenylquinazoline (11). Cross-coupling
reaction of iodobenzenze (408 mg, 225 mL, 2 mmol) with

M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
2903
7 (500 mg, 1 mmol) according to the general procedure B
(tZ48 h) gave after purification by column chromatography
(silica, eluent: dichloromethane) 189 mg (67%) of 11 as a
3.3.16. 2,20,60,200-Terpyrazine (16). Method 1—cross-
coupling reaction of 2,6-dichloropyrazine (282 mg,
1.89 mmol) with 4 (1.400 g, 3.79 mmol) according to the
general procedure B (tZ24 h) gave after purification by
recrystallization in methanol 333 mg (74%) of 16 as a grey
solid, mpO265 8C; compound 16 has a very low solubility
in the usual organic solvents; 1H NMR (CF3CD2OD): d 8.61
(d, JZ2.8 Hz, 1H), 8.76 (dd, JZ2.4, 1.6 Hz, 1H), 9.56 (s,
1H), 9.64 (d, JZ1.2 Hz, 1H); 13C NMR (CF3CD2OD): d
1
colorless solid, mp 115–116 8C (lit.17 118 8C); H NMR
(CDCl3): d 7.58 (m, 7H), 7.90 (m, 3H), 8.15 (d, JZ8.3 Hz,
1H), 8.17 (d, JZ8.3 Hz, 1H), 8.73 (m, 2H). NMR 13C
(CDCl3) d 121.7, 127.0, 128.5, 128.7, 129.2, 129.9, 130.2,
130.5, 133.5, 137.8, 138.2, 152.0, 160.2, 168.3. Anal. Calcd
for C20H14N2 (282.12): C, 85.08; N, 9.92; H, 5.00. Found:
C, 85.46; N, 9.75; H, 4.78. MS (EI) m/z 282 (MC, 100).
129.0, 129.2, 131.8, 131.9, 132.4, 133.7. IR (KBr) n (cmK1
)
3053.8, 3012.9, 1530.2, 1473.7, 1431.0, 1382.9, 1108.4,
1030.0, 1015.9, 858.9. MS (EI) m/z 236 (MC, 100).
3.3.12. 2-Phenylquinoxaline (12). Cross-coupling reaction
of iodobenzenze (408 mg, 225 mL, 2 mmol) with 8 (420 mg,
1 mmol) according to the general procedure B (tZ48 h)
gave after purification by column chromatography (silica,
eluent: dichloromethane) 131 mg (64%) of 12 as a yellow
Method 2—cross-coupling reaction of 2,6-bis(tributyltin)-
pyrazine 6 (1.17 mmol) with chloropyrazine (0.446 g,
3 mmol) according to the general procedure C (tZ48 h)
gave after purification by recrystallization in methanol
179 mg (65%) of 16. Anal. Calcd for C12H8N6 (236.24): C,
61.01; H, 3.41; N, 35.57. Found: C, 61.20; H, 3.42; N, 35.77.
1
solid, mp 74–75 8C (lit.17 73–75 8C); H NMR (CDCl3): d
7.54 (m, 3H), 7.75 (m, 2H), 8.15 (m, 4H), 9.32 (s, 1H). NMR
13C (CDCl3) d 127.5, 129.1, 129.5, 129.6, 130.1, 130.2,
136.8, 141.5, 142.3, 143.3, 151.8. Anal. Calcd for C14H10N2
(206.24): C, 81.53; N, 13.58; H, 4.89. Found: C, 81.46; N,
13.75; H, 4.78. MS (EI) m/z 206 (MC, 100).
3.3.17. 4,6-Bispyrazinylpyrimidine (17). Cross-coupling
reaction of 2,6-dichloropyrimidine (262 mg, 1.76 mmol)
with 4 (1.400 g, 3.79 mmol) according to the general
procedure B (tZ27 h) gave after purification by recrystal-
lization in ethanol then in ethyl acetate 254 mg (61%) of 17
as a pale yellow solid, mp 217–218 8C; 1H NMR (CDCl3): d
8.75 (s, 4H), 9.35 (d, JZ1.2 Hz, 1H), 9.45 (d, JZ1.2 Hz,
1H), 9.77 (s, 2H); 13C NMR (CDCl3): d 114.7, 144.1, 144.5,
146.8, 149.3, 160.0, 163.0. MS (EI) m/z 236 (100, MC).
Anal. Calcd for C12H8N6 (236.24): C, 61.01; H, 3.41; N,
35.57. Found: C, 60.18; H, 3.23; N, 35.61.
3.3.13. 2,3-Diphenylquinoxaline (13). Cross-coupling
reaction of iodobenzenze (612 mg, 340 mL, 3 mmol) with
9 (708 mg, 1 mmol) according to the general procedure B
(tZ48 h) gave after purification by column chromatography
(silica, eluent: dichloromethane) 110 mg (39%) of 13 as a
1
yellow solid, mp 123–124 8C (lit.18 124.5 8C); H NMR
(CDCl3): d 7.44 (m, 2H), 7.48 (m, 4H), 7.64 (dd, JZ7.2,
1.5 Hz, 4H), 7.88 (d, JZ6.4 Hz, 2H), 8.31 (d, JZ6.4 Hz,
2H). NMR 13C (CDCl3) d 128.7, 129.2, 129.6, 130.2, 130.4,
139.4, 141.6. Anal. Calcd for C20H14N2 (282.34): C, 85.08;
N, 9.92; H, 5.00. Found: C, 85.52; N, 9.65; H, 5.38. MS (EI)
m/z 235 (MC, 100).
3.3.18. 2-Phenyl-4-(pyrazinyl)quinazoline (18). Cross-
coupling reaction of 4-chloro-2-phenylquinazoline
(240 mg, 1.0 mmol) with 4 (738 mg, 2 mmol) according to
the general procedure B (tZ28 h) gave after purification by
column chromatography (silica, eluent: ethyl acetate/
dichloromethane (5/5)) 198 mg (70%) of 18 as a colorless
3.3.14. 2,6-Bispyrazinylpyridine (14). Cross-coupling
reaction of 2,6-dibromopyridine (237 mg, 1 mmol) with 4
(738 mg, 2 mmol) according to the general procedure B (tZ
15 h) gave after purification by column chromatography
(silica, eluent: ethyl acetate) 155 mg (66%) of 14 as a
1
solid, mp 206–207 8C; H NMR (CDCl3): d 7.46–7.52 (m,
5H), 7.58 (td, JZ8.29, 1.13 Hz, 1H), 7.86 (td, JZ8.3,
1.13 Hz, 1H), 8.12 (d, JZ8.3 Hz, 1H), 8.65 (dd, JZ7.5,
1.88 Hz, 2H), 8.86 (dd, JZ8.3, 1.13 Hz, 1H), 9.62 (s, 1H);
13C NMR (CDCl3): d 121.9, 127.6, 128.2, 129.0, 129.1,
131.2, 134.4, 138.1, 143.2, 145.5, 147.2, 152.7, 153.1,
160.2, 161.7. IR (KBr) n (cmK1) 3036.2, 2924.8, 2849.8,
1612.1, 1560.5, 1542.8, 1471.2, 1338.9, 1017.8, 853.8,
767.7, 705.0, 688.8, 649.2. MS (EI) m/z 284 (MC, 100), 205
(MKpyrazine, 24). Anal. Calcd for C18H12N4 (MwZ
284.11): C, 76.04; H, 4.25; N, 19.71. Found: C, 76.01; H,
4.24; N, 19.70.
1
colorless solid, mp 215–216 8C; H NMR (CDCl3): d 7.90
(t, JZ7.9 Hz, 1H), 8.35 (d, JZ7.9 Hz, 2H), 8.55 (m, 4H),
9.72 (d, JZ0.75 Hz, 2H). NMR 13C (CDCl3) d 122.4, 138.7,
143.8, 143.9, 145.1, 151.0, 154.1. MS (EI) m/z 235 (MC,
100). Anal. Calcd for C13H9N5 (235.25): C, 66.37; N, 29.77;
H, 3.86. Found: C, 66.36; N, 29.77; H, 3.85.
3.3.15. 2,5-Bispyrazinylpyridine (15). Cross-coupling
reaction of 2,5-dibromopyridine (237 mg, 1 mmol) with 4
(1.107 g, 3 mmol) according to the general procedure B (tZ
27 h) gave after purification by recrystallization in ethyl
acetate 150 mg (64%) of 15 as a colorless solid, mp 265–
266 8C; 1H NMR (CDCl3): d 8.39 (d, JZ8.0 Hz, 1H), 8.53
(dd, JZ8.4, 2.0 Hz, 1H), 8.56 (d, JZ2.4 Hz, 1H), 8.58 (d,
JZ2.8 Hz, 1H), 8.75 (d, JZ2.4 Hz, 1H), 8.76 (d, JZ
2.4 Hz, 1H), 9.03 (d, JZ1.6 Hz, 1H), 9.27 (d, JZ1.6 Hz,
1H), 9.37 (d, JZ0.8 Hz, 1H). NMR 13C (CDCl3) d 124.2,
135.0, 138.7, 143.6, 144.3, 145.1, 145.8, 146.7, 147.1,
149.9, 152.7, 153.2, 156.3. MS (EI) m/z 235 (MC, 100).
Anal. Calcd for C13H9N5 (MwZ235.25): C, 66.37; H, 3.86;
N, 29.77. Found: C, 66.55; H, 3.67; N, 29.82.
3.3.19. 2,6-Bis[30-(60-methoxypyridazinyl)pyrazine] (19).
Cross-coupling reaction of 2,6-bis(tributyltin)pyrazine 6
(770 mg, 1.17 mmol) with 3-chloro-6-methoxypyridazine
(0.338 g, 2.34 mmol) according to the general procedure C
(tZ48 h) gave after purification by column chromatography
(silica, eluent: petroleum ether/ethyl acetate (5/5)) 280 mg
(82%) of 19 as a colorless solid, mp 116–117 8C; 1H NMR
(CDCl3): d 3.90 (s, 6H), 6.94 (d, JZ8.7 Hz, 2H), 7.02 (t, JZ
7.9 Hz, 2H), 7.42 (td, JZ8.7, 1.5 Hz, 2H), 8.04 (dd, JZ7.9,
1.5 Hz, 2H), 9.0 (s, 2H); 13C NMR (CDCl3): d 56.1, 111.9,
120.3, 121.8, 131.9, 133.8, 158.8, 162.5, 166.7. MS (EI) m/z

2904
M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
292 (MC, 100). Anal. Calcd for C18H16N2O2 (292.12) C,
73.96; H, 5.52; N, 9.58. Found: C, 73.97; H, 5.50; N, 9.57.
(21%) of 24 as a colorless solid, mp 238–239 8C; 1H NMR
(CDCl3): d 4.20 (s, 3H), 7.12 (d, JZ9.05 Hz, 1H), 8.44 (d,
JZ9.05 Hz, 1H), 9.80 (s, 1H); 13C NMR (CDCl3): d 55.6,
118.4, 128.0, 143.0, 147.8, 153.4, 165.8. MS (EI) m/z 296
(MC, 100). Anal. Calcd for C14H12N6O2 (296.10) C, 56.75;
H, 4.08; N, 28.36. Found: C, 56.73; H, 4.05; N, 28.19.
3.3.20. 2,6-Bis[10-(20-methoxynaphtyl)]pyrazine (20).
Cross-coupling reaction of 2,6-bis(tributyltin)pyrazine 6
(770 mg, 1.17 mmol) with 1-bromo-2-methoxynaphthalene
(0.702 g, 3 mmol) according to the general procedure C (tZ
48 h) gave after purification by column chromatography
(silica, eluent: dichloromethane) 233 mg (51%) of 20 as a
3.3.25. 2,6-Bis[40-(20-methylsulfanylpyrimidinyl)]pyra-
zine (25). Cross-coupling reaction of 2,6-bis(tributyltin)-
pyrazine 6 (770 mg, 1.17 mmol) with 4-chloro-2-
methylsulfanylpyrazine (0.481 g, 3 mmol) according to
the general procedure C (tZ48 h) gave after purification
by column chromatography (silica, eluent: n-hexane/
dichloromethane/ethyl acetate (4/2/4)) 226 mg (59%) of
25 as a yellow solid, mp 208–209 8C; 1H NMR (CDCl3): d
2.61 (s, 6H), 8.00 (d, JZ4.9 Hz, 2H), 8.66 (d, JZ4.9 Hz,
2H), 9.72 (s, 2H); 13C NMR (CDCl3): d 14.7, 112.9, 134.6,
135.7, 145.3, 148.1, 159.0, 161.2, 173.6. MS (EI) m/z 328
(MC, 100), 313 (MKCH3, 10), 299 (MK2CH3, 45), 282
(MKSCH3, 15), 264 (MK2SCH3, 25). Anal. Calcd for
C14H12N6S2 (328.42): C, 51.20; H, 3.68; N, 25.59; S, 19.53.
Found: C, 51.25; H, 3.67; N, 25.82; S, 19.19.
1
colorless solid, mp 190–191 8C; H NMR (CDCl3): d 3.95
(s, 6H), 7.45–7.33 (m, 6H), 7.71 (d, JZ8.3 Hz, 2H), 7.83 (d,
JZ7.9 Hz, 2H), 7.95 (d, JZ9.0 Hz, 2H), 8.77 (s, 2H); 13C
NMR (CDCl3): d 55.5, 112.1, 119.4, 122.7, 123.4, 126.1,
127.1, 128.0, 130.0, 132.3, 144.2, 150.3, 153.8. MS (EI) m/z
392 (MC, 100). Anal. Calcd for C26H20N2O2 (392.15) C,
79.57; H, 5.14; N, 7.14. Found: C, 79.56; H, 5.14; N, 7.17.
3.3.21. 2,6-Di(20-thienyl)pyrazine (21). Cross-coupling
reaction of 2,6-bis(tributyltin)pyrazine
6 (770 mg,
1.17 mmol) with 2-iodothiophene (0.636 g, 3 mmol)
according to the general procedure C (tZ48 h) gave after
purification by column chromatography (silica, eluent:
dichloromethane/ethyl acetate (5/5)) 217 mg (76%) of 21
1
as a yellow solid, mp 187–188 8C; H NMR (CDCl3): d
3.3.26. 2,6-Bis(20-quinolyl)pyrazine (26). Cross-coupling
7.07–7.11 (m, 2H), 7.42 (dd, JZ4.89, 1.51 Hz, 2H), 7.66
(dd, JZ4.9, 1.51 Hz, 2H), 8.68 (s, 2H); 13C NMR (CDCl3):
d 126.4, 128.7, 129.5, 138.1, 141.7, 147.8. MS (EI) m/z 244
(100, MC). Anal. Calcd for C12H8N2S2 (244.34) C, 58.99;
H, 3.30; N, 11.46. Found: C, 59.06; H, 3.29; N, 11.44.
reaction of 2,6-bis(tributyltin)pyrazine
6 (770 mg,
1.17 mmol) with 2-chloro-quinoline (0.490 g, 3 mmol)
according to the general procedure C (tZ48 h) gave after
purification by washing with petroleum ether (3!5 mL)
1
356 mg (95%) of 26 as a colorless solid, mpO260 8C; H
NMR (CDCl3): d 7.61 (m, 2H), 7.80 (m, 2H), 7.91 (dd, JZ
8.3, 1.1 Hz, 2H), 8.25 (d, JZ8.3 Hz, 2H), 8.37 (d, JZ
8.7 Hz, 2H), 8.75 (d, JZ8.7 Hz, 2H), 9.97 (s, 2H); 13C NMR
(CDCl3): d 119.3, 127.7, 128.1, 128.8, 130.4, 137.3, 143.9,
144.2, 148.3, 150.0, 154.7. MS (FAB) m/z 335 (10), 154
(100), 136 (70). Anal. Calcd for C22H14N4 (334.38): C,
79.02; H, 4.22; N, 16.76. Found: C, 79.00; H, 4.21; N, 16.79.
3.3.22. 2,6-Di(20-pyridyl)pyrazine (22). Cross-coupling
reaction of 2,6-bis(tributyltin)pyrazine
6 (770 mg,
1.17 mmol) with 2-bromopyridine (0.294 g, 3 mmol)
according to the general procedure C (tZ48 h) gave after
purification by column chromatography (silica, eluent:
ethylacetate) 82 mg (30%) of 22 as a colorless solid, mp
1
167–168 8C; H NMR (CDCl3): d 7.33–7.38 (m, 2H), 7.85
(td, JZ7.91, 1.88 Hz, 2H), 8.51 (d, JZ7.92 Hz, 2H), 8.72
(dd, JZ3.76, 0.75 Hz, 2H), 9.64 (s, 2H); 13C NMR (CDCl3):
d 121.8, 124.8, 137.4, 143.1, 149.8, 154.7. MS (EI) m/z 234
(100, MC). Anal. Calcd for C14H10N4 (234): C, 71.78; H,
4.30; N, 23.92. Found: C, 71.64; H, 4.42; N, 23.84.
3.3.27. 2,6-Bis(20-quinoxalyl)pyrazine (27). Cross-
coupling reaction of 2,6-bis(tributyltin)pyrazine
6
(770 mg, 1.17 mmol) with 2-chloro-quinoxaline (0.494 g,
3 mmol) according to the general procedure C (tZ48 h)
gave after purification by washing with petroleum ether
(3!5 mL) 255 mg (65%) of 27 as a colorless solid,
mpO260 8C; 1H NMR (CDCl3): d 8.08–8.11 (m, 4H), 8.43–
8.49 (m, 4H), 10.17 (s, 2H), 10.33 (s, 2H). MS (EI) m/z 336
(MC, 100). Anal. Calcd for C20H12N6 (336.36): C, 71.42; H,
3.60; N, 24.99. Found: C, 71.42; H, 3.59; N, 25.04.
3.3.23. 2,6-Bis[20-(60-methoxypyridyl)]pyrazine (23).
Cross-coupling reaction of 2,6-bis(tributyltin)pyrazine 6
(770 mg, 1.17 mmol) with 2-chloro-6-methoxypyridine
(0.430 g, 3 mmol) according to the general procedure C
(tZ48 h) gave after purification by column chromatography
(silica, eluent: dichloromethane/ethanol: (98/2)) 206 mg
(60%) of 23 as a colorless solid, mp 178–179 8C; 1H NMR
(CDCl3): d 4.07 (s, 6H), 6.84 (d, JZ8.3 Hz, 2H), 7.75 (dd,
JZ8.3, 7.5 Hz, 2H), 8.14 (d, JZ7.5 Hz, 2H), 9.61 (s, 2H);
13C NMR (CDCl3): d 53.8, 112.5, 114.6, 139.8, 142.8,
149.8, 152.0, 164.0. MS (EI) m/z 294 (MC, 100), 263 (MK
OCH3, 34). Anal. Calcd for C16H14N4O2 (MwZ294.31) C,
65.30; H, 4.79; N, 19.04. Found: C, 65.35; H, 4.74; N, 19.01.
3.3.28. 2,6-Bis[40-(20-phenylquinazolyl)]pyrazine (28).
Cross-coupling reaction of 2,6-bis(tributyltin)pyrazine 6
(770 mg, 1.17 mmol) with 2-phenyl-4-chloro-quinazoline
(0.490 g, 3 mmol) according to the general procedure C (tZ
48 h) gave after purification by washing with petroleum
ether (3!5 mL) 405 mg (71%) of 28 as a colorless solid,
1
mpO260 8C; H NMR (CDCl3): d 7.59 (m, 8H), 7.93 (td,
JZ7.7 Hz, 1.15 Hz, 4H), 8.22 (d, JZ8.3 Hz, 2H), 8.78 (dd,
JZ7.7 Hz, 1.15 Hz, 4H), 9.01 (d, JZ8.3 Hz, 2H), 9.92 (s,
2H); 13C NMR (CDCl3): d 112.0, 127.5, 128.3, 129.0, 129.1,
129.8, 131.3, 134.4, 138.1, 147.2, 150.7, 153.2, 160.4,
161.3. MS (EI) m/z 488 (100, MC). Anal. Calcd for
C32H20N6 (488.54) C, 78.61; H, 4.13; N, 17.20. Found: C,
78.60; H, 4.20; N, 17.17.
3.3.24. 2,6-Bis[30-(60-methoxypyridazinyl)]pyrazine (24).
Cross-coupling reaction of 2,6-bis(tributyltin)pyrazine 6
(770 mg, 1.17 mmol) with 3-chloro-6-methoxypyridazine
(0.433 g, 3 mmol) according to the general procedure C (tZ
48 h) gave after purification by column chromatography
(silica, eluent: petroleum ether/ethyl acetate (1/1)) 73 mg

M. Darabantu et al. / Tetrahedron 61 (2005) 2897–2905
2905
¨
2907. (e) Pezet, F.; Routaboul, L.; Daran, J.-C.; Sasaki, I.; Aıt-
Haddou, H.; Balavoine, G. G. A. Tetrahedron 2000, 8489. (f)
Garcia, A. M.; Bassani, D. M.; Lehn, J.-M.; Baum, G.; Fenske,
D. Chem. Eur. J. 1999, 5, 1234.
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