Furazan-containing bromoarenes in the Suzuki-Miyaura reaction

Article abstract of DOI:10.1007/s11172-011-0353-y

The palladium-catalyzed cross-coupling reactions of 3-[bromo(het)aryl] furazans and bromobenzofurazans with arylboronic acids afford target biaryls in good yields. 3-Bromo-4-phenylfurazan containing a bromine atom in the furazan ring undergoes decomposition under the reaction conditions.

Full text of DOI:10.1007/s11172-011-0353-y

Russian Chemical Bulletin, International Edition, Vol. 60, No. 11, pp. 2306—2314, November, 2011
2306
Furazanꢀcontaining bromoarenes in the Suzuki—Miyaura reaction*
A. A. Vasil´ev,a M. I. Struchkova,a A. B. Sheremetev,a F. S. Levinson,b R. V. Varganov,b and K. A. Lyssenkoc
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: vasiliev@ioc.ac.ru; sab@ioc.ac.ru
bKazan State Technological University, 68 ul. Karla Marksa 420015 Kazan, Russian Federation.
cA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471
The palladiumꢀcatalyzed crossꢀcoupling reactions of 3ꢀ[bromo(het)aryl]furazans and
bromobenzofurazans with arylboronic acids afford target biaryls in good yields. 3ꢀBromoꢀ4ꢀ
phenylfurazan containing a bromine atom in the furazan ring undergoes decomposition under
the reaction conditions.
Key words: furazans, benzofurazans, bromoarenes, arylboronic acids, crossꢀcoupling,
Suzuki—Miyaura reaction.
Functionalized (het)arylꢀsubstituted derivatives of
At the same time, the ability of the furazan ring to be
opened under particular conditions can lead to the formaꢀ
tion of acyclic products (see, for example, the study8). The
ability of furazans to form complexes with transition metꢀ
als is another aspect that should be taken into account
when using these compounds.9 For example, the comꢀ
plexation observed in reactions of the furazan ring with
some catalysts interferes with the insertion of carbenes
into the C—H bond of monosubstituted furazans.10
At present, transition metalꢀcatalyzed crossꢀcoupling
reactions are widely used to design molecules containing
(hetero)aromatic rings linked together. In particular, the
formation of the C—C bond in the Suzuki—Miyaura reacꢀ
tion11 proceeds through the interaction of halo(het)arenes
with (het)arylboronic acids. This crossꢀcoupling was sucꢀ
cessfully performed with both fiveꢀ and sixꢀmembered
heterocycles. As for halogen derivatives of furazan, the
scarce data are described in patents and refer only to haloꢀ
benzofurazan derivatives. The coupling of 4ꢀchloroꢀ and
5ꢀbromobenzofurazans with simple arylboronic acids was
documented3,4,12 (in most cases, the yields of the products
were not reported). The Stille coupling of 5ꢀbromobenzoꢀ
furazan with complicated arylstannanes2,13 and the cataꢀ
lytic amination of 5ꢀbromobenzofurazan with piperidine
and piperazine derivatives14 were described. It was found2,3
that 4ꢀ and 5ꢀbromobenzofurazans can be transformed
into the corresponding benzofurazanylboronic acids (lithiꢀ
ation at –100 °C followed by the treatment with trialkyl
borates; the yield of about 30%), which were then coupled
with (het)aryl bromides.
furazan (1,2,5ꢀoxadiazole) are of interest as anticancer1
(e.g., combretafurazan 1) and antiasthmatic2—4 (e.g., comꢀ
pound 2) agents.
Despite the fact that the chemistry of furazans has
been well developed (see reviews5), the synthesis of the
aboveꢀmentioned structures by conventional methods preꢀ
sents numerous difficulties, and their yield is often low.
It should be noted that methods making halofurazans
readily available have been developed only recently.6 Data
on the reactivity of these compounds are scanty.7 Due to
the electronꢀwithdrawing character of the furazan ring,
the halogen atom bound to this ring should be highly labile.
In the present study, with the aim to extend the scope
of the catalytic crossꢀcoupling in the furazan series, we
* Dedicated to Academician of the Russian Academy of Sciences
O. M. Nefedov on the occasion of his 80th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2262—2269, November, 2011.
1066ꢀ5285/11/6011ꢀ2306 © 2011 Springer Science+Business Media, Inc.

Crossꢀcoupling of bromo furazans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011 2307
investigated the palladiumꢀcatalyzed reaction of bromo
derivatives of furazan, which contain a bromine atom both
directly in the furazan ring and in other parts of moleꢀ
cules, with (het)arylboronic acids (the Suzuki—Miyaura
reaction).
other compounds containing a bromine atom and the furaꢀ
zan ring, which are not directly bound to each other. It
appeared that bromophenylꢀsubstituted furazans 6a18 and
6b19 are readily crossꢀcoupled with 4ꢀmethoxyphenylboꢀ
ronic acid to give the expected products 7a,b (Scheme 3).
It should be noted that the presence of the unprotected
amino group in compound 6b does not interfere with the
reaction. The yields of both products are high and virtually
equal (87% for compound 7a and 84% for 7b).
Results and Discussion
It is known15 that 2ꢀbromoꢀ5ꢀphenylꢀ1,3,4ꢀoxadiꢀ
azole (3) is readily involved in the Suzuki—Miyaura reacꢀ
tion (Scheme 1) in the presence of Pd(PPh3)4 and Na2CO3
in aqueous DMF to give crossꢀcoupling product 4 in
85—93% yield.
Scheme 3
Scheme 1
Reagents and conditions: Pd(PPh3)4, DMF, Na2CO3, H2O, 85 °C.
R = Me (a), NH2 (b)
We made an attempt to perform this reaction with the
use of 3ꢀbromoꢀ4ꢀphenylfurazan (3ꢀbromoꢀ4ꢀphenylꢀ
1,2,5ꢀoxadiazole 5),16 which is an isomer of compound 3
distinguished by another arrangement of heteroatoms
in the ring (Scheme 2). When performing the Suzuꢀ
ki—Miyaura reaction17 according to the conventional proꢀ
cedure, the starting bromo(het)arene is first stirred with
Pd(PPh3)4 in DMF or 1,2ꢀdimethoxyethane (DME)
(~30 min), which provides the oxidative addition of aryl
bromide to a Pd0 complex, followed by the addition of
other reagents and heating of the mixture until the reacꢀ
tion is completed. It appeared that the mixture immediꢀ
ately turned black after the addition of Pd(PPh3)4 to
a solution of compound 5 in DME (in DMF, compound 5
decomposes even in the absence of a catalyst!). The subseꢀ
quent steps of the protocol (see Scheme 2) led to the forꢀ
mation exclusively of resinous products.
Reagents and conditions: 4ꢀMeOC6H4B(OH)2, Pd(PPh3)4, DME,
Na2CO3, H2O, Δ.
The crossꢀcoupling of bromothienyl compound 8 afꢀ
fords product 9 in 44% yield (Scheme 4); it should be
Scheme 4
Scheme 2
Reagents and conditions: Pd(PPh3)4, DME, Na2CO3, H2O, 85 °C.
To find out whether the halofurazan or furazan moiety
is cleaved in the Suzuki—Miyaura reaction, we studied
Reagents and conditions: 4ꢀMeOC6H4B(OH)2, Pd(PPh3)4, DME,
Na2CO3, H2O, Δ.

2308
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011
Vasil´ev et al.
noted that the use of 2ꢀbromothiophenes in the Suꢀ
zuki—Miyaura reaction usually gives good results.20 The
starting compound 8 was prepared by the treatment of
thienylfurazan 1021 with bromine in acetic acid.
The structures of products 7a,b, 9, 13, and 14a—g were
1
determined by IR spectroscopy, H and 13C NMR specꢀ
troscopy, and elemental analysis. Pyridylꢀsubstituted deꢀ
rivative 14f was studied by Xꢀray diffraction (Fig. 1).
According to the Xꢀray diffraction data, the geometric
parameters of compound 14f are typical of this class of
compounds. In particular, the C—C bond length alternaꢀ
tions in the benzofurazan moiety are observed, with the
C(6)—C(7) and C(8)—C(9) bonds being substantially
shorter (1.3713(9)—1.3617(10) Å). The pyridine ring is
rotated by 39.4°. In the crystal, molecules 14f form colꢀ
umns through π—πꢀstacking interactions between the benꢀ
zofurazan moieties (Fig. 2). The interplanar distance is
3.3 Å, and the shortest C...C and N...C contacts are charꢀ
acterized by the distances of 3.360(1) and 3.357(1) Å,
respectively.
To quantify the energy of stacking interactions, we
performed the topological analysis of the overall electron
density distribution derived from the highꢀprecision Xꢀray
diffraction data for the crystal of 14f in terms of Bader´s
Atoms in Molecules theory.24 The energy of interactions
was evaluated based on the semiquantitative Espiꢀ
nosa—Lecomte correlation,25 which was developed and
successfully used for the description of a wide range of
weak, including dispersion, interactions in crystals.26
The deformation electron density distribution in the
vicinity of the benzofurazan ring is characterized by exꢀ
pected features, such as the accumulation of electrons in
the vicinity of the C—C, C—N, and N—O bonds, as well
as of lone pairs of the oxygen and nitrogen atoms (Fig. 3).
It should be noted that the precipitation of palladium
black occurred in the beginning of the preparation of comꢀ
pounds 7a,b and 9 (after the addition of arylboronic acid
and an aqueous Na2CO3 solution and heating of the mixꢀ
ture to reflux). In the course of the initial stirring of the
starting bromo(het)arenes with Pd(PPh3)4 in DME at
room temperature, the mixture remained transparent and
only changed the color. Usually, the precipitation of palꢀ
ladium black leads to the removal of the metal from the
catalytic cycle and, as a consequence, to retardation of the
reaction and even its complete cessation (see the review22).
Nevertheless, examples of the catalysis of the Suzuꢀ
ki—Miyaura reaction by palladium black are known.23
We investigated the behavior of isomeric bromobenzoꢀ
furazans 11 and 12 in the Suzuki—Miyaura reaction (as
mentioned above, the use of isomer 12 in this reaction is
described in the patent literature3,4,13). In our experiments,
the reactions of both compounds with 4ꢀmethoxyphenylꢀ
boronic acid in the presence of Pd(PPh3)4 in aqueous DME
gave crossꢀcoupling products 13 and 14a (Scheme 5) in
high yields (~90%). As in the case of nonfused furazans,
the precipitation of palladium black was observed virtually
immediately after the temperature of the reaction mixture
reached the boiling point.
Scheme 5
N(1)
C(8)
C(5)
C(9)
O(2)
N(3)
C(11)
C(4)
C(7)
C(10)
N(12)
C(6)
C(15)
C(14)
C(13)
Fig. 1. Molecular structure of compound 14f; atoms are repreꢀ
sented as probability displacement ellipsoids (p = 50%).
14: Ar = 4ꢀMeOC6H4 (a), 3ꢀMeOC6H4 (b), 4ꢀN≡CC6H4 (c),
3ꢀN≡CC6H4 (d), 3ꢀH2NC6H4 (e), 3ꢀpyridyl (f),
2,4ꢀF2C6H3 (g)
Table 1. Selected bond lengths (d) in compound 14f
Bond
d/Å
Bond
d/Å
Reagents: i. 4ꢀMeOC6H4B(OH)2, Pd(PPh3)4, Na2CO3;
ii. ArB(OH)2, Pd(PPh3)4, Na2CO3.
N(1)—C(5)
N(1)—O(2)
O(2)—N(3)
N(3)—C(4)
C(4)—C(6)
1.3201(10)
1.3803(10)
1.3857(9)
1.3209(9)
1.4263(9)
C(4)—C(5)
C(5)—C(9)
C(6)—C(7)
C(7)—C(8)
C(8)—C(9)
1.4308(10)
1.4252(11)
1.3713(9)
1.4538(9)
1.3617(10)
Using compound 12 as an example, we showed that
a wide range of arylboronic acids containing both elecꢀ
tronꢀdonating and ꢀwithdrawing substituents can be used.

Crossꢀcoupling of bromo furazans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011 2309
C(9A)
C(8A)
N(1A)
C(9A)
C(4A)
C(8A)
C(5A)
C(9)
C(5A)
N(1A)
O(2A)
O(2A)
C(7A)
C(6A)
C(5)
N(1)
N(1B)
N(3A)
C(8)
C(11A)
C(7A)
C(10A)
C(4A)
C(9B)
C(5B)
N(3A)
N(12A)
C(14)
C(15)
C(10)
C(9)C(8)
C(13)
C(5)
C(6A)
C(11)
N(1)
O(2)
C(8B)
C(10)
C(13A)
N(12)
C(7)
C(6)
C(7)
C(6)
C(11B)
C(4)
O(2B)
N(3)
C(4)
C(11) N(12)
N(3)
C(15A)
N(12B)
C(14A)
C(13)
C(14)
C(13B)
C(7B)
C(10B)
C(4B)
C(8B)
C(9B)
N(3B)
C(15)
C(5B)
C(6B)
N(1B)
O(2B)
C(15B)
C(7B)
C(6B)
C(4B)
N(3B)
C(14B)
Fig. 2. Fragments of translationꢀrelated columns running along the axis b as an illustration of the overlap of the benzofurazan rings of
compound 14f.
An analysis of intermolecular interactions showed that
there are critical points (3, –1) not only for plausible stackꢀ
ing interactions but also for a number of C—H...O and
C—H...N interactions with the participation of both
atoms of the benzofurazan ring and the nitrogen atom of
pyridine. In addition, the crystal structure is stabilized by
weak H...H interactions. Unlike intramolecular interacꢀ
tions, all intermolecular interactions are of the closedꢀ
shell type and are characterized by positive values of the
Laplacian (∇2ρ(r)) and the electron energy density. In
particular, the values of ρ(r) and ∇2ρ(r) for the stacking
interactions are ~0.04 e Å–3 and ~0.46 e Å–5; for the
shortest C(15)—H(15)…N(12) contact (H...N, 2.45 Å;
CHN, 163°), ~0.05 e Å–3 and ~0.98 e Å–5, respectively.
The energies of intermolecular C...C and N...C interacꢀ
tions estimated with the use of the Espinosa—Lecomte
correlation are 0.8—1.0 kcal mol–1, and the energy for the
aboveꢀmentioned C—H...N interaction is 1.5 kcal mol–1
.
Therefore, despite a rather short distance between the
planes of the molecules in the stack, the total energy of
stacking interactions per molecule is small (2.6 kcal mol–1),
For comparison, the total crystal lattice energy estimated
by the summation of the energies of all binding interacꢀ
tions based on the results of topological analysis of the
electron density distribution is 13 kcal mol–1
.
The reaction of 4,6ꢀdibromobenzofurazan 15 with two
equivalents of 4ꢀmethoxyphenylboronic acid (Scheme 6)
afforded disubstitution product 16 in 95% yield. The reacꢀ
tion with the use of one equivalent of boronic acid gave
a mixture of regioisomeric monosubstitution products 17a
and 17b, which were separated by column chromatoꢀ
graphy. It was shown that these products were formed in
approximately equal amounts (45 and 50% yields, resꢀ
pectively).
Since we isolated both regioisomers 17a and 17b in the
individual state, their structures were determined based on
substantial differences in the 13C NMR spectra. The specꢀ
trum of isomer 17a shows a highꢀfield signal of the quaterꢀ
nary sp2ꢀhybridized carbon atom at δ 109.3 due to the
simultaneous –β effect of the imino group and the –α effect
of the bromine atom. In the spectrum of isomer 17b, the
Fig. 3. Deformation electron density distribution in the plane of
the benzofurazan ring. The maps are contoured at 0.1 e Å–3
intervals. The negative contours are indicated by dashed lines.

2310
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011
Vasil´ev et al.
Scheme 6
Reagents: 2.2 equiv. (i), 1 equiv. (ii) 4ꢀMeOC6H4B(OH)2.
highestꢀfield signal of the quaternary sp2ꢀhybridized
carbon atom appears at δ 126.2. In addition, the signal of
the =CH fragment adjacent to the furazan ring in isoꢀ
mer 17a is observed at δ 110.2, whereas this signal for
isomer 17b appears at δ 115.6, which is consistent with the
fact that the +β effect of bromine is usually 4—5 ppm
greater than this for the aryl group.
Therefore, we showed that bromo(het)arylꢀsubstituted
furazans and bromobenzofurazans are promising substrates
for the Suzuki—Miyaura reaction. The possibility of the
use of 3ꢀbromofurazans in the transition metalꢀcatalyzed
crossꢀcoupling requires additional investigation.
dried with MgSO4, and filtered through a thin layer of SiO2. The
filtrate was concentrated to ~3 mL and diluted with an equal
volume of pentane. The mixture was kept in a refrigerator for
3 h, and the precipitate was filtered off. A pale cream product was
obtained in a yield of 0.64 g (53%), m.p. 66—67 °C (cf. lit. data27
:
m.p. 64 °C). IR, ν/cm–1: 2960, 2924, 2852, 1596, 1508,
1444, 1408, 1384, 1264, 1116, 1076, 1052, 1036, 1008, 976, 896,
848, 832, 820, 728. 1H NMR (CDCl3), δ: 2.58 (s, 3 H, CH3);
7.69 (m, 4 H, Ar). 13C NMR (CDCl3), δ: 9.6 (CH3); 124.9
(C—Br and Cipso); 129.4, 132.3 (Ar); 149.4 (C—Ar); 152.9
(C—CH3). MS, m/z: 240, 238 [M]+, 210, 208 [M – NO]+, 199,
197, 183, 181, 169, 167, 157, 155. Found (%): C, 45.27; H, 2.99;
N, 11.64. C9H7BrN2O. Calculated (%): C, 45.22; H, 2.95;
N, 11.72.
3ꢀAminoꢀ4ꢀ(5ꢀbromoꢀ2ꢀthienyl)ꢀ1,2,5ꢀoxadiazole (8). A soluꢀ
tion of Br2 (0.28 g, 1.75 mmol) in AcOH (3 mL) was added
dropwise with stirring to a cold (10 °C) solution of 3ꢀaminoꢀ4ꢀ
(2ꢀthienyl)furazan (10)21 (0.28 g, 1.14 mmol) in glacial acetic
acid (5 mL) with maintaining the temperature not higher than
12 °C (cooling bath). Then the reaction mixture was allowed to
reach room temperature and was diluted with water (12 mL).
The precipitate was filtered off, washed with water (2×5 mL)
and hexane (2×5 mL), and dried. The product was obtained in
a yield of 0.33 g (80%), m.p. 133—135 °C; chromatorgaphically
pure, Rf 0.5 (CH2Cl2 : pentane, 1 : 1). The recrystallization from
Experimental
The melting points were determined using a Gallenkamp
melting point apparatus and are not corrected. The naturalꢀabunꢀ
dance 1H and 13C NMR spectra were recorded on a Bruker
AMꢀ300 spectrometer in CDCl3 or DMSOꢀd6 at 300.13 and
75.47 MHz, respectively. The mass spectra were obtained on
Varian MAT CHꢀ6 and Varian MAT CHꢀ111 instruments
(70 eV). The IR spectra were measured on a Specord Mꢀ82
spectrophotometer in KBr pellets. The TLC analysis was perꢀ
formed on Kieselgel 60 F254 plates (Merck, Cat. No. 1.05554).
Preparative chromatography was carried out with the use of siliꢀ
ca gel 40/100 (Merck). Elemental analysis was performed in the
Laboratory of Analytical Chemistry of the N. D. Zelinsky Instiꢀ
tute of Organic Chemistry of the Russian Academy of Sciences.
All solvents for the reactions or column chromatography were
preꢀdistilled. 3ꢀAminoꢀ4ꢀ(2ꢀthienyl)furazan,21 3ꢀbromoꢀ4ꢀphenylꢀ
furazan (1),16 and 3ꢀaminoꢀ4ꢀ(4ꢀbromophenyl)furazan (2b)19
were synthesized according to procedures described in the literꢀ
ature. Commercially available arylboronic acids were used as
received.
CCl4 gave pale cream crystals with m.p. 135—136 °C. IR, ν/cm–1
:
3448, 3328, 3240, 1632, 1584, 1560, 1496, 1428, 1324, 1288,
1220, 1008, 980, 940, 884, 788, 744, 732. 1H NMR (DMSOꢀd6),
δ: 6.34 (s, 2 H, NH2); 7.41 (d, 1 H, J = 4.0 Hz); 7.62 (d, 1 H,
J = 4.0 Hz). 13C NMR (DMSOꢀd6), δ: 114.9 (C—Br); 127.5 (C(3));
129.7, 131.6, 141.6 (C—Th); 154.2 (C—NH2). Found (%): C, 29.35;
H, 1.69; N, 17.00. C6H4BrN3OS. Calculated (%): C, 29.29;
H, 1.64; N, 17.08.
4ꢀBromoꢀ2,1,3ꢀbenzoxadiazole (11). Sodium azide (1.5 g,
0.023 mol) was added portionwise to a stirred suspension of
2,6ꢀdibromonitrobenzene28 (5.3 g, 0.02 mol) in DMSO (30 mL)
at room temperature, which was accompanied by spontaneous
heating of the reaction mixture to 35 °C. Then the mixture was
slowly heated to 120—125 °C, avoiding vigorous foaming, and
kept at this temperature until the completion of the reaction
(~30 min, TLC monitoring). The mixture was diluted with twice
the volume of water, and the product was steamꢀdistilled. The
precipitate was filtered off from the water distillate and dried in
3ꢀ(4ꢀBromophenyl)ꢀ4ꢀmethylꢀ1,2,5ꢀoxadiazole (6a). A 28%
aqueous ammonia solution (8 mL), 1ꢀ(4ꢀbromophenyl)ꢀ1,2ꢀdiꢀ
hydroxyiminopropane27 (1.31 g, 5.1 mmol), and urea (0.4 g,
6.7 mmol) were placed in a 30 mL autoclave. The reaction
mixture was heated at 150—155 °C for 6.5 h. After cooling,
the mixture was extracted with CCl4 (3×10 mL) and CH2Cl2
(10 mL). The combined extracts were washed with water (2×10 mL),

Crossꢀcoupling of bromo furazans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011 2311
air. The recrystallization from propanꢀ2ꢀol gave the product in
a yield of 2.63 g (66%), m.p. 107—108°C (cf. lit. data29: m.p.
107 °C). 1H NMR (CDCl3), δ: 7.30 (dd, 1 H); 7.63 (d, 1 H,
J = 7.0 Hz); 7.81 (d, 1 H, J = 8.9 Hz). 13C NMR (CDCl3), δ:
109.4 (C—Br); 115.7, 132.0, 133.8, 149.2, 149.5.
1028, 1012, 980, 892, 828, 816. 1H NMR (CDCl3), δ: 2.61
(s, 3 H); 3.88 (s, 3 H); 7.03 (d, 2 H, J = 8.8 Hz); 7.59 (d, 2 H,
J = 8.8 Hz); 7.71 (A part of the AB system, 2 H, J = 8.8 Hz); 7.79
(B part of the AB system, 2 H, J = 8.8 Hz). 13C NMR (CDCl3),
δ: 9.8 (CH3); 55.4 (CH3); 114.4 (CH); 124.2 (C); 127.2 (CH);
128.2 (CH); 128.4 (CH); 132.3 (C); 142.8 (C); 149.6 (C);
153.6 (C); 159.7 (C).
3ꢀAminoꢀ4ꢀ[4ꢀ(4ꢀmethoxyphenyl)phenyl]ꢀ1,2,5ꢀoxadiazole
(7b). The yield was 84%, white solid, m.p. 208—210 °C. Found (%):
C, 67.33; H, 5.21; N, 15.62. C15H13N3O2. Calculated (%):
C, 67.41; H, 4.90; N, 15.72 IR (KBr), νmax/cm–1: 3460, 3328,
3248, 2956, 2940, 2836, 1636, 1608, 1516, 1484, 1312, 1292,
1256, 1208, 1184, 1036, 1016, 988, 888, 828. 1H NMR (DMSOꢀd6),
δ: 3.81 (s, 3 H); 6.24 (br.s, 2 H); 7.06 (d, 2 H, J = 8.8 Hz); 7.70
(d, 2 H, J = 8.8 Hz), 7.81 (A part of the AB system, 2 H, J = 8.8 Hz);
7.84 (B part of the AB system, 2 H, J = 8.8 Hz). 13C NMR
(DMSOꢀd6), δ: 55.1 (CH3); 114.4 (CH); 123.6 (C); 126.5 (CH);
127.7 (CH); 128.0 (CH); 131.3 (C); 141.4 (C); 146.5 (C);
155.1 (C); 159.3 (C).
5ꢀBromoꢀ2,1,3ꢀbenzoxadiazole (12). 4ꢀBromoꢀ2ꢀnitroꢀ
aniline (7.9 g, 0.036 mol) was stirred in a mixture of water (5 mL)
and concentrated hydrochloric acid (15 mL) at 50 °C for 30 min
and then cooled to –5 °C. A solution of sodium nitrite (2.76 g,
0.04 mol) in water (10 mL) was added dropwise with maintainꢀ
ing the temperature not higher than 5 °C. The reaction mixture
was kept at 0 °C for 1 h, and then a solution of sodium azide
(2.8 g, 0.043 mol) in water (10 mL) was added. The precipitate of
4ꢀbromoꢀ2ꢀnitrophenyl azide that formed was filtered off, washed
with water, and transferred to a flask containing ethylene glycol
(15 mL). The reaction mixture was kept at 100—110 °C until
nitrogen evolution ceased (~1 h). After cooling to 60 °C, sodium
azide (2.3 g, 0.035 mol) and ethylene glycol (10 mL) were added.
The mixture was heated to 120 °C and kept at this temperature
for 3 h. Then the mixture was diluted with water (20 mL). The
product was steamꢀdistilled and dried in air. The yield of the
product was 5.26 g (73%), m.p. 74—75 °C (cf. lit. data30: m.p.
75 °C). 1H NMR (CDCl3), δ: 7.46 (d, 1 H, J = 8.3 Hz); 7.73
(d, 1 H, J = 8.3 Hz); 8.08 (s, 1 H). 13C NMR (CDCl3), δ: 117.7,
118.4, 126.2 (C—Br); 135.7, 147.6, 149.7.
4,6ꢀDibromoꢀ2,1,3ꢀbenzoxadiazole (15) was synthesized acꢀ
cording to a modified procedure.31 A solution of 4,6ꢀdibromoꢀ
benzofuroxane (11.84 g, 0.04 mol) in methanol (200 mL)
and P(OMe)3 (7.45 g, 0.06 mol) was refluxed for 3 h. Then
methanol and unconsumed P(OMe)3 were distilled off, and
the residue was diluted with water. The pale yellow precipitate
that formed was filtered off, washed with a large amount of
water, and recrystallized from ethanol. The yield of the product
was 9.0 g (81%), m.p. 70—71 °C (cf. lit. data.32: 71.5—72 °C).
1H NMR (CDCl3), δ: 7.67 (s, 1 H); 8.00 (s, 1 H). 13C NMR
(CDCl3), δ: 110.3 (C—Br); 117.3, 125.7 (C—Br); 137.2,
148.2, 149.2.
3ꢀAminoꢀ4ꢀ[5ꢀ(4ꢀmethoxyphenyl)thiophenꢀ2ꢀyl]ꢀ1,2,5ꢀoxaꢀ
diazole (9). The yield was 44%, greenish solid, m.p. 204—205 °C.
Found (%): C, 57.07; H, 4.15; S, 11.53. C13H11N3O2S. Calcuꢀ
lated (%): C, 57.13; H, 4.06; S, 11.73. IR (KBr), νmax/cm–1
:
3440, 3320, 3240, 3024, 2972, 2940, 2844, 1636, 1612, 1576,
1556, 1524, 1492, 1448, 1428, 1340, 1308, 1288, 1256, 1180,
1112, 1084, 1032, 1000, 964, 936, 900, 872, 828, 788. 1H NMR
(DMSOꢀd6), δ: 3.80 (s, 3 H); 6.34 (br.s, 2 H); 7.02 (d, 2 H,
J = 8.6 Hz); 7.53 (d, 1 H, J = 3.8 Hz); 7.68 (d, 2 H, J = 8.6 Hz);
7.77 (d, 1 H, J = 3.8 Hz). 13C NMR (DMSOꢀd6), δ: 55.5 (CH3);
114.6 (CH); 123.4 (CH); 123.6 (C); 125.3 (C); 127.0 (CH); 130.0
(CH); 142.3 (C); 146.3 (C); 154.3 (C); 159.6 (C).
4ꢀ(4ꢀMethoxyphenyl)ꢀ2,1,3ꢀbenzoxadiazole (13). The yield
was 89%, bright yellow crystals, m.p. 126—127 °C. Found (%):
C, 68.35; H, 4.44. C13H10N2O2. Calculated (%): C, 69.02;
H, 4.46. IR (KBr), νmax/cm–1: 3068, 3004, 2968, 2916, 2840,
1612, 1544, 1512, 1444, 1280, 1256, 1184, 1180, 1140, 1120,
1
1036, 884, 868, 836, 800, 788, 752. H NMR (CDCl3), δ: 3.90
Crossꢀcoupling reaction (general procedure). Reactions were
carried out in a twoꢀnecked flask equipped with a rubber septum
and a reflux condenser connected to a vacuum/argon manifold
according to procedures reported earlier.17 Then Pd(PPh3)4
(35 mg, ~3 mol.%) was added to a deaerated solution of the
starting bromo derivative (1 mmol) in 1,2ꢀdimethoxyethane
(2 mL), and the reaction mixture was stirred under argon for
30—40 min. Arylboronic acid (1.3 mmol) was added, and the
mixture was twice carefully deaerated by evacuating and filling
with argon. A freshly prepared deaerated solution of Na2CO3
(0.54 g) in water (2.1 mL) was syringed through the septum, and
the mixture was heated to reflux, which was accompanied by
precipitation of palladium black. The mixture was refluxed for 6
h, cooled, diluted with water, and extracted with CH2Cl2. The
combined extracts were dried (with CaCl2 or Na2SO4) and conꢀ
centrated in vacuo. The residue was purified by column chromꢀ
atography using a mixture of CH2Cl2 and petroleum ether as the
eluent (the CH2Cl2 content was chosen depending on the nature
of particular compounds).
(s, 3 H); 7.06 (d, 2 H, J = 8.8 Hz); 7.43—7.53 (m, 2 H); 7.75 (dd,
1 H, J = 7.8 Hz, J = 2.4 Hz); 7.98 (d, 2 H, J = 8.8 Hz). 13C NMR
(CDCl3), δ: 55.4 (CH3); 114.1 (CH); 114.1 (CH); 126.7 (CH);
127.7 (C); 129.6 (CH); 130.0 (C); 131.9 (CH); 148.7 (C); 149.9
(C); 160.5 (C).
5ꢀ(4ꢀMethoxyphenyl)ꢀ2,1,3ꢀbenzoxadiazole (14a). The yield
was 91%, yellow crystals, m.p. 123—124 °C. Found (%): C, 69.12;
H, 4.35. C13H10N2O2. Calculated (%): C, 69.02; H, 4.46.
IR (KBr), νmax/cm–1: 3072, 2968, 2936, 2836, 1608, 1572, 1520,
1508, 1468, 1444, 1408, 1380, 1284, 1256, 1244, 1184, 1032,
988, 876, 840, 800. 1H NMR (CDCl3), δ: 3.89 (s, 3 H); 7.04
(d, 2 H, J = 8.8 Hz); 7.61 (d, 2 H, J = 8.8 Hz); 7.71 (d, 1 H,
J = 8.1 Hz); 7.88 (d, 1 H, J = 8.1 Hz); 7.88 (s, 1 H). 13C NMR
(CDCl3), δ: 55.4 (CH3); 111.2 (CH); 114.6 (CH); 116.5 (CH);
128.5 (CH); 131.0 (C); 132.8 (CH); 143.7 (C); 148.4 (C);
149.8 (C); 160.5 (C).
5ꢀ(3ꢀMethoxyphenyl)ꢀ2,1,3ꢀbenzoxadiazole (14b). The yield
was 86%, white crystals, m.p. 107—108 °C. Found (%): C, 68.91;
H, 4.41. C13H10N2O2. Calculated (%): C, 69.02; H, 4.46.
IR (KBr), νmax/cm–1: 3080, 2980, 2940, 2832, 1608, 1580, 1540,
1492, 1464, 1432, 1288, 1204, 1168, 1056, 1000, 876, 860, 816,
780, 768. 1H NMR (CDCl3), δ: 3.89 (s, 3 H); 7.01 (d, 1 H,
J = 8.4 Hz); 7.17 (s, 1 H); 7.23 (d, 1 H, J = 7.7 Hz); 7.43 (t, 1 H,
J = 8.1 Hz); 7.70 (d, 1 H, J = 9.3 Hz); 7.90 (d, 1 H, J = 9.3 Hz);
4ꢀ[4ꢀ(4ꢀMethoxyphenyl)phenyl]ꢀ3ꢀmethylꢀ1,2,5ꢀoxadiazole
(7a), the yield was 87%, white solid, m.p. 139—140 °C. Found (%):
C, 72.43; H, 5.47; N, 10.56. C16H14N2O2. Calculated (%):
C, 72.17; H, 5.30; N, 10.52. IR (KBr), νmax/cm–1: 2900, 2936,
2840, 1604, 1508, 1460, 1444, 1292, 1272, 1256, 1204, 1184,

2312
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011
Vasil´ev et al.
7.94 (s, 1 H). 13C NMR (CDCl3), δ: 55.4 (CH3); 112.7 (CH);
113.2 (CH); 114.3 (CH); 116.6 (CH); 119.7 (CH); 130.2 (CH);
132.9 (CH); 140.2 (C); 141.1 (C); 148.6 (C); 149.6 (C);
160.2 (C).aaa
JC,F = 12.2 Hz); 163.3 (dd, CF, JC,F = 252.1 Hz, JC,F = 11.6 Hz).
19F NMR (CDCl3) δ (relative to CFCl3): –107.6, –111.4.
4,6ꢀBis(4ꢀmethoxyphenyl)ꢀ2,1,3ꢀbenzoxadiazole (16) was
synthesized from dibromide 15 with the use of 2.2 equiv. of
4ꢀmethoxyphenylboronic acid. The yield was 95%, bright yellow
crystals, m.p. 141—143 °C. Found (%): C, 72.22; H, 5.08; N, 8.39.
C20H16N2O3. Calculated (%): C, 72.28; H, 4.85; N, 8.43.
IR (KBr), νmax/cm–1: 3004, 2976, 2940, 2840, 1612, 1508, 1440,
1308, 1292, 1248, 1184, 1172, 1028, 860, 824. 1H NMR (CDCl3),
δ: 3.90 (s, 6 H); 7.04 (d, 2 H, J = 8.8 Hz); 7.07 (d, 2 H,
J = 8.8 Hz); 7.64 (d, 2 H, J = 8.8 Hz); 7.77 (s, 2 H); 8.01 (d, 2 H,
J = 8.8 Hz). 13C NMR (CDCl3), δ: 55.4 (CH3); 109.2 (CH);
114.4 (CH); 114.6 (CH); 127.8 (C); 128.3 (CH); 128.5 (CH);
129.7 (CH); 129.9 (C); 131.5 (C); 144.3 (C); 148.2 (C); 150.7 (C);
160.4 (C); 160.5 (C).
5ꢀ(4ꢀCyanophenyl)ꢀ2,1,3ꢀbenzoxadiazole (14c). The yield
was 74%, white solid, m.p. 173—174 °C. Found (%): 70.41;
H, 3.43; N, 18.83. C13H7N3O. Calculated (%): C, 70.58; H, 3.19;
N, 18.99. IR (KBr), νmax/cm–1: 3108, 3052, 2232, 1628, 1608,
1540, 1524, 1468, 1420, 1404, 1328, 1304, 1184, 1156, 1016,
996, 880, 844, 804, 772. 1H NMR (DMSOꢀd6), δ: 7.98 (d, 2 H,
J = 8.3 Hz); 7.99 (d, 1 H, J = 9.4 Hz); 8.04 (d, 2 H, J = 8.3 Hz);
8.16 (d, 1 H, J = 9.4 Hz); 8.41 (s, 1 H). 13C NMR (DMSOꢀd6),
δ: 111.8 (C); 113.9 (CH); 117.0 (CH); 118.5 (C); 128.4 (CH);
132.8 (CH); 133.0 (CH); 142.0 (C); 142.2 (C); 148.4 (C);
149.3 (C).
5ꢀ(3ꢀCyanophenyl)ꢀ2,1,3ꢀbenzoxadiazole (14d). The yield
was 88%, white solid, m.p. 177—178 °C. Found (%): C, 70.71;
H, 3.13. C13H7N3O. Calculated (%): C, 70.58; H, 3.19. IR (KBr),
Compounds 17a,b were synthesized from dibromide 15 with
the use of 1 equiv. of 4ꢀmethoxyphenylboronic acid and separatꢀ
ed by column chromatography on silica gel (gradient elution to
25% CH2Cl2 in petroleum ether), 17b being eluted first.
4ꢀBromoꢀ6ꢀ(4ꢀmethoxyphenyl)ꢀ2,1,3ꢀbenzoxadiazole (17a).
The yield was 50%, white solid, m.p. 131—132 °C. Rf 0.35 (40%
CH2Cl2 in petroleum ether). Found (%): C, 51.19; H, 2.88;
N, 9.09. C13H9BrN2O2. Calculated (%): C, 51.17; H, 2.97;
N, 9.18. IR (KBr), νmax/cm–1: 3088, 3004, 2920, 2844, 1608,
1508, 1444, 1288, 1260, 1196, 1172, 1064, 1032, 952, 892, 832,
792. 1H NMR (CDCl3), δ: 3.89 (s, 3 H); 7.03 (d, 2 H, J = 8.8 Hz);
7.57 (d, 2 H, J = 8.8 Hz); 7.81 (s, 1 H); 7.92 (s, 1 H). 13C NMR
(CDCl3), δ: 55.4 (CH3); 109.3 (C); 110.2 (CH); 114.7 (CH);
128.5 (CH); 129.8 (C); 135.2 (CH); 144.8 (C); 148.8 (C);
149.8 (C); 160.7 (C).
ν
max/cm–1: 3064, 2232, 1628, 1580, 1540, 1520, 1468, 1432,
1376, 1316, 1276, 1160, 1036, 1004, 880, 852, 792, 772, 692.
1H NMR (DMSOꢀd6), δ: 7.74 (t, 1 H, J = 7.9 Hz); 7.94 (d, 1 H,
J = 7.9 Hz); 8.03 (d, 1 H, J = 9.4 Hz); 8.17 (d, 1 H, J = 9.4 Hz);
8.20 (d, 1 H, J = 7.9 Hz); 8.36 (s, 1 H); 8.43 (s, 1 H). 13C NMR
(DMSOꢀd6), δ: 112.4 (C); 113.5 (CH); 116.9 (CH); 118.5 (C);
130.3 (CH); 131.2 (CH); 132.0 (CH); 132.6 (CH); 134.0 (CH);
138.9 (C); 141.8 (C); 148.4 (C); 149.4 (C).
5ꢀ(3ꢀAminophenyl)ꢀ2,1,3ꢀbenzoxadiazole (14e). The yield
was 78%, yellow solid, m.p. 129—131 °C. Found (%): C, 68.18;
H, 4.42. C12H9N3O. Calculated (%): C, 68.24; H, 4.29. IR (KBr),
ν
max/cm–1: 3392, 3332, 3240, 1668, 1644, 1604, 1588, 1540,
1496, 1468, 1448, 1328, 1312, 1208, 1160, 1128, 1068, 996, 884,
852, 816, 784, 768. 1H NMR (DMSOꢀd6), δ: 5.26 (br.s, 2 H);
6.70 (d, 1 H, J = 7.8 Hz); 6.95 (d, 1 H, J = 7.8 Hz); 7.00 (s, 1 H);
7.18 (t, 1 H, J = 7.8 Hz); 7.87 (d, 1 H, J = 9.8 Hz); 8.08 (s, 1 H);
8.11 (d, 1 H, J = 9.8 Hz). 13C NMR (DMSOꢀd6), δ: 111.1 (CH);
112.4 (CH); 114.9 (two overlapping signals of CH), 116.4 (CH);
129.7 (CH); 133.6 (CH); 138.6 (C); 144.7 (C); 148.4 (C); 149.3
(C); 149.6 (C).
6ꢀBromoꢀ4ꢀ(4ꢀmethoxyphenyl)ꢀ2,1,3ꢀbenzoxadiazole (17b).
The yield was 45%, yellow solid, m.p. 90—91 °C. Rf 0.41 (40%
CH2Cl2 in petroleum ether). Found (%): C, 51.27; H, 3.06;
N, 9.20. C13H9BrN2O2. Calculated (%): C, 51.17; H, 2.97;
N, 9.18. IR (KBr), νmax/cm–1: 3084, 2928, 2900, 2840, 1608,
1572, 1456, 1288, 1256, 1232, 1180, 1028, 1016, 960, 884, 868,
828. 1H NMR (CDCl3), δ: 3.89 (s, 3 H); 7.05 (d, 2 H, J = 8.8 Hz);
7.57 (s, 1 H); 7.95 (s, 1 H); 7.96 (d, 2 H, J = 8.8 Hz). 13C NMR
(CDCl3), δ: 55.4 (CH3); 114.5 (CH); 115.6 (CH); 126.2 (C);
126.7 (C); 129.8 (CH); 130.5 (CH); 131.2 (C); 147.5 (C);
150.5 (C); 161.0 (C).
5ꢀ(3ꢀPyridyl)ꢀ2,1,3ꢀbenzoxadiazole (14f). The yield was 83%,
beige solid, m.p. 139—140 °C. Found (%): C, 67.06; H, 3.58.
C11H7N3O. Calculated (%): C, 67.00; H, 3.58. IR (KBr),
ν
max/cm–1: 3028, 1628, 1592, 1512, 1468, 1420, 1408, 1376,
Xꢀray diffraction. Crystals of compound 14f (C11H7N3O,
M = 197.20) at 100 K are orthorhombic: a = 20.2365(3) Å,
1308, 1264, 1244, 1200, 1160, 1016, 996, 932, 896, 880, 848,
800, 788, 708. 1H NMR (CDCl3), δ: 7.46 (m, 1 H); 7.68 (d, 1 H,
J = 9.2 Hz); 7.91—8.05 (m, 3 H); 8.71 (s, 1 H); 8.93 (s, 1 H).
13C NMR (CDCl3), δ: 113.7 (CH); 117.4 (CH); 123.8 (CH);
132.0 (CH); 134.4 (C); 134.5 (CH); 141.1 (C); 148.3 (CH);
148.5 (C); 149.4 (C); 150.2 (CH).
5ꢀ(2,4ꢀDifluorophenyl)ꢀ2,1,3ꢀbenzoxadiazole (14g). The yield
was 93%, white solid, m.p. 108—110 °C. Found (%): C, 61.91;
H, 2.56. C12H6F2N2O. Calculated (%): C, 62.08, H, 2.60. IR
(KBr), νmax/cm–1: 3084, 3056, 1620, 1596, 1520, 1496, 1468,
1428, 1324, 1296, 1276, 1224, 1144, 1104, 1020, 1000, 972, 888,
848, 808. 1H NMR (CDCl3), δ: 6.94—7.09 (m, 2 H); 7.50 (q, 1 H,
3JH,H = 8.1 Hz, 4JH,F = 8.1 Hz); 7.59 (d, 1 H, J = 9.2 Hz); 7.90
(d, 1 H, J = 9.2 Hz); 7.92 (s, 1 H). 13C NMR (CDCl3), δ: 104.9
(t, CH, JCF = 26.0 Hz); 112.2 (dd, CH, JC,F = 21.6 Hz,
JC,F = 3.9 Hz); 115.5 (d, CH, JC,F = 2.8 Hz); 116.4 (CH); 123.1
(dd, C, JC,F = 13.3 Hz, JC,F = 3.9 Hz); 131.3 (dd, CH, JCF = 9.4 Hz,
b = 3.72030(10) Å, c = 11.9970(2) Å, V = 903.20(3) Å3, dcalc
=
= 1.450 g cm–1, space group Pca21, Z = 4. The intensities of
59404 reflections were measured on a Smart APREX2 CCD
automated diffractometer at 100 K (MoꢀKα radiation, graphite
monochromator, ωꢀscanning technique, 2θmax = 100°) of which
4848 independent reflections (Rint = 0.0381) were used in subseꢀ
quent calculations. The structure was solved by direct methods
and refined by the fullꢀmatrix leastꢀsquares method with isoꢀ
tropic and anisotropic displacement parameters based on F2.
The hydrogen atoms were located in difference electron densiꢀ
ty maps and refined isotropically. The final R factors were
as follows: wR2 = 0.1002, GOOF = 0.963 based on all reflecꢀ
tions (R1 = 0.0394 was calculated based on 8064 reflections
with I > 2σ(I)) with the use of the SHELXTL PLUS program
package.33
The multipole refinement of 14f was performed in terms of
the Hansen—Coppens formalism34 with the use of the XD proꢀ
gram package35 with the core and valence electron density deꢀ
JCF = 4.4 Hz); 133.5 (d, CH, JC,F = 3.3 Hz); 138.4 (d, C, JC,F
=
= 1.7 Hz); 148.3 (C); 149.3 (C); 160.0 (dd, CF, JC,F = 252.7 Hz,

Crossꢀcoupling of bromo furazans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011 2313
rived from wavefunctions fitted to a relativistic Dirac—Fock soluꢀ
tion. Before the refinement, the C—H bond lengths were norꢀ
malized to 1.08 Å. The multipole expansion for nitrogen, oxyꢀ
gen, and carbon atoms was taken up to the octupole level and for
the hydrogen atoms up to the dipole level. The refinement was
performed based on Fhkl. All covalently bonded pairs of atoms
satisfy the Hirshfeld rigidꢀbond test.36 The maximum residual
electron density was 0.21 e Å–3 (in the vicinity of the N(1) nuꢀ
cleus). Binding interactions were found and the topological charꢀ
acteristics of electron density distribution were calculated with
the use of the WINXPRO program.37 The final R factors were as
follows: R = 0.0262, Rw = 0.0259, GOOF = 0.9882 for 4283
reflections with I > 3σ(I).
P. C. Junk, F. R. Keene, J. Chem. Soc., Dalton Trans.,
2002, 2775.
10. A. E. Vasil´vitskii, A. B. Sheremetev, T. S. Novikova, L. I.
Khmel´nitskii, O. M. Nefedov, Izv. Akad. Nauk SSSR, Ser.
Khim., 1989, 2876 [Bull. Acad. Sci. USSR, Div. Chem. Sci.
(Engl. Transl.), 1989, 38, 2640].
11. (a) N. Miyaura, A. Suzuki, Chem. Rev., 1995, 95, 2457;
(b) A. Suzuki. in MetalꢀCatalyzed CrossꢀCoupling Reactions;
Eds F. Diederich, P. J. Stang, WileyꢀVCH, Weinheim, Gerꢀ
many, 1998, pp. 49—98; (c) S. Kotha, K. Lahiri, D. Kashiꢀ
nath, Tetrahedron, 2002, 58, 9633; (d) F. Alonso, I. P. Beꢀ
letskaya, M. Yus, Tetrahedron, 2008, 64, 3047.
12. (a) Pat. WO 2004/087684 [Chem. Abstr., 2004, 141,
350175]; (b) Pat. US 2005/0282818 [Chem. Abstr., 2006,
144:51590].
This study was financially supported in part by the
Council on Grants at the President of the Russian Federaꢀ
tion (Program for State Support of Young Scientists, Grant
MDꢀ237.2010.3).
13. (a) Appl. WO 97/18208 [Chem. Abstr., 1997, 127, 50650];
(b) N. Blouin, A. Michaud, D. Gendron, S. Wakim, E. Blair,
R. NeaguꢀPlesu, M. Belletéte, G. Durocher, Ye Tao,
M. Leclerc, J. Am. Chem. Soc., 2008, 130, 732.
14. Pat. WO 2006/035283 [Chem. Abstr., 2006, 144, 370098].
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16. R. Calvino, A. Serafino, B. Ferrarotti, A. Gasco, A. Sanfilipꢀ
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M. A. Siddiqui, V. Snieckus, J. Org. Chem., 1991, 56, 3763;
(с) S. I. Sviridov, A. A. Vasil´ev, N. L. Sergovskaya, M. V.
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