(E)-1,2-bis(5-aryl-1,3,4-oxadiazol-2-yl)ethenes

Article abstract of DOI:10.1055/s-1999-3511

A series of (E)-1,2-bis(1,3,4-oxadiazol-2-yl)ethenes with a variety of aromatic substituents in the 5-positions of the heterocycles was prepared by acylation of the corresponding tetrazoles with fumaryl chloride and subsequent thermal ring transformation. The modified Huisgen reaction renders a new pathway to 3-(1,3,4-oxadiazol-2-yl)propenoic acids and subsequently to the title compounds with different substituents.

Full text of DOI:10.1055/s-1999-3511

PAPER
999
(E)-1,2-Bis(5-aryl-1,3,4-oxadiazol-2-yl)ethenes
Heiner Detert, Dieter Schollmeier
Institut für Organische Chemie, Johannes Gutenberg-Universität Mainz, Duisbergweg 10–14, D-55099 Mainz, Germany
Fax +49(6131)395396; E-mail: deted000@mail.uni-mainz.de
Received 14 December 1998; revised 12 February 1999
Dedicated to Prof. H. Meier on the occasion of his 60th birthday
whiteners to hole conducting layers in light emitting
diodes. Contrary to the vast knowledge about these clas-
ses of compounds, hitherto only two 1,2-bis(1,3,4-oxadia-
zolyl)ethenes have been described.11,12 We are interested
Abstract: A series of (E)-1,2-bis(1,3,4-oxadiazol-2-yl)ethenes with
a variety of aromatic substituents in the 5-positions of the heterocy-
cles was prepared by acylation of the corresponding tetrazoles with
fumaryl chloride and subsequent thermal ring transformation. The
modified Huisgen reaction renders a new pathway to 3-(1,3,4-oxa- in molecules with extended conjugation and high electron
diazol-2-yl)propenoic acids and subsequently to the title com-
pounds with different substituents.
affinity as model compounds for poly(hetarylenevi-
nylene)s. Herein, the synthesis of aryl substituted (E)-1,2-
Key words: heterocycles, Huisgen reaction, stilbene, 1,3,4-oxadia-
zole
bis(1,3,4-oxadiazol-2-yl)ethenes by direct reaction of tet-
razoles with fumaryl chloride is reported. The Huisgen re-
action provides an elegant way to compounds sensitive to
drastic reaction conditions. The required tetrazoles are
easily accessible from nitriles and inorganic azides,13 or
primary acid amides employing triazidochlorosilane.14
Huisgen and co-workers prepared 2,5-bisaryl-1,3,4-oxa-
diazoles in excellent yields by heating solutions of tetra-
zoles and carboxylic acid chlorides in pyridine. This
procedure was not transferable to the reaction of tetrazoles
with fumaryl chloride. Using pyridine as base and solvent
led to several side reactions.15 In the absence of a base, us-
ing high-boiling ethers like diglyme as solvent, the acyla-
tion/ring transformation required elevated temperatures
resulting in decomposition of the tetrazole and to side re-
actions due to acidic cleavage of the solvent. Adding only
stoichiometric amounts of collidine or quinoline to a solu-
tion of fumaryl chloride and the tetrazole in aromatic
ethers like anisole or diphenyl ether and subsequent heat-
ing proved to be successful for the conversion to the title
compounds. A series of bis-oxadiazolylethenes with aro-
matic substituents and extended conjugation could be pre-
1,3,4-Oxadiazoles with aromatic substituents in the 2- and
5-position and bis(1,3,4-oxadiazolyl)arenes are classes of
compounds with wide technical importance. Their fluo-
rescence is used in plastic scintillators and optical whiten-
ers,1,2 their semiconducting properties and film forming
capabilities were recently utilised for electron conducting
layers in organic light emitting diodes.3,4 Polymeric com-
pounds, displaying tough mechanical properties and ex-
cellent heat resistance are advanced materials for high-
performance applications.4 In substituted 1,3,4-oxadiaz-
oles the heterocycle is, from the spectral and electronic
points of view, similar to a p-phenylene unit. The stability,
the hypsochromic shifted absorption maximum, intense
fluorescence, and the lowered HOMO and LUMO energy
levels5 are interesting features for the application in
electrooptical devices. Sinigersky, Wegner, and Shopov
investigated poly(arylenevinylene)s with alternating
p-phenylene and 1,3,4-oxadiazole units.6 The conductivi-
ty of these materials was close to that of poly(p-phenyl-
enevinylene). Balanced charge transporting properties for
both, electrons and holes and an efficient light emission
has been reported for poly(phenylenevinylene)s contain-
ing 2,5-diaryl-1,3,4-oxadiazole segments in the main
chain.7
pared in
a
one-pot procedure (Scheme). The
transformation of the heterocycles (1–6 to 7–12) was
monitored by the gas evolution, starting at bath tempera-
tures between 85 °C (7) and 180 °C (12). Tetrazoles with
electron-rich substituents (1, 2) proved to be more reac-
tive than those with arenes of higher electronegativity (4,
5), the reaction with phenylethenyl tetrazole 6 competed
with decomposition resulting in a low yield (16%) of 12.
There are two widely used general principles8 for the syn-
thesis of 1,3,4-oxadiazoles, cyclocondensation of acyl hy-
drazides and the thermal ring transformation of acylated
tetrazoles (Huisgen reaction). Recently, Kraft reported the
synthesis of 1,3,4-oxadiazole containing dendrimers via
palladium catalysed carbonylation of aromatic halides in
the presence of hydrazides or tetrazoles. The acylated in-
termediates were transformed to the oxadiazoles by dehy-
dration or thermally.9
Using an excess of fumaryl chloride in the presence of
collidine offered a straightforward access to the hitherto
nearly unknown16,17 b-(oxadiazolyl)acrylic esters (13, 14)
and, by hydrolysis of the ester, to the corresponding acids
(15, 16). Their transformation to the acid chlorides and
subsequent Huisgen reactions opened the possibility to
synthesise compounds with different substituents (17,
18).
The chemistry and physics of stilbene10 and stilbenoid oli-
gomers and polymers has been studied extensively. Their
application profile ranges from anthelmintics and optical
Attempts to prepare the corresponding (Z)-b-(oxadiaz-
olyl)acrylic acids or (Z)-1,2-bisoxadiazolylethenes from
Synthesis 1999, No. 6, 999–1004 ISSN 0039-7881 © Thieme Stuttgart · New York

1000
H. Detert, D. Schollmeier
PAPER
tetrazoles and maleic anhydride failed due to decomposi- These unexpected nuclear Overhauser effects from pro-
tion of the tetrazoles at the required reaction temperatures. tons on one side of the oxadiazole to hydrogen on the oth-
Huisgen reported similar results for the reaction of tetra- er side prompted us to calculate the spatial distances and
zoles with phthalic anhydride.5
the conformational distribution in this compound. Force
field calculations18 gave two groups of minima divided by
about 2 kcal/mol in their heats of formation. All minima
were essentially planar, the three predominant populated
conformers with s-trans geometry of the ethylene unit and
C=N bonds of the adjacent heterocycles were more stable
than the second group of minima with one or two s-cis ori-
entations. Rotation of the xylene moiety led to differences
in the heats of formation of 0.31 kcal/mol or less. The ab-
solute minimum was calculated to be planar and both
ortho-methyl groups had s-cis orientation to the oxygen of
the adjacent heterocycle, this conformation is depicted in
Figure 1. For these three low-energy conformers, the in-
tramolecular distances of protons responsible for the long
range NOEs were calculated to be in the range of 3.28 to
3.41 Å (ethene–methyl, 1% NOE) and 3.73 to 3.89 Å
(ethene-ortho-H, 1.7% NOE).
In accordance with the calculations, X-ray analysis re-
vealed the s-trans orientation of ethene and adjacent C=N
bonds (Figure 2). Contrary to the calculated gas phase
structure, we found s-trans geometry of ortho-methyl
groups and the heterocyclic oxygen in the solid state. The
distance of vinylene proton and aromatic ortho-hydrogen
was 3.62 Å, all dihedral angles of aromatic and alkenic
units were less than 3.5°. These investigations proved a
high degree of planarity in this molecule in the solid state
as well as in solution or in the gas phase.
In conclusion, we have extended the Huisgen reaction to
the synthesis of (E)-1,2-bis(1,3,4-oxadiazolyl)ethenes and
i) anisole or diphenyl ether, collidine or quinoline, 85–180 °C; ii) ani- oxadiazolyl propenoic acids with a variety of aromatic
sole, excess fumaryl chloride, collidine, 95 °C, then MeOH, r.t.; iii)
propan-2-ol, NaOH, H2O, 90 °C, then HCl; iv) PCl3, benzene, r.t.,
14 h, then tetrazole (2, 5), anisole, collidine, 120 °C.
substituents on the heterocycle. Compounds with extend-
ed conjugation and high electron affinity are accessible.
NMR and X-ray analysis revealed a high degree of planar-
ity even by ortho-substitution at the heteroanalogous bi-
Scheme
phenylene unit.
IR-Spectra: in KBr, Beckman Acculab 4. NMR Spectra: in CDCl3
or DMSO-d6, Bruker AC 200 and AM 400. Mass spectra: 70 eV,
The model compound 8 was studied by NMR spectrosco-
py. The trans-configuration of the vinylene protons was
Varian MAT 711. Mps: not corrected. Eluent mixtures are v/v. The
proved by the vicinal coupling constant of J = 16.4 Hz
(from 13C satellites). Irradiation into their signal caused
positive NOEs at the resonance frequencies of the aromat-
ic protons ortho to the oxadiazole (1.7%) and of the ortho
methyl groups (1.0%). The reverse experiments, irradia-
tion into the signal of the ortho-methyl group or the ortho-
hydrogen enhanced the intensity of the vinylene signal
(0.8%, 1.7%).
nitriles, except 4-[(E)-2-(4-methylphenylethen-1-yl]benzonitrile19
were commercially available. Chemicals were used as received, sol-
vents dried according to standard procedures and distilled.
Tetrazoles 1–6; General Procedure
Magnetically stirred mixtures of the corresponding nitrile (0.1 mol),
NH4Cl (6.9 g, 0.13 mol) and NaN3 (8.45 g, 0.13 mol) in anhyd DMF
(60 mL) were heated to 140 °C for 48 h. The cooled mixtures were
poured into H2O (300 mL) and acidified to pH = 2 with concentrated
hydrochloric acid. After 12 h at 4 °C, the suspension was filtrated
using a Büchner funnel, the residue was washed with H2O, H2O/
EtOH (1/1) and H2O and dried. Recrystallisation from EtOH or pro-
pan-2-ol gave analytically pure products.
5-(4-Methoxyphenyl)tetrazole20 (1)
Yield: 17.1 g (97%),white crystals, mp 235 °C, (Lit.: 237 °C).
5-(2,5-Dimethylphenyl)tetrazole (2)
Yield: 15.4 g (94%), white crystals.
Figure 1. Calculated Energy-Lowest Conformation of 8
Synthesis 1999, No. 6, 999–1004 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
(E)-1,2-Bis(5-aryl-1,3,4-oxadiazol-2-yl)ethenes
1001
Figure 2. X-ray Structure of 8
5-{4-[(E)-2-(4-Methylphenyl)ethen-1-yl]phenyl}tetrazole (3)
Prepared from 4-[(E)-2-(4-methylphenyl)ethen-1-yl]benzonitrile,19
yield: 23.9 g (91%), white crystals, mp 248 °C (dec.).
4-(2H-Tetrazol-5-yl)pyridine21 (4)
(E)-1,2-Bis[5-(2,5-dimethylphenyl)-1,3,4-oxadiazol-2-yl]ethene
(8)
Anisole was used as solvent, N2 evolution occurred above 95 °C.
Yield: 331 mg (89%), colourless crystals.
Yield: 12.3 g (84%), light brown crystals, mp 265 °C (dec.).
5-(1-Naphthyl)tetrazole22 (5)
Yield: 18.0 g (92%), mp 192 °C (dec.) (Lit.: 217–218 °C).
(E)-1,2-Bis{5-[4-((E)-2-{4-methylphenyl}ethen-1-yl)phenyl]-
1,3,4-oxadiazol-2-yl}ethene (9)
Diphenyl ether was used as solvent, N2 evolution started at 140 °C.
Purification by pouring the mixture into petroleum ether (100 mL),
filtration and subsequent washing with toluene, EtOAc and EtOH.
Stirring the crude product first with aq MeOH (1/1, 50 mL) and than
with hot CHCl3 (100 mL). Yield: 537 mg (92%), mp 368°C (dec.).
(E)-5-(2-Phenylethenyl)tetrazole (6)
Yield: 13.4 g (78%), light brown crystals, mp 154 °C (175 °C dec.).
Huisgen Reaction; General Procedure
IR (KBr): n = 3012 cm–1, 2895, 1588, 1530, 1496, 1408, 1084, 956,
A round-bottom flask was equipped with a magnetic stirring bar, the
tetrazole (1–6) (2 mmol), solvent (20 mL) and fumaryl chloride
(153 mg, 1 mmol) were added. While stirring, collidine (242 mg, 2
mmol) diluted with solvent (2 mL) was added dropwise and the
flask was connected to a gas burette. The flask was heated until gas
evolution occurred and kept at this temperature. As the gas evolu-
tion ceased, the bath temperature was raised about 20 °C and kept
for further 20 min. The mixture was cooled and poured on a chro-
matography column filled with silica gel and petroleum ether/tolu-
ene 1/1. After the solvent was eluted, toluene with gradually
increased content of EtOAc was used as an eluent.
828, 796, 740.
MS (m/z,%): 548 (13) [M+], 221 (42) [C16H13O+], 193 (5), 178 (29),
44 (100).
(E)-1,2-Bis[5-(4-pyridyl)-1,3,4-oxadiazol-2-yl]ethene (10)
Diphenyl ether was used as solvent, no base was added, nitrogen
evolution occurred above 170 °C. Yield: 203 mg (64%), colourless
crystals.
(E)-1,2-Bis[5-(naphth-1-yl)-1,3,4-oxadiazol-2-yl]ethene (11)
Anisole was used as solvent, N2 evolution occurred above 140 °C,
3 h. Yield: 349 mg (84%), colourless crystals.
(E)-1,2-Bis[5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-yl]ethene
(7)
Anisole as solvent, gas evolution started at 85 °C. Yield: 318 mg
(92%), colourless crystals.
Table 1 Selected Bond Lengths and Angles for 8 in the Solid State
distance
Å
bond angles
deg
torsion angles
deg
C1 – C7
C7 – N8
C7 – O11
N9 – C10
C10 – C14
C14 – C14´
1.458
1.291
1.367
1.284
1.440
1.323
C7 – C1 – C6
C3 – C2 – C1
C12 – C2 – C1
C1 – C7 – N8
N9 – C10 – C14
C10 – C14 – C14´
118.0
116.7
123.7
131.1
127.8
123.4
C6 – C1 – C2 – C12
C7 – C1 – C2 – C3
C7 – C1 – C2 – C12
C2 – C1 – C7 – N8
C6 – C1 – C7 – O11
N9 – C10 – C14 – C14´
–178.2
–175.6
4.5
3.4
2.9
177.7
Synthesis 1999, No. 6, 999–1004 ISSN 0039-7881 © Thieme Stuttgart · New York

1002
H. Detert, D. Schollmeier
PAPER
Table 2 Compounds 2, 3 and 6–18 Prepared
Prod-
uct
mp
(°C)
1H NMR : d, J (Hz)
13C NMR : d
MS m/z (rel.
int., %)
IR (KBr) n (cm–1)
(Yield)
2
174
2.32 (s, 3 H, CH3), 2.48 (s, 3 H, CH3), 19.8, 20.2, (CH3), 123.7 (C-1,
7.18 (d, 2 H, 3-H, 4-H), 7.23 (d, 1 H, Ph),155.3 (C-5), 129.7, 131.1, 131.2
174 (71) [M+], 3005, 2900, 2730,
145 (100), 131 2620, 1582, 1503,
(77) [M+-HN3] 1250, 1166, 1092,
993, 899, 818
(94%)
6-H)b
(C-3, C-4, C-6, Ph), 133.9, 135.3
(C-2, C-5, Ph)b
3
248
(dec.)
2.31 (s, 3 H, CH3), 7.21 (m, 3 H, 3-H 20.9 (CH3), 126.7, 127.1, 127.3,
5-H, Tol, 1-H, Tet), 7.24 (d, J = 16.5, 129.4 (ar CH), 126.3, 130.4 (Eth),
1 H, Eth), 7.37 (d, J = 16.5, 1 H, Eth), 122.8, 133.9, 137.6, 139.9 (Cq, ar),
7.51 (d, J = 7.5, 2 H, 2-H, 6-H, Tol),
7.78 (d, J = 7.9, 2 H, 3-H, 5-H, Ph),
8.02 (d, J = 8.1, 2 H 2-H, 6-H, Ph)b
262 (51) [M+], 3010, 2915, 2850,
234 (100) [M+- 2730, 1604, 1560,
(91%)
N2], 219 (30)
1508, 1488, 1433,
1156, 1056, 978,
840, 811, 752
155.2 (C-5, Tet)b
[M+-HN3]
6
154
(175°
dec.)
7.69 (d, J = 7.9 Hz, 2 H, 2-H, 6-H,
Ph), 7.64 (d, J = 16.5 Hz, 1 H, 2-H),
7.41 (m, 3 H, 3-H, 4-H, 5-H, Ph), 7.32
(d, J = 16.5 Hz, 1 H, 1-H)b
110.3, 127.4, 128.9, 129.5, , 137.8,
137.9, 154.6 (C-5)b
172 (16) [M+], 3005 , 2970, 2600,
144 (35) [M+-
N2], 115 (100)
1634, 1549, 1410,
1234, 1041, 968,
760
(78%)
+
[C9H7 ]
7
264
195
3.89 (s, 6 H, OCH3), 7.05 (d, J = 9, 4 55.5 (OCH3), 114.7 (C-2, C-5, Ph),
376 (42) [M+], 3050, 2930, 1600,
H, 3-H, 5-H, Ph), 7.58 (s, 2 H, Eth),
118.8 (Eth), 129.0 (C-3, C-5, Ph),
135 (100)
[C8H7O2 ]
1485, 1250, 1170,
1089, 1028, 832,
8.02 (d, J = 9, 4 H, 2-H, 6-H, Ph)a
162.6, 164.0 (C-2, C-5, Od)a
+
(92%)
8
2.41 (s, 6 H, 5-CH3), 2.82 (s, 6 H, 2-
20.7, 21.6 (2-CH3, 5-CH3, Xyl), 119.1 372 (100)
3070, 3010, 2970,
CH3), 7.25 (s, 4 H, 3-H, 4-H, Ph), 7.59 (Eth), 129.5, 131.9, 132.6, (C-3, C-4, [M+], 226 (28), 1553, 1527, 1495,
(89%)
(s, 2 H, Eth), 7.84 (s, 2 H, 6-H, Ph)a
C-6, Xyl), 122.0, 135.7, 136.0 (C-1,
133 (96)
1435, 1382, 1252,
1060, 996, 825,
816, 749, 740
C-2, C-5, Xyl), 162.0, 165.5 (C-2, C- [C9H9O+]
5, Od)a
10
345
(dec.)
7.97 (s, 2 H, Eth), 8.13 (d, J = 5.5, 2
120.5, 120.2 (C-3, C-5, Py, C-1, C-2, 318 (16) [M+], 3040, 1600, 1546,
H, 3-H, 5-H, Py), 8.89 (d, J = 5.5 Hz, Eth), 150.9 (C-2, C-6, Py)23b
106 (100)
1528, 1413, 1269,
(64%)
2 H, 2-H, 6-H, Py)b
[C6H4NO+], 78 1107, 980, 838,
(97) [C5H4N+]
752, 706, 681
11
228
7.76 (s, 2 H, Eth), 7.57 - 7.77 (m, 3 H), 119.5, 125.0, 126.1, 127.0, 128.5,
7.90 (d, J = 8.4, 2 H), 8.09 (d, J = 7.8, 128.9, 129.0, 133.4 [23] a
2 H), 8.30 (d, J = 7.3, 2 H), 9.27 (d, J
416 (1) [M+],
294 (29), 155
(100)
3015. ,1568, 1550,
1518, 1395, 1238,
1130, 1032, 996,
(84%)
= 8.4, 2 H)a
[C11H7O+], 127 965, 803, 771
(66)
12
320
145
7.07 (d, J = 16, 2 H, Eth), 7.28 - 7.38
(m, 8 H, 3-H, 4-H, 5-H, Ph, 1-H, 2-H,
Eth), 7.50 (m, 4 H, 2-H, 6-H, Ph), 7.67
(d, J = 16.0, 2 H, Eth)a
368 (4) [M+],
115 (100)
(CDCl3): 3040,
1631, 1508, 1258,
1200, 1030, 965,
799, 760, 701
(16%)
13
3.86 (s, 3 H, OCH3), 3.88 (s, 3 H,
OCH3), 6.85 (d, J = 16.6, 1 H, 1-H,
Eth), 7.01 (d, J = 8.8, 2 H, 3-H, 5-H,
55.5, 52.4 (OCH3), 114.7 (C-3, C-5,
Ph), 115.6 (C-1, Ph), 126.9, 125.3 (C- 135 (100)
260 (73) [M+], 3058, 2948, 1718,
1641, 1604, 1490,
1423, 1308, 1255,
1183, 1090, 1028,
930, 841, 753
+
(78%)
1, C-2, Eth), 129.1 (C-2, C-6, Ph),
[C8H7O2 ]
Ph), 7.59 (d, J = 16.6, 1 H, 2-H, Eth), 161.9, 162.9, 165.2, 165.4, (C-2, C-5,
8.02 (d, J = 8.8, 2 H, 2-H, 6-H, Ph)a Od, C-4 Ph, C=O)a
14
72
2.49 (s, 3 H), 2.68 (s, 3 H, CH3 Xyl), 20.8, 21.7 (CH3), 52.4 (OCH3), 122.0 258 (45) [M+], 3060, 3042, 2990,
3.85 (s, 3 H, OCH3), 6.88 (d, J = 16.6, (C-1, Ph), 125.4, 127.3, 129.6, 131.9, 133 (100)
1 H), 7.62 (d, J = 16.6, 1 H) (1-H, 2- 132.7, (C-3, C-4, C-6, Ph, C-1, C-2,
[C9H9O+]
H, Eth), 7.23 (m, 2 H, 3-H, 4-H, Ph), Eth), 135.8, 136.0 (C-2, C-5, Ph),
2948, 2920, 1710,
1642, 1528, 1440,
1358, 1305, 1222,
1181, 1170, 1000,
820, 748
(84%)
7.80 (s, 1 H, 6-H, Ph)a
161.8, 165.4, 165.7 (C-2, C-5, Od,
C=O)a
15
164
3.88 (s, 3 H, OCH3), 6.91 (d, J = 16.0, 55.5 (OCH3), 114.8, 128.8 (C-2, C-3, 246 (23) [M+], 3050, 2900, 1710,
(dec.)
1 H, 1-H,Eth), 7.15 (d, J = 8.0, 2 H, 3- C-5, C-6, Ph), 115.0, 124.1, 124.7,
H, 5-H, Ph), 7.42 (d, J = 16.0, 1 H, 2- (C-1, Ph, C-1, C-2, Eth), 161.7, 162.4, (100)
H, Eth), 8.05 (d, J = 8, 2 H, 2-H, 6-H, 164.3, 165.8 (C-2, C-5, Od, C-4, Ph, [C8H7O2 ]
Ph), 13.2 (br s, 1 H, OH)b C=O)b
202 (19), 135
1609, 1492, 1305,
1255, 1188, 1172,
1089, 1018, 987,
834, 754, 669
(73%)
+
Synthesis 1999, No. 6, 999–1004 ISSN 0039-7881 © Thieme Stuttgart · New York

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(E)-1,2-Bis(5-aryl-1,3,4-oxadiazol-2-yl)ethenes
1003
Table 2 (Continued)
Prod-
uct
mp
(°C)
1H NMR : δ, J (Hz)
13C NMR : δ
MS m/z (rel.
int., %)
IR (KBr) ν (cm–1)
(Yield)
16
227
183
2.48 (s, 3 H), 2.68 (s, 3 H, CH3), 6.83 19.8, 20.6 (CH3), 121.0 (C-1, Ph),
(d, J = 16.0, 1 H, 1-H, Eth), 7.25 (s, 2 123.6, 128.2, 128.5, 130.9, 131.7,
H, 3-H, 4-H, Ph), 7.51 (d, J = 16.0 Hz, (C-3, C-4, C-6, Ph, C-1, C-2, Eth),
1 H, 3-H, Eth), 7.80 (s, 1 H, 6-H, Ph)a 134.5, 134.9 (C-2, C-5, Ph), 161.0,
164.4, 165.4 (C-2, C-5, Od, C=O)b
244 (100)
3040, 2950, 1705,
[M+], 199 (15), 1645, 1528, 1470,
(75%)
133 (97)
[C9H9O+], 104
(98)
1280, 1245, 1175,
963, 948, 828, 768,
689, 640
17
8.07 (d, J = 9.0, 2 H, 2-H, 6-H, Ph),
7.84 (s, 1 H, 6-H, Xyl), 7.56 (s, 2 H,
1-H, 2-H), 7.26 (s, 2 H, 3-H, 4-H,
162.9, 162.1 (C-2, C-5, Od, C-4 An), 374 (55) [M+], 3070, 2920, 2838,
136.1, 135.8, 132.7, 132.0, 129.6,
129.1, 122.0, 119.2 (2 C), 118.8,
227 (43) 135
(100)
1608, 1528, 1490,
1306, 1260, 1179,
1090, 1030, 960,
845, 750, 696
(76%)
Xyl), 7.04 (d, J = 9 Hz, 2 H, 3-H, 4-H, 115.6, 114.8 (2 C) (CH, Cq), 55.6
Ph), 3.89 (s, 3 H, OCH3), 2.70 (s, 3 H, (OCH3), 21.7, 20.9 (CH3)a
2-CH3), 2.40 (s, 3 H, 5-CH3)a
[C8H7O+], 133
(41), 107 (6),
105 (19)
18
177
9.27 (d, J = 8.8 Hz, 1 H, Nap), 8.28
(dd, J = 7.6, J = 2.0, 1 H, Nap), 8.07
(d, J = 8.8, 1 H, Nap), 7.94 (d, J = 8.8, 132.0, 129.7, 129.0, 128.9, 128.5,
162.2, (Od), 141.0 (Cq), 136.1(Cq),
135.8 (Cq), 133.9 (Cq), 133.4, 132.8,
394 (100)
3040, 2910, 2840,
[M+], 155 (63) 1570, 1540, 1517,
[C11H7O+], 133 1470, 1393, 1130,
(27) [C9H9O+], 996, 954, 807, 770,
(76%)
1 H, Nap), 7.85 (s, 1 H, 6-H Xyl),
126.9, 126.1, 125.0, 122.7 (Cq),
7.76–7.55 (m, 3 H, Nap), 7.67 (s, 2 H, 119.6, 119.1, 21.8 (CH3), 20.9 (CH3)a 127 (34)
745
+
Eth), 7.26 (m, 2 H, 3-H, 4-H, Xyl),
2.71 (s, 3 H, CH3), 2.42 (s, 3 H, 2-
CH3)a
[C10H7 ]
Abbreviations: An: 4-methoxyphenyl, Eth: ethylene, Nap : 1-naphthyl, Od: 1,3,4-oxadiazole, Py: pyridine, Tet: tetrazole, Tol: 4-methylphenyl,
Xyl: 2,5-dimethylphenyl
a CDCl3
b DMSO-d6
(E)-1,2-Bis{5-[(E)-2-phenylethenyl]-1,3,4-oxadiazol-2-
yl}ethene (12)
alcohol distilled off and the crude acid (15, 16) isolated by filtration.
Recrystallization was from EtOAc.
Diphenyl ether was used as solvent, N2 evolution occurred above
180 °C. The mixture was diluted with petroleum ether (100 mL), fil-
tered, and the residue washed with toluene, MeOH, MeOH/H2O (1/
1), MeOH, and dried. Yield: 52 mg (16%), light brown crystals.
(E)-3-[5-(4-Methoxyphenyl)-1,3,4-oxadiazol-2-yl]propenoic
Acid (15)
Yield: 900 mg (73%), colourless crystals.
(E)-3-[5-(2,5-Dimethylphenyl)-1,3,4-oxadiazol-2-yl]propenoic
Acid (16)
Yield: 1.03 g (75%), pale yellow crystals.
(E)-3-(5-Aryl-1,3,4-oxadiazol-2-yl)propenoic Acid Methyl
Esters (13, 14); General Procedure
The tetrazole (1, 2) (0.01 mol) and fumaryl chloride (4.53 g, 0.03
mol) were dissolved in diphenyl ether (10 mL), collidine (1.46 g,
0.011 mol) was added dropwise and the stirred mixture was slowly
heated until gas evolution occurred (95 °C). As the gas evolution
ceased, heating was continued for further 15 min, the mixture
poured into abs. MeOH (60 mL) and stirred for 30 min. The MeOH
was evaporated and the residue washed with H2O (3 x 50 mL) and
brine (50 mL). Purification by chromatography. A second product
was isolated in low yield and identified as bis-aryloxadiaz-
olylethene (7, 8) by IR and mp.
(E)-1,2-Bis(5-aryl-1,3,4-oxadiazol-2-yl)ethenes with Different
Substituents (17, 18); General Procedure
The acrylic acid (15, 16) (1 mmol) was stirred in a mixture of PCl3
(0.4 mmol, 0.54 g) and benzene (5 mL) overnight at ambient temp.
The layers were separated, the solvent distilled off and the acid
chloride dissolved in anisole (10 mL). The tetrazole (2, 5) (1 mmol)
and collidine (121 mg, 1 mmol) were added, the conversion fol-
lowed the general procedure (vide supra).
(E)-1-[5-(2,5-Dimethylphenyl)-1,3,4-oxadiazol-2-yl]-2-[5-(4-
methoxyphenyl)-1,3,4-oxadiazol-2-yl]ethene (17)
Yield: 284 mg (76%).
(E)-3-[5-(4-Methoxyphenyl)-1,3,4-oxadiazol-2-yl]propenoic
Acid Methyl Ester (13)
Diphenyl ether as solvent, gas evolution starting at 95 °C. Yield:
2.03 g (78%), colourless crystals.
(E)-1-[5-(2,5-Dimethylphenyl)-1,3,4-oxadiazol-2-yl]-2-[5-(1-
naphthyl)-1,3,4-oxadiazol-2-yl]ethene (18)
Yield: 299 mg (76%).
(E)-3-[5-(2,5-Dimethylphenyl)-1,3,4-oxadiazol-2-yl]propenoic
Acid Methyl Ester (14)
Yield: 2.16 g (84%), pale yellow crystals.
X-ray structure determination of 8 was performed with an Enraf-
Nonius Turbo-CAD4 equipped with rotating anode using a trans-
parent, colourless single crystal. Crystal data: C22H20N4O2, M =
372.4 g mol–1, 0.12 x 0.16 x 1.28 mm, monoclinic, space group P
21/n, Cu-Ka, graphite monochromation: 1.54180 Å, T = 298 K, unit
cell dimensions: a = 888.07(2), b = 595.26(1), c = 1846.43(3) pm,
b = 96.785(2)°, V = 0.96926(3) nm³, Z = 2, Dcalc = 1.276 g cm–3, ab-
sorption coefficient µ = 0.68 mm–1, the Q range for data collection
3-(1,3,4-Oxadiazolyl)propenoic Acids; General Procedure
The ester (13, 14) (0.005 mol) was dissolved in propan-2-ol (15 mL)
and a solution of NaOH (0.8 g, 0.02 mol) in H2O (4 mL) was added.
The mixture was stirred and heated to reflux until the ester had dis-
appeared. The solution was neutralized with hydrochloric acid, the
Synthesis 1999, No. 6, 999–1004 ISSN 0039-7881 © Thieme Stuttgart · New York

1004
H. Detert, D. Schollmeier
PAPER
was 1.5°to 75° and the index ranges 0 £ h £ 11, 0 £ k £ 7, –23 £ l £
22. Number of reflections collected: 2006; independent reflections:
2006 [Rsigma’ = 0.0157]. The structure was solved by direct methods
(program SHELXS 93).24 Structure refinement by full-matrix least
squares on F² on 102 parameters, weighted refinement: w = 1/
[s²(F0²) + (0.0597 x P)² + 0.15 x P] with P = [max(F0²,0) + 2 x Fc²]/
3, hydrogen atoms located from difference Fourier synthesis and re-
fined isotropic assuming a riding motion model, all non-hydrogen
atoms refined with anisotropic temperature factors. Goodness-of-fit
on S = 1.078, maximum change of parameters 0.000 x e.s.d, final R
indices: R1 = 0.0397, wR2 = 0.0423, the final difference Fourier map
showed minimum and maximum values of –0.12 and 0.16 e Å-3.
(6) Sinigersky, V.; Wegner, G.; Shopov, T. Eur. Polym. J. 1993,
29, 617.
(7) Peng, Z.; Bao, Z.; Galvin, M. E. Adv. Mater. 1998 10 680.
(8) Hetzheim, A. In Houben-Weyl, 4th ed., Vol. E8c; Schaumann,
E., Ed.; Thieme: Stuttgart, 1994; p 526.
(9) Kraft, A. Chem. Commun. 1996, 77. Kraft, A. Liebigs Ann./
Recueil 1997, 1463.
(10) Becker, K. B. Synthesis 1983, 341.
Meier, H. Angew. Chem. 1992, 104, 1425 1446; Angew.
Chem., Int. Ed. Engl. 1992, 31,1399.
(11) Prossel, G.; Sahm, W.; Schinzel, E.; Roesch, G. (Hoechst AG)
DBP 2509514, 1976; Chem. Abstr. 1977, 86, 31016.
(12) Manabe et al., Yuki Kosei Yagaku Kyokeishi 1968, 355, 356;
Chem. Abstr. 1968, 69, 67291.
(13) Meier, H. R.; Heimgartner, H. In Houben-Weyl, 4th ed., Vol.
E8d; Schaumann, E., Ed.; Thieme: Stuttgart 1994, p 664–795.
(14) El-Ahl, A.-A. S.; Elmorsy, S. S.; Elbehhery, A. H.; Amer, F.
A. Tetrahedron Lett. 1997, 38, 1257.
Further details of the crystal structure investigation may be obtained
from the Fachinformationszentrum Karlsruhe, D-76344 Eggen-
stein-Leopoldshafen (Germany) on quoting the depository number
CSD-410648 (8).
(15) Zaderenko, P.; López, M. C.; Ballesteros, P. J. Org. Chem.
1996, 61, 6825.
(16) Siegrist, A. E.; Moergeli, E.; Hoelzle, K. (CIBA) U.S. Patent
2765304, 1953; Chem. Abstr., 1953, 51, 12983b.
(17) Le Berre, A.; Godin, J.; Garreau, R. C. R. Hebd. Séances
Acad. Sci. 1967, SerC 265, 570.
Acknowledgement
Generous financial support by the Deutsche Forschungsgemein-
schaft is gratefully acknowledged.
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Article Identifier:
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Synthesis 1999, No. 6, 999–1004 ISSN 0039-7881 © Thieme Stuttgart · New York