Synthesis of a novel β-diketone containing carbazole and 2,5-diphenyl-1,3,4-oxadiazole fragments

Article abstract of DOI:10.1134/S1070428009040150

A novel β-diketone containing carbazole and 2,5-diphenyl-1,3,4- oxadiazole fragments as hole- and electron-transporting functional groups, respectively, was synthesized via efficient and convenient procedure. The product attracts interest from the viewpoint of its potential applications as optoelectronic material.

Full text of DOI:10.1134/S1070428009040150

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 4, pp. 559–563. © Pleiades Publishing, Ltd., 2009.
Published in Russian in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 4, pp. 573–577.
Synthesis of a Novel β-Diketone Containing Carbazole
and 2,5-Diphenyl-1,3,4-oxadiazole Fragments*
Huaijun Tang, Zhiguo Zhang, Changjie Cong, and Keli Zhang
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, P.R. China
e-mail: klzhang@whu.edu.cn
Received November 16, 2007
Abstract—A novel β-diketone containing carbazole and 2,5-diphenyl-1,3,4-oxadiazole fragments as hole- and
electron-transporting functional groups, respectively, was synthesized via efficient and convenient procedure.
The product attracts interest from the viewpoint of its potential applications as optoelectronic material.
DOI: 10.1134/S1070428009040150
β-Diketones are very important and familiar ligands
in coordination chemistry due to their strong coordina-
tion ability, high stability, and extraordinary optical,
electronic, and magnetic properties of their complexes.
Synthesis and application of β-diketones have long
attracted great interest in chemistry, material science,
physics, and biochemistry. In the recent years, a great
deal of metal ion (e.g., Eu3+, Tb3+, Sm3+, Ir3+) com-
plexes derived from various β-diketones have been
used as optoelectronic materials such as light-emitting
materials in organic light-emitting diodes [1–4], mem-
ory materials in organic electrical memory devices
[5, 6], etc. It has been confirmed that carbazole frag-
ment is an excellent hole-transporting group [4, 7–10]
and that 2,5-diphenyl-1,3,4-oxadiazole group is an
excellent electron-transporting group [11, 12]; their
derivatives had been widely used in optoelectronic
devices [7–12], mainly due to their beneficial effect on
the device performance via enhancement of charge
conductivity. Apart from derivatives containing either
carbazole or 2,5-diphenyl-1,3,4-oxadiazole group,
organic molecules comprising both these are also very
important materials in optoelectronic devices; for ex-
ample, they were used as host [13] and light-emitting
materials [14] in organic light-emitting diodes. The
syntheses of β-diketones containing only carbazole [9]
or 2,5-diphenyl-1,3,4-oxadiazole [15] fragment and
their complexes have already been reported, whereas
β-diketones containing both carbazole and 2,5-diphen-
yl-1,3,4-oxadiazole fragments still remain unknown,
though such β-diketones should be very important and
promising for use in optoelectronic materials.
Generally, syntheses of β-diketones via traditional
Claisen condensation of appropriate ketones and esters
are not difficult; however, required initial ketones and
esters are sometimes difficultly accessible. In the
present article we describe an effective and convenient
synthesis of β-diketone containing both carbazole and
2,5-diphenyl-1,3,4-oxadiazole fragments (Scheme 1).
3-Acetyl-9-ethylcarbazole (II) necessary for the
subsequent Claisen condensation was synthesized in
two steps starting from carbazole. Initially, 9-ethyl-
carbazole (I) was prepared according to the procedure
described in [16]. The Friedel–Crafts acylation is
commonly catalyzed by Lewis acids, in particular by
AlCl3. However, this Lewis acid turned out to be inap-
propriate in the acylation of 9-ethylcarbazole, for mix-
tures of 3-acetyl and 3,6-diacetyl derivatives were
formed with large amounts of tarry products. There-
fore, we used BiCl3 as catalyst instead of AlCl3 [17]. In
addition, the procedure reported in [17] was modified
so that a larger amount of BiCl3 was applied and acetic
anhydride was replaced by more reactive acetyl chlo-
ride. As a result, we succeeded in raising the yield of
II from 60 to 81%.
Methyl 4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzoate
(VI) was previously synthesized under microwave ir-
radiation [18]. Although microwave-assisted synthesis
is rapid and efficient, the reaction is difficult to control
due to tremendous energy transferred to the reactants
in a very short time; furthermore, microwave-assisted
syntheses are difficult to perform on enlarged scale.
Taking into account the above stated, we tried to
synthesize the required ester following conventional
chemical approaches, i.e., from the corresponding acid
* The text was submitted by the authors in English.
559

HUAIJUN TANG et al.
560
Scheme 1.
O
Me
EtBr, KOH, Me2CO
AcCl, BiCl3, CH2Cl2
N
N
Et
I
N
H
Et
II
COOH
COOMe
COOMe
SOCl2, MeOH, 0–20°C
I2, NH3, H2O, THF
OCH
OCH
NC
III
IV
NaN3, NH4Cl
DMF, 100°C
PhCOCl, pyridine
reflux, N2
N
N
N
N
COOMe
COOMe
HN
N
O
Ph
V
VI
O
O
II, NaOMe, xylene
reflux, N2
N
N
N
O
Ph
Et
VII
amount of iodine and excess ammonia in aqueous
tetrahydrofuran to obtain nitrile IV. The subsequent
reaction of IV with sodium azide and ammonium
chloride in dimethylformamide at 100°C gave 5-sub-
stituted tetrazole V, and the latter was converted into
oxadiazole VI by the action of benzoyl chloride in an-
hydrous pyridine under nitrogen. Finally, Claisen con-
densation of ketone II with 1.5 equiv of ester VI in the
presence of freshly prepared sodium methoxide as
catalyst afforded the desired β-diketone VII possessing
both carbazole and 2,5-diphenyl-1,3,4-oxadiazole frag-
ments (Scheme 1).
and alcohol. 4-(5-Phenyl-1,3,4-oxadiazol-2-yl)benzoic
acid (VIII) can be prepared as described in [19]. How-
ever, we failed to obtain ester IX by esterification of
acid VIII with ethanol as shown in Scheme 2; instead,
the products were ethyl benzoate (X) and diethyl tere-
phthalate (XI) which were formed as a result of alco-
holysis of the 1,3,4-oxadiazole fragment. Therefore,
we developed a new synthetic route to ester VI
(Scheme 1). Methyl 4-formylbenzoate (III) was syn-
thesized by a modified procedure [20]. Replacement of
commonly used ethanol by methanol having a lower
boiling point facilitated removal of excess alcohol
under reduced pressure at room temperature. Com-
pound III was then treated with a nearly equimolar
All intermediate products and β-diketone VII were
1
characterized by elemental analyses and H NMR and
Scheme 2.
N
O
N
COOEt
Ph
N
N
EtOH, H2SO4
IX
COOEt
COOH
O
Ph
COOEt
VIII
+
EtOCO
X
XI
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009

SYNTHESIS OF A NOVEL β-DIKETONE
561
Scheme 3.
O
O
N
N
N
O
Ph
Et
H
·
H
·
·
O
O
O
O
N
N
N
N
N
N
O
O
Ph
Ph
Et
Et
IR spectra. It should be noted that the 1H NMR and IR
spectra of compound VII were not fully consistent
with the diketone structure. Presumably, it exists as
enol tautomers stabilized by intramolecular hydrogen
bonds [21] as shown in Scheme 3.
spectrum, ν, cm–1: 3047, 2929, 2854, 1597, 1484,
1467, 1453, 1384, 1326, 1229, 1150, 1128, 1081,
1055, 1018, 752, 722, 615. 1H NMR spectrum, δ, ppm:
1.45 t (3H, CH3, J = 7.2 Hz), 4.42 q (2H, CH2, J =
7.2 Hz), 7.24–7.30 m (2H, Harom), 7.44–7.54 m (4H,
H
arom), 8.15 d (2H, Harom, J = 8.1 Hz). Found, %:
EXPERIMENTAL
C 85.75; H 6.59; N 7.22. C14H13N. Calculated, %:
C 86.12; H 6.71; N 7.17.
All reagents were obtained from commercial
sources and were used without additional purification
unless otherwise stated. Column chromatography was
performed on silica gel (200–300 mesh). Yields refer
1-(9-Ethyl-9H-carbazol-3-yl)ethanone (II). Dry
9-ethylcarbazole (I), 7.80 g (40 mmol), was mixed
with 100 ml of anhydrous methylene chloride, 20.50 g
(65 mmol) of BiCl3 was added under stirring, a mix-
ture of 7.85 g (~7.0 ml, 100 mmol) of acetyl chloride
in 10 ml of anhydrous methylene chloride was added
dropwise, and the mixture was stirred for 2 h at room
temperature with a mechanical stirrer. Concentrated
hydrochloric acid, 50 ml, and water, 30 ml, were
added, and the mixture was stirred until the brown
precipitate dissolved completely. The mixture was then
extracted with methylene chloride (3×50 ml), the com-
bined extracts were dried over anhydrous sodium
sulfate, the solvent was distilled off, and the residue
was subjected to chromatography on silica gel using
methylene chloride as eluent. The product was addi-
tionally recrystallized from ethanol. Yield 7.70 g
(81%), colorless or pale yellow needles, mp 114.5°C.
IR spectrum, ν, cm–1: 3059, 2930, 1660, 1591, 1440,
1
to the isolated pure compounds. The H NMR spectra
were recorded from solutions in CDCl3 on a Varian
Mercury VX300 spectrometer (300 MHz) using TMS
as internal standard. The IR spectra were recorded in
KBr on a Shimadzu FTIR-8201PC spectrometer.
Elemental analysis was performed on a VarioEL III
analyzer. The melting points were determined from the
differential scanning calorimetry (DSC) curves which
were obtained on a Netzsch DSC 200 analyzer on heat-
ing at a rate of 10 deg/min in static air.
9-Ethyl-9H-carbazole (I). A mixture of 14.00 g
(250 mmol) of potassium hydroxide in 80 ml of ace-
tone was stirred for 20 min, 6.60 g (40 mmol) of carba-
zole was added, and the mixture was stirred for
40 min. A solution of 6.54 g (60 mmol) of ethyl
bromide in 20 ml of acetone was then added dropwise
with stirring, and the mixture was stirred for 10 h,
slowly poured into 1 l of water under stirring, and left
to stand for several hours. The crude product was col-
lected on a vacuum filter, washed with water, recrys-
tallized from ethanol, and dried in a vacuum oven.
Yield 7.0 g (91%), colorless needles, mp 68.6°C. IR
1
1384, 1353, 1244, 1157, 748. H NMR spectrum, δ,
ppm: 1.49 t (3H, CH3, J = 7.2 Hz), 2.78 s (3H,
COCH3), 4.43 q (2H, CH2, J = 7.2 Hz), 7.29–7.39 m
(1H, Harom), 7.46–7.56 m (3H, Harom), 8.15–8.21 m
(2H, Harom), 8.78 d (1H, Harom, J = 1.5 Hz). Found, %:
C 80.78; H 6.41; N 5.94. C16H15NO. Calculated, %:
C 80.98; H 6.37; N 5.90.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009

HUAIJUN TANG et al.
562
Found, %: C 52.65; H 4.23; N 27.68. C9H8N4O2. Cal-
Methyl 4-formylbenzoate (III). A mixture of
culated, %: C 52.94; H 3.95; N 27.44.
7.50 g (50 mmol) of dry 4-formylbenzoic acid and
150 ml of anhydrous methanol was cooled to 0°C, and
30 ml of thionyl chloride was added dropwise under
stirring. The mixture was stirred for 10 h at room
temperature, filtered, and evaporated, and the residue
was slowly poured into 500 ml of water. The product
was collected on a vacuum filter, washed with water,
and dried in a vacuum oven. Yield 7.65 g (93%), pale
yellow solid, mp 52.7°C (DSC). IR spectrum, ν, cm–1:
3421, 3019, 2958, 2887, 2846, 1952, 1726, 1706,
1682, 1612, 1577, 1503, 1437, 1391, 1285, 1202,
Methyl 4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzo-
ate (VI). Benzoyl chloride, 4.64 g (33 mmol), was
added dropwise under stirring to a solution of 6.12 g
(30 mmol) of methyl 4-(2H-tetrazol-5-yl)benzoate (V)
in 50 ml of anhydrous pyridine, and the mixture was
stirred for 4 h on heating under reflux in a nitrogen
atmosphere. The mixture was cooled and poured into
500 ml of water, and the precipitate was filtered off,
washed with water, and recrystallized from ethanol.
Yield 7.08 g (84%), pale yellow solid, mp 169.2°C. IR
spectrum, ν, cm–1: 3059, 3000, 2948, 1717, 1611,
1582, 1548, 1485, 1451, 1433, 1414, 1277, 1108,
1
1110, 1057, 1014, 958, 853, 809, 758, 686. H NMR
spectrum, δ, ppm: 3.97 s (3H, CH3), 7.96 d (2H, Harom
,
1
J = 7.8 Hz), 8.20 d (2H, Harom, J = 7.8 Hz), 10.11 s
(1H, CHO). Found, %: C 65.68; H 4.97. C9H8O3. Cal-
culated, %: C 65.85; H 4.91.
1073, 964, 865, 779, 716, 689. H NMR spectrum,
δ, ppm: 3.99 s (3H, CH3), 7.56–7.58 m (3H, Harom),
8.16–8.26 m (6H, Harom). Found, %: C 68.44; H 4.21;
N 9.78. C16H12N2O3. Calculated, %: C 68.56; H 4.32;
N 9.99.
Methyl 4-cyanobenzoate (IV). Iodine, 11.18 g
(44 mmol), was added under stirring to a mixture of
6.56 g (40 mmol) of methyl 4-formylbenzoate (III),
40 ml of tetrahydrofuran, and 30 ml of 28% aqueous
ammonia. The mixture was stirred for 4 h at room
temperature, a 0.1 M solution of Na2S2O3 was added
dropwise until the dark brown color disappeared, and
the mixture was extracted with methylene chloride
(3×50 ml). The extracts were combined and dried over
anhydrous Na2SO4, the solvent was distilled off, and
the residue was recrystallized from methanol. Yield
5.45 g (85%), pale yellow needles, mp 67.0°C (DSC).
IR spectrum, ν, cm–1: 3421, 3103, 3073, 3055, 3030,
3008, 2956, 2849, 2228, 1948, 1825, 1720, 109, 1565,
1441, 1405, 1317, 1277, 1196, 1104, 1017, 961, 866,
1-(9-Ethyl-9H-carbazol-3-yl)-3-[4-(5-phenyl-
1,3,4-oxadiazol-2-yl)phenyl]propane-1,3-dione
(VII). Freshly prepared sodium methoxide, 1.08 g
(20 mmol), was added to a mixture of 2.37 g
(10 mmol) of dry ketone II and 4.20 g (15 mmol) of
methyl 4-(5-phenyl-1,3,4-oxadiazol-2-yl)benzoate (VI)
in 50 ml of anhydrous xylene, and the mixture was
heated for 12 h under reflux while stirring in a nitrogen
atmosphere. The mixture was cooled, acidified with
hydrochloric acid, and extracted with xylene (3×
50 ml). The extracts were combined and dried over
anhydrous Na2SO4, the solvent was distilled off, and
the residue was subjected to chromatography on silica
gel using a mixture of petroleum ether (bp 60–90°C),
chloroform, and ethyl acetate (1:2:1, by volume) as
eluent. Yield 2.73 g (56%), yellow solid, mp 248.0°C.
IR spectrum, ν, cm–1: 3043, 2984, 2936, 1626, 1587,
1548, 1487, 1470, 1448, 1384, 1330, 1231, 1209,
1
834, 764, 691, 546. H NMR spectrum, δ, ppm: 3.97 s
(3H, CH3), 7.75 d (2H, Harom, J = 7.8 Hz), 8.14 d (2H,
Harom, J = 9.0 Hz). Found, %: C 67.15; H 4.43; N 8.60.
C9H7NO2. Calculated, %: C 67.07; H 4.38; N 8.69.
1
Methyl 4-(2H-tetrazol-5-yl)benzoate (V). Sodium
azide, 3.9 g (60 mmol), and ammonium chloride,
3.21 g (60 mmol) were added under stirring to a solu-
tion of 6.44 g (40 mmol) of methyl 4-cyanobenzoate
(IV) in 50 ml of N,N-dimemylformamide, and the
mixture was stirred for 24 h at 100°C. The mixture was
cooled, poured into 500 ml of water, and acidified to
pH ~1.0 with concentrated hydrochloric acid, and the
precipitate was filtered off, washed with water, and
dried in a vacuum oven. Yield 6.15 g (75%), white
solid, mp 225.7°C (DSC). IR spectrum, ν, cm–1: 3357,
3156, 3099, 3067, 2956, 2868, 2797, 1714, 1686,
1564, 1433, 1288, 1189, 1111, 1062, 997, 958, 863,
1122, 1069, 1048, 781, 753, 727, 709, 690. H NMR
spectrum, δ, ppm: 1.50 t (3H, CH3, J = 3.6 Hz), 4.44 q
(2H, CH2, J = 3.6 Hz), 7.08 s (1H, =CH, enol), 7.23–
7.60 m (7H, Harom), 8.17–8.30 m (8H, Harom), 8.84 s
(1H, Harom); signals from the enol OH protons were not
detected due to fast exchange. Found, %: C 76.82;
H 4.64; N 8.40. C31H23N3O3. Calculated, %: C 76.69;
H 4.77; N 8.65.
This work was supported by the National Natural
Science Foundation of China (grant no. 20071026).
REFERENCES
1
829, 783, 735, 706. H NMR spectrum, δ, ppm: 3.97 s
1. Kido, J., and Okamoto, Y., Chem. Rev., 2002, vol. 102,
(3H, CH3), 4.43 s (1H, NH), 8.10–8.20 m (4H, Harom).
p. 2357.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009

SYNTHESIS OF A NOVEL β-DIKETONE
563
2. Xin, H., Li, F.-Y., Shi, M., Bian, Z.-Q., and Huang, C.-
barian, N., and Kippelen, B., Adv. Mater., 1999, vol. 11,
H., J. Am. Chem. Soc., 2003, vol. 125, p. 7166.
p. 1266.
3. Wang, J.-F., Wang, R.-Y., Yang, J., Zheng, Z.-P.,
Carducci, M.D., Cayou, T., Peyghambarian, N., and
Jabbour, G.E., J. Am. Chem. Soc., 2001, vol. 123,
p. 6179.
4. Zhang, X.-W., Chen, Z., Yang, C.-L., Li, Z.-G.,
Zhang, K., Yao, H.-Q., Qin, J.-G., Chen, J.-W., and
Cao, Y., Chem. Phys. Lett., 2006, vol. 422, p. 386.
12. Liang, F.-S., Zhou, Q.-G., Cheng, Y.-X., Wang, L.-X.,
Ma, D.-G., Jing, X.-B., and Wang, F.-S., Chem. Mater.,
2003, vol. 15, p. 1935.
13. Guan, M., Chen, Z.-Q., Bian, Z.-Q., Liu, Z.-W.,
Gong, Z.-L., Baik, W., Lee, H.-J., and Huang, C.-H.,
Org. Electr., 2006, vol. 7, p. 330.
14. Cha, S.-W., Joo, S.-H., Jeong, M.-Y., and Jin, J.-L,
5. Fang, J.-F, You, H., Chen, J.-S., Lin, J., and Ma, D.-G.,
Synth. Met., 2005, vol. 150, p. 309.
Inorg. Chem., 2006, vol. 45, p. 3701.
15. Xiang, N.-J., Leung, L.-M., So, S.-K., and Gong, M.-L.,
6. Li, L., Ling, Q.-D., Lim, S.-L., Tan, Y.-P., Zhu, C.-X.,
Chan, D.S.-H., Kang, E.-T, and Neoh, K.G., Org.
Electr., 2007, vol. 8, p. 401.
7. Wong, W.-Y., Ho, C.-L., Gao, Z.-Q., Mi, B.-X.,
Chen, C.-H., Cheah, K.-W., and Lin, Z.-Y., Angew.
Chem., Int. Ed., 2006, vol. 45, p. 7800.
Spectrochim. Acta, Part A, 2006, vol. 65, p. 907.
16. Li, Z., Li, J., and Qin, J.-G., Huaxue Shiji (Chinese),
2001, vol. 23, p. 297.
17. Nagarajan, R. and Perumal, P.T., Synthesis, 2004, no. 8,
p. 1269.
18. Rostamizadeh, S. and Housaini, S. A. G., Tetrahedron
Lett., 2004, vol. 45, p. 8753.
8. Brunner, K., van Dijken, A., Borner, H., Bastiaan-
sen, J.J.A.M., Kiggen, N.M.M, and Langeveld, B.M.W.,
J. Am. Chem. Soc., 2004, vol. 126, p. 6305.
19. Javid, K. and Smith, D.M., J. Chem. Res., Synop., 1984,
p. 118.
9. Robinson, M.R., O’Regan, M.B., and Bazan, G.C.,
Chem. Commun., 2000, p. 1645.
10. Guan, M., Bian, Z.-Q., Li, F.-Y., Xin, H., and
20. Sharma, S.K., Tandon, M., and Lown, J.W., Eur. J.
Org. Chem., 2000, p. 2095.
Huang, C.-H., New J. Chem., 2003, vol. 27, p. 1731.
11. Wang, J.-F., Jabbour, G.E., Mash, E.A., Anderson, J.,
Zhang, Y.-D., Lee, P.A., Armstrong, N.R., Peygham-
21. Sloop, J.C., Bumgardner, C.L., Washington, G.,
Loehle, W.D., Sankar, S.S., and Lewis, A.B.,
J. Fluorine Chem., 2006, vol. 127, p. 780.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 4 2009