EFFICIENT SYNTHESIS OF 1,4-BIS(5-ARYL-1,3,4-OXADIAZOL-2-YL)-...
1325
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
[5-(4-chlorophenyl)-1,3,4-oxadiazole] (3d). Yield
83%, mp 120°C. IR spectrum, ν, cm−1: 1643 (C=N),
1075 (C–O–C), 1190 (C–F), 796 (C–Cl), 1597
δ 4.67 (NH2) and 10.09 ppm (NH), and multiplets in
the region δ 7.05–9.00 ppm were observed for aromatic
protons. The IR spectra of 3a–3l showed a band at
1600 cm−1 due to C=N stretching vibrations, which
confirmed formation of oxadiazole ring. The band at
~1172 cm−1 was assigned to the C–F bonds, and the
band at 1081 cm−1, to C–O–C stretching of the oxadi-
azole ring.
1
(C=Carom). H NMR spectrum (DMSO-d6), δ, ppm:
7.72 d (4H, J = 8.64 Hz), 8.09–8.17 d (4H, J =
8.64 Hz). Mass spectrum: m/z: 506 [M]+.
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
[5-(2-chlorophenyl)-1,3,4-oxadiazole] (3e). Yield
74%, mp 148°C. IR spectrum, ν, cm−1: 1648 (C=N),
1066 (C–O–C), 1162 (C–F), 1537 (C=Carom). 1H NMR
spectrum, δ, ppm: 7.51 d.d (2H, J = 8.24, 8.00 Hz),
7.74 d (2H, J = 8.24 Hz), 7.99 d (2H, J = 8.00 Hz),
8.21 s (2H).
In summary, a series of 1,4-bis(5-aryl-1,3,4-oxadi-
azole-2-yl)-2,3,5,6-tetrafluorobenzenes were synthe-
sized by a conventional method from substituted
aromatic acid hydrazides and 2,3,5,6-tetrafluorotere-
phthalic acid in the presence of phosphoryl chloride.
Hydrazides 1a–1l (general procedure). A clean and
dry 250-mL round-bottom flask was charged with 5 g
of the corresponding ethyl ester and 50 mL of ethanol,
and 5 g of hydrazine hydrate was added dropwise with
stirring at room temperature over a period of 15 min.
The mixture was then refluxed for 5 h (TLC) and
concentrated, and the solid product was filtered off and
recrystallized from methanol.
4,4′-[(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
(1,3,4-oxadiazole-5,2-diyl)]dianiline (3f). Yield 82%,
mp 191°C. IR spectrum, ν, cm−1: 1597 (C=N), 1063
(C–O–C), 1108 (C–F), 3327 (NH2), 1488 (C=Carom).
1H NMR spectrum (DMSO-d6), δ, ppm: 2.51 s (4H,
NH2), 7.4 d (4H, J = 7.28 Hz), 7.96 d (4H, J =
7.28 Hz).
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
[5-(4-methoxyphenyl)-1,3,4-oxadiazole] (3g). Yield
81%, mp 151°C. IR spectrum, ν, cm−1: 1645 (C=N),
1124 (C–O–C), 1164 (C–F), 1523 (C=Carom). 1H NMR
spectrum, δ, ppm: 3.89 s (6H, OCH3), 7.01 d (4H, J =
7.2 Hz), 7.04 d (4H, J = 7.2 Hz).
1,4-Bis(5-aryl-1,3,4-oxadiazole-2-yl)-2,3,5,6-
tetrafluorobenzenes 3a–3l (general procedure).
A mixture of hydrazide 1a–1l (2 mmol) and
2,3,5,6-tetrafluoroterephthalic acid (2) (1 mmol) in
5 mL of phosphoryl chloride was refluxed in a 25-mL
round-bottom flask until the reaction was complete
(TLC). The mixture was cooled to room temperature,
poured into 50 mL of ice water with stirring, and
neutralized. The solid product was filtered off, washed
with water, and recrystallized from ethanol.
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
[5-(4-methylphenyl)-1,3,4-oxadiazole] (3h). Yield
81%, mp 210°C. IR spectrum, ν, cm–1: 1615 (C=N),
1172 (C–O–C), 1175 (C–F), 1487 (C=Carom). 1H NMR
spectrum, δ, ppm: 2.51 s (6H, CH3), 7.4 d (4H, J =
7.28 Hz), 7.96 d (4H, J = 7.28 Hz).
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
(5-phenyl-1,3,4-oxadiazole) (3a). Yield 83%,
mp 231°C. IR spectrum, ν, cm–1: 1610 (C=N), 1081
(C–O–C), 1172 (C–F), 1545 (C=Carom). 1H NMR spec-
trum, δ, ppm: 7.5 d (2H, J = 7.24 Hz), 7.72 d.d (4H, J =
7.24, 7.32 Hz), 8.09 d (4H, J = 7.32 Hz). Mass spec-
trum: m/z: 439 [M]+.
4,4′-[(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
(1,3,4-oxadiazole-5,2-diyl)]diphenol (3i). Yield 76%,
mp 262°C. IR spectrum, ν, cm–1: 1601 (C=N), 1063
(C–O–C), 1124 (C–F), 3441 (O-H), 1488 (C=Carom).
1H NMR spectrum, δ, ppm: 7.47 d (4H, J = 8.44 Hz),
8.02 s (2H, OH), 8.04 d (4H, J = 8.44 Hz).
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
[5-(4-nitrophenyl)-1,3,4-oxadiazole] (3b). Yield 87%,
mp 220°C. IR spectrum, ν, cm−1: 1637 (C=N), 1039
(C–O–C), 1179 (C–F), 1449 (C=Carom).
3,3′-[(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
(1,3,4-oxadiazole-5,2-diyl)]diphenol (3j). Yield 74%,
mp 230°C. IR spectrum, ν, cm–1: 1645 (C=N), 1039
(C–O–C), 1119 (C–F), 3454 (O–H),1548 (C=Carom).
1H NMR spectrum, δ, ppm: 7.13 s (2H, OH), 7.29 s
(2H), 7.43 d (2H, J = 6.8 Hz), 7.60 d.d (2H, J = 6.8,
8.92 Hz), 7.73 d (2H, J = 8.92 Hz).
2,2′-(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
[5-(3-nitrophenyl)-1,3,4-oxadiazole] (3c). Yield 85%,
mp 251°C. IR spectrum, ν, cm–1: 1614 (C=N), 1060
1
(C–O–C), 1159 (C–F), 1526 (C=Carom). H NMR
spectrum, δ, ppm: 7.96 d.d (2H, J = 7.88, 8.04 Hz),
8.14 d (2H, J = 7.88 Hz), 8.53 d (2H, J = 8.04 Hz),
8.82 s (2H).
4,4′-[(2,3,5,6-Tetrafluorobenzene-1,4-diyl)bis-
(1,3,4-oxadiazole-5,2-diyl)]dipyridine (3k). Yield
82%, mp 222°C. IR spectrum, ν, cm−1: 1612 (C=N),
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 7 2020