1
346
EFIMOVA et al.
wave activation is most effective when the reaction is
carried in a nonpolar solvent or under solvent-free con-
ditions. This conclusion agrees well with the assump-
tion that the effect of microwave irradiation on the rate
and selectivity of organic reactions depends on the
solvent [16].
the organic phase was separated and evaporated under
reduced pressure, and the solid residue was dried in air.
Yield 84%, mp 99°C (from hexane) [18]. H NMR
1
spectrum, δ, ppm: 2.60 s (3H, CH ), 7.55–7.57 t (1H,
3
Harom), 7.99–8.02 t (1H, Harom), 8.15–8.17 d (1H,
Harom), 8.73 d (1H, Harom).
2
-Methyl-5-(pyridin-3-yl)-1,3,4-oxadiazole (IIf)
EXPERIMENTAL
was synthesized in a similar way. Yield 77%, mp 113–
14°C (from heptane). IR spectrum, ν, cm : 617, 679,
23, 960, 1016, 1046, 1086, 1132, 1252, 1350, 1429,
468, 1550, 1740, 2856, 2927, 2999, 3043, 3075,
438. H NMR spectrum, δ, ppm: 2.60 s (3H, CH ),
.57–7.60 t (1H, Harom), 8.31–8.34 d (1H, Harom),
.75 d (1H, Harom), 9.15 s (1H, Harom). Found, %:
–
1
1
The IR spectra were recorded from samples pre-
pared as KBr pellets on a Shimadzu FTIR-8400s spec-
trometer. The H NMR spectra were measured on
a Bruker WM-400 spectrometer from solutions in ace-
tone-d . Microwave-assisted reactions were carried out
in a Milestone P/N 44072 reactor. The purity of the
products was checked by TLC on Silufol plates using
ethyl acetate–carbon tetrachloride (2:3) as eluent.
8
1
3
7
8
1
1
3
6
C 59.78; H 4.40; N 25.95. C H N O. Calculated, %:
8
7
3
C 59.63; H 4.35; N 26.09.
-(4-Methoxyphenyl)-5-phenyl-1,3,4-oxadiazole
IIIa). A mixture of 6.8 mmol of 5-(4-methoxyphenyl)-
tetrazole and 2 g of benzoic anhydride was stirred for
5 min at 110°C under microwave irradiation. The
2
2
-(4-Methoxyphenyl)-5-methyl-1,3,4-oxadiazole
IIa). A mixture of 5.7 mmol of 5-(4-methoxyphenyl)-
tetrazole in 15 ml of acetic anhydride was stirred for
h at 90°C under microwave irradiation. The mixture
was cooled to 20°C, excess acetic anhydride was
removed under reduced pressure, and the solid residue
was washed in succession with 15 ml of 10% aqueous
sodium hydroxide and 20 ml of water and dried in air.
(
(
1
1
mixture was cooled to 20°C, 20 ml of 10% aqueous
sodium hydroxide was added, the mixture was stirred
for 1 h at 40°C, and the precipitate was filtered off,
washed with 20 ml of water, and dried in air. Yield
6%, mp 150°C (from ethanol) [19]. H NMR spec-
trum, δ, ppm: 3.16 s (3H, OCH ), 6.37–6.42 d
2H, Harom), 6.84-6.87 m (3H, Harom), 7.33–7.41 m
4H, Harom).
1
9
1
Yield 76%, mp 88°C (from water) [17]. H NMR spec-
3
trum, δ, ppm: 2.54 s (3H, CCH ), 3.88 s (3H, OCH ),
3
3
(
(
7
.08–7.11 d (2H, Harom), 7.91–7.94 d (2H, Harom).
Oxadiazoles IIb and IIc were synthesized in
a similar way, while in the synthesis of oxadiazole IId
the reaction mixture was stirred for 1 h at 100°C.
Oxadiazoles IIIb and IIIc were synthesized in
a similar way, while in the synthesis of oxadiazole IIId
the reaction mixture was stirred for 30 min at 110°C.
2
-Methyl-5-phenyl-1,3,4-oxadiazole (IIb). Yield
2
,5-Diphenyl-1,3,4-oxadiazole (IIIb). Yield 83%,
1
1
8
7%, mp 66°C (from ethanol) [17]. H NMR spectrum,
δ, ppm: 2.57 s (3H, CH ), 7.56–8.00 m (5H, Harom).
mp 139°C (from ethanol) [20]. H NMR spectrum, δ,
ppm: 6.88 s (6H, Harom), 7.40–7.43 m (4H, Harom).
3
2
-(4-Bromophenyl)-5-methyl-1,3,4-oxadiazole
2-(4-Bromophenyl)-5-phenyl-1,3,4-oxadiazole
(IIIc). Yield 74%, mp 170°C (from ethanol) [19].
H NMR spectrum, δ, ppm: 6.67 m (3H, Harom), 7.05–
7.09 d (2H, Harom), 7.32–7.43 m (4H, Harom).
(
IIc). Yield 73%, mp 118°C (from ethanol) [17].
H NMR spectrum, δ, ppm: 2.57 s (3H, CH ), 7.76–
.78 d (2H, Harom), 7.93–7.95 d (2H, Harom).
1
1
3
7
2
-Methyl-5-(4-nitrophenyl)-1,3,4-oxadiazole
2-(4-Nitrophenyl)-5-phenyl-1,3,4-oxadiazole
(
IId). Yield 80%, mp 170°C (from ethanol) [17].
(IIId). Yield 89%, mp 210–211°C (from ethanol) [13].
H NMR spectrum, δ, ppm: 6.90 m (3H, Harom), 7.46 d
1
1
H NMR spectrum, δ, ppm: 2.63 s (3H, CH ), 8.27–
3
8
.29 d (2H, Harom), 8.42–8.44 d (2H, Harom).
-Methyl-5-(pyridin-2-yl)-1,3,4-oxadiazole (IIe).
A mixture of 3.4 mmol of 5-(pyridin-2-yl)tetrazole in
5 ml of acetic anhydride was stirred for 1 h at 100°C
(2H, Harom), 7.72 s (4H, Harom).
2
2-Phenyl-5-(pyridin-2-yl)-1,3,4-oxadiazole (IIIe).
A mixture of 3.4 mmol of 5-(pyridin-2-yl)tetrazole and
5 g of benzoic anhydride was stirred for 15 min at
120°C under microwave irradiation. The mixture was
cooled to 20°C, 50 ml of 15% aqueous ammonia was
added, the mixture was stirred for 2 h at 40°C, and the
precipitate was filtered off, washed with 20 ml of
water, and dried in air. Yield 78%, mp 124–125°C
1
under microwave irradiation. The resulting solution
was cooled to 20°C, excess acetic anhydride was re-
moved under reduced pressure, the solid residue was
dissolved in 20 ml of chloroform, the solution was
washed with 20 ml of 2% aqueous sodium hydroxide,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 9 2008