Background:
Urea, thiourea, and 1,2,4-oxadiazole compounds are of great interest due to their
different activities such as anti-inflammatory, antiviral, analgesic, fungicidal, herbicidal, diuretic,
antihelminthic and antitumor along with antimicrobial activities.
Objective:
In this work, we provide a new series of potential biologically active compounds containing both
1,2,4-oxadiazole and urea/thiouprea moiety.
Materials and Methods:
Firstly, 5-chloromethyl-3-aryl-1,2,4-oxadiazoles (3a-j) were synthesized from the
reaction of different substituted amidoximes (2a-j) and chloroacetyl chloride in the presence of pyridine by
conventional and microwave-assisted methods. In the conventional method, 1,2,4-oxadiazoles were obtained in
two steps. O-acylamidoximes obtained in the first step at room temperature were heated in toluene for an average
of one hour to obtain 1,2,4-oxadiazoles. The yields varied from 70 to 96 %. 1,2,4-oxadiazoles were obtained under
microwave irradiation in a single step in a 90-98 % yield at 160 °C in five minutes. 5-aminomethyl-3-aryl-1,2,4-
oxadiazoles (5a-j) were obtained by Gabriel amine synthesis in two steps from corresponding 5-chloromethyl-3-
aryl-1,2,4-oxadiazoles. Finally, twenty new urea (6a-j) and thiourea (7a-j) compounds bearing oxadiazole ring
were synthesized by reacting 5-aminomethyl-3-aryl-1,2,4-oxadiazoles with phenyl isocyanate and isothiocyanate
in tetrahydrofuran (THF) at room temperature with average yields (40-70%).
Results and Discussions:
An efficient and rapid method for the synthesis of 1,2,4-oxadiazoles from the
reaction of amidoximes and acyl halides without using any coupling reagent under microwave irradiation has
been developed, and twenty new urea/thiourea compounds bearing 1,2,4-oxadiazole ring have been synthesized
and characterized.
Conclusion:
We have synthesized a new series of urea/thiourea derivatives bearing 1,2,4-oxadiazole ring. Also
facile synthesis of 3,5-disubstituted 1,2,4-oxadiazoles from amidoximes and acyl chlorides under microwave
irradiation was reported. The compounds were characterized using FTIR, 1H NMR, 13C NMR, and elemental
analysis techniques.
Insertion reactions of phenyl isocyanate into hafnium nitrogen bonds: synthesis and reactivity of hafnium complexes bearing substituted pyrrolyl ligands