1.3.4- Oxadiazoles, 2,5-disubstituted. synthesis

The synthesis and properties of heat-resistant polyazomethines containing 2,5-disubstituted oxadiazole fragments, being insulators convertible into semiconductors by doping with iodine, have been described. The radical copolymerization of alkenes with the fluorescent co-monomer 2-/-butyl-5-(4 -vinyl-4-biphenylyl)-l,3,4-oxadiazole has resulted in useful macromolecular scintillators. Anionic polymerization of 2-phenyl-l,3,4-oxadiazolin-5-one has produced a nylon-type product <1996CHEC-II(4)268>. 

Nearly all the disubstituted oxadiazoles mentioned in the literature contain at least one aromatic substituent. The fact that purely aliphatic derivatives have not been isolated until recently is obviously due to the difficulty of isolating these compoimds. The lower homologs are very volatile and cannot be separated by distillation from usual solvents. Dimethyloxadiazole, for instance, the synthesis of which was attempted by Nordmann in 1884 60), was only "perceived" through its odor only in 1959 could this product be identified after its isolation by salting out from an aqueous solution (5, 44 c). 

Dabiri et al. (2007) have developed a very simple, efficient, and eco-friendly synthesis of 2,5-disubstituted oxadiazoles by the reaction of different acyl hydra-zides and ortho esters in the presence of SSA under solvent-free conditions at room... 

A one-pot synthesis of 2,5-disubstituted 1,3,4-oxadiazoles from acids and acyl hydrazides has recently been reported. The method involves an activation of an acid with carbonyl diimidazole followed by the addition of benzoyl hydrazide and then the addition of CBr4 and Ph3P. Under the conditions, the dehydration proceeds smoothly to provide the desired oxadiazoles in high yields <2006TL4827>. 

Scheme 27 The synthesis of disubstituted 1,2,4-oxadiazoles in a microreactor setup [60]...

Adib M, Jahromi AH, Tavoosi N et al (2006) Microwave-assisted efficient, one-pot, three-component synthesis of 3, 5-disubstituted 1, 2, 4-oxadiazoles under solvent-free conditions. Tetrahedron Lett 47(17) 2965-2967... 

Bentiss, F., Lagrenee, M. and Barbry, D., Rapid synthesis of 2,5-disubstituted 1,3,4-oxadiazoles under microwave irradiation, Synth. Commun., 2001, 31, 935-938. 

Rostamizadeh et al. [19] found potassium fluoride to be an efihcient catalyst and solid support for the one-pot solvent-free synthesis of 3,5-disubstituted-l,2,4-oxadiazoles. 

An efficient one pot synthesis of unsymmetric 2,5-disubstituted-1,3,4-oxadiazoles has been developed by Pore et al. [39]. The target oxadiazoles were formed by the oxidation of acylhydrazones using trichloroisocyanuric acid (TCCA) at an ambient temperature. 

Xu et al. [44] reported the microwave assisted synthesis and antifungal activity of 2,5-disubstituted-l,3,4-oxadiazoles containing azulene moiety. The 5-aryl-2-(3-methylazulen-l-yl)-l,3,4-oxadiazoles (Lv) were obtained by the microwave... 

Sangshetti JN, Chabukswar AR et al (2011) Microwave assisted one-pot synthesis of some novel 2,5-disubstituted 1,3,4-oxadiazoles as antifungal agents. Bioorg Med Chem Lett 21 444-448... 

Mashraqui SH, Ghadigaonkar SG et al (2003) An expeditious and convenient one pot synthesis of 2,5-disubstituted-l,3,4-oxadiazoles. Synth Commun 33 2541-2545... 

Pore DM, Mahadik SM et al (2008) Trichloroisocyanuric acid-mediated one-pot synthesis of unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles at ambient temperature. Synth Commun 38 3121-3128... 

Jakopin Z, RoSkar R, Sollner Dolenc M. Synthesis of 3,5-disubstituted 1,2,4-oxadiazoles as peptidomimetic building blocks. Tetrahedron Lett. 2007 48 1465-1468. 64. 

Acylainino-4-acylimidazoles have been made from 3-amino-l,2,4-oxadiazoles and 1,3-dicarbonyl reagents (see Section 2.2.1 and Scheme 2.2.5). 4(5)-Acylimidazoles can be derived from 4-acylaininoisoxazoles (see Section 6.1.2 and Scheme 6.1.3). (See also the discussion in Section 2.2.1 on 4-acylimidazole synthesis.) 5-Acyl-l-arylimidazoles can be made from or-oxoketene-SJV-acetals and nitrosoaromatics (see Section 3.2 and Scheme 3.2.5), and 4-acyl-imidazoles by nitration of 1,3-dicarbonyl compounds in their enolic forms, reduction to iV-alkenylformamides and subsequent cyclization (see Section 3.2 and Scheme 3.2.4). Examples have also been isolated from reactions of 2-oximino-l,2,3-tricarbonyls and amines (see Section 4.1 and Scheme 4.1.7), from compounds such as 3-chloro-4,4-dimethoxy-2-butanone and 3,4-disubstituted 3-buten-2-ones (see Section 4.3 and Scheme 4.3.5), and by ultraviolet irradiation of 1-alkenyltetrazoles which bear an acyl group conjugated with the exocyclic double bond (see Section 6.1.2.3). 

C) starting from more complex oligocyclic epoxides (81TL-4553 81TL4557). A preparatively more interesting synthesis from 2,5-disubstituted 1,3,4-oxadiazoles and cyclopropenes led to 2,4,4,6-tetrasubstituted 4//-pyrans 155 (88TL3231). 

Synthesis of 2,5-disubstituted 1,3/4-oxadiazoles and their activity as insect growth regulators 06CJO1647. 

Among fluorinated LCs, the synthesis of 3,5-disubstituted 1,2,4-oxadiazoles by cyclocondensation of amidoximes with trifluoroacetic anhydride or fluorobenzoic acid derivatives has been reported. In these... 

Montazeri, N. and Rad-Moghadam, K. 2008. An expeditious and one-pot synthesis of unsym-metrical 2,5-disubstituted-l,3,4-oxadiazoles under microwave irradiation and solvent-free conditions. Chin. Chem. Lett. 19(10) 1143-1146. 

M. Kidwai, D. Bhatnagar, N.K. Mishra, Polyethylene glycol (PEG) mediated green synthesis of 2,5-disubstituted lA4-oxadiazoles catalyzed by ceric ammonium nitrate (CAN), Green Chem. Lett. Rev. 3 (2010) 55-59. 

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