1.3.4- Oxadiazole, diphenyl-, nitration

Bromination of the phenyl group in 5-(4-nitrophenyl)-2-phenyl-l,3,4-oxadiazole in the presence of potassium bromate yielded o- (16%), m- (14%), and /)-bromo (26%) products, together with low yields of dibromo products <84JCR(S)382>. Similar results were obtained on nitration of 2,5-diphenyl-1,3,4-oxadiazole with fuming nitric acid to give dinitro products. The ratio of o- w-.-/ -nitration... 

The addition of amyl nitrate to a suspension of 2,4-diphenyl-5-nitro-soimidazole (37) in ether results in a mixture of 2,4-diphenyl-5-nitroim-idazole (38) and 3-benzoyl-5-phenyl-l, 2,4-oxadiazole (39), but a similar reaction using 4-phenyl-5-nitrosoimidazole gives only 3-benzoyl-1,2,4-oxadiazole (40) (60MI1). 

The nitration of 2,5-diphenyl-l,3,4,-oxadiazole (44a) was first investigated by Grekov and Azen (61JGU1796), who reported that fuming nitric acid (d 1.51) alone results in a mixture of three isomers, the 2,5-bis(2-nitrophenyl), bis(3-nitrophenyl), and bis(4-nitrophenyl) products in yields of 40, 20, and 27%, respectively. They found that fuming nitric acid in sulfuric acid gives a preponderance of 3-nitrophenyI products with both the mononitro and the dinitro derivatives being obtained in yields of 31 and 38%, respectively. 

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