1.2.4- Oxadiazole, 5-phenyl-3-styryl

The methyl group in 5-methyl-3-phenyl-l,2,4-oxadiazole is likewise sufficiently activated to condense with benzaldehyde in the presence of zinc chloride to give a styryl derivative [Eq. (59)] in 65% yield.173 This... 

Finally, dianils of aromatic dialdehydes may react with 2 moles of a p-tolyl-substituted heterocycle. For example, 5-phenyl-2-(p-tolyl)-1,3,4-oxadiazole (71) reacts with Schiff s base from 2 moles of p-chloroaniline and 4,4 -diformylbiphenyl (72) to give 4,4 -bis[4-(5-phenyl-l,3,4-oxadiazol-2-yl)styryl]biphenyl (73).43 Along with further p-tolyl-substituted heteroaromatics, a number of carbocyclic aromatics have... 

Aromatic aldehydes give styryl derivatives (e.g., 584) by spontaneous dehydration of the intermediate alcohol (cf. Section 3.4.3.1.2). 5-Methyl-3-phenyl-l,2,4-oxadiazole 585 thus reacts with benzaldehyde in the presence of zinc chloride. 3-Nitrobenzaldehyde reacts with 5-methylisothiazole. The 4- and 5-methylthiazoles are unreactive. 

No hydrolysis is observed when 2,5-diphenyl-1,3,4-oxadiazole, which has a solubility in water of 0.03%, is treated with mineral acids. Neither concentrated HN03 nor treatment with fuming H2S04 at 100° for 4 hours attacks the oxadiazole ring. Similar stability is shown by 2-(o>-styryl)-5-aryl-l, 3,4-oxadiazole.19 On the other hand, the attempt to obtain the free acid by treatment of 2-phenyl-5-p-car-bethoxyphenyl-1,3,4-oxadiazole with caustic soda produces 1 -p-carboxybenzoyl-2-benzoylhydrazine.23 Other aryl-substituted compounds as well as 1,3,4-oxadiazoles substituted in the 2,5-position by various heterocyclic groups are hydrolyzed by mineral acids.26... 

Figure 28.3 Molecular structures of siloxane hybrid precursors. DCM= 4-dicyanomethy-lene-2-methyl-6-[p-(dimethylamino)styryl]-4/-/-pyran PBD= 2-(4-biphenylyl)-5-(4-ferf-butyl-phenyl)-1,3,4-oxadiazole NABUP= A/-(4-butyl-phenyl)-4-[(A/-2-hydroxyethyl)(methyl)amino] naphthalimide TPPy = 1,3,6,8-tetraphenylpyr-ene PHEMA= poly(2-hydroxyethyl...

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