1,2,5-Oxadiazoles, methyl-, side-chain

One of the earlier examples of a degenerate ring transformation involving the participation of a three-atom side chain is the interconversion of the isomers 3-benzoylamino-5-methyl-l,2,4-oxadiazole (133, X = H) and 3-acetylamino-5-phenyl-l,2,4-oxadiazole (134, X = H) (Scheme IV.51) (75JHC985 89H(29)737). Heating each of these compounds at 181°C furnished an identical equilibrium mixture of isomers, in which mixture isomer 134 (X = H) is predominant (X134/133 at 181°C is about 6.4). These data indicate that the conversion of isomer 133 (X = H) into 134 (X = H) is dri-... 

The methyl group as a side chain on the oxadiazole ring acts in a different way at C-5 than at C-3 because of the difference in the inductive and mesomeric effects at these positions (Section IV, F). On 5-methyl-3-phenyl-l,2,4-oxadiazole (72), treatment with lithium n-butyl at —70° gave what Micetich32 called lateral lithiation (73). Subsequent... 

An interesting rearrangement was observed35,36 during the preparation of4-hydroxy-JV-(5-methyl-3-isoxazolyl)-2-methyl-2/M,2-benzothiazine-3-carboxamide 1,1-dioxide (43) (Eq. 9). Sodium methoxide cleaved the benziso-thiazoline derivative 40 to the expected benzoate ester 41, but this was cyclized by base to a 4-hydroxy-2//-1,2-benzothiazine (42) with simultaneous conversion of the isoxazole moiety to an oxadiazole. Compound 42 was N-methylated by methyl iodide and the product converted to the desired amide 43 by treatment with triethylamine in xylene, a process which simultaneously reconverts the oxadiazole side chain to an isoxazole. 

PBD may exhibit short operating lifetimes due to recrystallization or aggregate formation. This leads to phase separation and formation of charge carrier traps that inhibit the desired emission. Therefore, it has been proposed to bond the PBD electron transporting structure to a polymer chain, which results in amorphous materials. For example, poly(methyl methacrylatejs with oxadiazole side chains have been reported [71]. The oxadiazole group may be part of the polymeric backbone, together with carbazole moieties or pheny-lene vinylene moieties [25,26]. 

An ethereal soln. of 5-methyl-3-phenyl-l,2,4-oxadiazole added dropwise to a stirred refluxing soln. of LiAlH4 in the same solvent, stirring and refluxing continued 1 hr. N-ethylbenzamidoxime. Y ca. 100%. F. e., also side chain reductions with NaBH4 without ring opening, s. M. Tavella and G. Strani, Ann. chim. (Rome) 51, 361 (1961). 

As a first approach, copol5miers and terpolymers combining main chain pyridine units, cross-linkable carboxylic acid side groups, and/or hydrophobic methyl groups were cross-linked [27]. The carboxylic acid groups can lead to thermally and chemically stable bond formation, as, for example, the creation of imidazole or oxadiazole rings. Thus, in our approach we... 

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