Ring cleavage nitration

The synthesis of nitrated hydroxy-terminated polybutadiene (NHTPB) (44) from the reaction of partially epoxidized hydroxy-terminated polybutadiene with dinitrogen pentoxide 

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The nitration of benzocyclobutene under neutral conditions has not been examined, and ititration under acidic conditions leads to considerable ring cleavage. See Homer, L Schmelzer, H.-G. Thompson, B. Chem. Ber. 1960,93,1774 (b) Ref. 46. 

The relatively low electron density at carbon, coupled with the possibility of protonation at nitrogen, makes electrophilic substitution at carbon difficult. A further problem is acid-catalyzed ring cleavage, particularly with alkyloxadiazoles. No examples of nitration or sulfonation of the oxadiazole ring have been reported and attempted brominations were unsuccessful. A low yield of 2-(2-furoyl)-5-phenyl-l,3,4-oxadiazole is obtained when 2-phenyl-l,3,4-oxadiazole is treated with 2-furoyl chloride in the presence of triethylamine (77LA159). 

Nitration of enol acetates a-nitro ketones. This reagent is more useful than acetyl nitrate (AciO/HNOj) for nitration of enol acetates of cyclohexanones, particularly those of 2-alkyIcyclohexanones, which can undergo ring cleavage. However, yields are low unless the 2-substituent is a primary alkyl group. 

Reactions of oxidizing agents with dibenzheterocycles have also been reported. Arsenic adds are stable in sulfuric acid and can be nitrated without ring cleavage ... 

The oxidation of cyclopropanone hemiacetals, e.g. 34, by copper(II) nitrate proceeded viacyclo-propanoxyl radicals to give 1,4-diesters.Ring cleavage of the initial radicals was followed by coupling of the 3-oxoalkyl radicals. 

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