5-Methyl-3-phenylisoxazole, nitration

Methyl-3-phenylisoxazole is nitrated as a conjugate acid at the meta position but as the free base at the para position of the phenyl group (79AHC(25)147). Phenyl groups attached to oxazole rings are nitrated or sulfonated in the para position, with relative reactivities of the phenyl groups in the order... 

Later work has shown that 3-methyl-5-phenylisoxazole is nitrated as the conjugate acid in mixed acid to give the 4-nitrophenyl product exclusively, whereas in nitric acid acetic anhydride, poor yields of 4-nitro-5-(4-nitro-phenyl)isoxazole are obtained as the only product. 

In another study of the nitration of 5-phenyl- and 3-methyl-5-phenylisox-azole the action of nitric acid sulfuric acid on 5-phenylisoxazoIe produced a 1 1 1 mixture of the ortho, meta, and para 5-(nitrophenyl) products with minor amounts of 4-nitro-5-(3-nitrophenyl)- and 4-nitro-5-(4-nitrophenyl)-dinitro products. The action of nitric acid acetic anhydride produced 4-nitro-5-phenylisoxazole as the major product with some nitrophenyl compounds as minor products. 3-Methyl-5-phenylisoxazole also gave a mixture of the ortho, meta, and para 5-(nitrophenyl) products when mixed acids were used, but no dinitro products were observed. The use of nitric acid acetic anhydride resulted in nitration at the 4-position of the isoxa-zole ring as the largely predominant product, with some phenyl ring substitution (89H1965). 

The kinetics of the nitration of 3-methyl-5-phenyl- and 5-methyl-3-phenylisoxazoles [183] and 5,5-dimethylisoxazole [184] were studied. During the nitration of 3,5-diphenylisoxazole by the sulfuric-nitric acid mixture only the phenyl group enters into the reaction [177, 185], In acetic anhydride, however, the main nitration product is 3,5-diphenyl-4-nitroisoxazole [185],... 

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