4- Phenylisothiazole, nitration

Phenylisothiazole is nitrated predominantly in the meta position of the phenyl group, whereas 4-phenylisothiazole is nitrated ortho and para in the phenyl group <72AHC(14)1). Nitration of 3-phenyl-l,2,4-oxadiazole gives a mixture of m- and p-nitrophenyl derivatives <6301196). 

In the case of 3-phenylisothiazoles, the parent compound is nitrated to give a mixture of 3-(4-nitrophenyl) and 3-(3-nitrophenyl)isothiazole, but a series of substituted compounds gave exclusively the 3-nitrophenyl products in each case (68CPB160). 

Isomer Distribution Obtained on Nitration in the Phenyl Ring of Phenylthiazoles and Phenylisothiazoles"... 

The nitration of the isothiazole (1,2-thiazole) ring takes place exclusively at position 4. The 4-substituted isothiazoles are either not nitrated at all [189, 190] or, as in the case of 4-phenylisothiazole, are nitrated in the benzene ring [191]. 

Nitration and Halogenation.—4-Phenylisothiazole undergoes electrophilic substitution under mild conditions, predominantly in the benzene ring. 

In contrast, nitration of 4-substituted 3-phenylisothiazoles (66) a 0 °C yields exclusively 3-(m-nitrophenyl) derivatives (67). 3-Phenylisothazole itself (66 R = R = H) produces, under these conditions, 3-(/> [and /n-]nitrophenyl)isothiazole (68). The nitro-compounds show the expected behaviour, being reducible to the corresponding amines [e.g. (69)], which... 

A study of the nitration of 3-, 4-, and 5-phenylisothiazoles reveals a strong deactivation of the benzene nucleus by the heterocyclic ring. The calculated electron densities of the phenylisothiazoles are not in entire agreement with the observed orientation of the nitro-groups in the resulting mixtures of mono-nitro-derivatives. ... 

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