Phenoxazine halogenation

Halogen-metal exchange reactions provide the main route to 3-lithiated derivatives of phenothiazine and phenoxazine and examples of metalated compounds formed by the use of such exchange reactions include the... 

Even the comparatively unreactive phenoxazine and phenothiazine systems undergo halogenation and nitration with ease and it is normal to prepare monosubstituted derivatives by stepwise procedures rather than by direct electrophilic attack. Indeed, the nitration of phenoxazine is uncontrollable and even N-acylphenoxazines afford a mixture of di- and tetra-nitro products (03CB475). Similarly phenothiazine and nitric acid produce a complex mixture of nitrated sulfoxides and sulfones. Chlorine in DMSO at 40 °C reacts with phenothiazine to yield 3,7-dichlorophenothiazine, whereas cupric chloride gives the 1,7-isomer (76JPR353). Direct bromination of phenoxazine produces a mixture of 3-bromo- and 3,7-dibromo-phenoxazines, while thionyl chloride affords the 1,3,7,9-tetrachloro derivative (60ZOB1893). 

Turpin s reaction has been widely used for preparing substituted phenoxazines.15-21 Unsymmetrically substituted halonitrobenzenes which have two nitro groups ortho to the reactive halogen produce two isomeric phenoxazines, although usually one isomer predominates.22... 

There have been reports of various phenothiazine and phenoxazine anion-radicals which are species which correspond to structure 244 and its substituted derivatives. Thus, reduction of phenothiazin-3-one in DMF gives 259 for which hyperfine splittings are indicated in gauss. The assignment of splittings was made following study of halogenated derivatives of 259 and McLachlan MO calculations. Similar anions from phenoxazin-... 

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