Nitrene-induced cyclisations accompanied by rearrangement in thermolyses of aryl 2-azidophenyl sulphones: a note on quantitative high-speed liquid chromatographic analysis of substituted phenothiazine 5,5-dioxides

Abstract

Thermolysis in decalin or triethyl phosphate at 192 °C of a series of aryl 2-azidophenyl sulphones (2-N₃C₆H₄·SO₂·C₆H₄R; R = 2-Cl, 3-Cl, 4-Cl, 2-Me, 3-Me, 4-Me, 2-OMe, 3-OMe, 4-OMe, 4-Bu^t, 2-CF₃, 3-CF₃, 4-CF₃, or 2, 6-Cl₂), characterised as the 2-triphenylphosphoranylideneamino-derivatives, have been studied and the products analysed quantitatively by high-speed liquid chromatography. The reactions gave small amounts of 2-amino-phenyl aryl sulphones (0–30%), and phenothiazine 5,5-dioxides (25–90%) which were mixtures of rearranged and unrearranged isomers, e.g. 2-azidophenyl 3-methylphenyl sulphone in decalin gave a mixture of methyl-phenothiazine 5,5-dioxides in the following proportions: 1-(62%), 2-(10%), 3-(20%), and 4-(8%). Consideration of the rearrangement ratio in each case points to cyclisation via an electrophilic nitrene, the position of attack being influenced mainly by the electronic character of the substituent, although proximity effects cannot be excluded. In most cases there was no significant difference between rearrangement ratios in decalin and in triethyl phosphate so, in this system, in general, there is no reason to invoke formation of and reaction via the species Ar[graphic omitted]–O–[graphic omitted](OEt)₃ in the latter case.

The reaction of 4-chlorophenyl 2-nitrophenyl sulphone with triethyl phosphite in boiling cumene gave no chlorophenothiazine dioxides; an intractable tar was obtained.