N-halogeno-compounds. Part 7. Synthesis and iodine-catalysed rearrangement to 6-chloroimino-1-azacyclohexadienes of 4-substituted 2-(dichloroamino)-3,5,6-trifluoropyridines

Abstract

Electrophilic chlorination of the fluorinated 2-aminopyridines 4-X·C₅F₃N·NH₂-2 [X = H, CI, or CF(CF₃)₂] with t-butyl hypochlorite gave the 2-(dichloroamino)-compounds 4-X·C₅F₃N·NCI₂-2; these isomerized to mixtures of the corresponding 3-chloro-6-chloroimino-1-azacyclohexa-1,4-(predominantly) and 5-chloro-6-chloroimino1 -azacyclohexa-1,3-dienes when treated with iodine. ‘Spontaneous’ formation of 3-chloro-6-chloroimino-2,3,5trifluoro-4-methyl-1-azacyclohexa-1,4-diene occurred following chlorination (Bu^tOCI) of 2-amino-3,5,6-trifluoro-4-methylpyridine. 3-Chloro-6-chloroimino-3,5-difluoro-4-X-2-oxo-1-azacyclohex-4-enes (X = H, Me, or CI) were obtained by displacement of fluorine from the corresponding 3-chloro-6-chloroimino-2,3,5-trifluoro1 -azacyclohexa-1,4-dienes with water; hydrolysis of 4,5-dichloro-6-chloroimino-2,3,5-trifluoro-1-azacyclohexa1,3-diene provided 4,5-dichloro-6-chloroimino-3,5-difluoro-2-oxo-1-azacyclohex-3-ene. Pyrolysis of the 2-(dichloroamino)pyridines 4-X·C₅F₃N·NCl₂-2 [X = CI or CF(CF₃)₂] gave the azo-compounds 2,2′-[4-X·C₅F₃N·N =]₂. The ¹⁹F n.m.r, spectra of the chloroimino-1-azacyclohexadienes have been analysed.