1,2,4-Triazolium Salts from the Reaction of 1-Aza-2-azoniaallene Salts with Nitriles

Aryl- and alkylhydrazones 1 of alkyl ketones and propanal are transformed to 1-chloroalkylazo compounds 2 with tert-butyl hypochlorite. Compounds 2 react with antimony(V) chloride or aluminum(III) chloride to give 1-aza-2-azoniaallene salts 3 as reactive intermediates, which are intercepted as 3H-1,2,4-triazolium salts 5 with nitriles. In most cases these salts rearrange spontaneously to form the corresponding 1H-triazolium salts 6. Benzophenone arylhydrazone 1x reacts with tert-butyl hypochlorite and antimony(V) chloride to furnish the 1-aryl-3-phenylindazolium salt 7. An X-ray diffraction analysis of a 1H-1,2,4-triazolium salt [6,7,8,9- tetrahydro-2-methyl-3-(2,4,6-trichlorophenyl)-5H-[1,2,4] triazolo [5,1-a]azepinium hexachloroantimonate (6n)] is reported.