Hydrazones of ketones 1, are transformed into 1-chloroalkylazo compounds, 2, which react with Lewis acids to give transient 1-aza-2-azoniaallene salts, 3. The cations 3 react with with acetylenes, olefins, isocyanates, carbodiimides, and nitriles under [3+ 2]-cycloadditions. The cycloadducts undergo consecutive reactions, eg [1, 2]-shifts of alkyl groups.
