Reactions with Carbo(heterylhydrazonoyl) Halides. I. Chemistry of Carbo(3‐phenylpyrazol‐5‐yl‐hydrazonoyl) Chlorides

The Carbo(3‐phenylpyrazol‐5‐yl‐hydrazonoyl) halides 1a , b react with active methylene compounds to yield the 1‐(3‐phenylpyrazol‐5‐yl)‐pyrazole derivatives 2a – k ( Scheme 1 ). The acyclic intermediates 3a , b could be isolated from reaction of 1a , b with acetylacetone, thus establishing the substitution mechanism for these reactions. Compounds 1a , b reacted with carbon disulfide, phenyl isothiocyanate, methyl cyanide, and with p ‐chlorobenzaldehyde to yield the corresponding heterocyclic derivatives 5 – 8 , respectively ( Scheme 2 ). The behaviour of compounds 2 with hydrazine hydrate is reported.