A new synthetic route to 4,6-diarylpyridazinones and some of their derivatives

A novel approach to the titled ring system starting from conveniently available chalcones 1 is proposed. It involves a catalysed exchange of hydrogen cyanide between acetone cyanohydrin and 1. The resulting γ-ketonitriles 2 give the expected 4,6-diarylpyridazinones 4 and 5 via hydrolysis and cyclisation by hydrazine. The action of phosphorus oxychloride on 5 followed by that of amines provides aminopyridazines 7.