A new approach to the synthesis of pyridazino[4,5‐<i>c</i>]pyridazinones

Abstract

Abstract The reaction of 5‐hydrazinopyridazin‐3(2 H )‐ones 1 with α‐keto diester 2 in acetic acid afforded the corresponding 4,6‐dihydropyridazino[4,5‐ c ]pyridazin‐5(1 H )‐ones 3 and pyrrolo[2,3‐ d )pyridazin‐4(5 H )‐ones 4 . Compounds 3 were also obtained from 4‐bromo‐5‐hydrazinopyridazin‐3(2 H )‐ones 8 and 2 under milder conditions. 5‐Bromo‐4‐hydrazinopyridazin‐3(2 H )‐one 9 , the regioisomer of 8b , also reacted readily with 2a to give 4,7‐dihydropyridazino[4,5‐ c ]pyridazin‐8(1 H )‐one 10b , the regioisomer of 3b .