Some aspects of the chemistry of pyrimido[1,2‐<i>B</i>]pyridazinones

Abstract

Abstract On reacting the 3‐aminopyridazines 1a,d,e with dimethyl acetylenedicarboxylate (DMAD), the pyrimido[1,2‐ b ]pyridazin‐2‐(2 H )‐ones 2e‐g , whereas starting from 1f , the 4(4 H )‐ones 5a and 3b,d were prepared. In the 2(2 H )‐one series, the reactions of 2b with various amino compounds resulted in various types of products. The reaction of N ‐methylaminopyridazines 1g,h with DMAD led to the endo‐N ‐substituted derivatives 8a,b , whereas 1h with diethyl ethoxymethylenemalonate (DEM) gave the exo‐N ‐substituted compound 1k. The constitution of the compounds was proved by spectroscopic and chemical evidences.