Synthesis and regiospecificity in methylation of pyrido[1,2‐<i>a</i>]pyrazinium‐1‐ and 3‐olates and pyrido[1,2‐<i>b</i>]pyridazinium‐2‐ and 4‐olates

Abstract

Abstract New methods have been developed for the synthesis of pyrido[1,2‐ a ]pyrazinium‐1‐ and 3‐olates 5a‐f, 9 and 1‐thiolate 24 as well as of pyrido[1,2‐ b ]pyridazinium‐4‐ and 2‐olates 14, 20 . The methylation of these new compounds was studied by soft and hard methylating agents. Depending on the nature of the reagent used, the pyrido[1,2‐ a ]pyrazinium‐1‐olates 5a‐f gave NMe 22a‐f and/or OMe 23a‐f products, whereas the 3‐olate 9 and both the 4‐ and 2‐pyridazinium‐olates 14, 20 afforded solely OMe compounds 10, 15, 21 . A selectivity rule for methylation is proposed.