Synthesis and cardiotonic activity of pyrimido[5,4‐<i>b</i>][1,4]oxazinones and 1,4‐dioxino[2,3‐<i>d</i>]pyrimidines

Abstract

Abstract The new pyrimido[5,4‐ b ][1,4]oxazinones 4a‐c and 6a,b, 7a,c were obtained from 6‐amino‐2,3‐dimethyl‐4(3 H )‐pyrimidone ( 1 ) and 4‐substituted pyrimido[5,4–6][1,4]oxazinones 5, 7a , respectively, while derivatives 8a‐e of the novel ring system 1,4‐dioxino[2,3‐ d ]pyrimidine were prepared starting from 2b . Compounds 4a, 4c and 7a showed positive inotropic effect.