Heterocyclic systems. Part 14. Condensation reactions of 2-(4-oxo-4H-1-benzopyran-3-yl)-1,3-dioxolane

Abstract

Nitrogen nucleophiles under 1,4-addition with the title acetal (4; R = H, Me, and Cl) to give an intermediate that ultimately produces in most cases the same product as is obtained from the corresponding aldehyde (3) under similar conditions. Thus, compound (4) condenses with piperidine and morpholine to give the enamino ketone (14; R¹R²=–[CH₂]₅^–, –[CH₂]₂O[CH₂]₂^–), with aniline to give the chromanone (15; Z = H, Me, and OMe), and with o-phenylenediamine to give the dihydrodiazepine (16), the latter being dehydrogenated to the unsaturated compound (17) by boiling in acetic acid. On being refluxed with hydrazine (5) in pyridine, the acetal (4; R = H) affords smoothly the benzoylpyrazole (20; R′= H, Ph), whereas (4; R = Me or Cl) even with equimolar proportions of hydrazine in refluxing ethanol gives predominantly, if not exclusively, the pyrazole (25; R′= H, Ph). Guanidine and urea with (4) give the fused aminopyrimidine (33) and the hydroxy analogue, respectively.