Synthesis of 5H-furo[3′,2′ : 6,7][1]benzopyrano[3,4-c]pyridin-5-ones and 8H-pyrano[3′,2′ : 5,6]benzofuro[3,2-c]pyridin-8-ones (pyridopsoralens)

Abstract

5H-Furo[3′,2′ : 6,7][1]benzopyrano[3,4-c]pyridin-5-ones (pyrido[3,4-c]psoralens)(3) have been obtained by the von Pechmann reaction starting from 6-hydroxy-2,3-dihydrobenzofuran acetates plus 1-benzyl-3-ethoxycarbonylpiperidin-4-one and subsequent dehydrogenation. The synthesis of their 8H-pyrano[3′,2′ : 5,6]benzofuro[3,2-c]pyridin-8-one isomers (14) and (17) was achieved by two ways using: (i) ring closure of 4-formyl-3-hydroxy-2-methylbenzofuro[3,2-c]pyridine, and (ii) cyclisation of piperidinone O-(4,7-dimethylcoumarin-7-yl) oxime derivatives and aromatization.