Preparation of New Nitrogen-bridged Heterocydes. 8. Syntheses of Some Fused Indolizine Derivatives<i>via</i>the Acid-catalyzed Cyclizations of Functionalized 1- and 3-Vinylindolizines
give the initially expected pyrano[2,3-b]indolizinones at all, but, instead of them, afforded 3-(methoxycarbonylmethylene)furo[2,3-b]indolizin-2-one derivatives in fair yields. Formation mechanisms and some physical properties are also discussed.