Preparation of New Nitrogen-bridged Heterocycles. 6. First Synthesis of 2-Aroylfuro[2,3-b]indolizine Derivatives

Alkaline treatment of 2-(aroylmethoxy)-3-(2,2-dicyanovinyl)indolizine derivatives, readily available from the step-by-step reactions of 1-(ethoxycarbonylmethyl)-2-picolinium salts with a base, (ethoxymethylene)malononitrile followed by some phenacyl bromides in ethanol, afforded smoothly the title compounds, 2-aroylfuro[2,3-b]indolizine derivatives, in good yields. These furoindolizines could be also obtained directly from the pyridinium salts without the isolation of intermediate 3-vinylindolizines. Formation mechanisms and some physical properties of these furoindolizines are also discussed.