PREPARATION OF NEW NITROGEN-BRIDGED HETEROCYCLES .37. SYNTHESIS AND REARRANGEMENT OF FULL-CONJUGATED OXEPINO[2,3-B]INDOLIZINE DERIVATIVES

The title compounds were first synthesized in considerably good yields by acid-catalyzed dehydration of the corresponding ethyl l-2,3-dihydr ooxepino[2,3-b]indolizin-4-carboxylate derivatives with methanesulfoni c acid in boiling chloroform. Although these full-conjugated oxepino[2 ,3-b]indolizines with a nonaromatic 16pi electron system were stable a t room temperature, upon heating them in boiling ethanol, they were sm oothly rearranged to ethyl enyl-1,2-dihydropyrido[1,2-a]indole-3-carbo xylates in good yields. The structures of these oxepino[2,3-b]indolizi nes and the rearranged pyrido[1,2-a]-indol-1 (2H)-ones were distinctly determined by physical and spectral means, including X-ray analyses.