Preparation of new nitrogen-bridged heterocycles. 49. A new access to thieno[3,4-b]indolizine derivatives

The title compounds, together with 3-vinylindolizine-1-carbonitriles (4-56%), were prepared in 1-18% yields from the S-alkylation of pyridinium 1-3-ethoxycarbonyl-1-cyanomethylthio(thiocarbonyl)]]all ylides with alkyl halides, followed by treatment of the resulting pyridinium salts with a base and then a dehydrogenating agent. In several reactions of pyridinium salts obtained from reaction of the allylides with benzylic halides, trace amounts of bis1-cyano-9-(ethoxycarbonyl)thieno3,4-b]indolizin-3-yl] disulfides with an interesting superimposed structure were also isolated. The structures of these compounds were confirmed by X-ray analyses.