PREPARATION OF NEW NITROGEN-BRIDGED HETEROCYCLES .33. A NEW PREPARATIVE METHOD FOR THIENO[3,2-A]INDOLIZINES

The treatment of 2-iminothieno[3,2-a]indolizine derivatives with potas sium tert-butoxide generated exclusively potassium 1-(2-cyanovinyl)ind olizine-2-thiolates through the ring opening of the initially formed t hiin-2-imide ions. These 2-indolizinethiolates reacted with various al kylating agents to give the corresponding S-alkylated 1-vinylindolizin e derivatives, and 2-acetonylthio- and 2-phenacylthio-1-(2-cyanovinyl) indolizines of these products smoothly underwent intramolecular Michae l addition under the conditions employed here to afford the correspond ing 2-acetyl- and 2-aroylthieno[3,2-a]indolizines in high yields with the elimination of a methylene compound.