Preparation of new nitrogen-bridged heterocycles. 50. Syntheses of some heterocyclic compounds starting from pyridinium 1-(ethoxycarbonylacetyl)methylides

The reactions of the title methylides with dialkyl acetylenedicarboxylates gave the corresponding 3-(ethoxycarbonylacetyl)-indolizine derivatives, whose 3-substituent was smoothly converted to a coumarin skeleton by Knoevenagel reaction with salicylaldehyde. The reactions of the methylides with carbon disulfide and alkylating agent in the presence of a base afforded pyridinium 1-[alkylthio(thiocarbonyl)](ethoxycarbonylacetyl)methylides, and the S-alkylations of these ylides with phenacyl bromides and subsequent alkaline treatment of the resulting pyridinium salts gave ethyl 3-alkylthio-1-(arylcarbonyl)thieno[3,4-b]indolizine-9-carboxylates.