The 1,3-Dipolar Cycloaddition Reactions of Heteroaromatic Dicyanomethylides with Phenylsulfinylethene and Bis(trimethylsilyl)ethyne: Synthesis of 1,2-Unsubstituted 3-Cyanoindolizines

Abstract

Abstract Pyridinium and diazinium dicyanomethylides underwent 1,3-dipolar cycloaddition-extrusion reactions with phenylsulfinylethene, producing the corresponding 3-cyanoindolizines in moderate to good yields. 1,3-Dipolar cycloadditions of these ylides with bis(trimethylsilyl)ethyne gave either the 1,2-bis(trimethylsilyl)-3-cyanoindolizines or the 1-trimethylsilyl-3-cyanoindolizines, or mixtures of these, depending on the substituents and the presence of another nitrogen atom in the pyridine ring. 1,2-Bis(trimethylsilyl)-3-cyanoindolizines underwent regiospecific protodesilylation at the 2-position upon a treatment with silica gel in refluxing chloroform, yielding 1-trimethylsilyl-3-cyanoindolizines. The 1,2-bis(trimethylsilyl)-, and 1-trimethylsilyl-3-cyanoindolizines suffered from quantitative protodesilylation under catalysis by tetrabutylammonium fluoride to afford 1,2-unsubstituted 3-cyanoindolizines.