Synthesis and reactions of 1,2‐fused 3‐cyanoindolizines

Abstract

Abstract With the intention that annulation of carbo‐ or heteroaromatic rings at the 1,2‐positions can activate 3‐cyanoindolizines as 1,3‐dipolar species, 6‐cyanobenz[ a ]indolizines, pyridazino[4,5‐ a ]indolizines and 5‐cyano‐1,3‐diphenylthiopheno[3,4‐ a ]indolizine were prepared. 6‐Cyanobenz[ a ]indolizines smoothly ‐underwent 1,3‐dipolar cycloaddition on to dibenzoylacetylene and diacetylacetylene to afford the corresponding indolizino[3,4,5‐ ab ]isoindoles, whereas 5‐cyano‐1,4‐diphenylpyridazino[4,5‐ a ]indolizine reacted with dimethyl acetylenedicarboxylate to give the 1:2 adduct. Only a 3% yield of 5‐cyano‐1,3‐diphenylthiopheno[3,4‐ a ]indolizine formed upon phosphorus pentasulfide treatment of 1,2‐dibenzoyl‐3‐cyanoindolizine.