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

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.