An Expeditious Synthesis of Heteroarenes through Carbanion-Induced Ring Transformation Reactions of Suitable Functionalized Pyran-2-ones

Abstract

Pyrazolo[1,5‐a]pyridines (3) and pyrano[4,3‐d]pyrazolo[1,5‐a]pyridines (4) have been synthesized from the reaction of pyran‐2‐one (1) and 5‐aryl‐3‐cyanomethyl‐1H‐pyrazole (2) through carbanion‐induced ring transformation reactions. A regioselective synthesis of highly functionalized polysubstituted pyrazolo[1,5‐a]pyridines (6, 7) has also been achieved from the reaction of 2 with polarised ketene dithioacetals (5) and arylidenemalononitrile, respectively. An analogous reaction of 1 with 2‐cyanomethyl‐1H‐benzimidazole (8) has also afforded the fused heterocycles 9 and 10. The cyano function in 9 has been exploited for acid‐catalysed cyclization with thiosemicarbazide to obtain 11 in high yield.