AN EXPEDITIOUS SYNTHESIS OF HETEROARENES THROUGH CARBANION-INDUCED RING TRANSFORMATION REACTIONS OF SUITABLE FUNCTIONALIZED PYRAN-2-ONES

Pyrazolo[1,5-a]pyridines (3) and pyrano [4,3-d]pyrazolo[1,5-a]pyridine s (4) have been synthesized from the reaction of pyran-2-one (1) and 5 -aryl-3-cyanomethyl-1H-pyrazole (2) through carbanion-induced ring tra nsformation reactions. A regioselective synthesis of highly functional ized polysubstituted pyrazolo[1,5-a]pyridines (6, 7) has also been ach ieved from the reaction of 2 with polarised ketene dithioacetals (5) a nd arylidenemalononitrile, respectively. An analogous reaction of 1 wi th 2-cyanomethyl-1H-benzimidazole (8) has also afforded the fused hete rocycles 9 and 10. The cyano function in 9 has been exploited for acid -catalysed cyclization with thiosemicarbazide to obtain 11 in high yie ld.