Synthesis of Methyl 4‐Aryl‐6‐methyl‐4,7‐dihydro‐1H‐pyrazolo(3,4‐b) pyridine‐5‐carboxylates from Methyl 4‐Aryl‐6‐methyl‐2‐oxo‐1,2,3,4‐ tetrahydropyridine‐5‐carboxylates.

Novel methyl 4,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5-carboxylates 3a–e have been prepared in a two step procedure from the readily available 2-oxo-1,2,3,4-tetrahydropyridine-5-carboxylates 1a–e by treatment with the Vilsmeier–Haack reagent. Further treatment of the novel o-chloroformyl substituted methyl 1,4-dihydropyridine-5-carboxylates 2a–e with hydrazine affords the corresponding methyl pyrazolo[3,4-b]pyridine-5-carboxylates in good yields. Semiempirical calculations reveal a favoured geometry with a boat conformation in the dihydropyridine system and a planar pyrazole ring.