SYNTHESIS OF METHYL -DIHYDRO-1H-PYRAZOLO[3,4-B]PYRIDINE-5-CARBOXYLATES FROM METHYL YL-2-OXO-1,2,3,4-TETRAHYDROPYRIDINE-5-CARBOXYLATES

Novel methyl 4,7-dihydro-1H-pyrazolo[3,4-b]pyridine-5 3a-e have been p repared in a two step procedure from the readily available 2-oxo-1,2,3 ,4-tetrahydropyridine-5-carboxylates 1a-e by treatment with the Vilsme ier-Haack reagent. Further treatment of the novel o-chloroformyl subst ituted methyl 1,4-dihydropyridine-5-carboxylates 2a-e with hydrazine a ffords 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 p yrazole ring.