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96. Friedländer Condensation of 5-Aminopyrazole-4-carbaldehydes with Reactive alpha-Methylene Ketones: Synthesis of Pyrazolo[3,4-b]pyridines
Jachak M. N., Avhale A. B., Tantak C. D., Toche R. B., Reidlinger C., Stadlbauer W., J. Heterocyclic Chem., 42, 1311-1319 (2005).

Abstract:
A series of 1,3,6-trisubstituted and 1,3,5,6-tetrasubstituted pyrazolo[3,4-b]pyridines 5 has been synthesized by Friedländer condensation of o-aminopyrazolecarbaldehydes 3 with a-methylene ketones such as acetone (4a) or acetophenones 4b-f with potassium hydroxide as basic catalyst. Condensation of o-aminopyrazolecarbaldehydes 3 and unsymmetric dialkylketones 6 yielded mixtures of isomeric pyrazolo[3,4-b]pyridine derivatives 7 and 8. Condensation of o-aminopyrazolecarbaldehydes 3 with CH-acidic acylacetonitriles 9 and acylacetates 11 with piperidine as basic catalyst yielded pyrazolo[3,4-b]pyridine-5-carbonitriles 10 and pyrazolo[3,4-b]pyridine-5-carboxylates 12; with diethyl malonate 13 as CH-acidic component, pyrazolo[3,4-b]pyridin-6-ones 14 were obtained.


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