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Paper | Regular issue | Vol 75, No. 7, 2008, pp.1695-1709
Published online, 14th March, 2008
DOI: 10.3987/COM-08-11356
Versatile Three Component Coupling for the Synthesis of Pyrazolopyridines and Other Pyrido Fused Systems

Carmen Almansa,* Marina Virgili, Elena Carceller, and Pedro Grima-Poveda

*Innovation and Drug Discovery, Palau Pharma S. A. (Grupo Uriach). Av. Camí Reial, 51-57, E-08184, Palau-Solità i Plegamans, Spain

Abstract

A new unexpected reaction of 1-(4-fluorophenyl)-2-(4-pyridyl)ethanone 2 with 3-aminopyrazole, involving loss of a 4-pyridylmethyl group, afforded 4,6-bis(4-fluorophenyl)-5-(4-pyridyl)-1H-pyrazolo[3,4-b]pyridine 1 in good yields. Investigation of the features of this cyclization led to the development of a new three component coupling for the synthesis of pyrazolo[3,4-b]pyridines, from a ketone, an aldehyde and a 3-aminopyrazole in the presence of acid catalysis and a protic solvent. The study of the scope of this reaction showed its remarkable versatility and its usefulness in the preparation of other bicyclic systems, such as thieno[3,2-b]pyridines, pyrrolo[3,2-b]pyridines, imidazo[4,5-b]pyridines, furo[2,3-b]pyridines, isoxazolo[5,4-b]pyridines and, isothiazolo[5,4-b]pyridines. The three component nature of this reaction makes it suitable for the preparation of combinatorial libraries since scaffold decoration can be easily achieved in one step.