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Elsevier, Tetrahedron Letters, 21(50), p. 2484-2486

DOI: 10.1016/j.tetlet.2009.03.035

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Unexpected product distributions in the synthesis of 2,6-bis-(indazolyl)pyridine and 2-(pyrazol-1-yl)-6-(indazolyl)pyridine

Journal article published in 2009 by Ruth Pritchard, Colin A. Kilner, Malcolm A. Halcrow ORCID
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

Reaction of 2-bromopyridine with 2equiv of sodium indazolide in diglyme at 140°C affords 2,6-bis-(indazol-1-yl)pyridine and 2-(indazol-1-yl)-6-(indazol-2-yl)pyridine in purified yields of 24% and 68% respectively. A similar reaction, using 1equiv of sodium indazolide at 70°C, gives a low-yield mixture of 2-(indazol-1-yl)-6-bromopyridine and 2-(indazol-2-yl)-6-bromopyridine. Both these intermediates are transformed into 2-(pyrazol-1-yl)-6-(indazol-1-yl)pyridine and 2,6-di(pyrazol-1-yl)pyridine upon treatment with 1equiv of sodium pyrazolide in diglyme at 140°C. These observations imply that the indazolyl group is a leaving group comparable to a bromo substituent under nucleophilic attack by pyrazolide or indazolide ions under these conditions. No reaction was observed between 2-(pyrazol-1-yl)-6-bromopyridine and 1equiv of sodium indazolide under the same conditions. A single crystal structure of its iron(II) complex confirmed the regiochemistry of 2,6-bis-(indazol-1-yl)pyridine, and revealed significant conformational flexibility in the distal ligand indazolyl groups.