Of pyrazolopyridines

Similarly, Yli-Kauhaluoma and co-workers have studied the 1,3-dipolar cycloaddition of polymer-bound alkynes to azomethine imines, generated in situ from A-ami nopyridine iodides, in the synthesis of pyrazolopyridines <06JCC344>. 

In previous work (85MI1 87AHC319), the synthesis and chemistry of pyrazolopyridines and pyrazolopyrimidines was surveyed. This chapter reports synthetic approaches to other aromatic 10 tt electron systems containing a pyrazole moiety, as well as the systems main chemical and physicochemical properties. 

Scheme 15 Synthesis of positional isomers of pyrazolopyridine carboxylic acid derivatives...

The reactions of pyrazolopyridines have not been studied in detail nevertheless, sufficient information is available to demonstrate similarities between the five isomers. 

The UV spectra of pyrazolopyridines are comparable to those of pyr-rolopyridines,7 showing up to three bands at 214-285, 263-298, and 291— 374 nm. Galasco et al.261 have discussed the spectra of 5 in relation to its electronic structure. 

A new method of preparing pyrazolopyridines from A -azinylpyridinium iV-aminides has been developed by Alvarez-Builla et al. <02SL1093> and features a radical addition to a pyridine. Initially, attempts to convert aminide 142 into pyrazolopyridine 143, through the slow addition of tris(trimethylsilyl)silane and AIBN to a refluxing acetonitrile - benzene solution of the two components, was thwarted by a competitive reduction of the N-N bond. Indeed, aminopyridine 144 was formed as the major product in 60% yield. However, through the simple expedient of adding potassium carbonate to the solution of aminide 142, that reduction pathway was almost completely shut down and the yield of pyrazolopyridine 143 was elevated from 2% to 56% (Scheme 39). 

An interesting synthesis of pyrazolopyridines has been presented by Alvarez-Builla (02S1093), using an intramolecular radical addition by the 3-pyridyl radical derived from 76a-d (Scheme 14) as well as 2-p5u-azinyl radicals to a p5uidine ring, with subsequent rearomatisation to produce cyclised products 77a-c (Scheme 17). 

In 2013, Neres and coworker reported the synthesis, biochemical, and microbiological evaluation of a series of pyrazolopyridine derivatives as normucleoside inhibitors of BasE, an adenylating enzyme in the sidero-phore biosynthetic pathway of the opportunistic pathogen Acinetobacter baumannii. The amino-pyrazolopyridine series was produced via direct... 

K. Haiju, 1. Kylanlahti, T. Paananen, M. Polamo, J. Nielsen, J. Yli-Kauhaluoma, Solid-phase synthesis of pyrazolopyridines from polymer-bound alkyne and azomethine imines. J. Comb. Chem. 2006, 8, 344-349. 

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