Pyrazolopyridines reactions

The imine (161), obtained from 1-aminopyridinium iodide and potassium carbonate, combines with dimethyl acetylenedicarboxylate yielding in the first place (162) which then with more ester gives dimethyl fumarate and the pyrazolopyridine (163), isolated in 15% yield. A corresponding reaction with isoquinoline imine gave 75% of the primary adduct [(cf. (162)]. ... 

With a change to non-polar solvent, the reaction of ylides 269 with alkynes and alkenes changed dramatically, as shown in Scheme 10. With DM AD in toluene the ylides give pyrazolopyridines 272 in good yield (91TL4977), and with methyl propiolate (MEP) give indolizines 273 (92H(33)203). The reaction with acrylates is much less clean, but the variety of products is said to be formed from a diazene intermediate, which splits to give a diradical (93H(35)851). 

Ketene dithioacetal 130 reacts with 3-amino-2-pyrazolin-5-one 129 to give the highly functionalized pyrazolopyridine 131, which is converted into the bispyrazolopyridine 132 by reaction with hydrazine hydrate (Scheme 9) <1997JCM256>. 

Hantzsch-type reaction between 5-amino-3-methyl-l-phenylpyrazole, 4-dimethyl-aminobenzaldehyde, and 2-aroylbenzimidazole is followed by elimination of 4-dimethylaminophelyl substituent [75]. The treatments that were carried out in boiling glacial acetic acids for 2 h yielded pyrazolopyridines 44 when Ry 4-NO2C6H4 (Scheme 19). 

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

Diazotization has been reported for all the pyrazolopyridines, and in some cases the salts have been isolated. A 7-aminopyrazolo[4,3-c]pyridine (191a) was converted to the corresponding hydroxy compound with sodium nitrite in hot glacial acetic acid.159 Analogous products were obtained from a 3-aminopyrazolo[3,4-b]-15 and 2-aminopyrazolo[l,5-a]pyridine.186 Decomposition of diazonium salts with hydrobromic acid afforded 3-bromo-pyrazolo[3,4-c]-u0 or -[4,3-bjpyridines111 deamination of 3-aminopyra-zolo[3,4-h]pyridines was achieved via treatment of the diazonium salts with hypophosphorous acid,10 titanous chloride,238 or ferrous ammonium sulfate.238 Kocevar et al.236 have made a detailed study of the reactions of the latter diazonium salt. 

Diaz-Ortiz, A., De la Hoz, A. andLanga, F., Microwave irradiation in solvent-free conditions an eco-friendly methodology to prepare indazoles, pyrazolopyridines and bipyrazoles by cycloaddition reactions, Green Chem., 2000, 2, 165-172. 

When a solution of 1-aminopyridinium iodide (143) in DMF was treated with anhydrous potassium carbonate, the mixture developed the deep blue color characteristic of pyridine 1-imine (144) addition of EP caused an immediate exothermic reaction giving the pyrazolopyridine 145 in 48% yield311 hydrolysis and decarboxylation gave a high yield of pyrazolo[l,5-a]pyridine (146).311 Many reactions of this type have now been carried out,312 and the regioselectivity for the cydization of 3-substituted derivatives has been examined,313... 

The Skraup reaction can be carried out with 3-, 4-, or 5-amino-pyrazoles giving pyrazolopyridines (63).280,646... 

The bis-diazo ketone (205) refluxed in 2,3-dimethylbuta-l,3-diene gives the pyrazolopyridine (207), presumably via (206) (71CC537). A Diels-Alder reaction gives the pyrazolo[l,2-a]pyridazine (208) which can be further elaborated to the aromatic salt (209 Scheme 63) (71JHC25). An alternative preparation of (201), carried out in the presence of buta-1,3-diene, gives (210), which is also obtained when the tetrahydropyridazine (211) is heated with the jS-keto ester (212 Scheme 64) (66JOC2867). 

Keywords quantitative, solid diazonium salt, pyrazolopyridine, azo coupling, solid-solid reaction, solid-solid reaction, solid-gas reaction, cascade reaction... 

A rearrangement of the type shown in Scheme 28 cannot be observed with C,N-diphenylnitrilimines, because these cyclize onto the aromatic ring bound to N, giving indazoles (Scheme 29). The reaction is virtually quantitative and therefore of synthetic value for the preparation of 3-arylindazoles and pyrazolopyridines (149).193,194 When the same reaction is carried out at 800°C (flash pyrolysis), a further molecule of N2 is extruded, giving a new carbene which cyclizes to fluorenes or azafluorenes (150), again in quantitative yields (Scheme 29).193... 

I-Aminobenziinidazoles are useful intermediates, and their alkylation may occur at either NHj or the =N— atom. On heating with an iodoalkane, only the 3-quatemary salt is obtained. This is cyclized on heating with an anhydride and sodium carbonate a lower yield is obtained when the carbonate is replaced by pyridine. When a 2-hydroxymethyM-aminopyridinium chloride is heated with acetic anhydride, the JV.O-diacetate is foimnl but in the presence of a base, this reaction yields the pyrazolopyridine. 

Pyrrolopyridines 75 have been prepared by reaction of 10 with arylpyrrolidinetriones 74 k 10 has been condensed with the hydrazine derivative 76 to yield pyrazoles 77 as well as pyrazolopyridines 78, depending on the concentration of 10 used. A larger amount of 10 favoured the formation of 78. ... 

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