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An iron-catalyzed route for the regioselective synthesis of 1,3- and 1,3,5-substituted pyrazoles from the reaction of diarylhydrazones and vicinal diols has been developed. This method was found to be practical with wide substrate scope.

A copper-free palladium-catalyzed convenient and efficient oxidative amidation protocol for synthesis of enamides by the cross-coupling of amides with acrylate has been developed. The thermodynamically disfavored Z-isomers are accessible by the intramolecular hydrogen bonding between the amido proton and carbonyl oxygen. The reactions were found to be acid catalyzed and p-TsOH gave the best result in enamide synthesis. The reactions were conducted at room temperature in presence of ambient air. This protocol has wide substrate scope allowing alkyl, aryl, substituted arylamides, urea, and its derivatives to react with methyl acrylate. The reactions are found to be tolerant to the steric demand of secondary amides and give the tertiary E-enamides in moderated to good yield.

Eight pyrazolo [3,4-b]pyridine derivatives have been synthesized by Friedländer condensation of 5-aminopyrazole-4-carbaldehyde with active methylene compounds in basic medium. These compounds have been screened for their antibacterial activity against two Gram-negative and two Gram-positive bacterium. Pyrazolopyridines having the carboxamide group at the 5-position showed moderate to good activity against P. aeruginosa, E. coli, S. pneumoniae, and B. cereus.The evolution of antibacterial resistance in bacterial strains against the currently available antibacterial agents is an increasing concern in recent years. For instance, Gram-positive bacterial pathogen such as Staphylococcus aureus is resistant to Methicillin, and Streptococcus pneumoniae and Enterococci are resistant to Penicillin and Vancomycin, respectively [1]. On the other hand, Gram-negative bacteria such as H. influenza and M. catarrahalis are resistant to β-lactams, quinolones, and macrolides [2]. In order to overcome the threat of widespread multidrug resistance in Gram-positive as well as Gram-negative bacterial strains, there is an ongoing demand for new antibacterials.Pyrazolo [3,4-b]pyridines as aza-analogs of indazoles [3] have long served as attractive targets in organic synthesis due to their excellent antibacterial activity [4]. Moreover, pyrazolo[3,4-b]pyridines also exhibit other promising biological activities, including anxiolytic (e.g., Tracazolate) [5], dopamine D3-receptor antagonist and partial agonist [6], dopamine D4 antagonist [7], adenosine A1-receptor antagonist [8,9], antiherpetic [10], antiinflammatory [11], and antiallergic [12] properties. The methods so far reported for the synthesis of pyrazolopyridines include: i) the annelation of the pyrazole ring onto the suitably substituted pyridine ring [13][14][15][16][17][18][19], and ii) the annelation of the pyridine ring onto the appropriately substituted pyrazole ring [13,[20][21][22][23][24][25][26][27][28][29][30]. As part of our ongoing program [31] for the development of new antibacterials, we are particularly interested in the synthesis of pyrazolo [3,4-b]pyridines by the latter method. Like others, our strategy involves the Friedländer condensation of 5-aminopyrazoles with active methylene compounds as the key step. In this paper we report the full details of our efforts on the synthesis of some novel pyrazolo[3,4-b]pyridine derivatives and their antimicrobial profile against two Gram-positive and two Gram-negative bacterium species.