A Mild And Efficient Synthesis Of Pyrazolo[1,5-a]Pyridines Induced By Pph₃/I₂

Nitrogen-containing heterocycle has always been an important research content in the field of pharmaceutical chemistry.Pyrazole and pyridine are two common nitrogen-containing heterocycle,which are widely used.Pyrazolopyridine compounds have attracted more and more attention due to their excellent pharmacological activities,which have become a hot spot in the field of medicine and agriculture.According to the different ring formation types of pyrazole and pyridine,the compound has three isomers,among which pyrazolo[1,5-a]pyridines are most widely used due to their outstanding inhibitory pharmacological activity.In this study,a method was developed for synthesis of diaryl substituted pyrazolo[1,5-a]pyridines from oxime induced by triphenylphosphine and iodine with imidazole as the base and tetrahydrofuran as the solvent.The experimental contents of condition optimization,substrate expansion and mechanism conjecture were carried out for this method,and the disadvantages of difficult synthesis of unstable substrates,single structure of target products and harsh reaction conditions were avoided at the same time.This method can be carrried under 30 ? within 40 minutes to complete the synthesis of target products with mild and efficient conditions,no metal catalyst involved,high yields,avoiding the separation and purification of high-energy intermediates.In this paper,a new synthesis method of pyrazolo[1,5-a]pyridines is reported,which avoids many disadvantages of the existing work.It possesses good innovation and makes supplement to the synthesis research of the thickened heterocyclic products,further promoting its synthesis research and application development.