Improved cyclization conditions to prepare 6-substituted pyrazolo[1,5- a ]pyridines and pyrazolo[1,5- a ]pyrazines using catalytic Ag(I) and Au(III) salts

An efficient synthesis of 6-substituted-pyrazolo[1,5-a]pyridines via an intramolecular cyclization of 1-amino-2-triethyl-silanylethynyl-pyridinium salts has been developed. The cyclization reaction proceeds in the presence of catalytic silver(I) and gold(III) salts to give 2-silyl pyrazolo[1,5-a]pyridines; while the use of stoichiometric silver(I) fluoride predominantly gives the des-silyl heterocycles.