Synthesis of 1,2,3-triazolo[1,5-a]pyridine ester derivatives

Lithiation of 1,2,3-triazolo[1,5-a]pyridines 4b and 4c with lithium diisopropylamide (LDA) gave the corresponding lithio derivatives 5b and 5c from which esters 6b and 6c were obtained by treatment with carbon dioxide and then dimethyl sulfate. Lithio derivatives 5a-5c reacted with DMF giving aldehydes 7a-7c. Esters 9a-9c were prepared from aldehydes 7a-7c and carbomethoxymethylenetriphenylphosphorane.