Pyridine N-oxides were converted to tetrazolo[1,5-a]pyridines in good to excellent yield by heating in the presence sulfonyl or phosphoryl azides and pyridine in the absence of solvent. Various sulfonyl and phosphoryl azides were screened for reactivity under a standard set of conditions. Diphenyl phosphorazidate was the most convenient reagent and gave high yields. Reaction optimization, scope, and scalability are discussed.
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John M. Keith (2006) studied this question.