Base-mediated [3 + 2]-cycloannulation strategy for the synthesis of pyrazolo[1,5-a]pyridine derivatives using (E)-β-iodovinyl sulfones

A unique cycloannulation of ( E )-β-iodovinyl sulfones with 1-aminopyridinium iodide/ N -tosylpyridinium imide followed by detosylation is realized to access 2-substituted-pyrazolo[1,5- a ]pyridines and their 3-sulfonyl analogues in good to high yields.