Synthesis of furo[2,3-b]pyridin-4(7H)-ones and related quinolinone via Brّnsted acid-promoted cyclisation of alkynes

N-Alkyl-4-alkoxy-3-alkynylpyridin-2(1H)-ones readily undergo acid-promoted 5-endo-heteroannulation to furopyridinium intermediates that are dealkylated in situ to provide the corresponding furo[2,3-b]pyridin-4(7H)-ones. The same strategy applies to the formation of furo[2,3-b]quinolin-4(9H)-ones. In the case of Me3Si-substituted alkynes, hydration of the triple bond was observed.