Transition-Metal-Free Cascade Approach toward 2‑Alkoxy/2-Sulfenylpyridines and Dihydrofuro[2,3‑b]pyridines by Trapping In Situ Generated 1,4-Oxazepine

An efficient cascade reaction via trapping in situ generated active intermediate 1,4-oxazepine, formed from base-promoted 7-exo-dig cyclization reaction of N-propargyl enaminone, has been developed. Alcohols/thiols and aldehydes were used as trapping agents, providing 2-alkoxy/2-sulfenylpyridines and dihydrofuro­[2,3-b]­pyridines in moderate to high yields. This cascade reaction was completed within 30 min at room temperature, generating 1 equiv of H2O as the sole byproduct.