Abstract A highly regio‐ and stereoselective hetero Diels–Alder cycloaddition of indene with N‐sulfonyl‐1‐aza‐1,3‐butadiene was achieved. Subsequent transformation of the 5H‐indeno [l,2‐b]pyridine via elimination and reduction provides a new route to azafluorenone (e.g., 1‐methyl‐4‐azafluorene) for the synthesis of onychnine.