Synthesis of Pyrano[3,2‐b]indole Derivatives Based on Intramolecular Hetero‐DielsAlder of 2‐Benzylidene‐2,3‐dihydro‐1H‐indol‐3‐ones

Pyrano[3,2‐b]indole derivatives 2–6 were synthesized in good yields from 1‐acetyl‐2‐benzylidene‐2,3‐dihydro‐1H‐indol‐3‐ones 8 and 13–15 by an intramolecular hetero‐DielsAlder reaction. The structures of compounds 2a, 3a, 4, 5, and 6 were unambiguously established by X‐ray analysis. Compounds 4 and 5 were further aromatized to the corresponding derivatives 16 and 17, respectively.