Formation of the 5-Benzonaphthopyran System during an Attempted Benzophenanthridine Synthesis

Article abstract of DOI:10.1021/jo01313a010

The condensation of the Schiff base 6 with the homophthalic anhydride 7 was used during elaboration of a compound, 9, suitable for closure of the B ring of the benzophenanthridine system.However, treatment of 9 with sodium hydride in THF resulted in formation of 3,4-dimethoxy-5-oxo-7-cyano-9,10-(methylenedioxy)-5-benzonaphtho<2,3-b>pyran (10) instead of the Dieckmann-Thorpe cyclization product 2.