Synthesis of pyrano[3,2- c ]quinolones and furo[3,2- c ]quinolones via acid-catalyzed tandem reaction of 4-hydroxy-1-methylquinolin-2(1 H )-one and propargylic alcohols.

Two acid-catalyzed tandem reactions between 4-hydroxy-1-methylquinolin-2(1 H )-one and propargylic alcohols are described. Depending mainly on the propargylic alcohol used, these tandem reactions proceed via either a Friedel-Crafts-type allenylation followed by 6- endo -dig cyclization sequence to form pyrano[3,2- c ]quinolones or a Friedel-Crafts-type alkylation and 5- exo -dig ring closure sequence to afford furo[3,2- c ]quinolones in moderate-to-high yields. The pyrano[3,2- c ]quinolones products could be further transformed to tetracyclic 4,9-dihydro-5 H -cyclopenta[ lmn ]phenanthridin-5-one derivatives.