Dihydro-3H-chromeno-[3,4-b][4,7]phenanthrolin-3-one and Chromeno[4,3-b]pyrano[3,2-f]quinolin-3(13H)-one Derivatives by Aza-Diels-Alder Reaction - Majumdar, K. C.; Ponra, Sudipta; Taher, Abu (Synthesis, 2011)