Reaction of 3H-Pyrano[3,4-b]indol-3-ones and 3H-2-Benzopyran-3-ones with Heterodienophiles: A Two Step Synthesis for Some 9H-Pyrido[3,4-b]indoles and Isoquinolines - Van Broeck, P; Van Doren, P; Hoornaert, G (Synthesis, 1992)