Formation of 8-Hydroxyphenanthridines by Microwave-Mediated IMDAF Reactions; Synthesis Directed towards Lycorine Alkaloids

8-Hydroxyphenathridines have been synthesized efficiently from N-propargyl-ortho-furylanilines employing microwave-mediated one-pot intramolecular Diels-Alder reaction on furans (IMDAF) reaction and subsequent aromatization. The 8-hydroxyphenathridines were also subjected to further functionalization; O-alkylation and conversion to the corresponding triflate followed by Suzuki coupling. N-Propargyl-7-furylindole and the corresponding indoline also underwent smooth IMDAF cyclization to give, after rearomatization, 7H-pyrrolo[3,2,1-de]phenanthridin-9-ol or the 4,5-dihydro analog. These cyclization products could be further functionalized, i.e. O- or N-alkylation and oxidation at C-6. The oxidation could lead to 6-oxo derivatives or pyrrolo[3,2,1-de]phenanthridin-6-ium salts depending on the reaction conditions and structure of the substrate. The 9-oxy-pyrrolophenanthridines synthesized are structurally closely related to bioactive lycorine alkaloids.