Palladium-Catalyzed Synthesis of 6H-Dibenzo[c,h]chromenes and 5,6-Dihydrobenzo[c]phenanthridines: Application to the Synthesis of Dibenzo[c,h]chromene-6-ones, Benzo[c]phenanthridines, and Arnottin I

6H-Dibenzo[c,h]chromenes and 5,6-dihydrobenzo[c]phenanthridines have been synthesized via Palladium (II)-catalyzed domino reactions of acetylenic substrates involving intramolecular trans-oxo/amino palladation onto the triple bond followed by nucleophilic addition of the intermediate to a tethered cyano/aldehyde. The scope of this reaction was extended through one step conversion of some of the products to 6H-dibenzo[c,h]chromen-6-ones and benzo[c]phenanthridines. Utilization of this methodology led to a formal total synthesis of the natural product Arnottin I.