Palladium-Catalyzed Hydride Addition/C–H Bond Activation Cascade: Cycloisomerization of 1,6-Diynes

The use of ammonium halide salts as metal hydride precursors in a new Pd-catalyzed cycloisomerization of 1,6-diynes, which affords unexplored silylated 2-azafluorenes, is reported. This cascade process includes the addition of a Pd–hydride species to a π-system, intramolecular carbopalladation, and C­(sp²)–H bond activation. A variety of functional groups are tolerated, and the synthetic utility of the resulting products has been demonstrated by a series of derivatizations.