Selectivity, Compatibility, Downstream Functionalization, and Silver Effect in the Gold and Palladium Dual-Catalytic Synthesis of Lactones.

The chemo- and regioselectivity and functional group compatibility in gold and palladium cooperatively catalyzed cross-coupling reactions were determined in the synthesis of lactones; the selectivity in the gold and palladium dual-metal catalysis system was distinct from that available for the same class of substrates in systems with only gold catalysis or only palladium catalysis rather than dual catalysis. The dual-catalytic rearrangement reaction selectively promoted oxidative addition at the C-O bond over the C-Br bond, providing a useful C-Br bond handle for downstream functionalization showcased via Suzuki-Miyaura and Sonogashira coupling reactions. Product classes were expanded from isocoumarins to three previously unpublished ring classes: pyrone, indolepyrone, and furopyrone.