Synthesis of Benzannulated [6,6]-Spiroketals by a One-Pot Carbonylative Sonogashira Coupling/Double Annulation Reaction.

A one-pot Pd-catalyzed carbonylative Sonogashira coupling in tandem with double annulation reaction to synthesize benzannulated [6,6]-spiroketals from o-iodophenols and terminal alkynols or alkynyl phenols was achieved. The protocol provides straightforward and facile access to benzannulated [6,6]-spiroketals in moderate to good yields and excellent diastereoselectivities under balloon pressure of CO at room temperature.

Synthesis of 2-substituted 3-chlorobenzofurans via TMSCl-mediated nucleophilic annulation of isatin-derived propargylic alcohols.

A TMSCl-mediated cascade annulation of isatin-derived propargylic alcohols for the synthesis of 2-substituted 3-chlorobenzofurans is now reported. Mechanistic investigations showed that this proceeded through a sequential Meyer-Schuster rearrangement/nucleophilic addition/intramolecular annulation. TMSCl not only acts as a promoter, but also acts as a chlorine source in this protocol.