Gold(I)-Catalyzed Formal Intramolecular Dehydro-Diels-Alder Reaction of Ynamide-ynes: Synthesis of Functionalized Benzo[b]carbazoles

A gold-catalyzed cycloisomerization of ynamide-ynes via a formal dehydro-Diels-Alder reaction has been developed, providing an attractive route to diversely substituted benzo[b]carbazoles. The reaction likely proceeds via regioselective attack of the pendant alkyne moiety to a keteniminium ion intermediate followed by benzannulation. The method offers several advantages such as high efficiency, mild reaction conditions, and wide functional group tolerance and serves as a highly useful complement to the thermal DDA reactions of ynamide-ynes.