Gold(I)-Catalyzed Highly Enantioselective [4+2]-Annulations of Cyclopentadienes with Nitrosoarenes via Nitroso-Povarov versus Oxidative Nitroso-Povarov Reactions

This work reports gold-catalyzed highly enantioselective nitroso-Povarov reactions between cyclopentadienes and nitrosoarenes in cold dichloroethane, in which nitrosoarenes serve as 4 pi-electron donors and cyclopentadienes as 2 pi-donors. High enantioselectivity has been achieved for substrates over a wide scope. With the same chiral catalyst, nitroso-4-fluorobenzenes in these reactions under DCM/THF/water/air led to oxidative nitroso-Povarov reactions also with high enantioselectivity. We performed O-18-labeling experiments to confirm that both water and O-2 participate in the reactions; these data support a mechanism involving nitrosoarenes as nucleophiles and gold-pi-dienes as electrophiles.