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 4π-electron donors and cyclopentadienes
as 2π-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 18O-labeling experiments to confirm that both water and O2 participate in the reactions; these data support a mechanism involving
nitrosoarenes as nucleophiles and gold-π-dienes as electrophiles.