A synergic catalytic method for asymmetric construction of N-bridged [3.2.1] rings by a phosphonium salt/silver co-catalyzed cyclization has been developed. This route affords fluorine-installed tropane derivatives in excellent stereoselectivities. The mechanistic results revealed that the silver nitrite was installed on the phosphonium salt via hydrogen bonding and simultaneously activated the dipole, in a “sandwich” reaction model.
We present an unprecedented synergic catalytic route for the asymmetric construction of fluorinated N-bridged [3.2.1] cyclic members of tropane family via a bifunctional phosphonium salt/silver co-catalyzed cyclization process. A broad variety of substrates bearing an assortment of functional groups are compatible with this method, providing targeted compounds bearing seven-membered ring and four contiguous stereocenters in high yields with excellent stereoselectivities. The gram-scale preparations, facile elaborations and preliminary biological activities of the products demonstrate the application potential. Moreover, both experimental and computational mechanistic studies revealed that the cyclization proceeded via a “sandwich” reaction model with multiple weak-bond cooperative activations. Insights gained from our studies are expected to advance general efforts towards the catalytic synthesis of challenging chiral heterocyclic molecules.Zum Volltext