Chiral Phosphoric Acid Catalyzed Enantioselective [4 + 2] Cycloaddition Reaction of α-Fluorostyrenes with Imines.

An enantioselective [4 + 2] cycloaddition reaction of α-fluorostyrenes with N-benzoyl imines was demonstrated using a chiral phosphoric acid catalyst. Cycloaddition products having fluorine functionality were formed in high yields with excellent diastereo- and enantioselectivities. Further manipulation of the enantioenriched cycloaddition product with silyl enol ether in the presence of BiCl3 catalyst afforded substitution product with retention of the dihydro-4H-1,3-oxazine framework through selective carbon-fluorine bond cleavage without loss of enantiomeric excess.