Aldehyde Activation by Binol-Derived Phosphoric Acids

Significance

An aza-ene-type reaction of glyoxylate 1 with various enecarbamates 2 catalyzed by binol-derived chiral phosphoric acids 3a or 3b is described. Whereas simple enecarbamates 2a and (E)-enecarbamates 2b furnished the products 4 in high yields along with high enantio- and dia­stereoselectivities, Z-isomers 2b gave rather poor results. DFT computational studies suggest the presence of a double hydrogen bond between the catalyst 3 and glyoxylate 1 (see scheme). On this basis the authors rationalized the experimental observation that bulky Ar groups lead to both decreased catalyst activity and enantioselectivity. However, an alternative mechanism involving bifunctional catalysis can also be envisaged (see scheme).