Palladium-Catalyzed Amide-Directed Enantioselective Carboboration of Unactivated Alkenes Using a Chiral Monodentate Oxazoline Ligand

A Pd-catalyzed
carboxamide-directed enantioselective 1,2-carboboration
reaction of unactivated alkenes with C–H nucleophiles
and B2Pin2 has been developed using a second
generation of chiral monodentate oxazoline (MOXca) ligand. The MOXca
ligand featuring a modular design of a N-linked carbazole side arm
can be readily synthesized from serine and NH-carbazoles and provided
further improved enantiocontrol of the AQ-directed nucleopalladation
over MOXin ligand. The use of KTFA additive and TFE solvent was critical
to obtain high reactivity in this difunctionalization reaction system.
Preliminary study showed that 1,2-aminoboration of 3-butenamide with imide N-nucleophiles and B2Pin2 under the same conditions proceeded in good yield and high enantioselectivity.