Controlling Pd(IV) reductive-elimination pathways enables Pd(II)-catalyzed enantioselective C(sp(3))–H fluorination

The development of a Pd(II)-catalyzed enantioselective fluorination of C(sp(3))–H bonds would offer a new approach to making chiral organofluorines. However, such a strategy is particularly challenging because of the difficulty in differentiating prochiral C(sp(3))–H bonds through Pd(II)-insertion, as well as the sluggish reductive elimination involving Pd–F bonds. Here, we report the development of a Pd(II)-catalyzed enantioselective C(sp(3))–H fluorination using a chiral transient directing group strategy. In this work, a bulky, amino amide transient directing group was developed to control the stereochemistry of C–H insertion step and selectively promote C(sp(3))–F reductive elimination pathway from Pd(IV)–F intermediate. Stereochemical analysis revealed that while the desired C(sp(3))–F formation proceeds via an inner-sphere pathway with retention of configuration, the undesired C(sp(3))–O formation occurs through an S(N)2-type mechanism. The elucidation of the dual mechanism allows us to rationalize the profound ligand effect on controlling reductive elimination selectivity from high-valent Pd species.