Ligand Bite Governs Enantioselectivity: Electronic and Steric Control in Pd‐Catalyzed Allylic Alkylations by Modular Fenchyl Phosphinites (FENOPs)

Modular fenchyl phosphinites (FENOPs) containing different aryl units—phenyl ( 1 ), 2‐anisyl ( 2 ), or 2‐pyridyl ( 3 )—are efficiently accessible from (−)‐fenchone. For comparison of the influence of the different aryl units on enantioselectivities and reactivities, these FENOPs were employed in Pd‐catalyzed allylic alkylations. The strongly chelating character of P,N‐bidentate 3 is apparent from X‐ray structures with PdCl 2 ([Pd( 3 )Cl 2 ]), and with allyl–Pd units in ([Pd( 3 )(η 1 ‐allyl)] and [Pd( 3 )(η 3 ‐allyl)]). FENOP3 gives rise to a PdL* catalyst of moderate enantioselectivity (42 % ee , R product). Surprisingly, higher enantioselectivities are found for the hemilabile, monodentate FENOPs 1 (83 % ee , S enantiomer) and 2 (69 % ee , S enantiomer). Only small amounts of 1 or 2 generate selective PdL* catalysts, while complete abolition of enantioselectivity appears with unselective PdL* 2 species with higher FENOP concentrations in the cases of 1 or 2 . Computational transition structure analyses reveal steric and electronic origins of enantioselectivities. The nucleophile is electronically guided trans to phosphorus. endo ‐Allyl arrangements are favored over exo ‐allyl orientations for 1 and 2 due to Pd–π–pyridyl interactions with short “side‐on” Pd‐aryl interactions. More remote “edge‐on” Pd–π–aryl interactions in 3 with Pd‐N(lp) coordination favor endo ‐allyl units slightly more and explain the switch of enantioselectivity from 1 ( S ) and 2 ( S ) to 3 ( R ).