The mechanism of nucleophilic addition to η3-allylpalladium complexes: the influence of ligands on rates and regiochemistry

A Versatile Synthesis of β‐Lactam‐Fused Oxacycles through the Palladium‐Catalyzed Chemo‐, Regio‐, and Diastereoselective Cyclization of Allenic Diols

“…In monosubstituted (h 3 -allyl)Pd complexes, the regioselectivity of the nucleophilic attack is known to be sensitive to many factors, such as steric and electronic influences from the substrate substituents, [32] regiochemical memory, [33] preferred configuration [34] and dynamic exchange in the (h 3 -allyl)Pd intermediate, [35] nucleophile, [36] and the nature of the ligands. [37][38][39] In contrast to reactions of (h 3 -allyl)Pd complexes with other nucleophiles, [40] and surpassing the regioselectivity for reactions of amines and phenols [41] or allylic fluorination, [42] a regioselective oxycyclization involving the substituted allylic carbon was obtained (Scheme 7).…”

Regioselectivity and memory effects in palladium catalyzed allylic alkylations with bidentate P^PS donor ligands

“…In the P^P complexes, there is greater donation and back donation in the shorter PdeP bond than in the longer PdeP bond. There will be less back donation to the h 2 bond than to the h 1 bond making the substituted terminal allyl position more electrophilic than the unsubstituted terminal allyl position [29]. Similarly, the symmetrically substituted 1,3-diphenyl allyl forms a distorted h 3 -allyl complex induced by heterodonor phosphinooxazoline ligands.…”

“…The nature of the P^P]S donor ligands is significantly different from that of the P^P donor ligands and can be considered to be responsible for the reversal of the normal selectivity. The rate of addition to the substituted terminus relative to the unsubstituted terminus of an allyl fragment is a balance between steric and electronic properties of the system [19,29,35,36]. In the case of the P^P]S donor ligands, the steric asymmetry primarily dictates the orientation of the substrate, while the electronic asymmetry directs nucleophilic attack.…”

“…Although a number of studies have been reported on the regioselectivity of allylic addition reactions based on bite angle [4] and donor effects [29] for palladium systems giving primarily linear product, high branched selectivity from palladium catalysts is far less common [10,11,30] and few studies have addressed this type of regioselectivity. Formation of branched products is potentially more important because a chiral center could be generated enantioselectively when addition occurs to the substituted terminus of an unsymmetrically substituted allyl fragment.…”

Reactivity control in palladium-catalyzed reactions: a personal account

“…He prepared an interesting novel heterobidentate ligand NOBIN (63) [40]; and others, such as MAP (64) [41], were in the blueprints (Scheme 15). In 1990, while I was in Sweden, I had an interesting discussion with Bjö rn Å kermark about a series of his papers, in which he demonstrated that the chemical shifts in the NMR spectra of h 3 -allylpalladium complexes 65 can be influenced by ligands L 1 and L 2 on Pd and that this ligand effect can be employed to control the regioselectivity of nucleophilic attack [42]. It occurred to me that, if a chiral, heterobidentate ligand were coordinated to palladium, an asymmetric induction could be attained through the combination of steric and electronic effects, which he accepted with cautious optimism.…”