Deconvoluting the memory effect in Pd-catalyzed allylic alkylation: Effect of leaving group and added chloride.

An analysis of product distributions in the Tsuji-Trost reaction indicates that several instances of reported "memory effects" can be attributed to slow interconversion of the initially formed syn- and anti-[Pd(eta3-allyl)] complexes. Addition of chloride triggers a true memory effect, in which the allylic terminus originally bearing the leaving group has a higher reactivity. The latter effect, termed regioretention, can be rationalized by ionization from a palladium complex bearing a chloride ion, forming an unsymmetrically substituted [Pd(eta3-allyl)] complex. DFT calculations verify that the position trans to the phosphine ligand is more reactive both in the initial ionization and in the subsequent nucleophilic attack.