The mechanism of enantioselective palladium(0)-catalyzed allylic alkylation with chiral oxazolinylpyridines: a DFT study

The density functional computations of the asymmetric allylic alkylation of (±)tans-1,3-dimethylallyl formate, 2, with malonaldehyde catalyzed by chiral Pd-oxazolinylpyridine are performed. All the structures are optimised completely at the B3LYP/LANL2DZ+P level. As illustrated, this allylic alkylation is endothermic and goes mainly through association of Pd-oxazolinylpyridine with trans-1,3-dimethylallyl formate, oxidative addition of HCOO− in 2 to Pd, nucleophilic addition of malonaldehyde anion to the π-allyl cation complex, and dissociation of the Pd-oxazolinylpyridine-product complex to generate the product with regeneration of the catalyst. The turnover-limiting step for this reaction is the nucleophilic addition of malonaldehyde anion. The main substitution product predicted theoretically is (S)-trans-1,3-dimethylallyl malonaldehyde. The transition states for the oxidative addition and the nucleophilic addition involve a twisted papilionaceous Pd-C-C-C four-membered ring.