ASYMMETRIC ALLYLIC ALKYLATION CATALYZED BY PALLADIUM-SPARTEINE COMPLEXES

The cationic complex [Pd(eta-3-C3H5)(sparteine)]PF6 (6) was found to be a suitable catalyst precursor for the asymmetric alkylation of allylic acetates with Na[CH(COOMe)2] as the nucleophile. This constitutes one of the first and still rare examples of a phosphine-free system for this type of Pd-catalyzed reaction. Using 5 mol % of 6, alkylation products were obtained in up to 90 % isolated yield and 85 % enantiomeric excess. The alkylation reaction was shown to occur with overall retention of configuration, indicating an analogous mechanism to the one previously proposed for phosphine-containing catalysts. The reactivity of allylic acetates is strongly dependent upon the nature of the substituents, open-chain aliphatic substrates being unreactive.