Chiral 4-(Diphenylphosphanyl)-1-(dialkylamino)butane Ligands – Synthesis, Applications in Asymmetric Alkylation and Theoretical Study

Various 4-(diphenylphosphanyl)-1-(dialkylamino)butane ligands were prepared from commercial (2S,3S)-2,3-O-isopropylidene-D-threitol. These ligands, associated with Pd2(dba)3, gave enantioselectivities of up to 75% in the alkylation of racemic 1,3-diphenylprop-2-enyl acetate with dimethyl malonate anion. A theoretical study shows the important role played by two factors in the alkylation reaction: steric control, leading to the formation of a unique diastereoisomer of the π-allylpalladium complex, and orbital control, which orients the attack of the nucleophile trans to the phosphorus atom.