Pd-catalysed methoxycarbonylation of vinylarenes using chiral monodentate phosphetanes and phospholane as ligands. Effect of substrate substituents on enantioselectivity.

Palladium complexes bearing phospholane 1 and phosphetane 2-4 ligands have been synthesised to be used as catalyst precursors in the asymmetric methoxycarbonylation of vinyl arenes. Single crystals of the complex [PdCl2(2)2] II were obtained from a toluene solution and analysed by X-ray crystallography. Using these complexes, excellent regioselectivity (up to 99%) to the branched esters was obtained. Phosphetane ligands provide higher enantioselectivity than the phospholane under the same reaction conditions and an important influence of the substrate was observed. Enantioselectivity up to 50% was obtained using 4-methoxystyrene.