Synthesis of Enantioenriched β-Aryl-β-aryloxy Esters via Sequential Photoisomerization and Enantioselective Hydrogenation.

A general method to prepare valuable chiral synthon β-aryl-β-aryloxy esters from enantioselective hydrogenation of (E)-β-aryl-β-aryloxy-α,β-unsaturated esters is described. The E-isomer was prepared via isomerization of the mixture of E- and Z-isomers using photocatalyst [Ir(ppy)2(dtbbpy)]PF6. A laser as the light source facilitated isomerization with only 0.05 mol % catalyst. The enantioselective hydrogenation was conducted with (NBD)2Rh(BF4) and a commercially available Josiphos ligand to provide the synthons in up to 95% yield with 97% ee.