Rhodium catalysed enantioselective hydroboration of alkenylboronic esters with catecholborane

Alkenylboronic esters such as (E)-2-(2-phenylethenyl)-1,3,2-dioxaborolane were subjected to catalytic hydroboration with catecholborane and with use of neutral and cationic rhodium complexes modified by various diphosphine ligands. The resulting 1,2-diboryl intermediate was oxidised with alkaline hydrogen peroxide to give the corresponding 1,2-diol with enantioselectivities up to 79 % e.e.