PREPARATION OF CHIRAL BUILDING-BLOCKS FOR A HIGHLY CONVERGENT VITAMIN-E SYNTHESIS - SYSTEMATIC INVESTIGATIONS ON THE ENANTIOSELECTIVITY OF THE SHARPLESS BISHYDROXYLATION

The enantioselective bishydroxylation of protected 2-methylprop-2-enol 15 and 3-methylbut-3-en-1-ol 16 to give the corresponding diols 18 an d 19, respectively, which can be transformed into building blocks for the synthesis of natural vitamin E, is described. It is shown that the enantioselectivity of the bishydroxylation reaction clearly depends o n the type of protecting group and its distance from the alkene moiety , with 96% ee for 16a and 16f as the best and 8% ee for 15d as the low est result.