2,2-Dimethyl-propionic acid (2R,3R)-3-{(4S,5S)-5-[(E)-(S)-4,5-bis-(tert-butyl-dimethyl-silanyloxy)-3-methylene-pent-1-enyl]-2-methoxy-[1,3]dioxolan-4-yl}-3-(tert-butyl-dimethyl-silanyloxy)-2-methyl-propyl ester