2-{4-[(2S,4S,5S,9S)-9-(tert-Butyl-dimethyl-silanyloxy)-4-((E)-3-hydroxy-propenyl)-6,6,8-trimethyl-2-phenyl-1,3-dioxa-spiro[4.5]dec-7-en-7-yl]-2-methyl-3-oxo-butyl}-malonic acid dimethyl ester