(7R,9R)-7-[(2E,8E)-(1R,5S,6R,11S,12S)-12,16-Bis-(tert-butyl-dimethyl-silanyloxy)-1,3,5,9,11-pentamethyl-6-triethylsilanyloxy-hexadeca-2,8-dienyl]-9-methyl-6,10-dioxa-spiro[4.5]decane