(2S,6R,8S,11R)-2-((S)-2-Benzenesulfonyl-1-methyl-ethyl)-11-benzyloxy-4-methyl-8-((R)-2,2,4-trimethyl-[1,3]dioxolan-4-ylmethyl)-1,7-dioxa-spiro[5.5]undec-4-ene