(2R,4aR,6S,8R,8aR)-8-(benzyloxy)-6-((1S,3S)-1-(benzyloxy)-3-((2S,6R,11S)-11-methyl-1,7-dioxaspiro[5.5]undecan-2-yl)butyl)-2-(but-3-en-1-yl)-2-methoxy-7-methyleneoctahydropyrano[3,2-b]pyran