(3R,4S,5S) methyl 2-acetoxy-4,5-isopropylidenedioxy-5-methyl-3-<(prop-2-ynyl)oxy> cyclohex-1-ene-1-carboxylate 生成 (3E,3aS,4RS,6S,7S,7aR)-methyl-3a-acetoxy-6,7-isopropylidenedioxy-6-methyl-3-[(tributylstannyl)methylidene]octahydrobenzofuran-4-carboxylate