(1S,2R,4S,4aS,5S,6R,8aR)-2,4-Diacetoxy-1-acetoxymethyl-6-benzyloxy-5-benzyloxymethyl-4a-(2-trimethylsilanyl-ethoxymethoxymethyl)-decahydro-naphthalene-1-carboxylic acid methyl ester