(2R,6S)-2-[2-Benzenesulfonyl-1-benzoyloxy-2-((1S,3S,3aS,4S,4aS,8aR,9aS)-1-methoxy-3-methyl-dodecahydro-naphtho[2,3-c]furan-4-yl)-ethyl]-6-methyl-piperidine-1-carboxylic acid tert-butyl ester