ethyl (3'S,4R,4aS,7aR,12bS)-4a,9-dihydroxy-3-methyl-2,3,4,4a,5,6-hexahydro-1H-spiro[4,12-methano[1]benzofuro[3,2-e]isoquinoline-7,2'-oxirane]-3'-carboxylate