(3S)-8α-Vinyl-3a,5aβ,7,8,9,10,10aα,10cβ-octahydro-3α-hydroxy-3aβ,8-dimethyl-4H-3,10bβ-ethano-1H,3H-benzo[h]furo[4,3,2-de]-2-benzopyran-4-one