rac-(3R,3aS,4S,5S,6aR,7R,7aS,8aR,9S,9aS)-3-(benzyloxy)-6a-hydroxy-4,5,7a,9-tetramethyldodecahydro-4,7-methanocyclopenta[4a,5]naphtho[2,3-b]oxiren-10-one