217. α-Santonin, (3S,5aR,9bS)-3,5a,9-trimethyl-3a,5,5a,9b-tetrahydronafto[1,2-b]furan-2,8(3H,4H)-dion^●; (3S,5aR,9bS)-3,3a,4,5a,9b-hexahydro-3,5a,9-trimethyl naphto (1,2-b) furan-2,8-dione°