2H,5H-4a,7-Ethano-2,4b-methanofuro[3',4':3,4]cyclopenta[1,2-b]pyran-5-one,7,7a,8,8a-tetrahydro-2,10-dimethyl-, [2S-(2a,4ab,4ba,7b,7aa,8aa,10R*)]-