(3a
R,9a
S,10
S)-10-bromo-5b-methyl-3-oxo-(3a
r,5a
t,5b
c,8a
c)-octahydro-1
t,8
t-methano-pentaleno[1,2-
c;3a,4-
c']difuran-8
c-carboxylic acid                                                                                                                                                              在
                                                                                                                                                                                 
potassium carbonate                                                                                                                                  作用下,
                                                                                                                                                                                                                            生成                                                 
(3aS)-3a-methyl-8-oxo-(3ar,3bt,7ac)-octahydro-1t,6at-ethano-pentaleno[1,2-c]furan-1c,6t-dicarboxylic acid