methyl (4S,4aS,4'R,7R,7aS)-4'-ethyl-1-methoxy-5'-oxooctahydro-1H,3'H-spiro[cyclopenta[c]pyran-7,2'-furan]-4-carboxylate                                                                                                                                                              在
                                                                                                                                                                                 
sodium hydroxide                                                                                                                                  作用下,
                                                                                                                                                                                                                            生成                                                 
(4aS,7R,4'R)-4'-ethyl-1c-methoxy-5'-oxo-(4ar,7ac)-octahydro-spiro[cyclopenta[c]pyran-7,2'-furan]-4t-carboxylic acid