The hydrolysis of exo-2-ethoxycarbonyl-7-oxabicyclo[2.2.1]hept-5-enes  1-3 by pig liver esterase is much faster than that of the endo isomers.  This allows an easy separation of an endo - exo mixture on a preparative  scale.
                                    猪肝
酯酶对外型-2-乙氧羰基-7-氧杂双环[2.2.1]庚-5-烯 1-3 的
水解速度比内型异构体快得多。  这样就可以在制备规模上轻松分离内-外异构体混合物。