There are many treasures in Woodward and Hoffmann’s (WH) classic monograph. One such is acetolysis of  the endo chloride (green), which is much much faster than that of the exo isomer (red). The explanation given in their article (p 805) confines itself to succinctly stating that only loss of the endo halogen can be concerted with a required disrotatory ring opening of the cyclopropane.