The ring opening reactions of trans-2,2-dichloro-1'-methyl-spiro〔cyclopropane-1,9'-fluorene〕 derivatives 〔1〕 with silver ion in alcohols and with n-Bu_3SnH in xylene gave (Z)-9-(1-chloro ethenyl)-9-methoxy-1-methylflouorene derivatives 〔6〕 and (Z)-9-(1-chloroethenyl)-1-methyl-fluorene derivatives 〔11〕, respectively. The thermal decomposition of 〔1〕 in HCB gave (Z)-9-chloro-9-(1-chloroethenyl)-1-methylflurene derivatives 〔9〕. In any cases, 9-alkylidenefluorene dervatives (such as 〔7〕 and 〔10〕)did not obtained. That is, it turned out that 1-methyl group in flurene ring controlled the direction led the products (〔6〕, 〔9〕 and 〔11〕) from the allyl cation 〔8〕, ring opening intermediate, by its steric evidence.