the alkylation of the enolate generated from a cyclopentane-1,2-dicarboxylic acid monoester is described. The alkylation of the Li enolate with an alkylating reagent having a hard leaving group such as Cl gave a contrasteric alkylation (alkylationfrom the more hindered side of the enolate) product, predominantly. An important factor effecting contrasteric alkylation was found to be complexation of