The Lewis acid-promoted reactions of 2,2-dialkoxycyclopropanecarboxylic esters 4a-c with aldehydes and unsymmetrical ketones to give gamma-lactones were investigated. TiBr, is an excellent catalyst and gives cis 3,4-substituted gamma-lactones in good yields with high diastereoselectivity. SnBr4 promotes the reaction of 4a-c with aldehydes with high cis-selectivity, but does not promote the reaction of 4a with unsymmetrical ketones. ZrCl4 is moderately trans-selective in the reaction of 4a with aldehydes, while being moderately cis-selective in the reaction of 4a with unsymmetrical ketones. Cis-gamma-lactones can be converted into their trans-isomers by treatment with NaOEt in EtOH.