A convenient method to obtain unknown chiral C2- and C3-functionalized aldono-1,4-lactone derivatives starting from l-ascorbic acid, which would be valuable in the synthesis of derivatives of various pharmacologically active agents for structure-activity studies, is described. The practicality of this approach is demonstrated by the synthesis of a series of 5,6-O-isopropylidene-2-allyl-3-keto-l-galactono-gamma-lactone and 5,6-O-isopropylidene-3-allyl-2-keto-l-galactono-gamma-lactone derivatives using the thermal Claisen rearrangement of the corresponding 3-O- and 2-O-allyl derivatives of 5,6-O-isopropylidene-l-ascorbic acid, respectively, followed by stereospecific reduction to the corresponding alcohols. The synthetic steps are shown to be efficient, and enantiospecific, and they proceed with high yields.