5-O-Benzyl-2,3-O-isopropylidene-D-ribono-1,4-lactone is used as a reagent in the synthesis of erythrose, ribose and substituted pyrrolidine containing thiazolidinedione derivatives which exhibit antihyperglycemic activity. Also a useful synthetic intermediate in the synthesis of Cyclopentenylcytosine (C989800).