Abstract: Fused cyclopentane—4-substituted 3,5-dioxalane lactone compounds useful as an intermediate in the synthesis of prostaglandin analogs are provided. The compounds have the formula A: wherein R represents an aryl group such as p-methoxyphenyl. This compound can be reacted with a lower alkyl aluminum compound to open the dioxalane ring and reduce the lactone to lactol, without over-reducing to diol. The resulting compound can be functionalized to insert chemical side groups of target prostaglandins, adding the required ?-side chain and then the required ?-side chain sequentially and independently of each other. The compounds and process are particularly suitable for preparing lubiprostone.