Abstract: A process for the preparation of optically active or racemic lactone diol derivatives of the formula ##STR1## (for use as intermediates in the Corey prostaglandin synthesis). Optically active or racemic lactone diol derivatives are inclosed, in whichR.sup.3 and R.sup.4 are the same or different and stand for a hydrogen, or a lower alkanoyl optionally substituted with one, two or three halogen atoms, or form together a ##STR2## group, in which R.sup.5 and R.sup.6 are the same or different and stand for a hydrogen, alkyl or aryl, with a process for preparing them.According to the invention the above compound are prepared by reacting optically active or racemic lactone of the formula II with formaldehyde or with a formaldehyde polymerisate, in the presence of the mixture of a strong acid and water or of a lower alkane carboxylic acid optionally substituted with one, two or three halogen atoms, and then optionally subjecting the obtained compound of the general formula I, in which R.sup.3 and/or R.sup.

Abstract: A compound of the formula is disclosed. ##STR1## wherein R.sup.3 and R.sup.4 are the same or different and are each hydrogen, lower alkanoyl, lower alkanoyl substituted by 1, 2, or 3 halogen atoms, or R.sup.3 and R.sup.4 together form an ##STR2## group in which R.sup.5 and R.sup.6 are the same or different and are each hydrogen, alkyl or aryl as well as a process for the preparation thereof.