Abstract A novel approach to Corey's aldehyde is described. A suitable substituted all cis 2, 3-dialkyl-l, 4-cyclopentanediol system is obtained by catalytic reduction of 2, 3-dialkyl-4- hydroxy-2-cyclopentenones. Epimerisation to the prostaglandin configuration occurs spontaneously when later on the Horner reaction is carried out.