PREPARATION OF PROSTAGLANDIN F

PURPOSE:To obtain the titled compound useful as a labor pain promotor or intestinal hyperkinetic agent, etc. from an easily available raw material in high yield in short step, by reducing a 7-sulfonyloxyprostaglandin F. CONSTITUTION:A 7-sulfonyloxyprostaglandin F of formula I (B is -CH2-CH2, -CH=CH- or -CidenticalC-,; R is H, 1-10C alkyl, phenyl or cycloalkyl, etc.; R is 1-14C alkyl, phenyl, etc.; R and R are H, OH, etc.; R is unsubstituted 1- 8C alkyl, phenyl, etc.; R is H, methyl, ethynyl, etc.; the dotted line part is a single or double bond) is reduced with a reducing reaction agent, e.g. sodium boron hydride, in a solvent, e.g. hexamethylphosphoric triamide or dimethyl sulfoxide, at 0-150 deg.C, preferably 30-100 deg.C, to give the aimed substance of formula II.