process for preparing prostanoic acid derivatives , in particular derivatives of 9 , 15 - dioxygenated prostanoic acid and prost - 13 - enoic acid , related additionally unsaturated derivatives , homologs thereof and intermediates therefor , in which a lower alkyl ester of 2 - cyclopent - 2 - en - 1 - one in which y is ch 2 ---- m wherein is ch 2 ch 2 , ch ═ ch or c . tbd . c and m is an integer from 2 - 4 is treated with nitromethane to yield 2 -- 3 - nitromethyl - cyclopentan - 1 - one and the latter compound or its corresponding 1 - hydroxy analog are converted to the corresponding aldehyde , 2 - cyclopentan - 1 - on - 3 - al or 1 - hydroxy - 2 - cyclopentan - 3 - al , respectively . treatment of the aldehyde with the ylid prepared from the appropriate wittig reagent , preferably a dimethyl 2 - oxoalkylphosphonate of the formula 2 pch 2 co n ch 3 in which n is an integer of from 1 - 6 and alk is an alkyl containing from 1 - 3 carbon atoms yields the corresponding derivatives of 2 -- 3 - cyclopentan - 1 - one or - 1 - o1 in which the oxygen functions may be selectively protected and transformed by conventional means , and in which the unsaturated bonds may be reduced to a single bond . the prostanoic acid derivatives possess prostaglandin like biological activities . methods for their use are also disclosed .