Unsaturated compounds of the cyclopentanophenanthrene series are prepared by reacting 3-oxo compounds of this series saturated in at least one of the a -positions relatively to the 3-oxo group with periodic acid, iodic acid, iodine pentoxide or compounds capable of supplying these compounds during the reaction, e.g. iodine oxides of the formula I2O4 and I4O9 and the salts of inorganic and organic acids in which iodine occurs as trivalent cation such as compounds of the formula IPO4, I(IO3)3, I(NO3)3 and I(CH3COO)3. Thus 1-dehydrocortisone, 1-dehydrocortisol, 1-dehydroaldosterone and their 2-alkyl and/or 9- and 12-halogen derivatives may be prepared by this process. The periodic acid, iodic acid, and iodine pentoxide may be used in the form of a salt thereof in which case a strongly dissociated acid such as a mineral acid should be present in the reaction mixture. The process may be carried out in an aqueous or non-aqueous polar organic solvent or in a mixture of a polar and a non-polar organic solvent. Preferably the reaction is carried out in the presence of an aliphatic carboxylic acid such as acetic or propionic acid, of a tertiary alcohol such as t-butanol or t-amyl alcohol, or of an N,N1-dialkylacylamide such as dimethyl formamide. The reaction may also be carried out in dioxane, glacial acetic acid, acetic acid anhydride, methanol, isopropanol, tetrahydrofuran, carbon tetrachloride, pyridine, ethyl acetate, acetonitrile and mixtures thereof, and mixtures of these solvents with the above tertiary alcohols. The above process enables D 4-3-oxo compounds to be prepared from 5b -3-ketones saturated in ring A, D 1-5a -3-oxo compounds to be prepared from 5a -3-ketones saturated in ring A, and D 1,4-3-oxo compounds to be prepared from both the 5a - and 5b -compounds previously referred to and from the D 4- and D 1 - 3 - oxo - steroids. By-products formed in the process are the 2-iodo- and 4-iodo-compounds respectively of 3-oxo-5a - and 3-oxo-5b -steroids which may be treated with hydrazine or a derivative thereof such as phenylhydrazine, 2,4-nitrophenylhydrazine and semicarbazide, and the product then converted into the corresponding D 1- or D 4-3-oxo-steroids by acid hydrolysis or by an exchange reaction with a ketone such as pyruvic acid, or with an aldehyde such as benzaldehyde, hydroxybenzaldehyde and carboxybenzaldehyde. The reactants used in the above process may have any steric configuration and may also occur as racemates, e.g. 3-ketones of compounds of the cholestane, spirostane, furostane, cholane, norcholane, bisnorcholane, pregnane and androstane series. If the reactant contains several oxo groups, it may be necessary to temporarily block an oxo group inducing the introduction of a non-desired double bond. In addition, if use is made of periodic acid it may be necessary in the case of a -diol or a -ketol reactants to protect at least one of the two groups, e.g. an hydroxyl group may be protected by esterification and an oxo group by ketalization. The reactants may have functionally converted hydroxy groups, e.g. by esterification with an acid such as an aliphatic, aromatic or heterocyclic carboxylic acid-particularly acetic, trimethylacetic, benzoic or furan carboxylic acid, by etherification to form groups such as tetrahydropyranyloxy, benzyloxy or triphenylmethoxy groups, or by functionally converted oxo groups such as ketal groups-particularly those derived from bivalent alcohols as exemplified by the ethylene dioxy group. The products may be converted partially or completely into their functional derivatives, e.g. into esters, ethers, enolesters, enolethers, ketals, thioethers, thioketals, oximes, hydrazones or enamines. In the examples the following compounds are prepared: 1-dehydrocortisone acetate, 1-dehydrocortisol acetate, D 1-4-3,17-dioxo-androstadiene, D 4- and D 1-3,17-dioxo-androstene, D 1,4,6- 3,17 - dioxo - androstatriene, D 1,4,6 - 11b ,17a ,21 - trihydroxy - 3,20 - dioxopregnatriene 21-acetate, 9a -fluoro-1-dehydrocortisol acetate, cortisone 21-acetate, cortisol 21-acetate, and D 1,4,6 - 17a ,21 - dihydroxy - 3,11,20 - tri-oxo-pregnatriene 21-acetate. By a similar manner there may be prepared D 1,4,6-17a ,21-dihydroxy - 9a - halo - 3,11,20 - trioxo - pregnatrienes, and D 1,4,6 - 11b ,17a ,21 - trihydroxy - 9a -halo-3,20-dioxo-pregnatrienes.