Compounds of the cyclopentanopolyhydrophenanthrene series having attached to the ring - C oxygen or a group containing oxygen, are prepared by treating a compound of this series which contains a nuclear double linkage at the 11-position with an agent known to be suitable for the formation of a free esterified or dehydrated glycol. The compounds so prepared may then, if desired, be treated with an oxidizing or reducing agent or with an agent which causes the isomerization of an oxide grouping into the keto form. Oxidizing agents mentioned for the attack of the nuclear double link include peroxides such as hydrogen peroxide, per acids, metal oxides, such as osmium tetroxide or vanadic acids, if desired in the presence of chlorates, also permanganates, lead tetra-acylates, aryliodoso-acylates, or a halogen-silver benzoate complex. In addition, hypohalous acids or salts, ethers or esters thereof, or substances such as bromacetamide or toluene sulpho-chloramine which yield hypohalous acids in the presence of water. Halogen hydrins formed as intermediate products can be converted into oxides by basic agents, particularly aluminium oxide. The halogen may be removed by reducing agents such as zinc dust and glacial acetic acid. Oxide groups introduced by the process of the invention may be split up by reducing agents of which a number are mentioned, or may be converted directly into keto groups, by such agents as dilute aqueous or alcoholic acids or alkalies, or zinc chloride or concentrated acids. The compounds so obtained may then be submitted to the known processes of esterification, etherification, saponification, halogenation, oxidation or reduction. The parent materials may be prepared as described in Specifications 560,811 and 560,812. Compounds mentioned as starting materials include D 11, 12-3-oxy-cholenic acid, D 11, 12-3-keto-cholenic acid, D 11, 12-3 : 7 - dioxycholenic acid, D 5, 6 ; 11, 12 - 3 - oxy - choladienic acid, D 5, 6 ; 11, 12 - 3 - keto-choladienic acid, D 11, 12-pregnene - 3 : 20 - dione, D 4, 5 ; 11, 12 - pregnadiene - 3 : 20 - dione, D 11, 12 - etiocholene-3 : 17-dione, D 4, 5 ; 11, 12-etiocholadiene-3 : 17-dione, and the lower homologues of these acids such as D 11, 12-3-oxy-, or D 11, 12-3-keto-etiocholenic acid, -nor-cholenic acid, or -bisnorcholenic acid. In examples: (1) D 11, 12-cholenic acid methyl ester is treated with bromacetamide in butyl alcohol and the product oxidized with chromic acid to give 11-keto-cholanic acid methyl ester; (2) D 11, 12-cholenic acid methyl ester is saponified and then treated with hypobromous acid, esterified with diazomethane and oxidized with chromic acid to give 11-keto-cholanic acid methyl ester; (3) D 11, 12-cholenic acid methyl ester is treated with sodium para toluenesulphochloramine oxidized with chromic acid to give 11-keto cholanic acid methyl ester. This is catalytically reduced to the 11-oxy-compound; (4) D 11, 12-3-keto cholenic acid methyl ester is treated with N-bromacetamide and oxidized with chromium oxide, the halogen removed by zinc dust and acetic acid to give 3 : 11-diketocholanic acid methyl ester together with D 9 : 11-3 : 12-diketocholenic acid methyl ester which are separated by chromatographic analysis; (5) D 11, 12-3-acetoxy-cholenic acid methyl ester is treated with N-bromacetamide and then with chromic oxide, the halogen removed with zinc dust and acetic acid to give a mixture of 3-acetoxy-11-keto-cholanic acid methyl ester and D 9, 11-3-acetoxy-12-keto cholenic acid methyl ester which are separated by chromatographic analysis. The first of these on hydrogenation gives the corresponding 11-oxy-compound, and on saponification gives 3-oxy-11-keto-cholenic acid. This compound on esterification with diazomethane followed by oxidation gives 3 : 11-diketo cholanic acid methyl ester. This compound may also be directly obtained by using for the N-bromacetamide-oxidation treatment the free 3-oxy compound instead of the acetylated compound. Reduction of the 3 : 11-diketocholanic acid methyl ester with hydrogen in the presence of platinum oxide gives 3-oxy-11-keto-cholanic acid methyl ester, which on acetylation of the 3-oxy-group and further reduction is converted into 3-acetoxy-11-oxy-cholanic acid methyl ester; (6) D 11, 12-3-keto etio-cholanic acid methyl ester is treated with N-bromacetamide to produce the 11 : 12-halo-hydrin which is then oxidized to the 11-keto-compound. Removal of the halogen is effected by zinc dust and water to give 3 : 11-diketo-etiocholanic acid methyl ester. After the debromination and crystallination of the 3 : 11-diketo-compound, the mother liquors yield more of this compound together with D 9; 11 - 3 : 12 - diketo etiocholanic acid methyl ester. Bromination of 3 : 11-diketo etiocholanic acid methyl ester gives the corresponding 4-bromo-compound which on boiling with pyridine produces D 4, 5-3 : 11-diketo-etiocholanic acid methyl ester. Hydrogenation of 3 : 11-diketo etiocholanic acid methyl ester in the presence of platinum oxide and glacial acetic acid gives the 3-oxy-11-keto-etiocholanic acid methyl ester which on acetylation gives the 3-acetoxy derivative, and on saponification gives the free 3-oxy-11-keto-etiocholanic acid; (7) D 11, 12-3-acetoxy-etiocholanic acid methyl ester is treated with bromacetamide and the bromhydrin oxidized with chromic acid to the keto-bromide and the halogen removed to give 3-acetoxy-11-keto etiocholanic acid methylester. This, on careful saponification with dilute alcoholic acid, gives 3-oxy-11-keto-etiocholanic acid methyl ester which is oxidized to the 3 : 11-diketo compound; (8) D 11, 12-cholenic acid methyl ester is converted with perbenzoic acid into 11 : 12-oxide-cholanic acid methyl ester which may be split up by reduction or isomerised directly to ketones; (9) D 11, 12-3-keto-cholenic acid is oxidized with alkaline potassium permanganate and esterified with diazomethane to give 3-keto 11 : 12-dioxy-cholanic acid methyl ester; (10) D 11, 12-cholenic acid methyl ester is treated with osmium tetroxide followed by alkaline sodium sulphite, esterified with diazomethane to give 11 : 12-dioxy cholanic acid methyl ester. Hydrolysis with alcoholic potash gives the free acid, and esterification with acetic anhydride gives 11 : 12-diacetoxy-cholanic acid methyl ester; (11) D 11, 12-cholenic acid methyl ester is treated with bromacetamide and purified by chromatography. A dibromide is first isolated and then an a -oxide, which on reduction with a Raney catalyst gives 11-oxy-cholanic acid methyl ester; (12) D 11, 12-3-keto cholenic acid methyl ester is treated with bromacetamide and chromatographed. There is thus isolated, 3-keto 11-12-dibromo-cholanic acid methyl ester, 11-12-a -oxido-3-keto cholanic acid methyl ester, and D 9, 11-3 : 12-diketo cholanic acid methyl ester. The oxide after reduction and acetylation gives 3-acetoxy cholanic acid methyl ester; (13) D 11, 12-pregnene 3 : 20-dione is treated with N-bromacetamide to give the corresponding 11 : 12-oxybromide, which on oxidation with chromic oxide gives 12-bromo-pregnane - 3 : 11 : 20 - trione. Treatment with zinc dust removes the bromine and forms pregnane 3 : 11 : 20-trione. If the mother liquors from the N-bromacetamide treatment are oxidized and debrominated, there is obtained in addition to a further quantity of the trione, a small amount of D 9, 11-pregnane-3 : 12 : 20-trione. Bromination of pregnane-3 : 11 : 20-trione gives 4-bromo-pregnane-3 : 11 : 20-trione. Treatment of this compound with pyridine produces 11-keto progesterone which is identical with that from corticosterone; (14) D 11-21-acetoxypregnane-3 : 20-dione is prepared by treating D 11-3-oxy-etiocholenic acid methyl ester with thionyl chloride and diazomethane to give first an oxy-diazo-ketone which is converted by glacial acetic acid to D 11-21-acetoxypregnane-3-ol-20 one and this by benzene acetone and aluminium phenolate into D 11-21-acetoxypregnane - 3 : 20 - dione. Using this material as the parent substance and treating it with N-bromacetamide followed by a chromic oxide oxidation, and a treatment with zinc dust and anhydrous sodium acetate there is obtained 21 - acetoxy - pregnane - 3 : 11 : 20 - trione. This compound may also be obtained from D 11-21-acetoxy-pregnene-3-ol-20-one by direct reaction with bromacetamide followed by oxidation and debromination. Treatment of 21-acetoxy pregnane-3 : 11 : 20-trione with bromine in glacial acetic acid results in 4-bromo-pregnane-3 : 11 : 20-trione-21-ol-acetate, which on boiling with pyridine and purification by chromography gives D 4 - pregnene - 3 : 11 : 20 - trione - 21 - ol-acetate (dehydrocorticosterone acetate) which may be saponified with methyl alcoholic potash to dehydrocorticosterone. A sample has been furnished under Sect. 2 (5) of 3a -acetoxy-9 : 11-oxido-cholanic acid methyl ester prepared from 3a -acetoxy-11a -oxycholanic acid methyl ester by treatment with phosphorus oxychloride in pyridine solution to form D 9-3a -acetoxy-cholenic acid methyl ester which is then treated with perbenzoic acid in chloroform solution to give the required product which is isolated and purified by a chromatographic separation. Specifications 488,814 and 567,393 also are referred to.