The present invention relates to a process for the synthesis of the known 17-acetoxy-11-β-[4-(dimethylamino)-phenyl]-21-methoxy-19-norpregna-4,9-dien-3,20-dione (further on CDB-4124) of formula (I)from 3,3-[1,2-etandiyl-bis(oxy)]-oestr-5(10),9(11)-dien-17-one of formula (II).Compound CDB-4124 belongs to the group of anti-hormones. The process according to the invention is the following: i) formation of an epoxide on the double bond in position 5(10) of 3,3-[1,2-ethandiyl-bis(oxy)]-oestr-5(10),9(11)-dien-17-one of formula (II) with hydrogen peroxide； ii) addition of hydrogen cyanide formed in situ on position 17 of the obtained 5,10α-epoxy-3,3-[1,2-ethandiyl-bis(oxy)]-5α-oestr-9(11)-en-17-one of formula (III) iii) silylation of the hydroxyl group in position 17 of the formed 5,10α-epoxy-3,3-[1,2-ethandiyl-bis(oxy)]-17α-hydroxy-5α-oestr-9(11)-en-17β-carbonitrile of formula (IV) with trimethyl chlorosilane； iv) reacting the obtained 5,10α-epoxy-3,3-[1,2-ethandiyl-bis(oxy)]-17-[trimethyl-silyl-oxy]-5α-oestr-9(11)-en-17β-carbonitrile of formula (V) with 4-(dimethylamino)-phenyl mag-nesium bromide Grignard reagent in the presence of CuCl (Teutsch reaction)； v) silylation of the hydroxyl group in position 5 of the formed 11β-[4-(dimethyl-amino)-phenyl]-3,3-[1,2-ethandiyl-bis(oxy)]-5-hydroxy-17α-[trimethylsilyl-(oxy)]-5α-oestr-9-en-17β-carbonitrile of formula (VI) with trimethyl chlorosilane； vi) reacting the obtained 11β-[4-(dimethylamino)-phenyl]-3,3-[1,2-ethandiyl-bis(oxy)]-5,17α-bis-[trimethyl-silyl-(oxy)]-5α-oestr-9-en-17β-carbonitrile of formula (VII) with diisobu-tyl aluminum hydride and after addition of acid to the reaction mixture vii) methoxy-methylation of the obtained 11β-[4-(dimethylamino)-phenyl]-3,3-[1,2-ethandiyl-bis(oxy)]-5,17α-bis-[trimethyl-silyl-(oxy)]-5α-oestr-9-en-17β-carbaldehide of for-mula (VIII) with methoxy-methyl Grignard reagent formed in situ, while hydrolyzing the trimethylsilyl protective groups； viii) oxidation of the hydroxyl group in
