Process for preparing .DELTA..sup.1,4 -pregnadiene-3,20-diones

A process for the preparation of a compound of the formula ##STR13## wherein the wavy line indicates the existence of two isomers, and reacting a compound of the formula ##STR14## wherein R is selected from the group consisting of hydrogen, acyl of an organic carboxylic acid of 1 to 8 carbon atoms, allyloxycarbonyl, alkyoxycarbonyl and aralkoxycarbonyl of up to 8 carbon atoms, and alkyl sulfonyl and arylsulfonyl of up to 8 carbon atoms with a bromination agent or chlorination agent and a formyloxylation agent in an acid medium to obtain a compound of the formula ##STR15## wherein R is defined as above and Hal is bromine or chlorine, reacting the latter with acetone in the presence of a strong acid to obtain a compound of the formula ##STR16## and reacting the latter with a dehalogenation agent to obtain a compound of formula I ##STR17## wherein R is selected from the group consisting of hydrogen, acyl of an organic carboxylic acid of 1 to 8 carbon atoms, allyloxycarbonyl, alkyoxycarbonyl and aralkoxycarbonyl of up to 8 carbon atoms, and alkylsulfonyl and arylsulfonyl of up to 8 carbon atoms reacting the latter with butanal in the presence of a strong acid catalyst to obtain a compound of the formula ##STR18## wherein R has the above definition and subjecting the latter to a solvolysis in a basic medium to form a compound of formula V.