Described herein is a process for the preparation of an acetal of formula (I) in which R1 is an alkyl, R2 is H or an acyl, X is &bgr;-OH and Y is H, comprising the acetalization with control of the epimeric distribution at the C-22 position, for treatment with R1 CHO in aqueous HBr or HI of a compound of formula (II) in which R2 has the meaning specified above, R3 and R4 are both H, or, taken together, are —C(R5)(R6)—, where R5 and R6, which may be the same or different from one another, are alkyl groups, and X and Y are chosen from among the following: A) X and Y, taken together, are an additional bond between C-9 and C-11; B) X is &bgr;-OH, and Y is H or an &agr;-halogen; C) X is &bgr;-OR7 where R7 is an acyl, and Y is H or an &agr;-halogen; and D) X and Y, taken together, are —O—.