17a-Hydroxy-16b-methyl-5,9(11)-pregnadiene-3, 20-dione-bis(diethylene ketal) (I) on treatment with 70% acetic acid was hydrolyzed to the parent 3,20-dione (II) in 88% yield, while compound I or II on treatment with 98% acetic acid was rearranged to 17a-hydroxy-16b,17b-dimethyl-D-homo-4,9(11)-androstanediene-3,17a- dione (III) in 68 or 89% yields, resp. I and II reacted with 70% acetic acid containing CaCl2 to give 16b,17ab-dimethyl-D-homo-4,9(11),15-androstrien-3,17-dione (IV) in 90% yield. The yield of compound IV is dependent on the concentration of CaCl2 and the time of reaction.

Key words: REACTION MECHANISM, STEROIDS, REARRANGEMENT REACTION, ACETIC ACID, PREGNENEDIONE