PURPOSE: To obtain the compd. of a steroid compd. synthesizing intermediate useful as a gestagenic action agent, etc., which high yield by using a triketal compd. as a starting raw material and bringing this compd. into reaction with a base under specific temp. conditions in an aq. medium.

CONSTITUTION: The compd. of the formula II is obtd. by using the triketal compd. of formula I as the starting raw material and bringing this compd. into reaction with the base at about 50 to 80°C, more preferably 40 to 80°C in the aq. medium, more preferably, in the aq. alcohol medium, such as aq. methanol. An alkaline metal hydroxide, such as sodium hydroxide, is used as the base and the amt. of the alkali to be used is an excessive amt., more preferably an excess amt. of 2 to 10 times mol the amt. of the compd. of the formula I. The compd. of the formula I is obtd. by converting the bicycle compd. of formula III to a mixed acid anhydride by using a trimethyl acetic acid (pivalic acid) chloride and processing this mixed acid anhydride with a Grignard reagent.