PURPOSE: To efficiently obtain the compd. useful for an intermediate of medicines or the like at high yield by bringing a compd. obtd. by oxidizing a specified compd. in the presence of water to solvolysis reaction in an acidic medium or the like and bringing this to deblocking reaction.

CONSTITUTION: A compd. of formula I [R1 is H, 1-4C alkyl, 2-4C alkenyl or alkynyl: R2 is 1-4C alkyl nuclei A to D have one or more double bond(s) and may be substituted by one or more (protected) hydroxy and ketone functional group(s), one or more halogen(s) and one or more 1-4C alkyl or the like] is treated by an oxidizer such as perbenzoic acid, hydrogen peroxide or the like in an at least partially water-miscible solvent in the presence of water to obtain a compd. of formula II, and this compd. is brought to solvolysis reaction in an acidic or basic solvent and is then brought to deblocking reaction of protected hydroxy and ketone functional groups capable of existing if necessary to obtain the compd. of formula II.