Compound can be prepared in two different ways both starting from 14-hydroxydihydronormorphinone (I): 1) By reaction of (I) with cyclopropylmethyl bromide (C) in DMF at 70 C. 2) Product (I) is ketalized with ethylene glycol (A) by means of p-toluenesulfonic acid giving the cyclic ketal (II), m.p. 311-3 C; this in turn, is treated with cyclopropyl carbonyl chloride (B) in a mixture of methylene chloride and triethylamine yielding the N,O-dicyclopropylcarbonyl derivative (III), mp 219-20 C. Compound (III) is reduced with LiAlH4, in refluxing THF yielding the ethylene ketal of naltrexone (IV), m.p. 221-2 C, which is finally hydrolyzed with aqueous HCl at 100 C.