Disclosed is a process for the preparation of a compound of formula ##STR00001## wherein R.sub.1 is hydrogen, hydroxyl, or unsubstituted or substituted alkyl or alkoxy, R.sub.2 is hydrogen or a substituent which can be converted to hydrogen, and n is 0, 1 or 2, comprising hydrogenating a compound of formula ##STR00002## wherein R.sub.1, R.sub.2 and n are as defined above, in the presence of a nickel or cobalt catalyst.