erein wherein Z is ##STR19## wherein R.sub.5 is hydroxy and R.sub.4 is lower alkyl of from 1 to 4 carbon atoms are prepared from the corresponding compound wherein Z is carbonyl by a Grignard reaction using a reagenthaving the formula R.sub.7 MgX wherein R.sub.7 is lower alkyl of from 1 to 4 carbon atoms, and X is a halogen atom.