A probucol or a probucol derivative can be efficiently converted to a monoester or monoether of probucol by reacting the free hydroxyl-containing probucol or a derivative thereof (by which is meant a probucol compound with at least one substituent that is different from that on the parent probucol molecule but which maintains the two free hydroxyl groups) with a Grignard reagent or a lithium reagent that produces a magnesium bromide or lithium salt of probucol or the probucol derivative. The probucol compound anion anion is then reacted with an ester or ether forming compound.