formula A--OCH.sub.2 --Z, as used herein are shown below although the present invention is not limited thereto. ##STR5##The precursors of the invention can be synthesized according to the reaction formula as described below: ##STR6## wherein A and Z are the same as defined above, and L is a halogen atom or a hydroxyl group.When L represents a hydroxyl group at the second reaction stage, carbodiim