The reaction according to method (cc) is conveniently carried out in an inert, water-miscible, organic solvent such as an aliphatic or cyclic ether, e.g. 1,2-dimethoxyethane, tetrahydrofuran or dioxan, or a lower alkanol such as ethanol at temperature between 50??? C. and 100??? C., preferably at the reflux temperature of the reaction mixture, or in an aromatic solvent such as benzene, toluene or