. . . "cular methyl, ethyl, n- or i-propyl, n-, i-, s- or t-butyl, cyclopropyl or cyclobutyl.A.sup.2 represents in particular methyl, ethyl, n- or i-propyl, n-, i-, s- or t-butyl, allyl, propargyl, but-2-en-1-yl, 2-methyl-prop-1-en-3-yl, cyanomethyl, methoxymethyl, ethoxymethyl, methoxyethyl, ethoxyethyl, methylthiomethyl,ethylthiomethyl, methylthioethyl, ethylthioethyl, dimethylaminomethyl, dimethylamin" .