A compound of the formula in which R 1 is isopropyl or sec-butyl; R 2 is H, or C 1 - 8 alkyl; R 3 is benzyl which carries, on the aromatic moiety, one to three substituents selected from the group consisting of OH, halogen, CN, NO 2, C 1 -C 2 alkyl, dimethylamino-C 1 -C 4 alkoxy, C 3 -C 6 cycloalkyl, C 1 -C 2 haloalkyl, C 1 -C 2 alkoxy, C 1 -C 2 haloalkoxy, phenoxy, phenyl-C 1 -C 6 alkyl, phenyl-C 1 -C 4 alkenyl, unsubstituted or chlorine- or methoxy-substituted phenoxy, unsubstituted or chlorine-, methoxy- or trichloromethyl-substituted benzyloxy, methylenedioxy, -C(=O)R 5, -O-C(=O)R 6 and NHC(=O)R 6; or R 3 is -CH 2 -C(=O)C 1 -C 12 alkoxy; or R 3 is -CH 2 -heterocyclyl, wherein the heterocyclyl group is selected from pyridyl, furanyl, tetrahydrofuranyl, pyranyl, tetrahydropyranyl, pyrazolyl, imidazolyl, thiazolyl, benzothienyl, quinolinyl, quinoxalinyl, benzofuranyl, benzimidazolyl, benzopyrrolyl, benzothiazolyl, indolyl, cumarinyl and indazolyl, where the radicals mentioned are unsubstituted or mono- or disubstituted independently of one another by halogen, trifluoromethyl, trifluoromethoxy or nitro; R 5 is H, OH, NH 2, NH(C 1 -C 2 alkyl), N(C 1 -C 2 alkyl) 2, -O-C 1 -C 2 alkyl-C(=O)-R 7, -NHC 1 -C 2 alkyl-C(=O)-R 7, C 1 -C 6 alkyl, C 1 -C 2 alkoxy, C 1 -C 2 alkoxy-C 1 -C 2 alkoxy, C 2 -C 4 alkenyloxy, C 2 -C 4 alkynyloxy; phenyl, phenoxy, benzyloxy, NH-phenyl, NH-C 1 -C 6 alkyl-C(=O)-R 7; or phenyl, phenoxy, benzyloxy, NH-phenyl which are substituted by halogen, nitro, methoxy, trifluoromethyl or trifluoromethoxy; R 6 is H, C 1 -C 3 alkyl, phenyl or benzyl; and R 7 is H, OH, NH 2, NH(C 1 -C 12 alkyl), N(C 1 -C 12 alkyl) 2, C 1 -C 12 alkyl, C 1 -C 12 alkoxy, C 1 -C 6 alkoxy-C 1 -C 6 alkoxy, C 2 -C 8 alkenyloxyl, phenyl, phenoxy, benzyloxy or NH-phenyl; or, if appropriate, an E/Z isomer, E/Z isomer mixture and/or tautomer thereof. R 1 is isopropyl or sec-butyl; R 2 is H, or C 1 - 8 alkyl; R 3 is benzyl which carries, on the aromatic moiety, one to three substituents selected from the group consisting of OH, halogen, CN, NO 2, C 1 -C 2 alkyl, dimethylamino-C 1 -C 4 alkoxy, C 3 -C 6 cycloalkyl, C 1 -C 2 haloalkyl, C 1 -C 2 alkoxy, C 1 -C 2 haloalkoxy, phenoxy, phenyl-C 1 -C 6 alkyl, phenyl-C 1 -C 4 alkenyl, unsubstituted or chlorine- or methoxy-substituted phenoxy, unsubstituted or chlorine-, methoxy- or trichloromethyl-substituted benzyloxy, methylenedioxy, -C(=O)R 5, -O-C(=O)R 6 and NHC(=O)R 6; or R 3 is -CH 2 -C(=O)C 1 -C 12 alkoxy; or R 3 is -CH 2 -heterocyclyl, wherein the heterocyclyl group is selected from pyridyl, furanyl, tetrahydrofuranyl, pyranyl, tetrahydropyranyl, pyrazolyl, imidazolyl, thiazolyl, benzothienyl, quinolinyl, quinoxalinyl, benzofuranyl, benzimidazolyl, benzopyrrolyl, benzothiazolyl, indolyl, cumarinyl and indazolyl, where the radicals mentioned are unsubstituted or mono- or disubstituted independently of one another by halogen, trifluoromethyl, trifluoromethoxy or nitro; R 5 is H, OH, NH 2, NH(C 1 -C 2 alkyl), N(C 1 -C 2 alkyl) 2, -O-C 1 -C 2 alkyl-C(=O)-R 7, -NHC 1 -C 2 alkyl-C(=O)-R 7, C 1 -C 6 alkyl, C 1 -C 2 alkoxy, C 1 -C 2 alkoxy-C 1 -C 2 alkoxy, C 2 -C 4 alkenyloxy, C 2 -C 4 alkynyloxy; phenyl, phenoxy, benzyloxy, NH-phenyl, NH-C 1 -C 6 alkyl-C(=O)-R 7; or phenyl, phenoxy, benzyloxy, NH-phenyl which are substituted by halogen, nitro, methoxy, trifluoromethyl or trifluoromethoxy; R 6 is H, C 1 -C 3 alkyl, phenyl or benzyl; and R 7 is H, OH, NH 2, NH(C 1 -C 12 alkyl), N(C 1 -C 12 alkyl) 2, C 1 -C 12 alkyl, C 1 -C 12 alkoxy, C 1 -C 6 alkoxy-C 1 -C 6 alkoxy, C 2 -C 8 alkenyloxyl, phenyl, phenoxy, benzyloxy or NH-phenyl; or, if appropriate, an E/Z isomer, E/Z isomer mixture and/or tautomer thereof.