Oximeester compounds of the formulae I, II, III and IVwhereinR1 is phenyl, C1-C20alkyl or C2-C20alkyl optionally interrupted by -O-, C2-C20alkanoyl or benzoyl, or R1 is C2-C12alkoxycarbonyl or phenoxycarbonyl; R1' is C2-C12alkoxycarbonyl, or R1' is phenoxycarbonyl, or R1' is -CONR10R11 or CN; R2 is C2-C12alkanoyl, C4-C6alkenoyl, benzoyl, C2-C6alkoxycarbonyl or phenoxycarbonyl; R3, R4, R5, R6 and R7 are hydrogen, halogen, C1-C12alkyl, cyclopentyl, cyclohexyl, phenyl, benzyl, benzoyl, C2-C12alkanoyl, C2-C12alkoxycarbonyl, phenoxycarbonyl or a group OR8, SR9, SOR9, SO2R9 or NR10R11; R4', R5' and R6' are hydrogen, halogen, C1-C12alkyl, cyclopentyl, cyclohexyl, phenyl, benzyl, benzoyl, C2-C12-alkanoyl, C2-C12alkoxycarbonyl, phenoxycarbonyl, or are a group OR8, SR9, SOR9, SO2R9, NR10R11; provided that at least one of R3, R4, R5, R6, R7, R'4, R'5 and R'6 is OR8, SR9 or NR10R