-6 -alkoxy radical; and R5 is H or a C1-4 -alkyl group; or R1 is a methyl group; R2 is a dimethylamino or a free or ketalized acetyl group, R3 is a C1-6 -alkoxy group or a C1-4 -alkoxymethyloxy or -alkylthiomethyloxy group; R4 is an alkoxymethyl group with 1 to 6 carbon atoms in the alkoxy radical; and R5 is H. 2.