The present invention further relates to a method of preparing a dimethyl-(3-aryl-but-3-enyl)-amine compound of formula I, where R1 is C1-5 alkyl and R2 denotes H or C1-5 alkyl, or R1 and R2 together represent --(CH2)2-4 --, --(CH2)2 --CHR7 or --CH2 --CHR7 --CH2 --, R3 denotes H or C1-5 alkyl, one of the radicals R4, R5 or R6 denotes OH and the other two radicals are H, R7 denotes C1-8 alkyl, C3-8