Patent ID: 8461331

Claim:
Process for the preparation of a compound of the formula I in which R 1 , R 2 each, independently of one another, denote H or A, R 3 , R 4 each, independently of one another, denote H, A, alkenyl having 2-6 C atoms or alkynyl having 2-6 C atoms R 5 , R 6 each, independently of one another, denote H or A, A denotes unbranched or branched alkyl having 1-10 C atoms, in which 1-7 H atoms may be replaced by F, or cyclic alkyl having 3-7 C atoms, or an acid-addition salt thereof, which comprises the reaction of a compound of the formula II in which R 1 , R 2 , R 3 , R 4 have the meanings indicated above, with a compound of the formula III in which R 5 , R 6 have the meanings indicated above, wherein the reaction is carried out in the presence of an organic or inorganic acid or an acidic cationic ion exchanger resin.