Process for the preparation of 4-aminobut-2-enolides starting from 4-alkoxyfuran-2(5H)-one or 4-arylalkoxyfuran-2(5H)-one

1. A process for the preparation of a 4-aminobut-2-enolide compound of formula (I)

comprising reacting a 4-alkoxyfuran-2(5H)-one compound or 4-arylalkoxyfuran-2(5H)-one compound of formula (II)

with an amine of formula (III)

in which

R 1 is hydrogen, C 1-12 -alkyl, C 2-12 -alkenyl, C 2-6 -alkynyl, C 3-8 -cycloalkyl, C 3-8 -cycloalkyl-C 1-6 -alkyl, C 1-12 -alkoxy, C 1-6 -alkyloxy-C 1-6 -alkyl, aryl-C 1-6 -alkyl, 2-fluoroethyl, 2,2-difluoroethyl, or 2-fluorocyclopropyl;

R 2 is C 1-12 -alkyl, or aryl-C 1-6 -alkyl; and

A is pyrid-2-yl, pyrid-4-yl or pyrid-3-yl, which are optionally substituted in the 6-position by F, Cl, Br, CH 3 , CF 3 , or OCF 3 , or is a substituted heterocyclyl of the following formula

in which

X is halogen or C 1-12 -alkyl, and

Y is halogen or C 1-12 -alkyl;

in the presence of a Brønstedt acid.

2. The process according to claim 1 , wherein, in formula (III),

R 1 is C 1-6 -alkyl, C 2-6 -alkenyl, C 2-6 -alkynyl C 3-8 -cycloalkyl, C 3-8 -cycloalkyl-C 1-6 -alkyl, or C 1-6 -alkyloxy-C 1-6 -alkyl; and

A is selected from 6-fluoropyrid-3-yl, 6-chloropyrid-3-yl, 6-bromopyrid-3-yl, 6-methylpyrid-3-yl, 6-trifluoromethylpyrid-3-yl, 6-trifluoromethoxypyrid-3-yl, 6-chloro-1,4-pyridazin-3-yl, 6-methyl-1,4-pyridazin-3-yl, 2-chloro-1,3-thiazol-5-yl or 2-methyl-1,3-thiazol-5-yl, 2-chloropyrimidin-5-yl, 2-trifluoromethylpyrimidin-5-yl, 5,6-difluoropyrid-3-yl, 5-chloro-6-fluoropyrid-3-yl, 5-bromo-6-fluoropyrid-3-yl, 5-iodo-6-fluoropyrid-3-yl, 5-fluoro-6-chloropyrid-3-yl, 5,6-dichloropyrid-3-yl, 5-bromo-6-chloropyrid-3-yl, 5-iodo-6-chloropyrid-3-yl, 5-fluoro-6-bromopyrid-3-yl, 5-chloro-6-bromopyrid-3-yl, 5,6-dibromopyrid-3-yl, 5-fluoro-6-iodopyrid-3-yl, 5-chloro-6-iodopyrid-3-yl, 5-bromo-6-iodopyrid-3-yl, 5-methyl-6-fluoropyrid-3-yl, 5-methyl-6-chloropyrid-3-yl, 5-methyl-6-bromopyrid-3-yl, 5-methyl-6-iodopyrid-3-yl, 5-difluoromethyl-6-fluoropyrid-3-yl, 5-difluoromethyl-6-chloropyrid-3-yl, 5-difluoromethyl-6-bromopyrid-3-yl or 5-difluoromethyl-6-iodopyrid-3-yl.

3. The process according to claim 1 , wherein the Brønstedt acid is selected from the group consisting of phosphoric acid, sulphuric acid, hydrochloric acid, hydrobromic acid, hydrofluoric acid, potassium hydrogensulphate, trifluoroacetic acid, acetic acid, methanesulphonic acid and p-toluenesulphonic acid.

4. The process according to claim 1 , wherein the molar ratio of the compound of the formula (H) to the amine of the formula (III) used is 1:0.5 to 1:10.

5. The process according to claim 1 , wherein the molar ratio of the Brønstedt acid used to the amine of the formula (III) is in the range from about 5:0.8 to about 1:1.5.

6. The process according to claim 2 , wherein the Brønstedt acid is selected from the group consisting of phosphoric acid, sulphuric acid, hydrochloric acid, hydrobromic acid, hydrofluoric acid, potassium hydrogensulphate, trifluoroacetic acid, acetic acid, methanesulphonic acid and p-toluenesulphonic acid.

7. The process according to claim 2 , wherein the molar ratio of the compound of the formula (H) to the amine of the formula (III) used is 1:0.5 to 1:10.

8. The process according to claim 3 , wherein the molar ratio of the compound of the formula (H) to the amine of the formula (III) used is 1:0.5 to 1:10.

9. The process according to claim 2 , wherein the molar ratio of the Brønstedt acid used to the amine of the formula (III) is in the range from about 5:0.8 to about 1:1.5.

10. The process according to claim 3 , wherein the molar ratio of the Brønstedt acid used to the amine of the formula (III) is in the range from about 5:0.8 to about 1:1.5.

11. The process according to claim 4 , wherein the molar ratio of the Brønstedt acid used to the amine of the formula (III) is in the range from about 5:0.8 to about 1:1.5.

12. The process of claim 1 , wherein formula (III) is N-[(6-chloropyridin-3-yl)methyl]-2,2-difluoroethylamine.