Patent ID: 7820815

Claim:
A process for preparing a compound of the general formula (I) or an enantiomer or salt thereof, wherein R 1 is a phenylcarbonylmethyl, benzyl, naphthylmethyl, pyridinylmethyl, pyrimidinylmethyl, quinolinylmethyl, isoquinolinylmethyl, quinazolinylmethyl, quinoxalinylmethyl, naphthyridinylmethyl or phenanthridinylmethyl group in which the aromatic or heteroaromatic moiety is in each case mono- or disubstituted by R a , where the substituents may be the same or different and R a is a hydrogen, cyano, methyl, trifluoromethyl, ethyl, phenyl, methoxy, difluoromethoxy, trifluoromethoxy or ethoxy group, or two R a radicals that are bonded to adjacent carbon atoms, may also be an —O—CH 2 —O— or —O—CH 2 —CH 2 —O— group, R 2 is a methyl, ethyl, propyl, isopropyl, cyclopropyl or phenyl group; and R 3 is a 2-buten-1-yl, 3-methyl-2-buten-1-yl, 2-butin-1-yl, 2-fluorobenzyl, 2-chlorobenzyl, 2-bromobenzyl, 2-iodobenzyl, 2-methylbenzyl, 2-(trifluoromethyl)benzyl or 2-cyanobenzyl group, the process comprising: reacting a compound of the general formula (III) with 3-(phthalimido)piperidine or an enantiomer thereof wherein X is a leaving group selected from the group consisting of halogens phenylsulphonyloxy, p-toluenesulphonyloxy, methylsulphonyloxy and trifluoromethylsulphonyloxy, and R 1 to R 3 are as defined above to obtain a compound of the general formula (II) wherein R 1 to R 3 are each defined as mentioned above; and deprotecting the obtained compound of the general formula (II) to obtain the compound of general formula (I).