Patent ID: 7002017

Claim:
A process for preparing a compound of the formula I: wherein R 1 and R 2 independently of one another denote hydrogen or a group which is selected from among the group consisting of C 1 –C 6 -alkyl, C 3 –C 8 -cycloalkyl, C 6 –C 10 -aryl and C 1 –C 4 -alkylene-C 6 –C 10 -aryl, optionally with one, two or three substituents, selected from the group consisting of OH, NH 2 , NH—CO—CH 3 or N(—CO—CH 3 ) 2 , halogen, C 1 –C 4 -alkoxy and CF 3 , while R 1 and R 2 do not simultaneously have the same meaning; R 3 denotes an aryl substituted in the meta position, which optionally comprises at least one other substituent, the substituents being selected from the group consisting of F, Cl, Br, I, OH, O—SO 2 —CF 3 , NO 2 , NH 2 , NH—SO 2 -(4-trifluoromethylpyridin-2-yl), N(—CH 2 -aryl) 2 , NY 1 Y 2 with Y 1 and Y 2 selected from H, COO-alkyl, COO—CH 2 -aryl, CO-alkyl and CO-aryl; R 4 is selected from the group consisting of H and C 1 –C 8 -alkyl; and R 5 is selected from the group consisting of H, Si(CH 3 ) 3 , Li, Na, K, Cs, N(R′) 4 , while all the R′ groups may be identical or different and are selected from C 1 –C 8 -alkyl and CH 2 -aryl; which process comprises hydrogenating a compound of the formula II wherein the groups R 1 to R 5 are as previously defined in this claim, in the presence of a catalyst which contains at least one ligand in the form of a chiral 1,2-bis(phospholano)maleic anhydride.