Patent ID: 8269033

Claim:
A process for preparing a compound of formula I wherein: R1 and R2 are each independently —(C 1 -C 4 )-alkyl; R3 is —C(O)—(C 1 -C 4 )-alkyl, which is monosubstituted by Cl or Br, or —C(O)—(C 3 -C 6 )-cycloalkyl; and Z is hydrogen or —(C 1 -C 10 )-alkyl; comprising reacting a compound of formula II wherein: R1 and R3 are each as defined in formula I; X is Cl, Br or —OH; and R4 is R2 or together with X form ═CH 2 or ═CH—(C 1 -C 3 )-alkyl; with carbon monoxide or a carbon monoxide-releasing compound in the presence of concentrated sulfuric acid, hydrogen fluoride or a superacid or mixtures thereof, and then a) adding water to give the compound of formula I wherein Z is hydrogen, or b) adding (C 1 -C 10 )-alkyl-OH when X is Cl or Br, or R4 together with X form ═CH 2 or ═CH—(C 1 -C 3 )-alkyl, to give the compound of formula I wherein Z is —(C 1 -C 10 )-alkyl, wherein the process is carried out in the presence of an additive which is converted rapidly under contact with carbon monoxide to metal carbonyls.