Patent ID: 7144993

Claim:
A process for the preparation of a compound of the formula which comprises converting a compound of the formula in an aprotic organic solvent in the presence of a catalytically active amount of a strong acid (catalyst) or of an agent that liberates a strong acid or of an ammonium salt of a strong acid, it also being possible for the catalyst to be part of the starting material/product, into a compound of formula I, wherein R 5 , R 6 and R 8 are each independently of the others a hydrogen atom, a nitro group, a sulfo group, a halogen atom, a pseudohalogen, a group COOR 1 or CONHR 2 , a C 1-8 alkyl, C 1-8 alkoxy or aryloxy radical, an amide group, a thioalkyl or thioaryl radical, an alkyl- or aryl-sulfonyl radical, an alkyl- or aryl-sulfinyl radical, a trifluoromethyl group or a phosphono group, R 1 and R 2 being a hydrogen atom or a C 1-8 alkyl radical or an aryl or aralkyl radical, R 10 is a group —C(O)CH 2 C(O)CH 3 and R 11 is a hydrogen atom or an acyl radical, or R 10 and R 11 are a group —C(O)CH 2 C(O)CH 3 .