Patent ID: 6908927

Claim:
A process for preparation of compound in the form of pure geometrical or optical isomers or a mixture of such isomers, of formula (I) in which R 1 is a hydrogen atom, a (C 1 -C 4 )alkyl group, a phenyl (C 1 -C 4 )alkyl group, a phenylhydroxy (C 1 -C 4 ) alkyl group, a furanyl(C 1 -C 4 )alkyl group, or a furanylhydroxy(C 1 -C 4 )alkyl group, R 2 is either a hydrogen or halogen atom or a trifluoromethyl, cyano, hydroxyl, nitro, acetyl, (C 1 -C 6 )alkyl or (C 1 -C 6 )alkoxy group or a group of general formula NR 4 R 5 in which R 4 is a hydrogen atom or a (C 1 -C 4 )alkyl or (C 1 -C 4 )alkanoyl group and R 5 is a hydrogen atom or a (C 1 -C 4 )alkyl group, or else R 4 and R 5 form, with the nitrogen atom which carries them, a C 4 -C 7 ring, or a phenyl or naphthyl group optionally substituted by a halogen atom or a trifluoromethyl, trifluoromethoxy, cyano, hydroxyl, nitro, acetyl, (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy or methylenedioxy group linked in the 2 and 3 positions of the phenyl ring, and R 3 is a hydrogen or halogen atom or a (C 1 -C 4 )alkyl group, in the state of a base or an addition salt to an acid wherein a compound of general formula (IV) in which R 2 and R 3 are as defined above is subjected to a dehydration in acid medium followed by a rearrangement at high temperature, to obtain a compound of general formula (Ia) in which, if desired, the substituents R 2 and R 3 are modified into other R 2 or R 3 substituents and/or a substituent R 1 such as defined above is introduced to afford compounds of Formula I.