Patent ID: 7250528

Claim:
A process for making a compound of formula wherein R 1 represents a formyl group, a —COCOOH group or a group of formula —(CO) n —R, n being 0 or 1 and R representing an optionally substituted phenyl group or a C 1-6 alkyl or alkenyl group optionally halogenated; R 2 represents a C 1-10 alkyl or alkenyl group; and at least one R 3 represents a hydrogen atom and the other R 3 represent each a hydrogen atom or a C 1-5 alkyl, alkenyl or alkoxy group; comprising the cyclisation, at a temperature above 10° C., of the corresponding compound of formula wherein each R 4 , taken separately, represents a formyl group or a —(CO) n —R group, or the R 4 , taken together, represent a —COCO— group; the wavy line indicates that the configuration of the carbon-carbon double bond is E or Z or a mixture thereof; and n, R, R 2 , R 3 and R 4 have the meaning as indicated above; in the presence of a compound, which promotes the reaction, selected from the group consisting of strong mineral protic acids, sulphonic acids, acidic zeolites and Lewis acids.