A process for making a compound of formula wherein the wavy line indicates that the double bond can be in a configuration E or Z or a mixture thereof; R 1, when taken separately, one represents a hydrogen atom and the other a C 1 -C 4 alkyl group; or the two R 1, when taken together, represent a C 3 -C 5 alkanediyl or alkenediyl group optionally substituted; R 2 or R 3 represents, taken separately, a hydrogen atom or a C 1 -C 6 alkyl group; R 2 and R 3, taken together, may represent a C 3 -C 10 alkanediyl or alkenediyl group optionally substituted; R 4 represents a C 1 -C 7 alkyl or fluorinated alkyl group, a C 7 -C 10 alkylaromatic optionally substituted, a C 1 -C 7 acyl group, or a -COCOOH or -COCH 2 COOH group; and R 5 represents a C 2 -C 9 alkanediyl or alkenediyl group optionally substituted; comprising the coupling of a compound of formula with a compound of formula wherein R 1 to R 3 have the meaning indicated in formula and each R 6, taken separately, represents a C 1 -C 7 alkyl or fluorinated alkyl group, a C 7 -C 10 alkylaromatic optionally substituted, a C 1 -C 7 acyl group, or the R 6, taken together, represent a COCO or COCH 2 CO group; or, respectively, the cyclisation of a compound of formula wherein R 1 and R 3 have the meaning indicated in formula, R 6 have the meaning indicated in formula, and R 5 have the meaning indicated in formula (I'); said processes being characterized in that it is carried out in the presence of a catalytic amount of only one catalyst selected from the group consisting of - a salt of formula MX n, M representing a transition metal selected from the group consisting of Fe, Co, Ni, Cu and Zn, X representing a mono-anion and n is an integer from 1 to 3; and - a boron compound of formula BY 3, characterized in that Y represents a fluoride or a phenyl group optionally substituted, and anyone of its adducts with a C 2 -C 10 ether or a C 1 -C 8 carboxylic acid. wherein the wavy line indicates that the double bond can be in a configuration E or Z or a mixture thereof; R 1, when taken separately, one represents a hydrogen atom and the other a C 1 -C 4 alkyl group; or the two R 1, when taken together, represent a C 3 -C 5 alkanediyl or alkenediyl group optionally substituted; R 2 or R 3 represents, taken separately, a hydrogen atom or a C 1 -C 6 alkyl group; R 2 and R 3, taken together, may represent a C 3 -C 10 alkanediyl or alkenediyl group optionally substituted; R 4 represents a C 1 -C 7 alkyl or fluorinated alkyl group, a C 7 -C 10 alkylaromatic optionally substituted, a C 1 -C 7 acyl group, or a -COCOOH or -COCH 2 COOH group; and R 5 represents a C 2 -C 9 alkanediyl or alkenediyl group optionally substituted; wherein R 1 to R 3 have the meaning indicated in formula and each R 6, taken separately, represents a C 1 -C 7 alkyl or fluorinated alkyl group, a C 7 -C 10 alkylaromatic optionally substituted, a C 1 -C 7 acyl group, or the R 6, taken together, represent a COCO or COCH 2 CO group; wherein R 1 and R 3 have the meaning indicated in formula, R 6 have the meaning indicated in formula, and R 5 have the meaning indicated in formula (I'); said processes being characterized in that it is carried out in the presence of a catalytic amount of only one catalyst selected from the group consisting of - a salt of formula MX n, M representing a transition metal selected from the group consisting of Fe, Co, Ni, Cu and Zn, X representing a mono-anion and n is an integer from 1 to 3; and - a boron compound of formula BY 3, characterized in that Y represents a fluoride or a phenyl group optionally substituted, and anyone of its adducts with a C 2 -C 10 ether or a C 1 -C 8 carboxylic acid. - a salt of formula MX n, M representing a transition metal selected from the group consisting of Fe, Co, Ni, Cu and Zn, X representing a mono-anion and n is an integer from 1 to 3; and - a boron compound of formula BY 3, characterized in that Y represents a fluoride or a phenyl group optionally substituted, and anyone of its adducts with a C 2 -C 10 ether or a C 1 -C 8 carboxylic acid.