Patent ID: 6838575

Claim:
A process for the preparation of a compound of formula: wherein: the wavy line indicates that the stereochemistry of the C═C double bond is not defined; R 1 represents a hydrogen atom or a methyl group; R 2 represents a methyl or ethyl group or a saturated or unsaturated gem-dimethyl C 6 ring, optionally substituted, provided that if R 1 is a hydrogen atom R 2 is a group having at least two carbon atoms; or said R 1 and R 2 taken together form a saturated or unsaturated gem-dimethyl C 6 ring, possibly substituted, or a saturated or unsaturated C 12 ring, said ring including the carbon atom of the carbonyl function and the carbon atom to which R 1 is bonded; and R 3 represents a hydrogen atom, a C 1 to C 4 linear or branched alkyl or alkenyl group, a linear or branched C 9 alkadienyl radical, or a CH 2 R group, R being a saturated or unsaturated gem-dimethyl C 5 ring that is optionally substituted; by reacting a starting ketone of formula: wherein R 1 and R 2 have the same meaning as in formula (I), with an aldehyde of formula: wherein R 3 bas the same meaning as in formula (I), in the presence of a metal complex of formula: M(OR 8 ) 4-n X n (VII) wherein M is a tetravalent metal cation selected from the group 4 consisting of Ti, 2r and Hf R 8 represents a C 1-6 linear or branched alkyl group, X represents an halide such as a Cl or F atom and the index n represents an integer from 1 to 3; and in the presence of a co-ingredient which is an alkyl or aromatic carboxylic acid anhydride containing 1 to 10 carbon atoms, BF 3 or an anhydrous salt selected from the group consisting of the sulfates, chlorides and bromides of a metal cation, wherein the metal cation is selected from the group consisting of Li + , Na + , K + , Cs + , Mg 2+ , Ni 2+ , Ca 2+ , Zn 2+ , Fe 3+ and Al 3+ .