Process for preparing perfuming intermediate

A process for the preparation of a compound of formula (I)

• in the form of any one of its stereoisomers or a mixture thereof, and wherein n is an integer between 1 and 4;
• R1 and R2, independently from each other, represent a hydrogen atom or a C1-3 alkyl group;
• and X represents a halogen atom or a OR′ group wherein R′ represents a hydrogen atom, a C1-6 alkyl group, a C2-6 alkenyl group, a benzyl group, a trimethylsilyl group, a tetrahydrofuran-2-yl group, a tetrahydro-2H-pyran-2-yl group, a CO(O)mR″ group, a CH2(OR′″) group, a CH(OR′″)CH3 group or a SO2R″″ group wherein m is 0 or 1, R″ represents a hydrogen atom, a C1-6 alkyl group or a phenyl group, R′″ represents a C1-6 alkyl group and R″″ represents a methyl, a trifluoromethyl, a phenyl or a tolyl group;
• by cross metathesis between compound of formulae (II)
• in the form of any one of its stereoisomers or a mixture thereof, and wherein n and R1 have the same meaning as defined in formula (I) and R3 and R4, independently from each other, represent a hydrogen atom or a C1-6 alkyl group optionally substituted by an oxo group;
• with compound of formula (III)
• in the form of any one of its stereoisomers or a mixture thereof, and wherein X and R2 have the same meaning as defined in formula (I) and R5, independently from each other, represent a hydrogen atom or a C1-5 alkyl group optionally substituted by a X group as defined above;
• in the presence of a metathesis catalyst.