To obtain a difunctionalized 6C-hydrocarbon by an economically excellent reaction path by subjecting one or more two kinds of specific olefins to self double decomposition or cross double decomposition in the presence of a homogeneous catalyst containing a specific ruthenium catalyst, etc.

A compound of the formula R-CH=CH-CH2-E and/or R1-CH= CH-CH2-E1 (E and E1 are each COOH or the like; R and R1 are each H, a 1-12C alkyl or the like) (e.g. 3-methyl pentenoate) is subjected to self double decomposition or cross double decomposition in the presence of a homogenous catalyst containing a ruthenium compound or a ruthenium complex to give a 6C compound of the formula E-CH2-CH=CH-CH2-E1 (e.g. methyl dehydroadipate). The catalyst used is preferably a ruthenium-alkylidene complex of the formula RuX'Y' (=CH-CH2R")L1L2 (X' and Y' are each an anionic ligand; R" is H, a 1-20C alkyl or the like; L1 and L2 are each an uncharged electron donor ligand).