Octadienyl esters of 2-ethylidene-hepta-3,5-dienoic and 2-vinyl-hepta-3,5-dienoic acids of formula C.sub.8 H.sub.11 COOC.sub.8 H.sub.13 and .delta.-lactone of formula ##STR1## or 2-ethylidene-hepta-6-ene-5-olide, are prepared by reaction of 1,3-butadiene with CO.sub.2 at a temperature comprised between about 20.degree. and 150.degree. C. and at a total pressure between about 10 and 500 atm in the presence of a phosphinic complex of palladium having the formula Pd[P(R).sub.3 ].sub.x, wherein x is an integer from 2 to 4, and (R).sub.3 is a homogeneous or heterogeneous group consisting of alkyls, cycloalkyls having up to 8 carbon atoms and of phenyls, also substituted, in an inert atmosphere.The obtained products are "per se" new and are valuable intermediates for synthesis of chemicals (fungicides, pesticides, etc.) and in particular as effective plasticizers.