Process for preparing 3-(4)-formyltricyclo-[5,2,1,0.sup.2,6 ]-decene-8

A process for preparing 3- or 4-formyltricyclo-[5,2,1,0.sup.2,6 ]-decene-8 which comprises contacting dicyclopentadiene with carbon monoxide and hydrogen in the presence of a rhodium catalyst at 110.degree. to 150.degree. C. and 50 to 400 atmospheres, said catalyst being present in an amount of 1 to 30 ppm of rhodium, based upon the amount of dicyclopentadiene employed, said rhodium being present in the form of an organic phosphine - carbon monoxide containing complex, said organic phosphine being an aliphatic straight or branched chain phosphine, a cycloaliphatic phosphine, an aromatic phosphine or an arylaliphatic phosphine or a phosphine with one or more substituted cyclic substituents or an organic phosphine with two or more phosphorus atoms having from 1 to 30 carbon atoms.