Method for the production of vinyl norbornene

In a method for producing vinyl norbornene by reacting butadiene and cyclopentadiene according to Diels-Alder reaction, the improvement comprising adding a polycyclic inhibitor to the reactants to reduce formation of polycyclic by-products normally formed during the said reaction by the addition of cyclopentadiene to vinyl norbornene and to increase the yield of vinyl norbornene to at least 30%, the reaction between butadiene and cyclopentadiene with the added polycyclic inhibitor being carried out in the absence of catalyst at a temperature of -10.degree. to 300.degree. C, said polycyclic inhibitor being a p-phenylenediamine compound represented by the following general formula:

• ##STR3## where each of R.sub.1 and R.sub.2 is an alkyl group, an aralkyl group, a cycloalkyl group, or an aryl group having 1 to 20 carbon atoms, and where a part of hydrogen atoms in said hydrocarbon groups may be replaced by a nitro group.