1, 3 butadiene. The Diels-Alder reaction is a conjugate addition reaction of a conjugated diene to an alkene (the dienophile) to produce a cyclohexene. The simplest diene is 1,3-butadiene. It can be viewed as the union of two vinyl groups. It would react with an alkene substitutient ethene to form cyclohexene which leads to the conversion of 2 Ď€-bonds into 2 new stronger Ď-bonds.