With acyclic dienes the reactions are regio and stereoselective. These both selectivities can be enhanced by Lewis acid catalysis. The stereochemical assignments of the adducts are performed on the basis of spectroscopie data. Then, the cycloadducts are transformed to cyclic (or polycyclic) dienic compounds by sequential oxydation and elimination reactions. Thus, the α-methylthio-acrylonitrile can be considered