Ab initio study of the low reactivity of thiophene in Diels–Alder reactions with carbon dienophiles

The utility of thiophene as a diene for Diels–Alder reactions was studied by ab initio methods. The reactivity was evaluated with three dienophiles, vinyl alcohol, ethylene and acrylonitrile. Qualitatively the reactivity was determined by comparison of the reactant's frontier orbital energies, bond orders and charge transfer in the transition states. Quantitatively the reactivity was determined by estimation of activation energy with RHF/6‐31G*, MP2/6‐31G*, MP3/6‐31G*//MP2/6‐31G*, and MP4/6‐31G//MP2/6‐31G* ab initio calculations. The results of the calculations predicts that the reactivity of thiophene with acrylonitrile is similar to butadiene and ethylene with a preferred formation of the endo isomer.