PM3 CALCULATIONS OF DIELS-ALDER REACTIONS OF PULL-PUSH ACTIVATED ISOPRENES WITH ACETONITRILE AND ACRYLONITRILE

PM3 calculations of the pull-push dienes in the Diels-Alder reactions with acetonitrile and acrylonitrile are presented. Two of the pull-pus h dienes, 1-dimethylamino-1-iodoisoprene and 1-fluoro-1-dimethylaminoi soprene where studied. In the iodo isomer the C-1 bond can be easily b roken and the actual species considered in the calculation is the corr esponding cation 3. Frontier orbitals and the energy barriers in the r eactions were considered for all possible cases in the two step, as we ll as in the concerted mechanism. The frontier orbital calculations of the reactants correctly predict the products of the reactions. Accord ing to the calculated energy barriers for the CN addition of acrylonit rile to cation 3 the two step addition is preferred over the concerted mechanism. In the case of the Diels-Alder reaction of fluoroisoprene and acrylonitrile the concerted mechanism was favored. The PM3 energy barriers of all possible cases suggest that in the endo acrylonitrile addition, the CC double bond rather than the CN triple bond is added t o the diene. The predicted PM3 products of the reactions are in full a greement with ones obtained experimentally.