A computational study towards the reactivity of 2-(2-ethynylphenyl-x-)pyrimidines in intramolecular Diels-Alder reactions

The reactivity of 2-(2-trimethylsilylethynylphenyl-X-)pyrimidines towards intramolecular Diels-Alder reactions to give tricyclic annelated pyridines, decreases in the order X = CO > O > CH2 > NH. A conformational study (MM calculations) and determination of the heat of activation (MNDO calculations) of their 2-(2-ethynylphenyl-X-)pyrimidine analogs showed that the order of reactivity is reflected by the probability of the molecules to be in a conformation which is able to react.