Small heterocyclic aromatic compounds such as thiophene, furan, and pyrrole are inert in Diels-Alder cycloaddition reactions. As a consequence, these and related materials cannot be used as reagents in one of the most important carbon-carbon bond formation reactions in organic chemistry, a reaction that has important applications in medicinal chemistry. To impart reactivity to these systems, we have asked the question whether reactivity can be induced by removing one electron. Framed more specifically, the question is whether radical cations of thiophene, furan, and pyrrole will react via cycloadditions with simple alkenes and alkynes. The answer to the question appears to be affirmative. Under the conditions of the rf-only-mode (ion-trap) event in a Fourier transform mass spectrometer, the reactant radical cations are smoothly transformed into products. The products are being characterized by tandem MS and by theoretical calculations. The outcome co uld be a new class of synthetic reactions for preparations of cycloadducts involving many substituted heterocyclic aromatic compounds.
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