High energy routes to reactive intermediates: Computational and experimental studies

We developed microwave flash pyrolysis (MFP), using graphite and other sensitizers to carry out high temperature reactions. Newly developed is a closed vessel MFP method. Studies to date include isomerization of azulene to naphthalene, generation of benzyne, cycloaromatizations, and rearrangements. New thermal sensitizers included silicon carbide, titanium dioxide and diverse metal oxides. Graphite remains the most effective thermal sensitizer. Sealed tube MFP was utilized to investigate the Brown rearrangement of aryl alkynes. CCSD(T)//M05-2X computations have been carried out for both concerted and stepwise mechanisms in dehydro-Diels-Alder reactions of ethene and ethyne with vinylacetylene and 1,3-butadiyne. Concerted transition states for enyne-ene and enyne-yne reactions are ca. 6--7 kcal/mol lower in energy than the stepwise transition states. Diyne-ene and diyne-yne reactions can proceed through a concerted mechanism to give 1,2,3-cyclohexatriene or ortho -benzyne; however the computed energy differences between the concerted and the stepwise transition states are \u3c 2 kcal/mol