The domino reaction between 4,6-dinitrobenzofuroxan and cyclopentadiene. Insights on the nature of the molecular mechanism

The molecular mechanism of the domino reaction between 4,6-dinitrobenzofuroxan, 1, and cyclopentadiene, Cp, to give the adduct 11 is examined through density functional theory (DFT) calculations at B3LYP/6-31G* level. This domino reaction comprises two consecutive formally [4 + 2] cycloadditions. The first one is a two-center addition initialized by the nucleophilic attack of Cp to the more electrophilic center of 1. The subsequent cyclization can take place along two competitive channels associated to the formation of a second C-C bond yielding the formally [2 + 4] cycloadduct 9, or a C-O bond yielding the formally [4 + 2] cycloadduct 10. The second cycloaddition is a stepwise process that is initialized by the nucleophilic attack of a second molecule of Cp to 10. The energetic results are in agreement with the experiments allowing to explain the formation of the final domino adduct 11. Inclusion of solvent effects, via a polarizable continuum model, decreases the activation energies of these polar processes. A DFT analysis of the indexes of reactivity provides a sound explanation on the reactivity of 1 on this domino reaction. (C) 2004 Elsevier B.V. All rights reserved.