Nitrofurans undergo intramolecular Diels-Alder reactions with tethered electron-poor dienophiles more rapidly and in higher yields than non-nitrated furans. Computational studies indicate that increased stabilization of a partial positive charge on the nitro-substituted carbon in both transition state and product is the driving force for these reactions. Frontier molecular orbital energy differences indicate a switch from normal to inverse electron demand upon nitration. There does not appear to be a contribution from any differences in aromatic stabilization energy between furans and nitrofurans. Calculations show that the nitrofuran reactions proceed via a highly asynchronous transition state allowing easier bond formation between two sterically hindered carbons.
Cowie, T. Y., Veguillas Hernando, M., Rae, R. L., Rougé, M., Zurek, J. M., Prentice, A. W., Paterson, M. J., & Bebbington, M. W. P. (2017). Intramolecular Nitrofuran Diels-Alder reactions: extremely substituent-tolerant cycloadditions from asynchronous transition states. Journal of Organic Chemistry, 82(13), 6656-6670. https://doi.org/10.1021/acs.joc.7b00781