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A Way to Avoid Using Precious Metals: The Application of High-Surface Activated Carbon for the Synthesis of Isoindoles via the Diels–Alder Reaction of 2H-Pyran-2-ones

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journal contribution
posted on 21.02.2016, 17:27 by Marko Krivec, Martin Gazvoda, Krištof Kranjc, Slovenko Polanc, Marijan Kočevar
The application of activated carbon (Darco KB) for the acceleration and direction of the transformation of various 2H-pyran-2-ones with N-substituted maleimides toward isoindole derivatives through the reaction sequence cycloaddition/elimination/dehydrogenation is described. In this reaction, the catalyst mainly influences the dehydrogenation step, which is essential to avoid the formation of bicyclo[2.2.2]­octenes as the other possible products. We found that the combination of Darco KB, as the metal-free catalyst, and decalin, as the solvent in a closed vessel, represents the most successful conditions. A comparison of the effect of various dehydrogenation catalysts and reaction conditions is also presented. In addition, we have proven that the aromatization occurs via a hydrogen transfer from the cyclohexadiene intermediate to the maleimide derivative (therefore producing succinimides). This transfer is facilitated by the active surface of the heterogeneous carbon-based catalyst.