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

Abstract

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.

Chloranil as an Efficient Oxidant of the Cyclohexadiene Intermediates Formed by a Cycloaddition of Substituted 2H‐Pyran‐2‐ones and Styrenes En Route to the Boscalid Derivatives

“…For this oxidation step, we (and others) have already successfully employed active charcoal Darco KB as a heterogeneous dehydrogenation catalyst (in such case, the excess of the styrene was acting as the oxidant, possibly in conjunction with the acceptorless pathway of the dehydrogenation taking place) . Alternatively, this dehydrogenation could also be achieved by the application of chloranil (tetrachloro‐1,4‐benzoquinone) as proved previously .…”

Application of PEDOT‐CNT Microelectrodes for Neurotransmitter Sensing

“…Furthermore, we attempted another experiment with a transition‐metal catalyst based on reports in the literature 5b,f,g. By adding the Pd/C catalyst to the reaction mixture of 1 a and 2 a , the reaction was then performed under standard reaction conditions and resulted in neither the exo,endo isomer nor the dehydrogenation product, isoindole, which was reported by Kocevar and co‐workers 5b,g. Only the bicyclo[2.2.2]octene product was obtained in 60 % yield.…”

A 26-Membered Macrocycle Obtained by a Double Diels–Alder Cycloaddition Between Two 2H-Pyran-2-one Rings and Two 1,1'-(Hexane-1,6-diyl)bis (1H-pyrrole-2,5-dione)s

“…[27][28][29][30][31] Namely, it was already observed that 2H-pyran-2-ones can act as "double" dienes, reacting in two consecutive Diels-Alder reactions with two distinctive molecules of the dienophiles, yielding bicyclo[2.2.2]octenes. 30 The initial cycloaddition step leads to the formation of CO 2 -bridged oxabicyclo[2.2.2]octenes that in the next step eliminate a molecule of CO 2 (via a retro-hetero-Diels-Alder reaction) providing cyclohexadiene systems that act as new dienes for another molecule of dienophile finally providing the double cycloadducts.…”