Catalytic dry reforming under industrially relevant conditions of high pressures and high temperatures poses severe challenges towards catalyst materials and process engineering. The demanding conditions under which the reaction is performed lead to a coupling of reactions occurring in the gas phase and reactions which are catalyzed by the material employed as catalyst. A profound analysis of the mechanisms occurring in gas phase and resulting products from gas phase reactions is key to understanding part of the challenges that any catalyst material, irrespective of its nature, will have to cope with. The deposition of coke on an active catalyst is as well one of the most limiting factors for catalyst lifetime and catalyst activity in dry reforming. Therefore, an understanding of the thermodynamics behind coke formation and an intricate description of the mechanisms driving the evolution of coke is a vital piece of the picture. Acid-base properties of the catalyst material and the role and nature of the active metal do also need to be considered. A large part of the review deals with mechanisms which are relevant for coke gasification and insights into materials properties, which are relevant to allow for reaction pathways along these lines. The review article focusses on research results which have been achieved using model systems -typically the analysis of model systems is a more rewarding exercise compared to fully formulated industrial catalyst systems, as here more elucidating structure-property relationships can be drawn. Additionally the article discusses dry methane reforming in the context of alternative syngas generation technologies and attempts to create an application perspective for the reader in the context of a sustainable approach towards carbon capture and storage.

The regioselectivities and the reactivities (relative rates) for the ene reaction of the enophile 4-nitronitrosobenzene (ArNO) with an extensive set of regiochemically defined acyclic and cyclic olefins have been determined. These experimental data establish that the ArNO enophile attacks the olefinic substrate along the novel skew trajectory, with preferred hydrogen abstraction at the corner (twix regioselectivity). This is in contrast to the isoelectronic species singlet oxygen ((1)O(2)), which abstracts at the higher substituted side of the double-bond (cis effect), and triazolindione (TAD), which undergoes the ene reaction at the more crowded end (gem effect). Ab initio computations (B3LYP/6-31+g) for the ene reaction of the ArNO with 2-methyl-2-butene reveal that the steric effects between the aryl group of the enophile and the substituents of the olefin dictate the skew trajectory. These computations identify the aziridine N-oxide (AI) as a bona fide intermediate in this ene reaction, whose formation is usually rate-determining and, thus, irreversible along the skew trajectory (twix selectivity). The reversible generation of the AI becomes feasible when conformational constraints outweigh steric effects, as manifested by enhanced twin regioselectivity.

The ene reaction of singlet oxygen ((1)O(2)), triazolinedione (TAD), and nitrosoarene, specifically 4-nitronitrosobenzene (ArNO), with the tetrasubstituted 1,3-allylically strained, chiral allylic alcohol 3,4-dimethylpent-3-en-2-ol (2) leads to the threo-configured ene products in high diastereoselectivity, a consequence of the hydroxy-group directivity. Hydrogen bonding favors formation of the threo-configured encounter complex threo-EC in the early stage of ene reaction. For the analogous twix deuterium-labeled allylic alcohol Z-2-d(3), a hitherto unrecognized dichotomy between (1)O(2) and the ArNO and TAD enophiles is disclosed in the regioselectivity of the tetrasubstituted alcohol: Whereas for ArNO and TAD, hydrogen bonding with the allylic hydroxy group dictates the regioselectivity (twix selectivity), for (1)O(2), the cis effect dominates (twin/trix selectivity). From the interdependence between the twix/twin regioselectivity and the threo/erythro diastereoselectivity, it has been recognized that the enophile also attacks the allylic alcohol from the erythro pi face without assistance by hydrogen bonding with the allylic hydroxy functionality.

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A one‐pot allylic amidation procedure, which employs the ene reaction of acylnitroso compounds 2 with electron‐rich olefins 3a,b, is presented; the acylnitroso enophile is generated in situ by oxidation of hydroxamic acids 1 with iodosobenzene diacetate. The resulting N‐allylhydroxamic acids 4 (ene products) are quantitatively acetylated for ease of handling; as an example, the reduction of the acetylated derivative 5b by samarium diiodide was carried out to afford the N‐allyl amide 6b in quantitative yields.