A simple method for cleavage of methoxymethyl (MOM)-ether and ester derivatives using bismuth trichloride (BiCl3) is described. Alkyl, alkenyl, alkynyl, benzyl and anthracene MOM ether derivatives as well as MOM...
The intramolecular Diels‐Alder (IMDA) reactions of N‐allyl‐furfurylamine (1a) and N‐trityl‐allyl‐furfurylamine (1b), were studied within the molecular electron density theory (MEDT) using density functional theory method [B3LYP/6‐31G(d)]. In spite of the high activation enthalpies, the low unfavourable activation entropies associated to these intramolecular processes permit these IMDA reactions to take place. The IMDA reaction of 1a is thermodynamically unfavourable. The presence of the bulky −CPh3 group in the amine nitrogen atom that destabilises the extended conformation of 1b turns the process into an exergonic one. This behaviour does not only affect the thermochemistry of the reaction, but also the kinetic parameters, thus accelerating the reaction. Electron localisation function topological analysis of the C−C single bond formation along the IMDA reaction of 1a shows a bonding pattern similar to non‐polar intermolecular Diels‐Alder reactions. The present MEDT study explains the experimental results; although the steric buttress is able to change the direction of these reversible IMDA reactions, this change is only possible due to the aromatic nature of the furanyl diene system.
These phosphorus cycloadducts are kinetically and thermodynamically more favorable than their nitrogen analogues, providing incentives to experimentalists in the quest to synthesise phosphorus containing heterocycles.
The synthesis of cyclopentadiene derivatives via the domino reaction of norbornadienes with dimethyl 1,2,4,5-tetrazine-3,6dicarboxylate, followed a retro-Diels-Alder reaction, was reported by Dalkılıç few years ago (Tetrahedron 2015;71 : 1966). In some cases, the formation of an unexpected dihydropyridazine (DHP) was observed, and explained by a 1,3-hydrogen shift. A density functional theory study is herein reported giving insights into the proposed mechanisms with different substitu-ents on norbornadiene. Based on the kinetic and thermodynamic data, the retro-Diels-Alder reaction is confirmed to explain the formation of cyclopentadienes plus pyridazines. The intramolecular 1,3-hydrogen shift mechanism was not sufficient to explain the exclusive formation of two DHPs. Thus, an alternative mechanism involving a stepwise tautomerisation is being reported for formation of DHPs.
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