1,3- versus 1,4-[π4+π2] Cycloadditions between methyl glyoxylate oxime and cyclopentadiene or cyclopentene

A Molecular Electron Density Theory Study of the Competitiveness of Polar Diels⁻Alder and Polar Alder-ene Reactions

The competitiveness of the BF₃ Lewis acid (LA) catalyzed polar Diels–Alder (P-DA) and polar Alder-ene (P-AE) reactions of 2-methyl-1,3-butadiene, a diene possessing an allylic hydrogen, with formaldehyde has been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. Coordination of BF₃ LA to the oxygen of formaldehyde drastically accelerates both reactions given the high electrophilic character of the BF₃:formaldehyde complex. As a consequence, these reactions present a very low activation enthalpy—less than 2.2 kcal·mol⁻¹—thus becoming competitive. In dioxane, the P-AE reaction is slightly favored because of the larger polar character of the corresponding transition state structure (TS). In addition, the Prins reaction between hexahydrophenanthrene and the BF₃:formaldehyde complex has also been studied as a computational model of an experimental P-AE reaction. For this LA-catalyzed reaction, the P-DA reaction presents very high activation energy because of the aromatic character of the dienic framework. The present MEDT study allows establishing the similarity of the TSs associated with the formation of the C–C single bond in both reactions, as well as the competitiveness between P-AE and P-DA reactions when the diene substrate possesses at least one allylic hydrogen, thus making it necessary to be considered by experimentalists in highly polar processes. In this work, the term “pseudocyclic selectivity” is suggested to connote the selective formation of structural isomers through stereoisomeric pseudocyclic TSs.

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Revisiting oxime–nitrone tautomerism. Evidence of nitrone tautomer participation in oxime nucleophilic addition reactions

Oxime–nitrone tautomerism takes place through a biomolecular mechanism. Participation of nitrone tautomer in nucleophilic addition reactions is evidenced by the first time.

On the scope of oxidation of tertiary amines: Meisenheimer rearrangements versus Cope elimination in 2-(cyanoethyl)-2-azanorbornanes

When oxidized, exo-2-(cyanoethyl)-2-azanorbornene is prone to [1,2]-Meisenheimer rearrangement, its endo isomer undergoes [2,3]-Meisenheimer and exo/endo-2-(cyanoethyl)-2-azanorbornanes afford N-hydroxylamines through Cope elimination.

2-Azanorbornane--a versatile chiral aza-Diels-Alder cycloadduct: preparation, applications in stereoselective synthesis and biological activity

The review presents the achievements in the field of preparation of chiral 2-azanorbornyl derivatives and their application in various stereoselective reactions as well as in biomimetic studies.

A DFT study of the role of the Lewis acid catalysts in the [3 + 2] cycloaddition reaction of the electrophilic nitrone isomer of methyl glyoxylate oxime with nucleophilic cyclopentene

The mechanism and stereoselectivity of the BH₃-catalysed 32CA reaction between C-methoxycarbonyl nitrone and cyclopentene has been studied using MPWB1K/6-31G(d) computational level.

New L-serine derivative ligands as cocatalysts for diels-alder reaction

New L-serine derivative ligands were prepared and tested as cocatalyst in the Diels-Alder reactions between cyclopentadiene (CPD) and methyl acrylate, in the presence of several Lewis acids. The catalytic potential of the in situ formed complexes was evaluated based on the reaction yield. Bidentate serine ligands showed good ability to coordinate medium strength Lewis acids, thus boosting their catalytic activity. The synthesis of the L-serine ligands proved to be highly efficient and straightforward.