Computational Examination of (4 + 3) versus (3 + 2) Cycloaddition in the Interception of Nazarov Reactions of Allenyl Vinyl Ketones by Dienes

Abstract

A computational examination of the tandem Nazarov/cycloaddition process involving an allenyl vinyl ketone with a diene has been carried out using the ωB97X-D/6-311++G(d,p)//ωB97X-D/6-31+G(d,p) method with solvation modeled by SMD-PCM. The barrier for the initial Lewis acid mediated Nazarov reaction, which provided the intermediate cyclic oxylallyl cation, was higher than that for any subsequent cycloaddition. The barrier for the first step of a subsequent stepwise reaction did not vary much with the diene, and the lowest barrier was with the diene in its s-trans conformation. Stepwise formation of a (4 + 3) cycloaddition product was not energetically feasible, but (3 + 2) cycloaddition products could have been produced through low energy pathways. The barrier for a concerted (4 + 3) cycloaddition did depend upon the diene, which was always in an s-cis geometry. The barriers for the compact and the extended geometries for the transition states of (4 + 3) cycloadditions were not much different.

Diels–Alder Reactivities of Benzene, Pyridine, and Di-, Tri-, and Tetrazines: The Roles of Geometrical Distortions and Orbital Interactions

“…Figure shows a potential energy surface along some reaction coordinate, and also defines the distortion/interaction model, also known as the activation strain model. , The activation energy Δ E ‡ act of the reaction is decomposed into the distortion energy of the reactants plus the interaction energy Δ E ‡ int between the distorted reactants at the transition geometry (Δ E ‡ act = Δ E ‡ dist + Δ E ‡ int ). The distortion energy Δ E ‡ dist is composed of the distortion energies of diene (Δ E ‡ dist_4e ) and dienophile (Δ E ‡ dist_2e ) to achieve the transition state geometry.…”

Multicomponent Double Diels–Alder/Nazarov Tandem Cyclization of Symmetric Cross‐Conjugated Diynones to Generate [6‐5‐6] Tricyclic Products

“…We propose that the mechanism involves alkyl migration of the oxyallyl cation intermediate to form a stabilized benzylic cation, followed by 1,2‐phenyl migration. This suggests that alternate pathways such as rearrangements, or oxyallyl cation trapping,, by excess diene or side products can account for the lower yield of product 6 , although we were unable to observe or isolate these products. We also looked at using the more Lewis acidic boron trichloride as a catalyst in an attempt to optimize the yield (Scheme b).…”

Novel d-Annulated Pentacyclic Steroids: Regioselective Synthesis and Biological Evaluation in Breast Cancer Cells

“…The relative energies of 2 b and 2"b and the energy of the transition state between these structures were evaluated by DFT calculations. The geometry optimization and energy calculations for 2 b and 2"b were performed at the ωB97X-D/6-311++G(d,p)//ωB97X-D/6-31+G(d,p) level of theory, according to the literature data [89]. The energy difference between the conformers is rather small (0.2 kcal/mol) and the energy barrier for conformational transitions is ca.…”