Accounting for Diradical Character through DFT. The Case of Vinyl Allene Oxide Rearrangement

The transformation of vinyl allene oxides into cyclopentenones is key to the biosynthesis of a number of hormone-like molecules in plants. Two competitive paths are generally accepted for this transformation: a concerted S_N2-like mechanism and a stepwise path with a diradical oxyallyl intermediate. Recently, a new stepwise closed-shell path has been proposed that circumvents the key oxyallyl intermediate. In this work, we conduct a thorough computational investigation, including dynamic effects, to identify the most likely mechanism for this transformation

CO₂ Complexes with Five-Membered Heterocycles: Structure, Topology, and Spectroscopic Characterization

In a first step toward the rational design of macrocyclic structures optimized for CO₂ capture, we systematically explored the potential of 30 five-membered aromatic heterocycles to establish coordinating complexes with this pollutant. The interactions between the two moieties were studied in several orientations, and the obtained complexes were analyzed in terms of electron density and vibrational fingerprint. The former is an aid to provide an in-depth knowledge of the interaction, whereas the latter should help to select structural motifs that have not only good complexation properties but also diagnostic spectroscopic signals

Lennard-Jones Potentials for the Interaction of CO₂ with Five-Membered Aromatic Heterocycles

We used M06-2X/Def2-TZVPP to calculate a broad set of rigid interaction profiles between CO₂ and 30 different aromatic heterocycles, based on pyrrole, furan, and thiophene with ring positions subsituted with up to four nitrogens. For each system, several orientations of the fragments were explored to both find the preferred interaction mode and have information about other interaction modes that can contribute to the binding energy when CO₂ is captured by complex systems. From these data, Lennard-Jones potentials were obtained, which can be used for the parametrization of force fields that correctly describe the multipolar and dispersion interactions at play between these kinds of fragments. These results are expected to contribute to the development of new force fields for the study of chemical systems for the capture and sequestration of CO₂ and also directly for the design of such systems

Mechanism of the Molybdenum-Mediated Cadogan Reaction

Oxygen atom transfer reactions are receiving increasing attention because they bring about paramount transformations in the current biomass processing industry. Significant efforts have therefore been made lately in the development of efficient and scalable methods to deoxygenate organic compounds. One recent alternative involves the modification of the Cadogan reaction in which a Mo­(VI) core catalyzes the reduction of <i>o</i>-nitrostyrene derivatives to indoles in the presence of PPh₃. We have used density functional theory calculations to perform a comprehensive mechanistic study on this transformation, in which we find two clearly defined stages: an associative path from the nitro to the nitroso compound, characterized by the reduction of the catalyst in the first step, and a peculiar mechanism involving oxazaphosphiridine and nitrene intermediates leading to an indole product, where the metal catalyst does not participate

[MoO₂]²⁺-Mediated Oxygen Atom Transfer via an Unusual Lewis Acid Mechanism

Density functional theory is applied to the study of the oxygen atom transfer reaction from sulfoxide (DMSO) to phosphine (PMe₃) catalyzed by the [MoO₂]²⁺ active core. In this work, two fundamentally different roles are explored for this dioxometal complex in the first step of the catalytic cycle: as an oxidizing agent and as a Lewis acid. The latter turns out to be the favored pathway for the oxygen atom transfer. This finding may have more general implications for similar reactions catalyzed by the same [MoO₂]²⁺ core

Mechanism of the Molybdenum-Mediated Cadogan Reaction

Oxygen atom transfer reactions are receiving increasing attention because they bring about paramount transformations in the current biomass processing industry. Significant efforts have therefore been made lately in the development of efficient and scalable methods to deoxygenate organic compounds. One recent alternative involves the modification of the Cadogan reaction in which a Mo­(VI) core catalyzes the reduction of <i>o</i>-nitrostyrene derivatives to indoles in the presence of PPh₃. We have used density functional theory calculations to perform a comprehensive mechanistic study on this transformation, in which we find two clearly defined stages: an associative path from the nitro to the nitroso compound, characterized by the reduction of the catalyst in the first step, and a peculiar mechanism involving oxazaphosphiridine and nitrene intermediates leading to an indole product, where the metal catalyst does not participate

Opening Access to New Chiral Macrocycles: From Allenes to Spiranes

Chiral macrocycles offer great potential and versatility regarding their applications. They have been employed in asymmetric catalysts, as chiral sensors, and as chiral supramolecular frameworks. For these reasons, they have been attracting increasing interest over the years. Despite all of the work developed in this area, most of the reported chiral macrocycles are not conformationally stable and present weak chiroptical responses. Such features substantially limit the scope of applications for these compounds. On the other hand, we have shown that axially chiral allenes can be introduced into macrocycles, conferring conformational stability and outstanding chiroptical responses. However, these allenes photoisomerize when conjugated with electron-donating groups, hampering the possibility of synthesizing systems with tuned optical properties. To overcome all of these limitations with a single structural motif, we propose the use of spiranes to construct new stable, conformationally rigid, and chemically functionalizable macrocyclic structures with strong chiroptical responses. As a first step in this new direction, we theoretically predict the chiroptical responses for macrocycles bearing spiranes to be as strong as with their allenic counterparts. As a side product, we also test the popular Minnesota functional, M06-2X, and compare it with cam-B3LYP, which has been previously analyzed with respect to experimental data in our laboratory. Thus, we hereby propose that spiranes are a good alternative to allenes for the construction of new chiral macrocycles

From Hydrindane to Decalin: A Mild Transformation through a Dyotropic Ring Expansion

An unexpected ring expansion converting hydrindane cores into decalins has been observed. The process occurs under very mild conditions and with exquisite transfer of chiral information. The ring expansion provides access to decorated decalins with complete stereocontrol. The reaction mechanism is studied in order to gain insight into the underlying causes for the low thermal requirements in this reaction and the nature of the chirality transfer process. Interestingly, both result from an unprecedented dyotropic reaction involving a mesylate group

From Hydrindane to Decalin: A Mild Transformation through a Dyotropic Ring Expansion

An unexpected ring expansion converting hydrindane cores into decalins has been observed. The process occurs under very mild conditions and with exquisite transfer of chiral information. The ring expansion provides access to decorated decalins with complete stereocontrol. The reaction mechanism is studied in order to gain insight into the underlying causes for the low thermal requirements in this reaction and the nature of the chirality transfer process. Interestingly, both result from an unprecedented dyotropic reaction involving a mesylate group