Global Diastereoconvergence in the Ireland–Claisen Rearrangement of Isomeric Enolates: Synthesis of Tetrasubstituted -Amino Acids

<div><div><div><p>A dual experimental/theoretical investigation of the Ireland–Claisen rearrangement of tetrasubstituted a-phthalimido ester enolates to afford a-tetrasubstituted, b-trisubstituted a-amino acids (generally >20:1 dr) is described. For trans allylic olefins, the Z and E-enol ethers proceed through chair and boat transition states, respectively. For cis allylic olefins, the trend is reversed. As a result, the diastereochemical outcome of the reaction is preserved regardless of the geometry of the enolate or the accompanying allylic olefin. We term this unique convergence of all possible olefin isomers as global diastereoconvergence. This reaction manifold circumvents limitations in present-day technologies for the stereoselective enolization of a,a-disubstituted allyl esters. Density func- tional theory paired with state-of-the-art local coupled-cluster theory (DLPNO-CCSD(T)) was employed for the accurate determina- tion of quantum mechanical energies.</p></div></div></div>

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Theoretical Electronic and Rovibrational Studies for Anions of Interest to the DIBs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313016098 ◽

2013 ◽

Vol 9 (S297) ◽

pp. 344-348 ◽

Cited By ~ 4

Author(s):

R. C. Fortenberry

Keyword(s):

Excited State ◽

Excited States ◽

State Of The Art ◽

Spectroscopic Constants ◽

Coupled Cluster ◽

Electronic Excitations ◽

Electronically Excited States ◽

Coupled Cluster Theory ◽

Electronically Excited ◽

Enolate Anion

AbstractThe dipole-bound excited state of the methylene nitrile anion (CH2CN−) has been suggested as a candidate carrier for a diffuse interstellar band (DIB) at 803.8 nm. Its corresponding radical has been detected in the interstellar medium (ISM), making the existence for the anion possible. This work applies state-of-the-art ab initio methods such as coupled cluster theory to reproduce accurately the electronic excitations for CH2CN− and the similar methylene enolate anion, CH2CHO−. This same approach has been employed to indicate that 19 other anions may possess electronically excited states, five of which are valence in nature. Concurrently, in order to assist in the detection of these anions in the ISM, work has also been directed towards predicting vibrational frequencies and spectroscopic constants for these anions through the use of quartic force fields (QFFs). Theoretical rovibrational work on anions has thus far included studies of CH2CN−, C3H−, and is currently ongoing for similar systems.

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Accurate Ionization Potentials, Electron Affinities and Electronegativities of Single-Walled Carbon Nanotubes by State-of-the-Art Local Coupled-Cluster Theory

Bulletin of the Chemical Society of Japan ◽

10.1246/bcsj.20180254 ◽

2019 ◽

Vol 92 (1) ◽

pp. 170-174 ◽

Cited By ~ 2

Author(s):

Masaaki Saitow ◽

Achintya K. Dutta ◽

Frank Neese

Keyword(s):

Carbon Nanotubes ◽

State Of The Art ◽

Single Walled Carbon Nanotubes ◽

Ionization Potentials ◽

Coupled Cluster ◽

Electron Affinities ◽

Coupled Cluster Theory ◽

Cluster Theory ◽

Single Walled Carbon ◽

Walled Carbon Nanotubes

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A comparative study using state-of-the-art electronic structure theories on solid hydrogen phases under high pressures

npj Computational Materials ◽

10.1038/s41524-019-0243-7 ◽

2019 ◽

Vol 5 (1) ◽

Cited By ~ 4

Author(s):

Ke Liao ◽

Xin-Zheng Li ◽

Ali Alavi ◽

Andreas Grüneis

Keyword(s):

Monte Carlo ◽

Density Functional ◽

High Pressures ◽

State Of The Art ◽

Solid Hydrogen ◽

Coupled Cluster ◽

Temperature Phase ◽

Diffusion Monte Carlo ◽

Coupled Cluster Theory ◽

Cluster Theory

AbstractIdentifying the atomic structure and properties of solid hydrogen under high pressures is a long-standing problem of high-pressure physics with far-reaching significance in planetary and materials science. Determining the pressure-temperature phase diagram of hydrogen is challenging for experiment and theory due to the extreme conditions and the required accuracy in the quantum mechanical treatment of the constituent electrons and nuclei, respectively. Here, we demonstrate explicitly that coupled cluster theory can serve as a computationally efficient theoretical tool to predict solid hydrogen phases with high accuracy. We present a first principles study of solid hydrogen phases at pressures ranging from 100 to 450 GPa. The computed static lattice enthalpies are compared to state-of-the-art diffusion Monte Carlo results and density functional theory calculations. Our coupled cluster theory results for the most stable phases including C2/c-24 and P2$${}_{1}$$1/c-24 are in good agreement with those obtained using diffusion Monte Carlo, with the exception of Cmca-4, which is predicted to be significantly less stable. We discuss the scope of the employed methods and how they can contribute as efficient and complementary theoretical tools to solve the long-standing puzzle of understanding solid hydrogen phases at high pressures.

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State-of-the-art density matrix renormalization group and coupled cluster theory studies of the nitrogen binding curve

The Journal of Chemical Physics ◽

10.1063/1.1783212 ◽

2004 ◽

Vol 121 (13) ◽

pp. 6110-6116 ◽

Cited By ~ 147

Author(s):

Garnet Kin-Lic Chan ◽

Mihály Kállay ◽

Jürgen Gauss

Keyword(s):

Renormalization Group ◽

Density Matrix ◽

State Of The Art ◽

Coupled Cluster ◽

Density Matrix Renormalization Group ◽

Coupled Cluster Theory ◽

Cluster Theory ◽

Density Matrix Renormalization ◽

Binding Curve

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Excitonic Coupled-cluster Theory: Part I, General Formalism

10.26434/chemrxiv.5330773.v2 ◽

2017 ◽

Cited By ~ 1

Author(s):

Yuhong Liu ◽

Anthony Dutoi

Keyword(s):

Electron Correlation ◽

Degrees Of Freedom ◽

Model Systems ◽

Coupled Cluster ◽

Effective Hamiltonian ◽

Coupled Cluster Theory ◽

Cluster Theory ◽

Companion Article ◽

High Level ◽

Fragment Interaction

<div> <div>A shortcoming of presently available fragment-based methods is that electron correlation (if included) is described at the level of individual electrons, resulting in many redundant evaluations of the electronic relaxations associated with any given fluctuation. A generalized variant of coupled-cluster (CC) theory is described, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction is pre-computed and permanently folded into the effective Hamiltonian. This article provides a high-level description of the CC variant, establishing some useful notation, and it demonstrates the advantage of the proposed paradigm numerically on model systems. A companion article shows that the electronic Hamiltonian of real systems may always be cast in the form demanded. This framework opens a promising path to build finely tunable systematically improvable methods to capture precise properties of systems interacting with a large number of other systems. </div> </div>

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Excitonic Coupled-cluster Theory: Part I, General Formalism

10.26434/chemrxiv.5330773.v1 ◽

2017 ◽

Author(s):

Yuhong Liu ◽

Anthony Dutoi

Keyword(s):

Electron Correlation ◽

Degrees Of Freedom ◽

Model Systems ◽

Coupled Cluster ◽

Effective Hamiltonian ◽

Coupled Cluster Theory ◽

Cluster Theory ◽

Companion Article ◽

High Level ◽

Fragment Interaction

<div> <div>A shortcoming of presently available fragment-based methods is that electron correlation (if included) is described at the level of individual electrons, resulting in many redundant evaluations of the electronic relaxations associated with any given fluctuation. A generalized variant of coupled-cluster (CC) theory is described, wherein the degrees of freedom are fluctuations of fragments between internally correlated states. The effects of intra-fragment correlation on the inter-fragment interaction is pre-computed and permanently folded into the effective Hamiltonian. This article provides a high-level description of the CC variant, establishing some useful notation, and it demonstrates the advantage of the proposed paradigm numerically on model systems. A companion article shows that the electronic Hamiltonian of real systems may always be cast in the form demanded. This framework opens a promising path to build finely tunable systematically improvable methods to capture precise properties of systems interacting with a large number of other systems. </div> </div>

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α-Alkoxyalkyl Triphenylphosphonium Salts: Synthesis and Reactions

Current Organic Chemistry ◽

10.2174/1385272823666190926092242 ◽

2019 ◽

Vol 23 (16) ◽

pp. 1738-1755

Author(s):

Humaira Y. Gondal ◽

Zain M. Cheema ◽

Abdul R. Raza ◽

Ahmed Abbaskhan ◽

M. I. Chaudhary

Keyword(s):

Carbonyl Compounds ◽

Claisen Rearrangement ◽

Alder Reaction ◽

Coupling Reactions ◽

Phosphonium Salts ◽

Organic Transformations ◽

Enol Ethers ◽

Wide Range ◽

Synthetic Methodologies ◽

Alkoxy Groups

Following numerous applications of Wittig reaction now functionalized phosphonium salts are gaining attention due to their characteristic properties and diverse reactivity. This review is focused on α-alkoxyalkyl triphenylphosphonium salts: an important class of functionalized phosphonium salts. Alkoxymethyltriphenylphosphonium salts are majorly employed in the carbon homologation of carbonyl compounds and preparation of enol ethers. Their methylene insertion strategy is extensively demonstrated in the total synthesis of a wide range of natural products and other important organic molecules. Similarly enol ethers prepared thereof are important precursors for different organic transformations like Diels-Alder reaction, Claisen rearrangement, Coupling reactions, Olefin metathesis and Nazarov cyclization. Reactivity of these α-alkoxyalkylphosphonium salts have also been studied in the nucleophilic substitution reactions. A distinctive application of this class of phosphonium salts was recently reported in the phenylation of carbonyl compounds under very mild conditions. Synthesis of structurally diverse alkoxymethyltriphenylphosphonium salts with variation in alkoxy groups as well as counter anions are reported in literature. Here we present a detailed account of different synthetic methodologies for the preparation of this unique class of quaternary phosphonium salts and their applications in organic synthesis.

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