Search

Solvent effects on 31P‐NMR parameters for triphenylphosphine oxide and triphenylphosphine in chloroform have been extensively investigated by testing different solvation models. The solvent is described implicitly, mixed implicitly/explicitly, and using full explicit models. Polarizable continuum model (PCM), molecular dynamic (MD) simulations, and hybrid quantum mechanics/molecular mechanics (QM/MM) calculations are used to disclose the effects of solute/solvent interactions and, more generally, the role of the embedding in NMR simulations. The results show the beneficial effect of carrying out QM/MM optimizations on top of geometries directly extracted from classical MD simulations, used to ensure representative conformational sampling. The nuclear shielding convergence has been tested against a different number of snapshots and with the inclusion of solvent shells into the QM region. An automated MD//QM/MM//GIAO protocol, implemented in the COBRAMM package, is here proposed and tested on trimethyl phosphite showing that our approach boosts the convergence of nuclear shielding satisfactorily. The present work aims to be a stepping‐stone to assess proper QM/MM computational strategies in simulating chemical shifts in non‐homogeneous systems like supramolecular and biological systems. [ABSTRACT FROM AUTHOR]

The reaction of Ti(NMe2)4 with the salan ligand precursor H2N2O2H2 led to the formation of [(L*)Ti(NHMe2)2] (L*=N2O24−) that forms [(H2N2O2)TiCl2] upon reaction with two equiv. of Me3SiCl. [(L*)Ti(py)2] was obtained from the reaction of [Ti(NtBu)Cl2(py)3] with the sodium salt H2N2O2Na2. Treatment of [(L*)Ti(NHMe2)2] with two equiv. of tBuNCO led to the insertion of the isocyanate molecules into the Ti−Nsalan bonds with the formation of [{L*(N(tBu)CO)2}Ti]. Conversely, the reaction of [(H2N2O2)Ti(OiPr)2] with two equiv. of tBuNCO led to the insertion of one isocyanate molecule into a Ti−Nsalan bond with the formation of [{(HN2O2)(N(tBu)CO)}Ti(OiPr)]. Computational studies were performed to gain insight into the reactivity of isocyanates with salan‐based Ti(IV) complexes. [ABSTRACT FROM AUTHOR]

Achieving the selective modification of symmetric poly‐hydroxylated compounds presents a significant challenge due to the presence of identical active sites. Herein, we address this challenge through the design of a ternary catalytic system that includes a photoredox catalyst, a hydrogen atom transfer promotor and a carbonation catalyst. This catalytic system enables the reversible carbonation of acyclic polyols under CO2 atmosphere, which modulates the reactivity of its distinct C−H bonds toward hydrogen atom transfers. An exquisite selectivity for the monoalkylation is achieved in a variety of unprotected light polyols, yielding valuable building blocks in short reaction times. Mechanistic and computational studies demonstrate that the formation of an intramolecular hydrogen bond between the transient carbonate and the free alcohol is pivotal for the kinetic and thermodynamic activation of a specific alcohol. [ABSTRACT FROM AUTHOR]

Achieving the selective modification of symmetric poly‐hydroxylated compounds presents a significant challenge due to the presence of identical active sites. Herein, we address this challenge through the design of a ternary catalytic system that includes a photoredox catalyst, a hydrogen atom transfer promotor and a carbonation catalyst. This catalytic system enables the reversible carbonation of acyclic polyols under CO2 atmosphere, which modulates the reactivity of its distinct C−H bonds toward hydrogen atom transfers. An exquisite selectivity for the monoalkylation is achieved in a variety of unprotected light polyols, yielding valuable building blocks in short reaction times. Mechanistic and computational studies demonstrate that the formation of an intramolecular hydrogen bond between the transient carbonate and the free alcohol is pivotal for the kinetic and thermodynamic activation of a specific alcohol. [ABSTRACT FROM AUTHOR]

A computational study of the aza-Cope rearrangement leading to angularly substituted 1-azabicyclic ring systems is presented. The calculations estimate the probability of the proton transfer between reaction intermediates and protic solvents, explain the experimentally observed reaction selectivity, and suggest new potentially more efficient systems for further in vitro and in silico investigations. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

α‐Amino acid derivatives are key components of the molecules of life. The synthesis of α‐amino carbonyl/carboxyl compounds is a contemporary challenge in organic synthesis. Herein, we report a practical method for the preparation of α‐amino acid derivatives via direct hydrative amination of activated alkynes under mild conditions, relying on sulfinamides as the nitrogen source. Computational studies suggest that the reaction is enabled by a new type of sulfonium [2,3]‐sigmatropic rearrangement. [ABSTRACT FROM AUTHOR]

The direct synthesis of ketones via carbon–carbon bond formation represents one of the most important challenges in organic synthesis. Hydroacylation of alkenes offers perhaps the most efficient and atom-economical approach for the preparation of ketones employing carbonyl compounds and alkenes as feedstocks. State-of-the-art hydroacylation is typically achieved by a transition metal-catalysed coupling of an aldehyde and an alkene but is plagued by competing decarbonylation, requiring the installation of directing groups in the aldehyde reactant. Herein, we present a method for the hydroacylation of alkenes employing amides in a metal-free regime, proceeding by a new mechanism and offering orthogonal reactivity to the conventional, metal-catalysed alternatives. [ABSTRACT FROM AUTHOR]

A computational study of the electrocyclic ring‐opening of 2‐substituted cyclobutenecarboxylic acids is presented. Detailed calculations suggest a model to predict whether the product of nucleophilic alkylation of a bicyclic lactone electrophile will be a cyclobutenecarboxylic acid or its dienoic acid isomer, based on the used nucleophile. Open, Sesame: A computational study of the electrocyclic ring‐opening of 2‐substituted cyclobutenecarboxylic acids is presented. Quantum chemical calculations analyse and clarify experimental evidence. [ABSTRACT FROM AUTHOR]