Isomerization of surface functionalized SWCNTs and the critical influence on photoluminescence: static calculations and excited-state dynamics simulations

Single-walled carbon nanotubes (SWCNTs) functionalized with sparse surface chemical groups are promising for a variety of optical applications such as quantum information and bio-imaging. However, the luminescence efficiencies and stability, two key aspects, undoubtedly govern their practical usage. Herein, we assess the surface migration of oxygen and triazine groups on as-modified SWCNT fragments by adopting transition state theory and explore the de-excitation of oxygen-functionalized SWCNT fragments by performing non-adiabatic excited-state dynamics simulations. According to the predicted moderate or even small reaction barriers, the migration of both oxygen and triazine groups is feasible from an sp3 defect configuration forming an energetically more stable sp2 configuration at moderate or even room temperatures. Such isomerization leads to drastically different light emission capabilities as indicated by the large or zero oscillator strengths. During the dynamics simulations, the lowest excited singlet (S1) state rapidly decays in energy within 20 fs and then fluctuates until the end, providing insights into the emission mechanism of SWCNTs. This study highlights the potential intrinsic limitations of surface-functionalized SWCNTs for luminescence applications.

Unveiling the Stereoselectivity and Regioselectivity of the [3+2] Cycloaddition Reaction between N-methyl-C-4-methylphenyl-nitrone and 2-Propynamide from a MEDT Perspective

[3+2] cycloaddition reactions play a crucial role in synthesizing complex organic molecules and have significant applications in drug discovery and materials science. In this study, the [3+2] cycloaddition (32CA) reactions of N-methyl-C-4-methyl phenyl-nitrone 1 and 2-propynamide 2, which have not been extensively studied before, were investigated using molecular electron density theory (MEDT) at the B3LYP/6-311++G(d,p) level of theory. According to an electron localization function (ELF) study, N-methyl-C-4-methyl phenyl-nitrone 1 is a zwitterionic species with no pseudoradical or carbenoid centers. Conceptual density functional theory (CDFT) indices were used to predict the global electronic flux from the strong nucleophilic N-methyl-C-4-methyl phenylnitrone 1 to the electrophilic 2-propynamide 2 functions. The 32CA reactions proceeded through two pairs of stereo- and regioisomeric reaction pathways to generate four different products: 3, 4, 5, and 6. The reaction pathways were irreversible owing to their exothermic characters: -136.48, -130.08, -130.99, and -140.81 kJ mol^-1, respectively. The enthalpy of the 32CA reaction leading to the formation of cycloadduct 6 was lower compared with the other path owing to a slight increase in its polar character, observed through the global electron density transfer (GEDT) during the transition states and along the reaction path. A bonding evolution theory (BET) analysis showed that these 32CA reactions proceed through the coupling of pseudoradical centers, and the formation of new C-C and C-O covalent bonds did not begin in the transition states.

Continuous-flow synthesis of 3,5-disubstituted pyrazoles via sequential alkyne homocoupling and Cope-type hydroamination

A flow chemistry-based approach is presented for the synthesis of 3,5-disubstituted pyrazoles via sequential copper-mediated alkyne homocoupling and Cope-type hydroamination of the intermediary 1,3-diynes in the presence of hydrazine as nucleophilic reaction partner. The proposed multistep methodology offers an easy and direct access to valuable pyrazoles from cheap and readily available starting materials and without the need for the isolation of any intermediates.

A telescoped continuous-flow method is presented for the synthesis of 3,5-disubstituted pyrazoles via copper-mediated alkyne homocoupling and Cope-type hydroamination of the intermediary 1,3-dialkynes.

Competing mechanisms and origins of chemo- and stereo-selectivities of NHC-catalyzed reactions of enals with 2-aminoacrylates

A DFT study on competing mechanisms of NHC-catalyzed reactions of enals with 2-aminoacrylates has been performed for the first time.

Insights into the isothiourea-catalyzed asymmetric [4 + 2] annulation of phenylacetic acid with alkylidene pyrazolone

A computational study on the isothiourea-catalyzed asymmetric [4 + 2] annulation of phenylacetic acid with alkylidene pyrazolone was performed using the DFT method.

Insights into N-heterocyclic carbene-catalyzed [3 + 4] annulation reactions of 2-bromoenals with N-Ts hydrazones

A DFT study toward N-heterocyclic carbene-catalyzed [3 + 4] annulation reactions of 2-bromoenals has been performed for the first time.

Insights into the NHC-catalyzed cascade Michael/aldol/lactamization reaction: mechanism and origin of stereoselectivity

A DFT study of the NHC-catalyzed cascade Michael/aldol/lactamization reaction has been performed for the first time.

Base-Mediated Hydroamination of Alkynes

Inter- or intramolecular hydroamination reactions are a paradigmatic example of modern sustainable organic chemistry, as they are a catalytic, 100% atom-economical, and waste-free process of fundamental simplicity in which an amine is added to an alkyne substrate. Many enamines are found in many natural and synthetic compounds possessing interesting physiological and biological activities. The development of synthetic protocols for such molecules and their transformation is a persistent research topic in pharmaceutical and organic chemistry. Hydroamination is conspicuously superior to the other accessible methods, such as the imination of ketones or the aminomercuration/demercuration of alkynes, that involve the stoichiometric use of toxic reagents. Additionally, the hydroamination of alkyne substrates has been successfully employed as a key step in synthesizing target molecules through total syntheses containing substituted indoles, pyrroles, imidazoles, and other heterocycles as core moieties. Many research groups have explored inter- or intramolecular hydroamination of alkynes for the synthesis of diversely substituted nitrogen heterocycles using expensive metal catalysts. However, in contrast to metal-catalyzed hydroamination, the base-mediated hydroamination of alkynes has not been extensively studied. Various inorganic (such as hydroxides, phosphates, and carbonates) and organic bases have been proven to be valuable reagents for achieving the hydroamination process. This method represents an attractive strategy for the construction of a broad range of nitrogen-containing compounds that prevents the formation of byproducts in the creation of a C-N linkage. The presence of a base is thought to facilitate the attack of nitrogen nucleophiles, such as indoles, pyrroles, and imidazoles, on unsaturated carbon substrates through the activation of the triple bond and thus transforming the electron-rich alkyne into an electrophile. In the past few years, we have been involved in the development of methods for the nucleophilic addition of N-heterocycles onto terminal and internal alkynes using alkali base catalysts to achieve new carbon-nitrogen bond-forming reactions. During our study, we discovered the regioselective preferential nucleophilic addition of N-heterocycles onto the haloarylalkyne over N-arylation of the aryl halide. In this Account, we summarize our latest achievements in regio-, stereo-, and chemoselective hydroamination chemistry of N-nucleophiles with alkynes using a superbasic medium to produce a broad range of highly functionalized vinyl and styryl enamines, which are valuable and versatile synthetic intermediates for the synthesis of bioactive compounds. Interestingly, the stereoselectivity of the addition products (kinetically stable Z and thermodynamically stable E isomers) was found to be dependent upon time. It is worthwhile to note that hydroaminated products formed by the addition reaction can further be utilized for the synthesis of indolo-/pyrrolo[2,1-a]isoquinolines, naphthyridines, and bisindolo/pyrrolo[2,1-a]isoquinolinesvia tandem cyclization. This chemistry is expected to find application in organic synthesis for constructing a diverse variety of fused π-conjugated compounds, enaminones, and C-C coupled products.

DFT perspective toward [3 + 2] annulation reaction of enals with α-ketoamides through NHC and Brønsted acid cooperative catalysis: mechanism, stereoselectivity, and role of NHC

The DFT perspective toward the [3 + 2] annulation reaction through NHC and Brønsted acid cooperative catalysis has been investigated.

A DFT study on PBu3-catalyzed intramolecular cyclizations of N-allylic substituted α-amino nitriles for the formation of functionalized pyrrolidines: mechanisms, selectivities, and the role of catalysts

The detailed mechanisms and stereoselectivities of PBu₃-catalyzed intramolecular cyclizations for the formation of functionalized pyrrolidines have been investigated using a DFT method.

A DFT study on NHC-catalyzed intramolecular aldehyde–ketone crossed-benzoin reaction: mechanism, regioselectivity, stereoselectivity, and role of NHC

A computational study on NHC-catalyzed intramolecular aldehyde–ketone crossed-benzoin reaction has been performed using a DFT method.

A computational study on the N-heterocyclic carbene-catalyzed Csp2–Csp3 bond activation/[4+2] cycloaddition cascade reaction of cyclobutenones with imines: a new application of the conservation principle of molecular orbital symmetry

A new application of the conservation principle of molecular orbital symmetry has been suggested for disclosing the role of NHC.

Mechanistic and stereoselectivity study for the reaction of trifluoropyruvates with arylpropenes catalyzed by a cationic Lewis acid rhodium complex

The mechanism and stereoselectivity of a Lewis acid catalyzed carbonyl–ene reaction of trifluoropyruvates with arylpropenes have been investigated using a DFT method.

Metal-free synthesis of 3,5-disubstituted 1H- and 1-aryl-1H-pyrazoles from 1,3-diyne-indole derivatives employing two successive hydroaminations

The uncatalyzed synthesis of 3,5-disubstituted 1H- and 1-aryl-1H-pyrazoles derived from 1,3-diyne indoles was successfully carried out in PEG 400. The scope and limitations of the reaction were studied.

A quantum mechanical study of the mechanism and stereoselectivity of the N-heterocyclic carbene catalyzed [4 + 2] annulation reaction of enals with azodicarboxylates

The mechanism and stereoselectivity of the NHC-catalyzed [4 + 2] annulation reaction of enals with azodicarboxylates have been investigated using the DFT method.

An eco-friendly synthesis of novel 3,5-disubstituted-1,2-isoxazoles in PEG-400, employing the Et3N-promoted hydroamination of symmetric and unsymmetric 1,3-diyne-indole derivatives

PEG-400 proved to be a useful solvent for the mild and efficient synthesis of 3,5-disubstituted 1,2-isoxazoles derived from 1,3-diyne indoles. The scope and limitations of the reaction were also studied.