Showing papers in "Journal of Organic Chemistry in 2021"
TL;DR: A quinoline-linked and ionic liquid-decorated covalent organic framework was prepared by incorporation of a multicomponent Povarov reaction and postsynthetic modification as discussed by the authors.
Abstract: A quinoline-linked and ionic liquid-decorated covalent organic framework was prepared by incorporation of a multicomponent Povarov reaction and postsynthetic modification. The imidazolium and sulfonic acid-decorated COF-IM-SO3H can be a highly efficient Bronsted acid catalyst to promote the Biginelli reaction under solvent-free conditions in a heterogeneous way. In addition, a scaled-up Biginelli reaction has been readily realized over a COF-IM-SO3H@chitosan aerogel-based cup reactor.
71 citations
TL;DR: In this Perspective, the importance of time economy in total synthesis is described, as well as the general considerations underlining the timely production of desired molecules.
Abstract: It is often said that "time is money". This is certainly true in a multistep synthesis when a high-valued product or set of products is needed urgently. Fulfilling this need requires the sensible balancing of atom economy, step economy, and redox economy with the time taken to make the product. In this age of flu-based pandemics, the need for rapid provision of effective therapeutic agents makes the importance of "time economy" particularly clear. In this Perspective, the importance of time economy in total synthesis is described, as well as the general considerations underlining the timely production of desired molecules. As case studies, the syntheses of Tamiflu, Corey lactone, and ibuprofen are discussed, with emphasis on comparing classical and contemporary approaches to a rapid total synthesis. By using modern tactics such as one-pot reaction procedures and versatile synthetic methodologies such as organocatalyst mediated domino reactions coupled with strict-control technologies such as flow chemistry, Tamiflu and Corey lactone can now be synthesized within 60 and 152 min, respectively, using one vessel via a batch system. Tamiflu and ibuprofen can be prepared via flow system, and their total residence times are 11.5 and 3 min, respectively.
65 citations
TL;DR: In this article, the structure, reactivity, and synthetic applications of N-nitrosamines with an emphasis on alkyl N-Nitrosamines are discussed, as well as their role as water contaminants and the methods for their detection.
Abstract: N-Nitrosamines are a class of compounds notorious both for the potent carcinogenicity of many of its members and for their widespread occurrence throughout the human environment, from air and water to our diets and drugs. Considerable effort has been dedicated to understanding N-nitrosamines as contaminants, and methods for their prevention, remediation, and detection are ongoing challenges. Understanding the chemistry of N-nitrosamines will be key to addressing these challenges. To facilitate such understanding, we focus in this Perspective on the structure, reactivity, and synthetic applications of N-nitrosamines with an emphasis on alkyl N-nitrosamines. The role of N-nitrosamines as water contaminants and the methods for their detection are also discussed.
50 citations
TL;DR: A standard protocol to evaluate cation alkaline stability within KOH/CD3OH solution at 80 °C is used to compare 26 model compounds, including benzylammonium, tetraalkylam monium, spirocyclicammonium and phosphonium, to identify their degradation pathways and lead to the advancement of cations with improved alkaline stabilities.
Abstract: Understanding the degradation mechanisms of organic cations under basic conditions is extremely important for the development of durable alkaline energy conversion devices. Cations are key functional groups in alkaline anion exchange membranes (AAEMs), and AAEMs are critical components to conduct hydroxide anions in alkaline fuel cells. Previously, we have established a standard protocol to evaluate cation alkaline stability within KOH/CD3OH solution at 80 °C. Herein, we are using the protocol to compare 26 model compounds, including benzylammonium, tetraalkylammonium, spirocyclicammonium, imidazolium, benzimidazolium, triazolium, pyridinium, guanidinium, and phosphonium cations. The goal is not only to evaluate their degradation rate, but also to identify their degradation pathways and lead to the advancement of cations with improved alkaline stabilities.
49 citations
TL;DR: In this paper, the authors have designed and synthesized phenanthroimidazole (PI) based derivatives TPE-PI-1, TPEPI-2, PTZPI-3 and PTZ PI-4 where in donors tetraphenylethylene-TPE and phenothiazine-PTZ (D') of contrasting donor abilities are attached to the N and C atom positions of PI.
Abstract: Organic materials possessing solid-state emission responsive to external stimuli have significance in a variety of material, biomedical, and optoelectronic applications. Organic molecules having different donor-acceptor architectures integrated with aggregation-induced emission (AIE) fluorophores have been utilized in development of mechanofluorochromic (MFC) materials. In this work, we have designed and synthesized phenanthroimidazole (PI) based derivatives TPE-PI-1, TPE-PI-2, TPE-PI-3, PTZ-PI-1, PTZ-PI-2, and PTZ-PI-3 where in donors tetraphenylethylene-TPE (D) and phenothiazine-PTZ (D') of contrasting donor abilities are attached to the N and C atom positions of PI. The position and mode of attachment of the donors have been changed, and an additional PTZ spacer has been introduced which has a direct consequence on their photophysical and electronic properties. The PI derivatives manifest AIE, solvatochromic, and mechanochromic behavior. The single crystal X-ray analysis of TPE-PI-1 and PTZ-PI-2 reveals bent structures for the PTZ unit and a twisted conformation for TPE moieties. The density functional theory calculations were used to obtain optimized ground-state structures of the PI derivatives. The work shows a comprehensive comparison of the photophysical, electronic, AIE, and MFC properties of the PI derivatives as an effect of variations in the position of donor, donor-acceptor strength, and change in molecular conformation on use of spacer.
45 citations
TL;DR: In this paper, a substrate-based screening approach led to the discovery of tert-butyloxycarbonyl (Boc)-protected indole-2-carboxyesters as suitable motifs for the intermolecular [2 + 2] cycloaddition reaction.
Abstract: Indole and indoline rings are important pharmacophoric scaffolds found in marketed drugs, agrochemicals, and biologically active molecules. The [2 + 2] cycloaddition reaction is a versatile strategy for constructing architecturally interesting, sp3-rich cyclobutane-fused scaffolds with potential applications in drug discovery programs. A general platform for visible-light mediated intermolecular [2 + 2] cycloaddition of indoles with alkenes has been realized. A substrate-based screening approach led to the discovery of tert-butyloxycarbonyl (Boc)-protected indole-2-carboxyesters as suitable motifs for the intermolecular [2 + 2] cycloaddition reaction. Significantly, the reaction proceeds in good yield with a wide variety of both activated and unactivated alkenes, including those containing free amines and alcohols, and the transformation exhibits excellent regio- and diastereoselectivity. Moreover, the scope of the indole substrate is very broad, extending to previously unexplored azaindole heterocycles that collectively afford fused cyclobutane containing scaffolds that offer unique properties with functional handles and vectors suitable for further derivatization. DFT computational studies provide insights into the mechanism of this [2 + 2] cycloaddition, which is initiated by a triplet-triplet energy transfer process. The photocatalytic reaction was successfully performed on a 100 g scale to provide the dihydroindole analog.
39 citations
TL;DR: The development in the field of photocatalytic carbonylation is described by compiling the literature of the last 40 years, and their reaction mechanisms have been emphatically discussed.
Abstract: In the last few decades, photocatalytic radical carbonylation strategies have received considerable attention as they are becoming a formidable tool in the toolbox of organic synthesis. These carbonylation strategies involve the incorporation of a carbon monoxide into organic molecules in an atom- and step-economical manner. Mostly, these strategies rely on the generation of an acyl radical as a key intermediate, which would be created via incorporation of CO molecule to an alkyl/aryl radical. The production of alkyl/aryl radical in these methodologies required either the high-intensity light-induced transition-metal (TM)-catalyzed systems or visible-light-induced photocatalytic systems that would be capable of mediating single electron transfer (SET) to the C(sp3)- or C(sp2)-hybridized coupling partners. Here, in this review, the development in the field of photocatalytic carbonylation is described by compiling the literature of the last 40 years, and their reaction mechanisms have been emphatically discussed. In addition, to aid readers, we have assimilated redox potentials of photocatalysts and substrates for a better sense of spontaneity of these photoredox carbonylation reactions.
37 citations
TL;DR: A straightforward and selective reduction of nitroarenes with various alcohols was efficiently developed using an iron catalyst via a hydrogen transfer methodology, which led specifically to imines in 30-91% yields, with a good functional group tolerance.
Abstract: A straightforward and selective reduction of nitroarenes with various alcohols was efficiently developed using an iron catalyst via a hydrogen transfer methodology. This protocol led specifically t...
37 citations
TL;DR: In this paper, an efficient protocol for the synthesis of thioether directly from heteroarenes has been developed in the presence of visible light in a one-pot manner at room temperature.
Abstract: An efficient protocol for the synthesis of thioether directly from heteroarenes has been developed in the presence of visible light in a one-pot manner at room temperature. This method involves two...
34 citations
TL;DR: In this article, the authors compare chemical and electrochemical redox reactions, including concepts of free energy, voltage, kinetic barriers, and overpotential, to increase the accessibility of electrochemistry for organic chemists.
Abstract: Redox reactions are ubiquitous in organic synthesis and intrinsic to organic electrosynthesis. The language and concepts used to describe reactions in these domains are sufficiently different to create barriers that hinder broader adoption and understanding of electrochemical methods. To bridge these gaps, this Synopsis compares chemical and electrochemical redox reactions, including concepts of free energy, voltage, kinetic barriers, and overpotential. This discussion is intended to increase the accessibility of electrochemistry for organic chemists lacking formal training in this area.
33 citations
TL;DR: A comparative study using a D-A-D (donor-acceptor-donor) system demonstrated that not only the electron push-pull substituent effect but also subunit combinations influence photophysical and electrochemical properties.
Abstract: A series of asymmetric donor-acceptor (D-A) perylene-based compounds, 3-(N,N-bis(4'-(R)-phenyl)amino)perylene (Peri-DPA(R)), were successfully prepared to explore their intramolecular charge transfer (ICT) properties. To induce ICT between the donor and acceptor, diphenylamine (DPA) derivatives (electron donor units) with the same functional groups (R = CN, F, H, Me, or OMe) at both para positions were linked to the C-3 position of perylene to produce five Peri-DPA derivatives. A steady-state spectroscopy study on Peri-DPA(R)s exhibited a progressively regulated ICT trend consistent with the substituent effect as it progressed from the electron-withdrawing group to the electron-donating group. In particular, a comparative study using a D-A-D (donor-acceptor-donor) system demonstrated that not only the electron push-pull substituent effect but also subunit combinations influence photophysical and electrochemical properties. The different ICT characters observed in Lippert-Mataga plots of D-A(CN) and D-A-D(CN) (CN-substituted D-A and D-A-D) led to the investigation on whether ICT emission of two systems with differences in subunit combinations is of the same type or of a different type. The femtosecond transient absorption (fs-TA) spectroscopic results provided direct evidence of ICT origin and confirmed that D-A(CN) and D-A-D(CN) exhibited the same transition mix of ICT (from donor to acceptor) and reverse ICT (rICT, from arylamine to CN unit). Density functional theory (DFT)/TD-DFT calculations support the presence of ICT for all five compounds, and the experimental observations of rICT presented only for CN-substituted compounds.
TL;DR: AC-assisted Ni-catalyzed amination, etherification, and esterification of aromatic bromides showed higher yields and selectivity compared to that observed in the control experiments with direct current, suggesting the importance of both reduction and oxidation processes in the maintenance of the AC-assisted catalytic reactions.
Abstract: The coupling of transition-metal to photoredox catalytic cycles through single-electron transfer steps has become a powerful tool in the development of catalytic processes. In this work, we demonst...
TL;DR: In this paper, the strategies toward scaling up find an ally in continuous-flow reactor technology comparing dielectric and conductive heating, which has been widely studied and deliberated, opening up some controversial issues as well.
Abstract: Microwave-assisted organic synthesis has been widely studied and deliberated, opening up some controversial issues as well. Nowadays, microwave chemistry is a mature technology that has been well demonstrated in many cases with numerous advantages in terms of the reaction rate and yield. The strategies toward scaling up find an ally in continuous-flow reactor technology comparing dielectric and conductive heating.
TL;DR: In this article, the sensitivity of DP4+ when using improper [μ,σ,ν] sets was analyzed and the results led to the development of a customizable DP4+, which allows preliminary calculations at any desired level of theory using a small set of training molecules.
Abstract: DP4+ is a popular tool for structural elucidation using GIAO NMR calculations. The method was built with 16 statistical parameters [μ,σ,ν], which depend on the level of theory. Herein, we deeply analyzed the sensitivity of DP4+ when using improper [μ,σ,ν] sets, a common situation found in the literature. The results led us to develop a customizable DP4+ methodology that allows preliminary calculations at any desired level of theory using a small set of training molecules.
TL;DR: The chemical investigation of the South China Sea soft coral Sinularia humilis has resulted in the isolation of a library of diverse diterpenoids, including four new cembranoids, namely, Humilisins A-D (1-4), Humilisin E and F (5 and 6), and eight known related compounds (7-14) as discussed by the authors.
Abstract: The chemical investigation of the South China Sea soft coral Sinularia humilis has resulted in the isolation of a library of diverse diterpenoids, including four new cembranoids, namely, humilisins A-D (1-4), two new uncommon diterpenoids possessing a tetradecahydrocyclopenta[3',4']cyclobuta[1',2':4,5]cyclonona[1,2-b]oxirene ring system, namely, humilisins E and F (5 and 6), and eight known related compounds (7-14). Humilisin A (1) is the first cembranoid with an ether linkage between C-3 and C-7. The structures and absolute configurations of 1-8 were determined by extensive spectroscopic data analyses, chemical reactions, and a series of quantum chemical calculations including quantum mechanical-nuclear magnetic resonance (QM-NMR), time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD), and optical rotatory dispersion (ORD) methods. In bioassay, compound 6 displayed anti-inflammatory activity in lipopolysaccharide (LPS)-stimulated BV-2 microglia cells.
TL;DR: In this paper, a visible-light-induced decarboxylation reaction was developed for the synthesis of alkylated benzimidazo[2,1-a]isoquinoline-6(5H)-ones and indolo[2.1]-isoquinolin-6 (5H]-ones under metal-free conditions.
Abstract: A visible-light-induced decarboxylation reaction was developed for the synthesis of alkylated benzimidazo[2,1-a]isoquinoline-6(5H)-ones and indolo[2,1-a]isoquinolin-6(5H)-ones under metal-free conditions. Impressively, metal catalysts and traditionally volatile organic solvents could be effectively avoided.
TL;DR: A blue-light-emitting diode (LED) promoted coupling of aryl diazoacetates with sulfur ylides is described and a wide range of trisubstituted olefins is obtained in moderate to good yield.
Abstract: A blue-light-emitting diode (LED) promoted coupling of aryl diazoacetates with sulfur ylides is described. This protocol features mild conditions, good functional group tolerance, and broad substrate scope for both aryl diazoacetates with sulfur ylides. Under optimal reaction conditions, a wide range of trisubstituted olefins is obtained in moderate to good yield, which can be further transferred to other biologically important heterocycles after a two-step simple operation.
TL;DR: In this paper, a ruthenium complex was found to be a general and efficient catalyst for the N-methylation of amines with methanol in the presence of carbonate salt.
Abstract: A ruthenium complex [(p-cymene)Ru(2,2'-bpyO)(H2O)] was found to be a general and efficient catalyst for the N-methylation of amines with methanol in the presence of carbonate salt. Moreover, a series of sensitive substituents, such as nitro, ester, cyano, and vinyl groups, were tolerated under present conditions. It was confirmed that OH units in the ligand are crucial for the catalytic activity. Notably, this research exhibited the potential of metal-ligand bifunctional ruthenium catalysts for the hydrogen autotransfer process.
TL;DR: A green method for the synthesis of spiro[4.5]trienones through an electrochemical oxidative halocyclization with N-aryl alkynamides is developed with good to excellent yields with a broad scope and functional group tolerance.
Abstract: We developed a green method for the synthesis of spiro[4.5]trienones through an electrochemical oxidative halocyclization with N-aryl alkynamides. This reaction was conducted under metal-catalyst- and exogenous-oxidant-free conditions at room temperature. Using readily available LiCl, LiBr, and LiI as the halogen source, a variety of dearomative halo-spirocyclization products were obtained in good to excellent yields with a broad scope and functional group tolerance.
TL;DR: In this paper, the synthesis, characterization, and reactivity of [(NHC)PdCl2(aniline)] complexes are reported, and broadly available anilines are introduced as stabilizing ligands for well-defined Pd(II)-NHC catalysts.
Abstract: We report the synthesis, characterization, and reactivity of [(NHC)PdCl2(aniline)] complexes. These well-defined, air- and moisture-stable catalysts are highly active in the Suzuki-Miyaura cross-coupling of amides by N-C(O) activation as well as in the Suzuki-Miyaura cross-coupling of esters, aryl chlorides, and Buchwald-Hartwig amination. Most crucially, this study introduces broadly available anilines as stabilizing ligands for well-defined Pd(II)-NHC catalysts. The availability of various aniline scaffolds, including structural and electronic diversity, has a significant potential in fine-tuning of challenging cross-couplings by Pd-NHCs. The parent catalyst in this class, [Pd(IPr)(AN)Cl2], has been commercialized in collaboration with Millipore Sigma, offering broad access for reaction screening and optimization.
TL;DR: Daphnenoids A-C (1-3), three unusual sesquiterpenes with distinctive ring skeletons, together with a biogenetically related daphnenoid D (4) were obtained from the herb of Daphne penicillata by molecular networking strategies.
Abstract: Daphnenoids A-C (1-3), three unusual sesquiterpenes with distinctive ring skeletons, together with a biogenetically related daphnenoid D (4) were obtained from the herb of Daphne penicillata by molecular networking strategies. Daphnenoid A (1) possesses a unique caged tetracyclo [5.3.2.01,6.04,11] dodecane scaffold by unexpected cyclizations of C-1/C-11 and C-2/C-14. Daphnenoids B and C (2 and 3) were the first discovered natural sesquiterpenes with unique 5/5 spirocyclic systems in nature. Their structures were determined by NMR spectroscopic analysis, computer-assisted structure elucidation methods, quantum chemical calculations, and X-ray diffraction. A hypothetical biogenetic pathway begins with typical guaiane sesquiterpene (a), including a key intermediate (4) was proposed. Daphnenoids B and C (2 and 3) exhibited potential inhibitory activities on the production of NO against LPS-induced BV2 microglial cells.
TL;DR: In this article, the authors present their own, biased perspective with a focus on their own chemistry that evaluates recent advances in the field and provides their opinion on the challenges for the development of new chemistry, so that it may have an impact on imaging.
Abstract: 18F-fluorination is an important and growing field in organic synthesis that has attracted many chemists in the recent past. Here we present our own, biased perspective with a focus on our own chemistry that evaluates recent advances in the field and provides our opinion on the challenges for the development of new chemistry, so that it may have an impact on imaging. We hope that the manuscript will provide a useful guide to chemists to develop reliable and robust reaction chemistry suitable for radiofluorination to have a real impact on human health.
TL;DR: In this paper, the usefulness of linear free energy relationships (LFERs) is highlighted to unravel the effect of solvents on coordinate bonding (e.g., cation-crown ether), hydrogen bonding, halogen bonding, dipolar aggregation, and π-π-stacking).
Abstract: The proper choice of solvent is of major importance for all studies in supramolecular chemistry, including molecular recognition in host-guest systems, intramolecular folding, self-assembly, and supramolecular polymerization. In this Perspective, the usefulness of linear free energy relationships (LFERs) is highlighted to unravel the effect of solvents on coordinate bonding (e.g., cation-crown ether), hydrogen bonding, halogen bonding, dipolar aggregation, and π-π-stacking. For all of these intermolecular interactions widely applied in supramolecular systems, LFER relationships between the Gibbs binding energies and common solvent polarity scales including ET(30), π*, α or β based on solvatochromic dyes, scales derived from binding processes such as Gutmann donor and acceptor numbers or hydrogen bond donor and acceptor scales, or physical functions like the Kirkwood-Onsager or the Liptay-Onsager functions could be demonstrated. These relationships can now be applied toward a better understanding of the prevailing intermolecular forces for supramolecular interactions. They further enable a rational selection of the most suitable solvent for the preparation of self-assembled materials and the estimation of binding constants without the need for time-consuming comprehensive investigations of solvents.
TL;DR: In this paper, the simple synthesis of 3-halochromones and various halogenated electron-rich arenes has been realized with electrode oxidation by employing the simplest sodium halide (NaX, X = Cl, Br, I) as halogen source.
Abstract: Without employing an external oxidant, the simple synthesis of 3-halochromones and various halogenated electron-rich arenes has been realized with electrode oxidation by employing the simplest sodium halide (NaX, X = Cl, Br, I) as halogen source. This electrochemical method is advantageous for the simple and mild room temperature operation, environmental friendliness as well as broad substrate scope in both C-H bond donor and halogen source components.
TL;DR: In this paper, the authors explored the mode of activation and catalysis of bidentate iodine(III)-based halogen donors by means of state-of-the-art computational methods.
Abstract: The poorly understood mode of activation and catalysis of bidentate iodine(III)-based halogen donors have been quantitatively explored in detail by means of state-of-the-art computational methods. To this end, the uncatalyzed Diels-Alder cycloaddition reaction between cyclohexadiene and methyl vinyl ketone is compared to the analogous process mediated by a bidentate iodine(III)-organocatalyst and by related, highly active iodine(I) species. It is found that the bidentate iodine(III)-catalyst accelerates the cycloaddition by lowering the reaction barrier up to 10 kcal mol-1 compared to the parent uncatalyzed reaction. Our quantitative analyses reveal that the origin of the catalysis is found in a significant reduction of the steric (Pauli) repulsion between the diene and dienophile, which originates from both a more asynchronous reaction mode and a significant polarization of the π-system of the dienophile away from the incoming diene. Notably, the activity of the iodine(III)-catalyst can be further enhanced by increasing the electrophilic nature of the system. Thus, novel systems are designed whose activity actually surpasses that of strong Lewis acids such as BF3.
TL;DR: The present challenges in oligonucleotide synthesis, purification, and isolation are summarized; potential solutions are highlighted; and synergies between academia; contract research, development and manufacturing organizations; and the pharmaceutical industry are encouraged.
Abstract: With a renewed and growing interest in therapeutic oligonucleotides across the pharmaceutical industry, pressure is increasing on drug developers to take more seriously the sustainability ramifications of this modality. With 12 oligonucleotide drugs reaching the market to date and hundreds more in clinical trials and preclinical development, the current state of the art in oligonucleotide production poses a waste and cost burden to manufacturers. Legacy technologies make use of large volumes of hazardous reagents and solvents, as well as energy-intensive processes in synthesis, purification, and isolation. In 2016, the American Chemical Society (ACS) Green Chemistry Institute Pharmaceutical Roundtable (GCIPR) identified the development of greener processes for oligonucleotide Active Pharmaceutical Ingredients (APIs) as a critical unmet need. As a result, the Roundtable formed a focus team with the remit of identifying green chemistry and engineering improvements that would make oligonucleotide production more sustainable. In this Perspective, we summarize the present challenges in oligonucleotide synthesis, purification, and isolation; highlight potential solutions; and encourage synergies between academia; contract research, development and manufacturing organizations; and the pharmaceutical industry. A critical part of our assessment includes Process Mass Intensity (PMI) data from multiple companies to provide preliminary baseline metrics for current oligonucleotide manufacturing processes.
TL;DR: Moderate to good yields of sulfonated benzothiophenes bearing important and useful functional groups have been achieved at a constant current and preliminary mechanistic studies indicated a tandem radical addition-cyclization pathway.
Abstract: A green and practical electrochemical method for the synthesis of C-3-sulfonated benzothiophenes from 2-alkynylthioanisoles and sodium sulfinates was developed under oxidant- and catalyst-free conditions. Moderate to good yields of sulfonated benzothiophenes bearing important and useful functional groups have been achieved at a constant current. Preliminary mechanistic studies indicated a tandem radical addition-cyclization pathway. Moreover, the protocol is easy to scale up and exhibits good reaction efficiency.
TL;DR: In this article, the authors explored the activity of the acridine-derived SNS-Ru pincer for the activation of methanol to apply it as a C1 building block in different reactions.
Abstract: Methanol can be employed as a green and sustainable methylating agent to form C-C and C-N bonds via borrowing hydrogen (BH) methodology. Herein we explored the activity of the acridine-derived SNS-Ru pincer for the activation of methanol to apply it as a C1 building block in different reactions. Our catalytic system shows great success toward the β-C(sp3)-methylation reaction of 2-phenylethanols to provide good to excellent yields of the methylated products. We investigated the mechanistic details, kinetic progress, and temperature-dependent product distribution, which revealed the slow and steady generation of in situ formed aldehyde, is the key factor to get the higher yield of the β-methylated product. To establish the environmental benefit of this reaction, green chemistry metrics are calculated. Furthermore, dimerization of 2-naphthol via methylene linkage and formation of N-methylation of amine are also described in this study, which offers a wide range of substrate scope with a good to excellent yield.
TL;DR: In this article, the influence of direct hetero-arylation on the optical properties of 2-(2'-hydroxyphenyl)benzoxazole ESIPT emitters was investigated.
Abstract: Excited-state intramolecular proton transfer (ESIPT) dyes typically show strong solid-state emission, but faint fluorescence intensity is observed in the solution state owing to detrimental molecular motions. This article investigates the influence of direct (hetero)arylation on the optical properties of 2-(2'-hydroxyphenyl)benzoxazole ESIPT emitters. The synthesis of two series of ESIPT emitters bearing substituted neutral or charged aryl, thiophene, or pyridine rings is reported herein along with full photophysical studies in solution and solid states, demonstrating the dual solution-/solid-state emission behavior. Depending on the nature of substitution, several excited-state dynamics are observed: quantitative or partially frustrated ESIPT process or deprotonation of the excited species. Protonation studies revealed that pyridine substitution triggered a strong increase of quantum yield in the solution state for the protonated species owing to favorable quinoidal stabilization. These attractive features led to the development of a second series of dyes with alkyl or aryl pyridinium moieties showing strong tunable solution/solid fluorescence intensity. For each series, ab initio calculations helped rationalize and ascertain their behavior in the excited state and the nature of the emission observed by the experimental results.
TL;DR: In this article, a multivariate linear regression analysis is used to obtain a simple model predicting nucleophilicity parameters for virtually any class of nucleophiles in different solvents for a set of 341 data points.
Abstract: The concept of nucleophilicity is at the basis of most transformations in chemistry Understanding and predicting the relative reactivity of different nucleophiles is therefore of paramount importance Mayr's nucleophilicity scale likely represents the most complete collection of reactivity data, which currently includes over 1200 nucleophiles Several attempts have been made to theoretically predict Mayr's nucleophilicity parameters N based on calculation of molecular properties, but a general model accounting for different classes of nucleophiles could not be obtained so far We herein show that multivariate linear regression analysis is a suitable tool for obtaining a simple model predicting N for virtually any class of nucleophiles in different solvents for a set of 341 data points The key descriptors of the model were found to account for the proton affinity, solvation energies, and sterics