Site Selectivity In Reactions Research Articles

Bipolar Photoelectrochemistry for Phase-Modulated Optoelectronic Hybrid Nanomotor.

Complex micro/nanorobots may be constructed by integrating several independent, controlled nanomotors for high degrees of freedom of maneuvering and manipulation. However, designing nanomotors with distinctive responses to the same global stimuli is challenging due to the nanomotors' simple structure and limited material composition. In this work, we demonstrate that a nanomotor can be designed with the same principles of electronic circuits, where the motion of semiconductor particles can be controlled with synchronized electric and optical signals. This technique relies on transient bipolar photoelectrochemistry in semiconductor microparticles, where the reaction site selectivity is realized by modulating the light pulse in the time domain. Due to the microparticles' intrinsic resistance and surface capacitance, the nanomotors can be designed as an electronic circuit, enabling distinctive responses to the global electric/optical field and achieving the desired movement or deflection/rotation. This work gives new insight into the manipulation technique for independent and untethered nanomotor control. Ultimately, it exploits the potential for particle sorting based on geometry in time and frequency domain modulation.

New thiazol-pyridazine derivatives as antimicrobial and antiviral candidates: Synthesis, and application

In this manuscript, we are motivated to investigate the reaction site-selectivity for the hydrazo thiazole derivatives (6a–c) with different types of active methylene groups such as malononitrile, and ethyl cyanoacetate. Based on their structural investigations and spectrum data, the results of these reactions have been established to be iminopyridazines (7a–c) and 6-oxopyridazine derivatives (8a–c). We tested the ability of the newly synthesized pyridazine derivatives to inhibit the microbes and COVID-19 proteins. Human coronavirus 229E (HCoV-229E) was used to investigate the antiviral efficacy of prepared compounds. Green monkey kidney (Vero-E6) cell lines were used to investigate MTT and cytopathic effect (CPE). The new 6-oxopyridazine derivatives (8a–c) revealed significant inhibitory efficacy and were capable of inhibiting the human coronavirus 229E. Moreover, the antimicrobial result showed that compounds iminopyridazine (7c) followed by iminopyridazine (7a) followed by iminopyridazine (7b) exhibited excellent antimicrobial properties toward all utilized strains, usually greater than that of common reference drugs, with MIC values ranging from 13 to 21 ppm, from 9 to 14 ppm, and from 8 to 19 ppm whereas, the remaining substances appeared to be promising effective. Structure-activity relationship (SAR) revealed that pyridazine scaffolds containing NH group, as well as substituted electron withdrawal group (Cl) in para-position for benzene ring attributed to thiazole moiety have the best activity. The current study successfully illustrated the possible application of heterocyclic derivatives with pyridazie nucleus including thiazole ring as the main compound in the development of dual antiviral (COVID-19) and antibacterial pharmaceuticals in the future.

Ligand-modulated regiodivergent alkenylboration of allylarenes: Reaction development and mechanistic study

Chain-walking has emerged as a promising strategy in organic synthetic methodology, but achieving site-selectivity in reactions involving competition among multiple potential positions remains a challenge. In this study, we presented a novel approach to ligand-modulated, nickel-catalyzed regiodivergent alkenylboration of allylarenes. Our method allows for highly chemoselective preparation of two classes of structurally different alkenyl boronates from the same starting by simply switching the ligand. Mechanistic investigations involving experiments and calculations suggest that the ligand-modulating regiodivergence arises from either regioselective β-H elimination or oxidative addition with organic halides. Our findings offer valuable insight into addressing site-selective issues in chain-walking reactions with multiple thermodynamically stable factors.

Theoretical Prediction and Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyrimidine, Perfluoropyridazine, and Perfluoropyrazine.

Perfluoroaromatics, such as perfluoropyridine and perfluorobenzene, are privileged synthetic scaffolds in organofluorine methodology, undergoing a series of regioselective substitution reactions with a variety of nucleophiles. This unique chemical behavior allows for the synthesis of many perfluoroaromatic derived molecules with unique and diverse architectures. Recently, it has been demonstrated that perfluoropyridine and perfluorobenzene can be utilized as precursors for a variety of materials, ranging from high performance polyaryl ethers to promising drug scaffolds. In this work, using density functional theory, we investigate the possibility of perfluoropyrimidine, perfluoropyridazine, and perfluoropyrazine participating in similar substitution reactions. We have found that the first nucleophilic addition of a phenoxide group substitution on perfluoropyrimidine and on perfluoropyridazine would happen at a site para to one of the nitrogen atoms. While previous literature points to mesomeric effects as the primary cause of this phenomenon, our work demonstrates that this effect is enhanced by the fact that the transition states for these reactions result in bond angles that allow the phenoxide to π-complex with the electron-deficient diazine ring. The second substitution on perfluoropyrimidine and on perfluoropyridazine is most likely to happen at the site para to the other nitrogen. The second substitution on perfluoropyrazine is most likely to happen at the site para to the first substitution. The activation energies for these reactions are in line with those reported for perfluoropyridine and suggest that these platforms may also be worth investigation in the lab as possible monomers for high performance polymers.

Gold(I)-Catalyzed Cross-Coupling Reactions of Arenediazonium Salts with Alkynoic Acids

The reaction of simple alkynoate salts with isolated arenediazonium tetrafluoroborate salts that had been pre-conditioned with the gold(I) catalyst AuCl(Me2S) led to the formation of cross-coupled products via a decarboxylative Sonogashira reaction process in modest yield and under mild conditions. The major by-product is a defunctionalized aryl moiety stemming from the diazonium salt, which competitively forms via hydrodediazonation. Good functional group tolerance and reaction site selectivity were attained in this limited investigation.

Theoretical Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyridine.

Pentafluoropyridine, a potentially useful precursor in organofluorine methodology, undergoes selective substitution of a fluorine with a phenoxide at the site para to the nitrogen. Subsequent aryloxide substitutions can be accomplished at the ortho-positions with aryloxide groups containing various functional groups para to the phenoxide oxygen. During this phase of the reaction, "reverse reactions" involving substitutions of the original para substituent with a free fluoride or with another aryloxide moiety are observed with a frequency that depends on the functional group para to the oxygen on the aryloxide. Herein, we provide a theoretical explanation of these observations through use of density functional theory.

Shaking up reaction-site selectivity

Chemistry It seems intuitive that putting vibrational energy into a chemical bond ought to promote selective cleavage of that bond. In fact, the relation of vibrational excitation to reactivity has generally proven subtler and more complex. Thomas et al. studied how strong coupling of specific vibrational modes to an optical cavity might influence a molecule with two competing reactive sites. The molecule had two silicon centers that could react with fluoride by respective cleavage of a Si–C or Si–O bond. Exciting the vibrations at either center slowed down the overall reaction while favoring otherwise disfavored Si–O cleavage. Science , this issue p. [615][1] [1]: /lookup/doi/10.1126/science.aau7742

ChemInform Abstract: A C‐3‐Selective Direct Alkylation of Coumarins by Using a Microwave‐Assisted Xanthate‐Based Radical Reaction.

A xanthate-based oxidative radical process for the direct alkylation of the coumarin ring system is presented. In the reaction, a vinylic and unactivated C–H bond of the coumarin system is replaced by an α-acyl functionality under neutral conditions. This reaction has a high reaction site selectivity, which can realize alkylation at the C-3 position.

A C‐3‐Selective Direct Alkylation of Coumarins by Using a Microwave‐Assisted Xanthate‐Based Radical Reaction

AbstractA xanthate‐based oxidative radical process for the direct alkylation of the coumarin ring system is presented. In the reaction, a vinylic and unactivated C–H bond of the coumarin system is replaced by an α‐acyl functionality under neutral conditions. This reaction has a high reaction site selectivity, which can realize alkylation at the C‐3 position.

ChemInform Abstract: Palladium‐Catalyzed Desulfitative Arylation of 5‐Alkoxy‐3,4‐dibromo‐2(5H)‐furanone with Sodium Arylsulfinates.

A palladium-catalyzed desulfitative arylation reaction of 5-alkoxy-3,4-dibromo-2(5H)-furanones to provide 5-alkoxy-4-aryl-3-bromo-2(5H)-furanones is reported. This reaction has a high reaction site selectivity, which can realize arylation at the C4-position. Various sodium arylsulfinates are well tolerated under the mild reaction conditions. The current study makes the arylation of general alkenyl halides possible by the use of cheap and easily available sodium arylsulfinates as aryl sources.

Palladium‐Catalyzed Desulfitative Arylation of 5‐Alkoxy‐3,4‐dibromo‐2(5H)‐furanone with Sodium Arylsulfinates

AbstractA palladium‐catalyzed desulfitative arylation reaction of 5‐alkoxy‐3,4‐dibromo‐2(5H)‐furanones to provide 5‐alkoxy‐4‐aryl‐3‐bromo‐2(5H)‐furanones is reported. This reaction has a high reaction site selectivity, which can realize arylation at the C4‐position. Various sodium arylsulfinates are well tolerated under the mild reaction conditions. The current study makes the arylation of general alkenyl halides possible by the use of cheap and easily available sodium arylsulfinates as aryl sources.

Site selectivity in reactions of hydrazonoyl halides with heterocycles containing amino and thione groups leading to fused heterocycles of potential antimicrobial activity

Reaction of hydrazonoyl halides with 6-(benzylidenamino)-2-thioxo-2,3-dihydro-1H-pyrimidin-4-one and 2,3-diaminoquinazolin-4-one site-selectively afforded 3-substituted-7-(benzylidenamino)-1-phenyl-[1,2,4]triazolo[4,3-a]-pyrimidin-5(1H)-ones, [1,2,4,5]tetrazino[6,1-b]quinazolin-6(4H)-one, and 3-methyl-2-(4-substituted-phenylhydrazo)-[1,2,4]triazino[3,2-b]quinazolin-10-ones in good yields. The structures of the newly synthesized compounds were elucidated by chemical evidence and their IR, 1H, 13C NMR, and MS spectra. Furthermore, some of the products were screened against different strains of bacteria and fungi.

Site Selectivity in Reactions of Hydrazonoyl Halides with Heterocycles Containing Amino and Thione Groups Leading to Fused Heterocycles of Potential Antimicrobial Activity

Site Selectivity in Reactions of Hydrazonoyl Halides with Heterocycles Containing Amino and Thione Groups Leading to Fused Heterocycles of Potential Antimicrobial Activity

Catalytic, enantioselective, intramolecular carbosulfenylation of olefins. Preparative and stereochemical aspects.

The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a cocatalytic Brønsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50-92%) and high enantioselectivities (71:29-97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron-rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron-deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with monoactivated arene nucleophiles.

Transition‐State Stabilization by a Secondary Substrate–Ligand Interaction: A New Design Principle for Highly Efficient Transition‐Metal Catalysis

A library of monodentate phosphane ligands, each bearing a guanidine receptor unit for carboxylates, was designed. Screening of the library gave some excellent catalysts for regioselective hydroformylation of beta,gamma-unsaturated carboxylic acids. A terminal alkene, but-3-enoic acid, was hydroformylated with a linear/branched (l/b) regioselectivity up to 41. An internal alkene, pent-3-enoic acid was hydroformylated with regioselectivity up to 18:1. Further substrate selectivity (e.g., acid vs. methyl ester) and reaction site selectivity (monofunctionalization of 2-vinylhept-2-enoic acid) were also achieved. Exploration of the structure-activity relationship and a practical and theoretical mechanistic study gave us an insight into the nature of the supramolecular guanidinium-carboxylate interaction within the catalytic system. This allowed us to identify a selective transition-state stabilization by a secondary substrate-ligand interaction as the basis for catalyst activity and selectivity.

Selective oxidation of carbolide C–H bonds by an engineered macrolide P450 mono-oxygenase

Regio- and stereoselective oxidation of an unactivated C-H bond remains a central challenge in organic chemistry. Considerable effort has been devoted to identifying transition metal complexes, biological catalysts, or simplified mimics, but limited success has been achieved. Cytochrome P450 mono-oxygenases are involved in diverse types of regio- and stereoselective oxidations, and represent a promising biocatalyst to address this challenge. The application of this class of enzymes is particularly significant if their substrate spectra can be broadened, selectivity controlled, and reactions catalyzed in the absence of expensive heterologous redox partners. In this study, we engineered a macrolide biosynthetic P450 mono-oxygenase PikC (PikC(D50N)-RhFRED) with remarkable substrate flexibility, significantly increased activity compared to wild-type enzyme, and self-sufficiency. By harnessing its unique desosamine-anchoring functionality via a heretofore under-explored "substrate engineering" strategy, we demonstrated the ability of PikC to hydroxylate a series of carbocyclic rings linked to the desosamine glycoside via an acetal linkage (referred to as "carbolides") in a regioselective manner. Complementary analysis of a number of high-resolution enzyme-substrate cocrystal structures provided significant insights into the function of the aminosugar-derived anchoring group for control of reaction site selectivity. Moreover, unexpected biological activity of a select number of these carbolide systems revealed their potential as a previously unrecorded class of antibiotics.

Recent developments in aminopyrazole chemistry

Recently reported syntheses of 3(5)-aminopyrazoles, 4-aminopyrazoles, and 1-aminopyrazoles as well as of diaminopyrazoles and their general pattern of reactivity towards mono- and bidentate electrophiles have been surveyed. Emphasis has also been laid on techniques for ascertaining the site selectivity in reactions with electrophiles, including single crystal X-ray structure analysis, 1 H- 15 N HMBC, and NOE intensity difference experiments as well as other modern 2D NMR techniques. Some thermally induced cycloadditions have also been treated.

ChemInform Abstract: Site Selectivity in Reaction of Hydrazonoyl Halides with 2‐(Aroylmethyl)‐6‐methylpyrimidin‐4(3H)‐ones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Site selectivity in reaction of hydrazonoyl halides with 2-(aroylmethyl)-6-methylpyrimidin-4(3H)-ones

Reaction of hydrazonoyl halides 1 with 2-(aroylmethyl)-6-methylpyrimidin-4(3H)-ones 3 proved to be site selective and gave 2-(3-acetyl-1,5-diarylpyrazol-4-yl)-6-methylpyrimidin-4(3H)-ones 5 via dehydrative cyclisation of the hydrazone intermediates 4. The structures of both 4 and 5 were elucidated by spectral data and alternative synthesis. The mechanism of the reaction was discussed.

Ti═NR vs Ti−R′ Functional Group Selectivity in Titanium Imido Alkyl Cations from a DFT Perspective

The reactions of Ti(NtBu)(Me3[9]aneN3)Me+ (1) with a series of polar and nonpolar unsaturated organic substrates give different kinds of products, resulting either from cycloaddition to the Ti═N bond (PhCCH) or from insertion into the Ti−Me bond (PhCCPh, iPrNCNiPr, ethylene polymerization). DFT(B3PW91) calculations of the reaction pathways for cycloaddition and insertion on small model systems illustrate the basic electronic properties in terms of reaction site selectivity. In all cases the cycloaddition is shown to be the preferred pathway kinetically. ONIOM(B3PW91:HF) calculations on the experimental systems allow the evaluation of the influence of the steric bulk of the ligand set on the outcome of the reaction. Introduction of the actual ligands results essentially in a destabilization of the cycloaddition pathway and leads both to a cancellation of the kinetic preference for cycloaddition and to a reduced thermodynamic stability of the cycloaddition product. Only for the terminal alkyne PhCCH does cy...