Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• substituents (Scheme 5), and (v) the rate-determining step (i.e., breaking of the C–H bond) was suggested to follow a first-order kinetic isotope effect (KH/KD = 5). As such, a library of benzothiazole derivatives was reported using this methodology, and a plausible mechanism is shown in Figure 9. Synthesis of

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• [30]. Das and co-workers reported the C3–H alkenylation of 7-azaindole using Pd(OAc)2 as a catalyst, Ph3P as a ligand, and Cu(OTf)2 as an oxidative cocatalyst, with molecular oxygen as the oxidant [31]. Carrow and co-workers reported mechanistic, kinetic, and selectivity studies of the C–H

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• hydrogen-donating organocatalysts and kinetic experiments suggest that the catalysts bind stronger to the starting silyl ketene acetals than to transition structures thus leading to inefficient rearrangement reactions. Keywords: DFT calculations; green solvents; H-bonding catalysts; Ireland–Claisen

• rearrangement, we tried to optimize its reaction course under mild conditions using various bases, solvents, and hydrogen-bond-donating catalysts. We also present a computational explanation and NMR kinetic study for the inefficient Ireland–Claisen rearrangement under thiourea and squaramide catalysis. Results

• performed a kinetic study of the reaction using 1H NMR spectroscopy. Figure 5a shows a comparison of product formation in the presence of 0, 10, and 50 mol % of catalyst C12. As can be seen, the catalyst hindered product formation and at 50 mol % catalyst loading product 3c practically does not form. A

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• . Indeed, besides the influence on kinetic properties by changing the conserved motifs, many bacterial TCs are able to produce novel skeletons through mutations of other active-site residues. This could result in either the arrest of catalytic intermediates or the creation of new trajectories to quench the

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• were optimized by using the Berny algorithm at the same level of theory [40]. Theoretical calculations were carried out in the gas phase. Theoretical kinetic studies were carried out at the PBE0-D3/6-31G** level of theory by considering all possible transition states and minimum-energy conformers for

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• ) in the kinetic resolution of primary amines 60 via their electrocatalytic oxidation to the corresponding ketones 62, and remaining amines (R)-60 were obtained with very high enantioselectivity. The controlled potential electrolysis was carried out in a divided cell in the presence of a base and a

• catalytic amount of 61 (Scheme 24) [59]. A similar strategy using N-oxalyl radicals as chiral mediators has also been explored for the enantioselective electrocatalytic oxidation of secondary alcohols [60]. Tanaka and co-workers subsequently published another article on the kinetic resolution of sec

• electrochemical asymmetric oxidation of 1,2-diols 74 and amino alcohols 77 in presence of a Br- mediator using Cu(OTf)2 and (R,R)-Ph-BOX 76 as the catalytic system (Scheme 29). The method enabled an asymmetric synthesis of α-hydroxycycloalkanones 75 and α-amino esters 78 along with the kinetic resolution of

A photochemical determination of luminescence efficiency of upconverting nanoparticles

• Baptiste Amouroux,
• Clément Roux,
• Jean-Claude Micheau,
• Fabienne Gauffre and
• Christophe Coudret

Beilstein J. Org. Chem. 2019, 15, 2671–2677, doi:10.3762/bjoc.15.260

• kinetic traces were recorded at 650 nm and the data was processed in order to obtain the initial rate of the photoreaction (Figure 3). Beside these experiments, controls were made to rule out the possibility of thermal effect (irradiation of the actinometer alone with the 976 nm laser) or the possible

• (red line) UV–vis absorption spectra and the Er-UCNP emission spectrum (green line). UCNPs (black dots) are irradiated inside the cylindrical CW 976 nm laser beam. Absorbed laser power is recorded with a power-meter. The UV–vis spectrophotometer axis is perpendicular to the laser beam. Kinetic trace at

1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

• Vito A. Fiore,
• Chiara Freisler and
• Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

• vinylphosphonium ion, and a proton transfer finally yields the 1,4-betaine. A kinetic study of the PPh3/DMAD/Meldrum’s acid reaction by spectrophotometric and stopped-flow methods has been published [14]. The initial 1,3-betaine has also been trapped with other electrophiles. The stable 1,4-betaines betaines III

Ultrafast processes triggered by one- and two-photon excitation of a photochromic and luminescent hydrazone

• Alessandro Iagatti,
• Baihao Shao,
• Alberto Credi,
• Barbara Ventura,
• Ivan Aprahamian and
• Mariangela Di Donato

Beilstein J. Org. Chem. 2019, 15, 2438–2446, doi:10.3762/bjoc.15.236

• are observable at a later timescale, the transient signal almost completely recovers on a ca. 140 ps timescale, which is similar to the fluorescence lifetime of the Z-isomer measured in this solvent. To extract a quantitative kinetic information from the transient absorption data, they have been

• fitted using a global analysis procedure, which consists in the simultaneous fit of the kinetic traces in the entire probed spectral window with a combination of exponential decay functions [30]. The number of exponential components is determined by performing a preliminary SVD (singular value

• decomposition) analysis of the kinetic traces matrix [31]. In this case, although three exponential functions could be sufficient to satisfactory fit the data, the addition of a fourth long living component, associated to a small spectral offset remaining on the long timescale, substantially improved the fit

Targeted photoswitchable imaging of intracellular glutathione by a photochromic glycosheet sensor

• Xianzhi Chai,
• Hai-Hao Han,
• Yi Zang,
• Jia Li,
• Xiao-Peng He,
• Junji Zhang and
• He Tian

Beilstein J. Org. Chem. 2019, 15, 2380–2389, doi:10.3762/bjoc.15.230

• the high sensitivity of Glyco-DTE@MnO2 hybrid sensor towards GSH, which allows the detection of intracellular GSH in the complex physiological environment of cells. The kinetic analysis of Glyco-DTE@MnO2 in the presence of GSH (Supporting Information File 1, Figure S3C) suggests a short response time

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• details of the reaction dynamics, we performed global analyses with singular value decomposition (SVD) with the Glotaran program (http://glotaran.org) [43]. We tentatively used the three-state sequential kinetic model for benzil (Equation 1) and the five-state sequential kinetic model for Benzil-PIC

• (Equation 2) convolved with Gaussian pulse. The detail of the SVD analyses are shown in Supporting Information File 1. The evolution associated spectra (EAS) thus obtained indicate the resolved transient absorption spectra into each component of the kinetic models. Because the time window of our

Synthesis of acremines A, B and F and studies on the bisacremines

• Nils Winter and
• Dirk Trauner

Beilstein J. Org. Chem. 2019, 15, 2271–2276, doi:10.3762/bjoc.15.219

• isolated from fungi of the genus Acremonium. Here, we present the asymmetric total synthesis of acremine F which hinges on a modestly enantioselective dihydroxylation and a subsequent kinetic resolution via a highly selective asymmetric reduction. Chemoselective oxidation of acremine F gave access to

• . The use of a chiral oxazaborolidine catalyst led to kinetic resolution and increased the optical purity of 17 to 95% ee. Deprotection of the diol moiety followed by Stille cross coupling with vinyl stannane 18 finally gave 5 in excellent yield (Scheme 2). Since acremine F (5) can be expected to be the

• modestly enantioselective oxidation and a highly enantioselective reduction with kinetic resolution to access the acremine framework. The route proved to be scalable and delivered 300 mg of the natural product. Acremine F could further be converted into acremines A (1) and B (2) by a selective oxidation

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles

• Chenxia Zhang,
• Kaori Morinaka,
• Mahmut Kose,
• Takashi Ubukata and
• Yasushi Yokoyama

Beilstein J. Org. Chem. 2019, 15, 2161–2169, doi:10.3762/bjoc.15.213

• reversible photochromic triazoles (Figures S10–S13 in Supporting Information File 1). The kinetic data of the thermal back reactions of 1c–3c in toluene are shown in Table 3 together with the literature data of related compounds 9c [39] and 10c [40] shown in Scheme 4. As shown in Table 3, the thermal back

• reaction is fast when the aromatic stabilization energy of the central aromatic ring is large. Although Ea of 10 is smaller than that of 1 and 2, the pre-exponential factors (A) of 1 and 2 are about 104 times and 103 times larger, respectively, than that of 10. When the thermal kinetic data of 1, 2 and 3

• ring opening of the closed forms. Wavelengths of absorption maxima of the closed forms of photochromic triazoles. Absorption spectral data of triazoles and other related photochromic compounds. Kinetic data of thermal back reactions and aromatic stabilization energy of 1c–3c, 9c and 10c. Natural charge

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• kinetic resolution of epoxides with CO2 remains a big challenge. Recently, Ema and co-workers described a chiral binaphthyl strapped Zn(II) porphyrin with triazolium halide units as a bifunctional catalyst for the kinetic resolution of epoxides with CO2 [63]. The condensation of click-reaction-derived

• nonmethylated precursors of 18 have the same fast kinetic exchange. In nondissociating solvents in acid conditions there is a smaller repulsion between the 1,2,3-triazolium moieties and as a result the U-shape is more tightened than the one in more dissociating solvents such as CD3CN or DMSO-d6, which decreases

• the kinetic rate of the equilibrium between 18a and 18b, making both rotamers observable in the 1H NMR spectra. Conversely, after deprotonation of the ammonium moieties the macrocycle 18a is forced to adopt a helix-type contracted conformation (two slowly interconverting rotamers 18c and 18d) with a

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• cNDI 6 is realized in this experiment. Obviously, there is a strong difference between the absorbance of cNDI 6 and its photoredox catalytic activity profile with respect to the irradiation wavelength which was further studied by more detailed kinetic measurements. Time-dependent product analysis was

• . Kinetic analysis of yields of product 14 in the presence (solid lines) and in the absence (dashed lines) of cNDI 6: 500 mM 12, 250 mM 13, 50 mM organocatalyst 15, 500 mM 2,6-lutidine in 1.3 mL DMF, stirring, irradiation by LEDs. Synthesis of reference NDI 1 and cNDIs 2–6; bottom: image of saturated

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• OriginPro. Kinetic measurements were performed in MeCN at 60 °C (Supporting Information File 1). Activation process parameters for the E→Z isomerisation in MeCN at 60 °C, B3LYP, def-TZVP basis for C, H, N, F, DGZVP all electron basis for iodine. Grimme D3 dispersion correction was applied. Values were

• kinetic studies, computational methods, and X-ray crystallographic details. Acknowledgements We acknowledge the Fonds der Chemischen Industrie for a material cost allowance grant (B.M.S) and the Strategic Research Fund of Heinrich Heine University (F-2018/1460-4). E.N. is supported by a

Halide metathesis in overdrive: mechanochemical synthesis of a heterometallic group 1 allyl complex

• Ross F. Koby,
• Nicholas R. Rightmire,
• Nathan D. Schley,
• Timothy P. Hanusa and
• William W. Brennessel

Beilstein J. Org. Chem. 2019, 15, 1856–1863, doi:10.3762/bjoc.15.181

• reflect the fact that products often do not have time to equilibrate or go from metastable to more stable products [9][11]. There can be multiple reasons for this, starting with the high energy environment of grinding that may be far from equilibrium [25], allowing the kinetic products to be the ones most

Norbornadiene-functionalized triazatriangulenium and trioxatriangulenium platforms

• Roland Löw,
• Talina Rusch,
• Tobias Moje,
• Fynn Röhricht,
• Olaf M. Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1815–1821, doi:10.3762/bjoc.15.175

• these mixed monolayers. Experimental For detailed experimental procedures, including NMR, UV–vis, MS spectra and STM measurements see Supporting Information File 1, chapters I–IV, and for kinetic studies see chapter V. Structures of the norbornadiene platform 1a and the quadricyclane platform 1b (for

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

Beilstein J. Org. Chem. 2019, 15, 1769–1780, doi:10.3762/bjoc.15.170

• analogous mesylate derivatives were relatively unreactive. Triflate 69 was a highly reactive substrate that could only be prepared in about 80% purity. The less reactive mesylate derivative 75 was therefore prepared and used for kinetic studies. The triflates 61, 68, and 69 (with electron-withdrawing groups

• trans to trimethylsilyl) were all solvolyzed in CD3CO2D and results are shown in Scheme 14. Since the triflate 69 was highly reactive and could not be isolated in pure form, the mesylate derivative 75 was used in kinetic studies that were carried out in the 40–60 °C range. Rates of reaction of mesylate

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• both pairs of ethyl esters [26]. When a mixture of tert-butyl esters (2R,1'S)-5d and (2S,1'S)-5d was subjected to kinetic resolution in the presence of potassium tert-butoxide in tetrahydrofuran (2R,1'S)-5d was produced with low 40% de [27]. The absolute configuration at C2 in esters 5 was established

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Transient and intermediate carbocations in ruthenium tetroxide oxidation of saturated rings

• Manuel Pedrón,
• Laura Legnani,
• Maria-Assunta Chiacchio,
• Pierluigi Caramella,
• Tomás Tejero and
• Pedro Merino

Beilstein J. Org. Chem. 2019, 15, 1552–1562, doi:10.3762/bjoc.15.158

• , the rate-limiting step of the reaction takes place through a highly asynchronous (3 + 2) concerted cycloaddition through a single transition structure (one kinetic step). The ELF analysis identifies the reaction as a typical one-step-two-stages process and corroborates the existence of a transient

• between RuO4 and the alkane, and it has been studied both experimentally and computationally having some initial controversy. The first studies were reported by Bakke et al. in 1986 who suggested the formation of intermediate ionic species on the basis of kinetic isotopic effects and solvent and

• Waegell et al. proposed a new (3 + 2) asynchronous concerted mechanism [19][20], both groups converged to the latter proposed mechanism when Bakke et al. changed the interpretation of their kinetic isotopic experiments [21][22][23][24]. The (3 + 2) concerted mechanism was further confirmed by DFT

Diazocine-functionalized TATA platforms

• Roland Löw,
• Talina Rusch,
• Fynn Röhricht,
• Olaf Magnussen and
• Rainer Herges

Beilstein J. Org. Chem. 2019, 15, 1485–1490, doi:10.3762/bjoc.15.150

• trans-configurations and to predict thermodynamic and kinetic stabilities, we performed DFT calculations at the M06-2X/def2-TZVP level of theory (Table 1, for details see Supporting Information File 1, chapter VI). As expected for diazocine-based molecules our calculations predict the cis configuration

• ) surfaces. Further studies will include IRRAS measurements to determine the trans→cis isomerization kinetics on Au(111) surfaces. Experimental For detailed experimental procedures, including NMR, UV–vis and MS spectra see Supporting Information File 1, chapters I–IV, for kinetic studies see Supporting

• activation energies (Ea) are calculated from the linear fit of an Arrhenius plot. Supporting Information Supporting Information File 526: Analytical methods, experimental procedures, NMR and UV spectra, kinetic studies and DFT calculations. Acknowledgements The authors gratefully acknowledge financial

Efficient resolution of racemic crown-shaped cyclotriveratrylene derivatives and isolation and characterization of the intermediate saddle isomer

• Sven Götz,
• Andreas Schneider and
• Arne Lützen

Beilstein J. Org. Chem. 2019, 15, 1339–1346, doi:10.3762/bjoc.15.133

• formation of diastereomeric esters were also used for other chiral CTV derivatives [63][64][65][66][67]. However, performing the separation on the stage of a monomeric CTV always bears the risk of racemization because of the flexibility of these molecules and kinetic studies for several CTVs demonstrate

• kinetics. Although the presence of the in-between lying saddle isomer indicates a more complex kinetic, we decided, for the sake of comparability, to determine rate constants and energy barrier ΔG≠ for the racemization also with the assumption of first order kinetics (see Supporting Information File 1 for

Bambusuril analogs based on alternating glycoluril and xylylene units

• Tomáš Lízal and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2019, 15, 1268–1274, doi:10.3762/bjoc.15.124

• common synthesis of bambusuril which employs reversible acidic conditions enabling a transformation of kinetic products to thermodynamic products [12]. Only a small quantity of macrocycle 2 in the crude mixture was identified. This minor product should be present in 4 isomeric forms, but we were not able