Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• behavior was explained by the large energy gap between the ground states of the E- and Z-forms of indigo as well as low activation energy of inversion for derivatives 13. In the same year, Nielsen, Hecht and co-workers achieved a remarkable stabilization of the Z-isomer of N,N'-disubstituted indigo 24 by

Unraveling the role of prenyl side-chain interactions in stabilizing the secondary carbocation in the biosynthesis of variexenol B

• Moe Nakano,
• Rintaro Gemma and
• Hajime Sato

Beilstein J. Org. Chem. 2023, 19, 1503–1510, doi:10.3762/bjoc.19.107

• possibility of through-space interactions with prenyl side chains using DFT calculations. Our calculations show that (i) the unstable secondary carbocation is stabilized by the cation–π interaction from prenyl side chains, thereby lowering the activation energy, (ii) the four-membered ring formation is

• interacts with the secondary carbocation at C10, reducing the activation energy of the first step by approximately 4.7 kcal/mol. Moreover, due to the stabilization of the secondary carbocation-like intermediate IM2, the reaction proceeds stepwise rather than concertedly [7]. It was found that the final

• the stabilization of the intermediate IM2b is greater in path b, the activation energy suggests that path a is more favorable. Generally, the activation energies for terpene cyclization reactions are often below 10 kcal/mol. However, in the case of complex rearrangement reactions involving secondary

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• and regenerates the tert-butoxyl radical to complete the entire catalytic cycle. The formation of hydrogen bonds between the oxygen of the carbonyl group and the hydrogen of the 2,2,2-trifluoroethanol (TFE) reduces the activation energy of the radical reaction and improves the coupling efficiency. In

Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control

• Carlee A. Montgomery and
• Graham K. Murphy

Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86

• ]. Computational investigations were conducted to better understand these reactions, and it was determined that the changing alkyl motif (e.g., dimethyl, cyclopentyl, adamantyl) had minimal impact on the activation energy of the fluorination reactions. The reaction coordinate was calculated for Meldrum’s acid

• comparing ylides 31 and 70 in this reductive elimination step, which suggested that the ortho-nitro group of 72 (and 71, by extension) played a role other than lowering the activation energy of this step. Given that other optimized halogen- and hydrogen-bonded conformations were found between thioamide and

• . Proposed mechanism of the formal C–H insertion of pyrrole under blue LED irradiation. Mechanistic proposal for the X–H insertion reactions of iodonium ylides. Calculated reaction coordinate for the radiofluorination of iodonium ylide 60. Difference in Gibbs activation energy for ortho- or para-anisyl

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• Gibbs activation energy of enantiomer 53 for the racemization process was determined as 33.0 kcal mol−1 at 298 K. The CPL spectra of M-53 and P-53 showed an emission maximum at 560 nm with glum value of 2.3 × 10−4. Instead of helicene formation in the final Scholl-type ring formation step, Martín and co

Computational studies of Brønsted acid-catalyzed transannular cycloadditions of cycloalkenone hydrazones

• Manuel Pedrón,
• Jana Sendra,
• Irene Ginés,
• Tomás Tejero,
• Jose L. Vicario and
• Pedro Merino

Beilstein J. Org. Chem. 2023, 19, 477–486, doi:10.3762/bjoc.19.37

• model [30] the distortion energy (ΔE≠d) corresponds to the difference between the single point corresponding to interacting 3 and 4, and the sum of single-point calculations for TS2-a and TS2b. The apparent activation energy (ΔE≠app) refers to the energy difference between TS2 and the interacting

B–N/B–H Transborylation: borane-catalysed nitrile hydroboration

• Filip Meger,
• Alexander C. W. Kwok,
• Franziska Gilch,
• Dominic R. Willcox,
• Alex J. Hendy,
• Kieran Nicholson,
• Andrew D. Bage,
• Thomas Langer,
• Thomas A. Hunt and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2022, 18, 1332–1337, doi:10.3762/bjoc.18.138

• activation energy supported the proposed routes (see Supporting Information File 1 for details). Conclusion In summary, a borane-catalysed hydroboration of nitriles to give primary amines has been developed, transforming the previously stoichiometric reagent H3B·SMe2 into a catalyst. B-N/B–H transborylation

Polymer and small molecule mechanochemistry: closer than ever

• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1225–1235, doi:10.3762/bjoc.18.128

• is observed [46]. This difference is believed to be related to the exertion of tensile forces along the glycosidic linkage of the polymer chain during ball milling, which may lower the activation energy for the depolymerization of chitin. Indeed, DFT calculations using the N-acetylglucosamine dimer

• as the model compound showed that the application of pulling forces to selected atoms in the dimer perturb the reaction, making the depolymerization easier to occur [45]. In contrast, no change in the activation energy of the deacetylation step was observed with the introduction of the pulling forces

• . The decrease in the activation energy for the mechanochemical depolymerization of chitin was attributed to force-induced conformational changes in the structure, which destabilize the reactant state upon the introduction of a sufficient pulling force (Figure 3). Evidently, ball milling techniques

Experimental and theoretical studies on the synthesis of 1,4,5-trisubstituted pyrrolidine-2,3-diones

• Nguyen Tran Nguyen,
• Vo Viet Dai,
• Nguyen Ngoc Tri,
• Luc Van Meervelt,
• Nguyen Tien Trung and
• Wim Dehaen

Beilstein J. Org. Chem. 2022, 18, 1140–1153, doi:10.3762/bjoc.18.118

• with an activation energy of about 10.7 kcal·mol−1. On the other hand, if the removal of one H2O molecule occurs from the O–H and N–H groups, IS5 transforms into IS9 through TS14 with a high barrier of 31.8 kcal·mol−1. IS9 is then converted to product 10ab based on the shifting of H atom from the O–H

• bond to N atom (Scheme 4). This process is thermodynamically favorable by a Gibbs free energy (ΔG) of −6.5 kcal·mol−1. In addition, a second way from 4a, through the TS5 transition state, to form the IS3 intermediate requires an activation energy of ca. 33.7 kcal·mol−1. IS3 could release one H2O

• IS8 can be omitted because it is so fast with a small activation energy of 2.1 kcal·mol−1), the formation of product 10ab is superior as compared to its isomer. In terms of the value of the rate constant k, the direction of 10ab formation is in the range of 103–106 times faster than 10ab-v2. The

Comparative study of thermally activated delayed fluorescent properties of donor–acceptor and donor–acceptor–donor architectures based on phenoxazine and dibenzo[a,j]phenazine

• Saika Izumi,
• Prasannamani Govindharaj,
• Anna Drewniak,
• Paola Zimmermann Crocomo,
• Satoshi Minakata,
• Leonardo Evaristo de Sousa,
• Piotr de Silva,
• Przemyslaw Data and
• Youhei Takeda

Beilstein J. Org. Chem. 2022, 18, 459–468, doi:10.3762/bjoc.18.48

• in electron density on the acceptor and the electron-donating power of POZ. Therefore, gradual increase of electron-donating strength brings T1 energy closer to the acceptor T1 energy and leads to a smaller EST gap. But, the activation energy Ea for the DF process, which was calculated from the

• Arrhenius plot obtained from the increase of the DF intensity against temperature, was lower for 1 (Ea = 27 meV) when compared to POZ-DBPHZ (Ea = 47 meV, Table 2) in Zeonex®. The directly determined activation energy of the D–A-type compound is half than that of the D–A–D compound, which is in contradiction

• to the ΔEST value (Table 2). If we support the observation with the DF/PF results that present a stronger TADF property for the mono-substituted derivative 1, the conclusion of misleading ΔEST comparison can be reached. To avoid confusion, a more effective way is to compare only the activation energy

Iridium-catalyzed hydroacylation reactions of C1-substituted oxabenzonorbornadienes with salicylaldehyde: an experimental and computational study

• Angel Ho,
• Austin Pounder,
• Krish Valluru,
• Leanne D. Chen and
• William Tam

Beilstein J. Org. Chem. 2022, 18, 251–261, doi:10.3762/bjoc.18.30

• hypothesized the reductive elimination step was the RDS for rhodium-catalyzed intramolecular hydroacylation reactions [74]. Based on the activation energy of the reverse step of reductive elimination 3TS2 (37.4–41.4 kcal/mol), we predict reductive elimination, and subsequent C–C formation, to be irreversible

• reductive elimination transition states, 2bTS3b is the more energetically accessible transition state with an energy barrier of 5.9 kcal/mol, that is 4.9 kcal/mol lower in energy compared to 2aTS3a. This large difference in activation energy (ΔΔG‡) between the two competing transition states offers

• an activation energy of 4.8 to 5.6 kcal/mol, respectively, to produce the aforementioned thermodynamically stable Ir(I) alkoxide intermediates INa3 and INb3. Based on the extremely high energy barrier required for acyl migration over hydride migration, we hypothesize iridium-catalyzed hydroacylation

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

Fritsch–Buttenberg–Wiechell rearrangement of magnesium alkylidene carbenoids leading to the formation of alkynes

• Tsutomu Kimura,
• Koto Sekiguchi,
• Akane Ando and
• Aki Imafuji

Beilstein J. Org. Chem. 2021, 17, 1352–1359, doi:10.3762/bjoc.17.94

• ), and the C1–Cl bond (C1···Cl: 3.22 Å) was cleaved. The activation energy for this reaction was estimated to be 14.9 kcal/mol. The IRC calculation revealed that the chlorine atom gradually dissociated from the carbenoid carbon atom as the phenyl group approached the carbenoid carbon atom [38][39]. Then

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• °C provided a hydrocarbon oil in 92% yield, 71.4% of which were attributable to styrene monomer [156]. A decrease of 56 kJ mol−1 for the activation energy of PS depolymerisation was calculated in the presence of the catalysts. More recently, high-porosity montmorillonite (Mt) was used to prepare Mg

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• analogue (dC–O = 1.438 Å) and strongly inhibits the formation of the α-(trifluoromethyl)bisarylcarbenium ion, as illustrated by the higher activation energy needed for the dehydration (ΔECF3 = 21.0 kcal⋅mol−1 vs ΔECH3 = 14.8 kcal⋅mol−1 at the B3LYP/6-31+G(d,p) level). On the other hand, the first arylation

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• opposite to the CF2 moiety, which was followed by the recyclization of the intermediate diradical (Scheme 42). The activation energy for the rearrangement of 90 was lower by 9.4 kcal/mol than for the parent hydrocarbon system 92. The activation energy of the trans-isomer 91 was greater than that of cis

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• species to the alkyne 5, as in I (Figure 2). The first step TS1 has a low activation energy (ΔG‡ = 12.2 kcal⋅mol−1) to form the unstable cyclic intermediate II. This short-lived species rapidly reopens through TS2 (ΔΔG‡ = 8.1 kcal⋅mol−1) to give the pentadienyl cation III, which presents a high stability

• derivative 1 (Figure 3), confirming the differences that the 2- and 3-substitution, respectively, exert in the reaction outcome. Starting with V, the acetate rearrangement is rate determining (ΔΔG‡ = 14.2 kcal⋅mol−1), and more importantly, the activation energy for the cyclization in TS6 is very low (ΔΔG

• conjugation. However, according to the energy profile, this observation does not have a reflection in the deprotonation step, which seems to be affected partially by the steric hindrance around the two hydrogen atoms, being clearly higher in Ha (a 2.2 kcal⋅mol−1 higher activation energy of TS10 than for TS8

Dirhamnolipid ester – formation of reverse wormlike micelles in a binary (primerless) system

• David Liese,
• Hans Henning Wenk,
• Xin Lu,
• Jochen Kleinen and
• Gebhard Haberhauer

Beilstein J. Org. Chem. 2020, 16, 2820–2830, doi:10.3762/bjoc.16.232

• contour length decreases with increasing temperature according to the following Arrhenius equations, Equation 9 and Equation 10 [32]: where Ea is the activation energy, R is the gas constant, and A is the preexponential factor. The semilogarithmic plots of η0 and τR versus 1/T (Figure 7b and c) indicate

• an Arrhenius plot like behavior, and the activation energy calculated from the slopes of the two plots equals 119 kJ/mol, close to those found in other wormlike micelles [48][49][50][51][52]. According to Equation 10, G0 is independent of the temperature, which is not true in our case. This might be

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• photocatalysts (PCs) generate excited state substrates that can then undergo reactions that would be impossible in the ground state [4]. A challenge for enantioselective catalysis is stifling the racemic background reaction, which is generally achieved through a lower activation energy for the catalysed process

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• reactions. Keywords: C–H activation; energy transfer; fluorination; photocatalysis; photosensitization; visible light; Review 1 Introduction 1.1 Importance of direct C–H fluorination/trifluoromethylation and photosensitization in organic synthesis 1.1.1 Importance of fluorine atoms in organic molecules

• electrophilic fluorinating source. Thereafter, the AQN–Selectfluor® exciplex abstracts a hydrogen atom from the C3 position of pentane to form a secondary radical, a Selectfluor® N-radical cation, HF and AQN. The activation energy barrier relative to RC2 was only 9.9 kcal⋅mol−1 (Scheme 17). The Selectfluor® N

• -radical cation can abstract a hydrogen atom from the C3 2° C–H bond of another pentane molecule in an overall exergonic process with an activation energy barrier of 2.0 kcal⋅mol−1 from Int4 to afford Int5 and ultimately Int6 (Scheme 18). The authors did not mention the possibility of a mechanism whereby

One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway

• Esra Demir,
• Ozlem Sari,
• Yasin Çetinkaya,
• Ufuk Atmaca,
• Safiye Sağ Erdem and
• Murat Çelik

Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148

• the transition state and so lowering the activation energy barrier (Figure 3a). On the other hand, stabilization of the benzylic cation is not possible along the IRC path for TS1′ (Figure 3b), since the bond distance C2–C(Ph) is found as around 1.50 Å showing a single bond character. This can be the

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• corresponding activation energy (Equation 1) and free activation energy (Equation 2) were calculated for compound 12 and found 3.14 and 2.95 kcal/mol, respectively. These values were used in Equation 3 in order to calculate the rate constant for the N−O bond dissociation. Accordingly, kr, was found to be 4.27

• characterized accordingly as stationary points (minima or maxima) on the corresponding potential energy surfaces (PESs). Equations 1–5 were used for the calculations of the rates and the physicochemical data of the N−O bond dissociation of the most active compound 12 in radicals. The corresponding activation

• energy and free energy of activation are given in Equation 1 and Equation 2, respectively: For the calculation of the rate constant, kr, the Eyring’s classical Equation 3 was used, where in the above equation kB is the Boltzmann’s constant (1.380662∙10−23 J/K), h is the Planck’s constant (6.626176∙10−34

The reaction of arylmethyl isocyanides and arylmethylamines with xanthate esters: a facile and unexpected synthesis of carbamothioates

• Narasimhamurthy Rajeev,
• Toreshettahally R. Swaroop,
• Ahmad I. Alrawashdeh,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Seegehalli M. Anil,
• Kuppalli R. Kiran,
• Chandra,
• Paris E. Georghiou,
• Kanchugarakoppal S. Rangappa and
• Maralinganadoddi P. Sadashiva

Beilstein J. Org. Chem. 2020, 16, 159–167, doi:10.3762/bjoc.16.18

• been reported for other carbene hydrolyses [37][38][39]. As can be seen from Figure 5, the highest activation energy barrier is 42.2 kJ/mol. We had previously considered an alternative mechanism in which a benzylic proton is instead removed by the base [40]. For the previous mechanism, which we have

• now recalculated at the B3LYP/6-311++G(d,p) level of theory in DMF (using a PCM, see Scheme S1 and Figures S15 and S16, Supporting Information File 1), an activation energy barrier of 20.6 kJ/mol was obtained for the formation of the resulting benzylic α-carbanion and H2. This benzylic α-carbanion

• anion, either by a stepwise or by a concerted five-membered ring transition state, followed by several subsequent steps could lead to the observed products. However, the mechanism involving all of those steps required an improbably higher overall activation energy of 173.9 kJ/mol (Figure S16, Supporting

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• , leading to intermediate I, and the overall transformation proceeded with remarkable stabilization. In the next step, dissociation of the C−O bond occurred through transition state II, finally leading to alkene III. The activation energy for the C−O bond cleavage in 20, a tertiary alcohol, was similar to

• activation energy (31.0 kcal/mol), which was followed by slight stabilization of the formed γ-carbanion (−6.1 kcal/mol). The latter should then undergo intramolecular C–S bond formation, followed by hydrolysis, finally leading to the rearranged product. It was then decided to investigate the

Understanding the role of active site residues in CotB2 catalysis using a cluster model

• Keren Raz,
• Ronja Driller,
• Thomas Brück,
• Bernhard Loll and
• Dan T. Major

Beilstein J. Org. Chem. 2020, 16, 50–59, doi:10.3762/bjoc.16.7

• . Here, the energy gain was likely due to the fact that the carbocation in intermediate C was located 4.21 Å away from the pyrophosphate group, which stabilized it (Table 1 and Figure 2). Moreover, π–cation interactions with F107 contributed to the stabilization as well. The activation energy for the

• site model. The required activation energy to form D was 4.1 kcal/mol lower in the active site model than the gas phase, likely due to π–cation interactions with F107 and F149 and greater proximity to the negatively charged pyrophosphate group. Another conformational difference between the gas phase

• formed interactions with N103, W186, and especially with I181. The relative energy difference between H and I was also similar in the gas phase and in the enzyme model. However, the activation energy was higher by 3.0 kcal/mol in the active site model, possibly due to steric effects. I was stabilized via