Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• activation of F2 give intermediate F3. Finally, protonolysis provides the desired product 45 and an active Co(III)Cp*. Due to the low activation energy, the thermodynamically less stable Z diastereomer is preferred in the reaction, which is in contrast to the rhodium(III)-catalyzed reaction [82]. Later, Li

Water-soluble SNS cationic palladium(II) complexes and their Suzuki–Miyaura cross-coupling reactions in aqueous medium

• Alphonse Fiebor,
• Richard Tia,
• Banothile C. E. Makhubela and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1859–1870, doi:10.3762/bjoc.14.160

• parameterised for transition metal systems and has been found to give geometries, relative energies and activation energy trends in good agreement with high-level density functional theory (DFT) results at a fraction of the computational cost [45][46]. It is therefore adequate for studies in which the prime

• ) (Figure 4). The Pd–Br distance is calculated to be 2.60 Å and is consistent with similar Pd–Br bond lengths found in the literature for single crystal X-ray structures [47][48]. This oxidative addition step involves a low activation energy barrier of −43.9 kcal/mol. This negative energy implies that there

DFT calculations on the mechanism of copper-catalysed tandem arylation–cyclisation reactions of alkynes and diaryliodonium salts

• Tamás Károly Stenczel,
• Ádám Sinai,
• Zoltán Novák and
• András Stirling

Beilstein J. Org. Chem. 2018, 14, 1743–1749, doi:10.3762/bjoc.14.148

• aryl transfer is followed by the O–C bond formation which results in the oxazoline ring. This step requires a moderate 6.5 kcal/mol activation energy (TSrcB) which indicates that this step is very fast under the reaction conditions. After the ring is formed the system is stabilised by releasing a large

Rh(II)-mediated domino [4 + 1]-annulation of α-cyanothioacetamides using diazoesters: A new entry for the synthesis of multisubstituted thiophenes

• Jury J. Medvedev,
• Ilya V. Efimov,
• Yuri M. Shafran,
• Vitaliy V. Suslonov,
• Vasiliy A. Bakulev and
• Valerij A. Nikolaev

Beilstein J. Org. Chem. 2017, 13, 2569–2576, doi:10.3762/bjoc.13.253

• catalyst, proton transfer and, finally, 1,3-shift of alkoxycarbonyl group in the intermediate imine D to produce thiophenes 3 and 5. However, this pathway seems to be less probable, since intramolecular cyclization B → C should have lower activation energy relative to intermolecular interaction of C=S

A mechanochemical approach to access the proline–proline diketopiperazine framework

• Nicolas Pétry,
• Hafid Benakki,
• Eric Clot,
• Pascal Retailleau,
• Farhate Guenoun,
• Fatima Asserar,
• Chakib Sekkat,
• Thomas-Xavier Métro,
• Jean Martinez and
• Frédéric Lamaty

Beilstein J. Org. Chem. 2017, 13, 2169–2178, doi:10.3762/bjoc.13.217

• proton from the amine and to facilitate the departing of the methoxy group by transferring a proton. The activation energy from 16a-solv was computed to be ΔG# = 22.8 kcal mol−1, in good agreement with an easy reaction at room temperature. The reaction was strongly exoergic with ΔG = −17.3 kcal mol−1 and

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• [64]. The stability of the wave functions of all the transition states was checked. An unrestricted wave function was used to calculate the activation energy of the cis/trans isomerization of the (Z,E)-germacranolide. All energies were reported with zero-point energy corrections and all TS geometries

• °C (temperature at which the biogenetic transformation was performed) [36]. In case of path N, the activation energy of 4 to reach the Cope TS (TS4-2) is 25.9 kcal/mol, and the relative energy of TS4-2 is 35.0 kcal/mol. The chair TS was, as expected, less energetic than the boat TS. However, before

• difference between TS5-3 and TS6-3 is almost the same than in TS1b-2 and TS4-2, but the energy of boat TS (TS5-3) decreases to 38.0 kcal/mol, which is small enough to be overcome at 200 °C. Thus, hemiacetalization lowers the activation energy of the boat Cope TS which allows the reaction to be completed at a

Mechanochemical N-alkylation of imides

• Anamarija Briš,
• Mateja Đud and
• Davor Margetić

Beilstein J. Org. Chem. 2017, 13, 1745–1752, doi:10.3762/bjoc.13.169

• imides and bromides were used to determine the activation energies. It was found that for benzyl and ethyl bromides the activation energy differences are 2–3 kcal mol−1 in favor of the N1 positions in uracil and 7,8-dimethylalloxazine. These calculations are in good accordance with the experimentally

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• reaction leading to the intermediate delocalized diradical occurs via a transition state with very low activation energy. On the other hand, the calculated spin densities suggest the preference of the formation of the six-membered ring of the 1,4-dithiane, and this reaction course is observed in the case

• of thiobenzophenone S-methanide 1 (Ar1 = Ar2 = Ph). On the other hand, in the hetaryl functionalized thiocarbonyl S-methanide 8 the lowest activation energy was found for the C–C bond formation between C(2) atoms of the selenophen-2-yl ring, leading to the twelve-membered macrocyclic product 9

NMR reaction monitoring in flow synthesis

• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31

• , temperature gradients, starting concentration and residence times, against a reaction conversion model enables the reaction order, rate constant, Arrhenius parameters, pre-exponential factor, and activation energy values to be determined in a rapid manner from one single flow experiment. The two latter

Direct arylation catalysis with chloro[8-(dimesitylboryl)quinoline-κN]copper(I)

• Sem Raj Tamang and
• James D. Hoefelmeyer

Beilstein J. Org. Chem. 2016, 12, 2757–2762, doi:10.3762/bjoc.12.272

• pass through an intermediate with a formal oxidation state of +3, which may undoubtedly have a large activation energy. Rather, a concerted pathway through a 4-membered transition state will have less localization of charge. A concerted process for coupling of nucleophiles with arylhalides on copper

Synthesis, dynamic NMR characterization and XRD studies of novel N,N’-substituted piperazines for bioorthogonal labeling

• Constantin Mamat,
• Marc Pretze,
• Matthew Gott and
• Martin Köckerling

Beilstein J. Org. Chem. 2016, 12, 2478–2489, doi:10.3762/bjoc.12.242

• observed for all nitro derivatives due to the limited change of the piperazine chair conformation. Therefore, two coalescence points were determined and their resulting activation energy barriers were calculated using 1H NMR. To support this result, single crystals of 1-(4-nitrobenzoyl)piperazine (3a

• the two expected signals at increased temperatures (>67 °C). At the coalescence temperature Tc, the exchange rate is given by the equation kexc = π·Δν/21/2 [25]. As a result, the activation energy (ΔG#exp) to the amide bond rotation can be calculated using the Eyring equation [14][16]. In general

Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

• Ilya V. Efimov,
• Marsel Z. Shafikov,
• Nikolai A. Beliaev,
• Natalia N. Volkova,
• Tetyana V. Beryozkina,
• Wim Dehaen,
• Zhijin Fan,
• Viktoria V. Grishko,
• Gert Lubec,
• Pavel A. Slepukhin and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233

• geometry distortion of nitrile oxide 6a has a major contribution to the activation energy barrier, whereas the geometry distortion energy of the enamine is minor. Also, the analysis shows close values of the orbital interaction energy for all the found transition states (Table 1). It should be noted the

• , resulting in smaller geometry distortions. Thus, the lowest electronic activation energy of transition state 1a_1−3a among all calculated transition states is a result of both, an easier attainability of the state governed by longer range orbital interactions, and a smaller value of the total geometry

• experimentally observed regioisomer. The reason for the lowest electronic activation energy leading to the experimentally observed product among all calculated transition states, is caused by both relatively better stabilizing orbital interactions and relatively smaller geometry distortion energies. Experimental

Methylenelactide: vinyl polymerization and spatial reactivity effects

• Judita Britner and
• Helmut Ritter

Beilstein J. Org. Chem. 2016, 12, 2378–2389, doi:10.3762/bjoc.12.232

• our postulated radical formation process into account, the dipolar solvent DMF stabilizes the polar educt MLA more than the less polar 1,4-dioxane. Since the formed radical is planar and less polar, the activation energy to this radical formation must be higher in DMF than in 1,4-dioxane [16

Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes

• Lucie Brulíková,
• Aidan Harrison,
• Marvin J. Miller and
• Jan Hlaváč

Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184

• distance between C–O to that between C–N was more than one, whereas in the product, this was reversed (Figure 2). Using RB3LYP/6-31G*//RB3LYP/6-31G* theory, for the model reaction between HNO and butadiene, the favored endo-transition state activation energy was found to be 8.6 kcal/mol lower than for the

• exo state. When a number of substituted nitroso compounds were subsequently investigated, the endo-transition state persisted in having a lower activation energy for all compounds tested, relative to the exo. This preference is due to the “exo lone pair effect” resulting from the repulsion between the

Experimental and theoretical investigations on the high-electron donor character of pyrido-annelated N-heterocyclic carbenes

• Michael Nonnenmacher,
• Dominik M. Buck and
• Doris Kunz

Beilstein J. Org. Chem. 2016, 12, 1884–1896, doi:10.3762/bjoc.12.178

• containing the tert-butyl substituted dipyridocarbene ligand dipiytBu. For iridium complexes [Ir(CO)2Cl(NHC)] (NHC = imidazolidin-2-ylidene) a preferred cis-CO exchange was reported and an activation energy of 12.7–12.9 kcal/mol was determined by NMR spectroscopy for this process [60]. However, an exchange

Cp₂TiCl/D₂O/Mn, a formidable reagent for the deuteration of organic compounds

• Antonio Rosales and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2016, 12, 1585–1589, doi:10.3762/bjoc.12.154

• for both species, which in turn, is dependent upon the zero point for the vibrational energy of both isotopic molecules. As the mass of deuterium is about twice the mass of hydrogen there is a larger activation energy for the C–D bond dissociation than for the C–H bond [4]. The KIE observed allows

Ring-whizzing in polyene-PtL₂ complexes revisited

• Oluwakemi A. Oloba-Whenu,
• Thomas A. Albright and
• Chirine Soubra-Ghaoui

Beilstein J. Org. Chem. 2016, 12, 1410–1420, doi:10.3762/bjoc.12.135

• , therefore, 6 can always interact with it. On the other hand, the LUMO in the π system may not always have the correct symmetry to interact with the b2 orbital on ML2 and it is the evolution of this overlap that has an important impact on the reaction path and activation energy. We will also have an occasion

• halves of the pentalene ligand. The Pt(dpe) group can migrate from one ring to the other via the η3 structure, 42. Again the activation energy associated with the transition state 43 is predicted to be small at 8.6 kcal/mol. We anticipate that pentalene–Pt(PR3)2 will be a highly fluxional molecule. The

• point shortly. One might think that the overlap between b2 ML2 and the LUMO, 49, from the η2 ground state to η4 will be retained and, thus, the activation energy will be small. However, note that at η4 the overlap between the filled b1 fragment orbital, 7, and the au HOMO on C10F8 is turned on and this

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• enantioselectivity is determined by the ratio of Z- to E-enamine, which in turn depends on the activation energy difference in the irreversible C–C bond forming steps. Having developed an enamine catalysis system where the iminium’s conformation in the conjugate addition step determines the enantioselectivity of the

Enantioselective carbenoid insertion into C(sp³)–H bonds

• J. V. Santiago and
• A. H. L. Machado

Beilstein J. Org. Chem. 2016, 12, 882–902, doi:10.3762/bjoc.12.87

• attributed to the stabilization of the partial positive charge on the divalent carbon of the transition state TS-40 provided by the phenyl donor group. The second reason concerns the large difference between the activation energy of these reactions which relies on the development of steric strain through the

Recent advances in C(sp³)–H bond functionalization via metal–carbene insertions

• Bo Wang,
• Di Qiu,
• Yan Zhang and
• Jianbo Wang

Beilstein J. Org. Chem. 2016, 12, 796–804, doi:10.3762/bjoc.12.78

• metal center to the ligand and to carbon dioxide was supported by experimental data and DFT studies. Such interaction increases the electrophilicity of the carbene moiety and thus lowers the activation energy for C–H bond insertion. Other ligands have also been explored for the metal–carbene C(sp3)–H

Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

• M. Fernanda N. N. Carvalho,
• M. João Ferreira,
• Ana S. O. Knittel,
• Maria da Conceição Oliveira,
• João Costa Pessoa,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2016, 12, 732–744, doi:10.3762/bjoc.12.73

• cycloreversion for the model compound obtained from glycine and glyoxal (see Supporting Information File 3) showed that this reaction has a moderate activation energy but is endothermic and therefore not probable to occur in our reaction conditions. Since the barrier towards the Strecker degradation of the

• mechanisms should have an appreciable barrier (activation energy) and therefore give an indication for the viability of different reaction paths. For the ninhydrin reaction with amino acids, a concerted mechanism with simultaneous elimination of CO2 and H2O from an intermediate aminal (carbinolamine) has

• zwitterions. Intramolecular reactions of non-zwitterionic ground state 6g to 11 (top) or 8 (bottom). The activation energy ΔEa denotes the calculated energy difference (in kcal/mol) between the TS and the optimized ground state 6g. A similar activation barrier was found for the conversion 6g → 10 (50.3 kcal

cis–trans-Amide isomerism of the 3,4-dehydroproline residue, the ‘unpuckered’ proline

• Vladimir Kubyshkin and
• Nediljko Budisa

Beilstein J. Org. Chem. 2016, 12, 589–593, doi:10.3762/bjoc.12.57

• energies with the pKa of the ammonium groups in the corresponding free amino acids (Scheme 2). The resulting correlation indicates a remarkable offset in the activation energy in the 3,4-double bond containing residues (Figure 3). This effect was not only observed in water, but also persisted in organic

Interactions between 4-thiothymidine and water-soluble cyclodextrins: Evidence for supramolecular structures in aqueous solutions

• Vito Rizzi,
• Sergio Matera,
• Paola Semeraro,
• Paola Fini and
• Pinalysa Cosma

Beilstein J. Org. Chem. 2016, 12, 549–563, doi:10.3762/bjoc.12.54

• of the cathodic peak potential is reasonable because a higher activation energy would be expected under such conditions. As described in [39], this observed increased difficulty is due to the inclusion of the pyrimidine ring inside the cavity of the CDs hindering the interaction with the electrode

• the reduction of the involved groups in the inclusion complex need less activation energy. On the other hand, when TRIMEB CD was considered, while the cathodic peak potential can be considered constant, the current intensity decreases after the first CD addition then it remains constant (Figure 3E

Amino-functionalized (meth)acryl polymers by use of a solvent-polarity sensitive protecting group (Br-t-BOC)

• Helmut Ritter,
• Monir Tabatabai and
• Markus Herrmann

Beilstein J. Org. Chem. 2016, 12, 245–252, doi:10.3762/bjoc.12.26

• this in mind, the bromo-tert-butyloxycarbonyl (Br-t-BOC) group represents the first known solvent-polarity sensitive amino-protecting group. As shown in Figure 1, this group is stable in nonpolar solvents because of high activation energy and easily decomposes in a more polar environment because of

• reduced activation energy. This effect is a result of an increased polarity of the transition state in comparison to the starting molecule (Figure 1). In contrast to the classical t-BOC protecting group, the Br-t-BOC group can be easily removed without pH adjustments. Since the published papers from L. A

• (s, νC-H (R-CH3)); DSC: Tg = 125.9 °C; GPC (THF): = 8900 g/mol, = 6000 g/mol, D = 1.48. Schematic representation of a deprotection taking the relatively high polarity of the transition state and the solvent polarity into account: high activation energy in nonpolar solvents and low activation energy

Solving the puzzling competition of the thermal C²–C⁶ vs Myers–Saito cyclization of enyne-carbodiimides

• Anup Rana,
• Mehmet Emin Cinar,
• Debabrata Samanta and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 43–49, doi:10.3762/bjoc.12.6

• and the decision between the two reaction channels for 7 is not necessarily guided by the free activation energy of the two initial steps, but by the inability of the Myers–Saito diradical to compete in follow-up reactions, either inter- or intramolecular, with the C2–C6 (Schmittel) channel. Results

• over formation of 13DA, suggesting that in the thermolysis the Myers–Saito product 12 should prevail. Due to the low free activation energy for the strongly exergonic intramolecular hydrogen abstraction 11_INTMS → 11_INTγHT of only 1.5 kcal mol−1, the diradical cyclization step is now rate determining