Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-ʟ-arabinose

• Lukáš Kerner and
• Paul Kosma

Beilstein J. Org. Chem. 2020, 16, 9–14, doi:10.3762/bjoc.16.2

• -benzyl-protected gluco and galacto derivatives [20][27][30][31]. In addition to exocyclic glycals mimicking putative planar transition states of substrates involved in enzymatic reactions, such as glycosyl transfer, mutase, and epimerization, endo-glycals are also of interest [21][22][32][33][34][35

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

• difficult due to their rather nonpolar transition states, which are difficult to be addressed by catalysts [29]. Several stereoselective [3,3]-sigmatropic rearrangements are realized with chiral Brønsted acids [30][31][32][33][34]. Jacobsen reported guanidinium-catalyzed enantioselective Claisen

• activate the enolates or the corresponding silyl ketene acetals or stabilize the corresponding transition states. In addition, chiral organocatalysts could induce diastereo- as well as enantioselectivity. Therefore, we examined the Ireland–Claisen rearrangement of ester 1c in the presence of a range of

• rearrangements proceed via isopolar transition states and, therefore solvent effects are rather small. For this reason and due to the complete lack of enantioselectivity, at this stage, we did not investigate other solvents with the catalysts collected in Figure 1. In order to gain further insight into 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

• derivatives are predicted to occur through a transition state in which the N atom next to the benzene ring linearizes in an inversion mechanism (see B-type transition states in Figure 2 for 4pzH-F2 and 4pzMe-F2, and Figure S1 in Supporting Information File 1 for the rest of di-ortho-substituted photoswitches

• the possible conformers both in the Z- and E-forms were fully optimized by using the hybrid exchange-correlation PBE0 functional [37] including the Grimme’s dispersion correction in its latest version (D3) [38]. The split-valence Pople’s basis set 6-31G** was used throughout [39]. Transition states

• 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

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• computations on carbocation intermediates and transition states were carried out with the B3LYP functional and 6-31+G(d,p) basis set, using the polarizable continuum model in dichloroethane to model solvation [42]. Each stationary point was characterized as a minimum or transition state by vibrational

Thermal stability of N-heterocycle-stabilized iodanes – a systematic investigation

• Andreas Boelke,
• Yulia A. Vlasenko,
• Mekhman S. Yusubov,
• Boris J. Nachtsheim and
• Pavel S. Postnikov

Beilstein J. Org. Chem. 2019, 15, 2311–2318, doi:10.3762/bjoc.15.223

• electrophilic hypervalent iodine atom in its ground state or directly influences its reactivity by stabilizing reactive intermediates or transition states. In recent years, a plethora of cyclic and pseudocyclic iodanes have been developed with covalently attached stabilizing ligands L2 and applied in a variety

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• (2a’) derivatives would lead to higher energy anti-aromatic transition states [1][2][9][15]. Additionally, upon conversion to the dipole forms (Scheme 1), the fulvene loses total planarity through the exocyclic carbon sp2 → sp3 hybridisation, allowing some loss of energy (and gain in stability

The cyclopropylcarbinyl route to γ-silyl carbocations

• Xavier Creary

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

• spectra of new compounds. Supporting Information File 74: M062X/6-611+G** calculated structures, energies, and Cartesian coordinates for carbocations and transition states.

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

• can lead to different products in a ratio that depends on reaction dynamics [31][32][33]. The study of molecular dynamics trajectories has allowed characterization of ambimodal transition states in reactions involving carbocations [34][35]. We have demonstrated computationally the presence of

Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy

• Daniela Imperio,
• Erika Del Grosso,
• Silvia Fallarini,
• Grazia Lombardi and
• Luigi Panza

Beilstein J. Org. Chem. 2019, 15, 1355–1359, doi:10.3762/bjoc.15.135

• stereoselectivity in the hydroboration reaction we hypothesized the transition states bearing to the two epimers. We assumed that borane would react firstly with the free hydroxy group generating an intermediate alkoxyborane, and that the hydroboration reaction occurs intramolecularly on such intermediate. Based on

• these premises, two transition states can be identified (Figure 4) for the hydroboration reaction on each of the two diastereotopic faces of the double bond. The transition state deriving from the attack on the si face, which leads to the arabino-configurated product, contains two destabilizing

• conserved into the analogues). Structures of boron analogues. Synthetic strategy. Postulated transition states for the hydroboration reaction. Synthesis of 2-deoxy analogue 8. Synthesis of 2,3-dideoxy analogue 11. Supporting Information Supporting Information File 488: Experimental procedures and

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• sulfonylhydrazine 6 (1.2 equiv) in CH2Cl2 led to the desired N-tosylhydrazone 7 in 83% yield and with 82% ee (Scheme 3b). The absolute configuration was assigned on the basis of the structure of 7, which was confirmed unambiguously by an X-ray crystallographic study [39]. Tentative transition states to account for

Mechanistic investigations on multiproduct β-himachalene synthase from Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 1008–1019, doi:10.3762/bjoc.15.99

• vanished crosspeak. Combining the information deduced from the extensive incubation experiments stated above, a structural model for the reactive conformation of cation D is proposed (Figure S19, Supporting Information File 1). This intermediate, or structurally related transition states for the

An anomalous addition of chlorosulfonyl isocyanate to a carbonyl group: the synthesis of ((3aS,7aR,E)-2-ethyl-3-oxo-2,3,3a,4,7,7a-hexahydro-1H-isoindol-1-ylidene)sulfamoyl chloride

• Aytekin Köse,
• Aslı Ünal,
• Ertan Şahin,
• Uğur Bozkaya and
• Yunus Kara

Beilstein J. Org. Chem. 2019, 15, 931–936, doi:10.3762/bjoc.15.89

• and B, we use the notation A/B throughout the article. Figure 3 shows the relative energy profile for the reaction mechanism shown in Scheme 4. The rate-determining steps for the formation of 10, 11, and 12 are the transition states 9/14, 9/11, and 9/12, respectively. The difference between the

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

Study on the regioselectivity of the N-ethylation reaction of N-benzyl-4-oxo-1,4-dihydroquinoline-3-carboxamide

• Pedro N. Batalha,
• Luana da S. M. Forezi,
• Maria Clara R. Freitas,
• Nathalia M. de C. Tolentino,
• Ednilsom Orestes,
• José Walkimar de M. Carneiro,
• Fernanda da C. S. Boechat and
• Maria Cecília B. V. de Souza

Beilstein J. Org. Chem. 2019, 15, 388–400, doi:10.3762/bjoc.15.35

• media considered, the N–C–Br bond angle (α) on the transition states were slightly higher for the carboxamide group (Table 3). These results are consistent with the one previously found. As already shown, the oxoquinoline conjugate base is more stabilized when compared to the carboxamide one. Such

• . Table 4 illustrates the optimized geometry for the transition states for each possible reaction path. The comparison of the two possible reaction paths shows that although N-ethylation of the carboxamide site is associated with a lower energy barrier, addition of solvent stabilizes the transition state

• . Since experimentally, this is not observed, it can be concluded that only the N–H site of oxoquinoline undergoes deprotonation. That is, the conjugate base of the carboxamide is not generated in the process. Observing the predicted N–C–Br (α) angle in the calculated transition states, none of the

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• ’ were considered which would lead to five-membered ring transition states in which the aryl group occupies a preferential pseudo-equatorial or a less favorable pseudo-axial orientation, respectively (Scheme 3) [33][34]. The authors also showed that phosphine oxide (E)-3f could be reduced to the

• leading to zwitterronic intermediates 8 and 8’. This would result in an increase of conformational flexibility thereby facilitating the nucleophilic displacement of the ammonium by the phosphinite through transition states TS1 and TS2 (SN2-type process), respectively. Oxaphospholanium zwitterions 9 and 9

• activation barriers of the reactions leading to 8 and 8’, regardless of the aromatic substituent. Since 8 and 8’ were in rapid equilibrium with phosphinite 6, the diastereoselectivity should depend on the relative stabilities of the transition states TS1 and TS’1. An electron-donating group at the para

Synthesis of 1,2-divinylcyclopropanes by metal-catalyzed cyclopropanation of 1,3-dienes with cyclopropenes as vinyl carbene precursors

• Jesús González,
• Alba de la Fuente,
• María J. González,
• Laura Díez de Tejada,
• Luis A. López and
• Rubén Vicente

Beilstein J. Org. Chem. 2019, 15, 285–290, doi:10.3762/bjoc.15.25

• refluxed in toluene (24 h) partial isomerization was observed (endo/exo = 1:1.6). This behavior can be attributed to the high substitution at one of the alkenes, which might lead to sterically overcrowded transition states required for the rearrangement [27]. Besides, the diastereoisomeric mixture of 3j

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• points/transition states, as well as experimental details can be found in Supporting Information File 1. CCDC-1833170 (BIFOXSiCl2 (7)), CCDC-1833171 (BIFOXSiCl(OH) (8)), CCDC-1833172 (BIFOXSi(OH)2 (9, dimer)), CCDC-1833173 (BIFOXSi(OH)2 (9, tetramer)), CCDC-1833174 (BIFOXSiCl(OH) 8·acetone) and CCDC

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

• Łukasz Gułajski,
• Andrzej Tracz,
• Katarzyna Urbaniak,
• Stefan J. Czarnocki,
• Michał Bieniek and
• Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

• Marcus postulated a trans-phase hydrogen bonding from water OH groups to H-bond acceptor sites of organic reactants contributing to a stabilisation of organic transition states enables the on-water catalysis [77]. Ben-Amotz et al. demonstrated that the effect of the water OH groups depends either on the

Computational characterization of enzyme-bound thiamin diphosphate reveals a surprisingly stable tricyclic state: implications for catalysis

• Ferran Planas,
• Michael J. McLeish and
• Fahmi Himo

Beilstein J. Org. Chem. 2019, 15, 145–159, doi:10.3762/bjoc.15.15

• the substrate analog inhibitor, (R)-mandelate. In that study all intermediates and transition states were located and characterized. Intriguingly, we identified the tricyclic TCH+ state of the cofactor as an off-cycle intermediate species. It was found to be about 5 kcal/mol lower in energy than the

The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• saturated NHC is considered, the substitution reduces dramatically the barriers of the first two transition states. Then the cycle I→VI is more exothermic with the substituted systems. On the other hand, the unsaturated system does not reduce the energy barriers with the substituted indenylidene moieties

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• )-geometry of the crotylboronate, while the 2,3-anti relationship can be rationalized by invoking Cornforth-like transition states [40][41][42][43]. Eventually, silylation of the homoallylic alcohol 12b afforded the expected compound 13b in 68% overall yield from 5 after purification, compared to 29% using a

Green synthesis of new chiral 1-(arylamino)imidazo[2,1-a]isoindole-2,5-diones from the corresponding α-amino acid arylhydrazides in aqueous medium

• Nadia Bouzayani,
• Jamil Kraїem,
• Sylvain Marque,
• Yakdhane Kacem,
• Abel Carlin-Sinclair,
• Jérôme Marrot and
• Béchir Ben Hassine

Beilstein J. Org. Chem. 2018, 14, 2923–2930, doi:10.3762/bjoc.14.271

• imino-carboxylic acid form likely evolves to its iminium-carboxylate form B [50]. This last intermediate involves the existence of two possible transition states for the cyclization of the imidazolidinone core of which one of them is favored by an intramolecular hydrogen bond (Scheme 5). This control is

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

• Magdalena Jawiczuk,
• Angelika Janaszkiewicz and
• Bartosz Trzaskowski

Beilstein J. Org. Chem. 2018, 14, 2872–2880, doi:10.3762/bjoc.14.266

• transition states). In the second step we performed solvation energy calculations using the Poisson–Boltzmann self-consistent polarizable continuum method as implemented in Jaguar v.7.9 (Schrodinger, 2013) to represent dichloromethane, using the dielectric constant of 8.93 and the effective radius 2.33 Å

A challenging redox neutral Cp*Co(III)-catalysed alkylation of acetanilides with 3-buten-2-one: synthesis and key insights into the mechanism through DFT calculations

• Andrew Kenny,
• Alba Pisarello,
• Arron Bird,
• Paula G. Chirila,
• Alex Hamilton and
• Christopher J. Whiteoak

Beilstein J. Org. Chem. 2018, 14, 2366–2374, doi:10.3762/bjoc.14.212

• M06/def2-TZVP [38][39][40][41]. Frequencies calculations approximated the ZPE correction and entropic contributions to the free energy term as well as confirming all intermediate were true with no imaginary modes and all transition states had the correct critical frequency of decomposition (imaginary

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• enantioselectivity (52 vs 53). Moreover, the more electron-deficient 3,4,5-trifluorophenyl analog 54 was found to be less enantioselective. The authors proposed that the benzylic groups can stabilize the cationic intermediates and/or transition states through cation–π interactions, which play an important role in