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

• properties: they can be chemically or photochemically controlled, can undergo a configurational change by acid or base addition and have interconversion timescales which can span over several orders of magnitude. Furthermore, a substantial shift of their absorption profile can be enabled through substitution

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• different catalysts, such as palladium, copper, silver, iron, nickel, ruthenium, cobalt, etc. Palladium catalysis Palladium is a member of the nickel triad in the periodic table, and palladium complexes exist in three oxidation states, Pd(0), Pd(II), and Pd(IV). Straightforward interconversion between

Synthesis and anion binding properties of phthalimide-containing corona[6]arenes

• Meng-Di Gu,
• Yao Lu and
• Mei-Xiang Wang

Beilstein J. Org. Chem. 2019, 15, 1976–1983, doi:10.3762/bjoc.15.193

• ]. The observation of the single set of proton and carbon resonance signals of 3 indicated the presence of the conformer with high symmetry or most likely a mixture of conformers which underwent very fast interconversion relative to the NMR time scale. In comparison to diethyl terephthalate, a

Synthesis, enantioseparation and photophysical properties of planar-chiral pillar[5]arene derivatives bearing fluorophore fragments

• Guojuan Li,
• Chunying Fan,
• Guo Cheng,
• Wanhua Wu and
• Cheng Yang

Beilstein J. Org. Chem. 2019, 15, 1601–1611, doi:10.3762/bjoc.15.164

• interconversion can only occur when the guest molecule decomplexed from the cavity [19][20][21]. Several strategies have been established to block the interconversion of the Sp and Rp conformers: Implanting a guest moiety in the pillar[5]arene cavity by rotaxanation or introducing a fused side ring into one of

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• orientations of the two 2,3-dibutoxynaphthalene moieties; but the same number of peaks in NMR spectra should be observed. Nevertheless, only one set of signals are observed, suggesting that either only one conformation is predominant in solution or the conformational interconversion is fast at the NMR

• timescale. H3 is diastereotopic and could be split when the conformational interconversion is slow on the NMR timescale, as observed for oxatub[4]arene [30] and zorb[4]arene [32]. When lowering the temperature to 223 K, H3 of 1 was split to two peaks while other peaks become broadened (Figure 1b). This

• suggests that the conformational interconversion is slow at this temperature and only one conformer is predominant in the solution at 298 K. However, the exact conformer cannot be assigned because the two conformers have the same number of peaks. In contrast, H3 of 2 are broadened even at room temperature

Selective detection of DABCO using a supramolecular interconversion as fluorescence reporter

• Indrajit Paul,
• Debabrata Samanta,
• Sudhakar Gaikwad and
• Michael Schmittel

Beilstein J. Org. Chem. 2019, 15, 1371–1378, doi:10.3762/bjoc.15.137

• sites. The structural changes are accompanied by a huge spatial contraction/expansion of the zinc porphyrin–zinc porphyrin distances that change from 31.2/38.8 Å to 6.6 Å and back. The supramolecular interconversion was used for the highly selective detection of DABCO in a mixture of other similar

• compounds. Keywords: copper; detection; fluorescence; interconversion; macrocycles; self-assembly; self-sorting; zinc porphyrin; Introduction Since dynamic multicomponent supramolecular structures are nowadays abundant [1][2], the weak intercomponent binding [3][4][5][6][7][8][9] is often instrumentalized

• dual-state supramolecular transformation driven by addition/removal of DABCO (4) and it requires a transition between completive vs incomplete self-sorting [27][28]. The fact that DABCO (4) exclusively drives the supramolecular interconversion was further developed into a fluorescent reporter system

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

• amount of 1-S is nearly constant over the course of the racemization, e.g., at 40 °C there are about 3% and at 70 °C about 4.5% of 1-S present in solution (see Supporting Information File 1). In the past, Collet determined rate constants for the interconversion of 1 under the assumption of first order

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

• macrocycle, we envisioned that the signal broadening is caused by rapid interconversion between several preferred conformers of the macrocycle. The DFT optimization performed at the CAM-B3LYP/6-31G(d) level of theory revealed that 1a can occur in form of two preferred conformers 1a-1 and 1a-2 (Figure 2). The

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• Discussion The general viability of the α-ketoester to α-diazoester functional group interconversion envisaged in Scheme 2 (10 → 3) was readily established on a simpler but closely structurally-related system (Scheme 3). Thus, the known Z-hydrazone 12, previously prepared by us from α-ketoester 11 in 75

Conformational signature of Ishikawa´s reagent using NMR information from diastereotopic fluorines

• Laize A. F. Andrade,
• Lucas A. Zeoly,
• Rodrigo A. Cormanich and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2019, 15, 506–512, doi:10.3762/bjoc.15.44

• complex than the study of six-membered cyclic compounds, which usually exhibit only two conformations as the result of chair interconversion [26]. Results and Discussion The preferred conformation along the H–C2–C1–F fragment in 1 was first analyzed using 3JH,F(pro-S/R) SSCC data, since such an NMR

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• case of 172, the Hoveyda-type analogue of 164 (Figure 32), for which a room temperature interconversion between syn and anti rotamers, observed at a ratio of 7.8:1, was revealed by NOE experiments. Surprisingly, despite such rotation the reactivity profiles and the enantioselectivities observed for 164

• catalytic cycle, catalysts 173 and 174, possessing additional substituents on the N-aryl group, were synthesized in moderate yields (42–44%, Figure 32). Both complexes were isolated as a mixture of rotamers, with a prevalence of the syn isomer and no interconversion between the syn/anti rotational isomers

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• enabled isomerization of the central exocyclic double bond, sDTEs form a three-state system undergoing interconversion between ring-open E- and Z-isomers and a ring-closed C-isomer (Scheme 1). Here we describe the oxidatively and reductively induced isomerization behavior of sDTEs as investigated by

Microwave-assisted synthesis of biologically relevant steroidal 17-exo-pyrazol-5'-ones from a norpregnene precursor by a side-chain elongation/heterocyclization sequence

• Gergő Mótyán,
• László Mérai,
• Márton Attila Kiss,
• Zsuzsanna Schelz,
• Izabella Sinka,
• István Zupkó and
• Éva Frank

Beilstein J. Org. Chem. 2018, 14, 2589–2596, doi:10.3762/bjoc.14.236

• between these latter isomers is low and their interconversion is rapid on the NMR timescale, only average signals can be observed for the 4'-H and NH/OH protons [31]. Pharmacological studies The pharmacological activities of the synthesized 17-exo-heterocycles 6a–j and 7a–j were studied in vitro. Their

Carbonylonium ions: the onium ions of the carbonyl group

• Daniel Blanco-Ania and
• Floris P. J. T. Rutjes

Beilstein J. Org. Chem. 2018, 14, 2568–2571, doi:10.3762/bjoc.14.233

• organylated) carbonyl (1) and hydroxy (or organyloxy) carbenium ion (2): two possible representations of the same intermediate. Oxacarbenium, oxocarbenium, oxycarbenium and carboxonium ions. Acid-catalyzed interconversion of carbonyls, hydrates, hemiacetals and acetals.

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• if there are examples, where this was not the case [21][22]. Access to partially unsaturated eunicellane systems could also be of interest for studies on biosynthesis and chemical interconversion [7][10]. Results and Discussion Dihydrocarvone 9 was converted to the enolate and quenched with ethyl

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• by trace amounts of acid [51][52] or photochemically [53]. The interconversion usually prevents a sufficient separation of the two isomers on the laboratory timescale. However, substitution of the TTF molecule by electron-withdrawing groups can stabilize the isomers [54] and a separation becomes

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

• Carmine Gaeta,
• Carmen Talotta and
• Placido Neri

Beilstein J. Org. Chem. 2018, 14, 2112–2124, doi:10.3762/bjoc.14.186

• and cone conformations. The interconversion between them cannot be obtained by simple rotation around the ArCH2Ar bonds of the calixarene wheel, which is blocked by the presence of the axle inside its cavity. Therefore, it can only be obtained through a mechanism of de-threading/re-threading of the

• ascertained at 328 K in CDCl3; below this temperature the conformations of 1 were frozen, while at temperatures above 328 K the conformational interconversion is fast with respect to the NMR time scale (400 MHz). From the coalescence data we calculated a barrier of 14.6 kcal/mol for this process. In summary

• to consider the interconversion between the two isomeric pseudorotaxane 2+11,2,3-alt and 2+1cone. It could take place through two possible mechanisms (Figure 5): a) de-threading of axle 2+ from 2+11,2,3-alt and a subsequent re-threading with 1 in a cone conformation; b) a direct conformational

The phenyl vinyl ether–methanol complex: a model system for quantum chemistry benchmarking

• Dominic Bernhard,
• Fabian Dietrich,
• Mariyam Fatima,
• Cristóbal Pérez,
• Hannes C. Gottschalk,
• Axel Wuttke,
• Ricardo A. Mata,
• Martin A. Suhm,
• Melanie Schnell and
• Markus Gerhards

Beilstein J. Org. Chem. 2018, 14, 1642–1654, doi:10.3762/bjoc.14.140

• minimum due to broad or high interconversion barriers must have their OH stretching fundamental at 3625 ± 5 cm−1 or be significantly less abundant. If one were to trust the relative harmonic wavenumber predictions from the preceding subsection (cf. Table 1), this would imply a single docking motif, as

• elusiveness would be a low interconversion barrier. However, rotational spectroscopy further reveals the presence of the OH–P isomer as a second isomer, being less populated, which is not observed with the less sensitive FTIR technique and might be superimposed by fragmentation of larger clusters in the

A conformationally adaptive macrocycle: conformational complexity and host–guest chemistry of zorb[4]arene

• Liu-Pan Yang,
• Song-Bo Lu,
• Arto Valkonen,
• Fangfang Pan,
• Kari Rissanen and
• Wei Jiang

Beilstein J. Org. Chem. 2018, 14, 1570–1577, doi:10.3762/bjoc.14.134

• macrocycles possess multiple conformers due to the naphthalene flipping in analogy with the phenyl-ring flipping seen in the more common calixarenes. The conformers so formed undergo quick interconversion and each one has a slightly different cavity. Thus, these conformers consist of a complex conformational

Lanyamycin, a macrolide antibiotic from Sorangium cellulosum, strain Soce 481 (Myxobacteria)

• Lucky S. Mulwa,
• Rolf Jansen,
• Dimas F. Praditya,
• Kathrin I. Mohr,
• Patrick W. Okanya,
• Joachim Wink,
• Eike Steinmann and
• Marc Stadler

Beilstein J. Org. Chem. 2018, 14, 1554–1562, doi:10.3762/bjoc.14.132

• . The only remaining NH group finally filled the gap between the amide C-27 (δC 171 ppm) and C-26 (δC 75 ppm) based on the HMBC correlation H-26/C-27 thus forming the unusual and unstable N-acyl hemiaminal that explains the interconversion of lanyamycin isomers 1 and 2. The E configuration of the diene

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

• fission of the intermediate to a 2´,3´-cyclic phosphate, leading to pH-independent cleavage, is much slower (Scheme 1). The rate of this reaction (black line in Figure 6) is only 2% of the interconversion rate of 2´,5´- and 3´,5´-diesters [44]. Studies with various uridine 3´-alkylphosphates have, however

Nucleophilic dearomatization of 4-aza-6-nitrobenzofuroxan by CH acids in the synthesis of pharmacology-oriented compounds

• Alexey M. Starosotnikov,
• Dmitry V. Shkaev,
• Maxim A. Bastrakov,
• Ivan V. Fedyanin,
• Svyatoslav A. Shevelev and
• Igor L. Dalinger

Beilstein J. Org. Chem. 2017, 13, 2854–2861, doi:10.3762/bjoc.13.277

• doublets at 4.71 and 5.15 ppm (J = 2.4 Hz) corresponding to H1’ and H7 atoms were observed. Another set of signals was referred to tautomers 6b. Due to fast interconversion of these tautomers the signals of their methyl groups represent broad singlets at 2.06 and 2.40 ppm. The reaction of ANBF with 1

• that may be attributed to dioxo- and enolic forms. However, analysis of their 1H and 13C NMR spectra was quite complicated due to the broadening of the signals as a result of interconversion of tautomers. On the contrary, 1H NMR spectra in acetone-d6 are much simpler: in each case the single set of

Fluorination of some highly functionalized cycloalkanes: chemoselectivity and substrate dependence

• Attila Márió Remete,
• Melinda Nonn,
• Santos Fustero,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2017, 13, 2364–2371, doi:10.3762/bjoc.13.233

• fluorination based on hydroxy–fluorine interconversion seems to be an eloquent, simple and efficient procedure for the creation of a certain fluorinated organic molecule, regio- and stereoselectivity, stereocontrol and substrate influence remain a challenge in the case of highly functionalized frameworks

Base-promoted isomerization of CF₃-containing allylic alcohols to the corresponding saturated ketones under metal-free conditions

• Yoko Hamada,
• Tomoko Kawasaki-Takasuka and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 1507–1512, doi:10.3762/bjoc.13.149

• by way of the latter intermediate would be occurred at the CF3-attached carbon atom to produce the corresponding allenyl type intermediate. Furthermore, its keto–enol interconversion would result in construction of the isomerized α,β-unsaturated ketones (E)-5 [4][5][6]. For a better comprehension of

Cycloheximide congeners produced by Streptomyces sp. SC0581 and photoinduced interconversion between (E)- and (Z)-2,3-dehydroanhydrocycloheximides

• Li Yang,
• Ping Wu,
• Jinghua Xue,
• Huitong Tan,
• Zheng Zhang and
• Xiaoyi Wei

Beilstein J. Org. Chem. 2017, 13, 1039–1049, doi:10.3762/bjoc.13.103

• , anhydroisoheximide (4), cycloheximide (5), and isocycloheximide (6), were obtained from the cultures of Streptomyces sp. SC0581. Their structures were elucidated by extensive spectroscopic analysis in combination with theoretical conformational analysis and ECD computations. The photoinduced interconversion between

• , anhydroisoheximide (4) [6], together with cycloheximide (5) and isocycloheximide (6) [10]. Their structures were elucidated by spectroscopic analysis, theoretical conformational analysis, and ECD/TDDFT calculations. The photoinduced interconversion between 2 and 3 was observed and verified, and the possible reaction

• path and mechanism were proposed by theoretical computations. All the isolated compounds were evaluated for antifungal activity and cancer cell toxicity. Herein are reported the isolation, structural elucidation, and biological activities of these compounds and the interconversion between 2 and 3