Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• the decomposition of iminoxyl radicals 2 generated from oximes 1 under the action of Ag2O [53] were studied by K. U. Ingold et al. (Figure 2). In most cases, the reaction was accompanied by the release of N2 and N2O, as well as the corresponding carbonyl compounds (3a–c). Dimerization of iminoxyl

• corresponding to the free iminoxyl radical, which indicates the reversibility of dimerization [53]. During the oxidation of pivalic aldoxime 1e by Ag2O, the formation of nitrile oxide 6e was observed, which then slowly dimerized to the corresponding furoxan 7e. The kinetics of the decomposition of dialkyl

• radical that did not undergo decomposition and dimerization in the solution for a time sufficient to use it as a reagent was the di-tert-butyliminoxyl radical (8) [45][59]. It was obtained by oxidation of di-tert-butyl ketoxime (1f) with silver(I) oxide (Ag2O) in benzene at 25 °C (Scheme 2). This radical

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• HEH were used as H donors for both the benzyl and thiyl radicals, respectively. The HEH was needed to avoid the dimerization of the thiophenol to the disulfide (Scheme 11). Fu and co-workers have demonstrated the huge versatility of rhodium porphyrins for photocatalysis. In 2015, they showed that the

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• compensated by the dimerization entropy (ca. 128 J mol−1 K−1) due to the fact that the entropy obtained in vacuo calculations are not realistic in condensed phase. Computed reaction mechanism of the 3-phospholene oxide (1) 2-phospholene oxide (4) isomerization under acidic conditions at MP2/6-311++G(2d,2p

Towards triptycene functionalization and triptycene-linked porphyrin arrays

• Gemma M. Locke,
• Keith J. Flanagan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2020, 16, 763–777, doi:10.3762/bjoc.16.70

• carried out using standard Sonogashira cross-coupling conditions and the product was isolated as a green solid in 19% yield. A major side-product of the reaction was the Glaser product, i.e., dimerization of two ethynyl triptycene molecules 12. The synthesis of this molecule offers future avenues to

Preparation and in situ use of unstable N-alkyl α-diazo-γ-butyrolactams in Rh^II-catalyzed X–H insertion reactions

• Maria Eremeyeva,
• Daniil Zhukovsky,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2020, 16, 607–610, doi:10.3762/bjoc.16.55

• found to be unstable and to undergo unproductive dimerization to bishydrazones, were successfully converted immediately to various X–H insertion products with alcohols, aromatic amines and thiols via an in situ RhII-catalyzed reaction. With aliphatic amines or unreactive, sterically hindered anilines

• demonstrated that the scope of α-diazo-γ-butyrolactams being capable to undergo RhII-catalyzed X–H insertion reactions with alcohols, thiols, and aromatic amines can be extended to unstable N-alkyl derivatives, for which rapid, unproductive dimerization was previously observed. This was achieved through the

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• indolium nitrogen resulting in a decrease of the molar extinction coefficient (ε) as well. Aggregation/dimerization can cause such phenomena, which typically leads to a decrease of absorption at the considered absorption maximum and a pronounced non-radiative deactivation resulting in a decrease of Φf

Reversible photoswitching of the DNA-binding properties of styrylquinolizinium derivatives through photochromic [2 + 2] cycloaddition and cycloreversion

• Sarah Kölsch,
• Heiko Ihmels,
• Jochen Mattay,
• Norbert Sewald and
• Brian O. Patrick

Beilstein J. Org. Chem. 2020, 16, 111–124, doi:10.3762/bjoc.16.13

• electrocyclization or E-to-Z isomerization reactions, whereas the well-established photochromic cycloaddition–cycloreversion equilibrium to establish photoswitchable DNA binders has so far been widely neglected. In fact, there is only one reported example for the use of the reversible photoinduced dimerization of

• triclinic space group . Both XRD analyses clearly showed that both cyclobutane products were formed as rctt configured dimers 4b and 4c (Figure 8). The products 4b and 4c may have formed by a syn head-to-tail dimerization of the E-configured substrate 3a and 3b or by an anti head-to-tail photodimerization

A green, economical synthesis of β-ketonitriles and trifunctionalized building blocks from esters and lactones

• Daniel P. Pienaar,
• Kamogelo R. Butsi,
• Amanda L. Rousseau and
• Dean Brady

Beilstein J. Org. Chem. 2019, 15, 2930–2935, doi:10.3762/bjoc.15.287

• alkoxide anions. This reduces the occurrence of undesirable side-reactions, e.g., intermolecular aldol reaction, lactone/ketonitrile product dimerization and ring-opening polymerization. The application of this method to produce the analogous hemiketal 6 from γ-butyrolactone was not as efficient. Although

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• derivatives (3 and 4) showed irreversible oxidation waves, which is a function of the electrochemically unstable carbazole-based radical cation that can subsequently undergo dimerization [34]. The oxidation waves shifted cathodically upon increasing the donor strength from carbazole (3 and 4) to diphenylamine

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

• mixture during the electroreduction of acetophenone on a mercury cathode induces optical activity in the product (alcohol 24a, Scheme 7) [29]. Additionally, pinacol (23) was also obtained via dimerization along with chiral alcohols. The same method was reinvestigated by Wang and Lu in 2013 using a silver

• electrolysis strategy allowed the electroreduction of acetophenone (22a) to pinacol (23) with 6.4% ee (Scheme 21). As mentioned by the author, the radical intermediate diffuses from the double layer, and dimerization occurs in the chiral solvent sphere in the solution phase. Chiral supporting electrolyte

• alkylation, reduction and catalytic hydrogenolysis, (+)-199 was converted to desired product (−)-200 with 80% ee (Scheme 62). An electrochemical method for the asymmetric oxidative dimerization of cinnamic acid derivatives was developed by Watanabe in 2016 [109]. The substrates for the electrochemical

Synthesis of novel sulfide-based cyclic peptidomimetic analogues to solonamides

• José Brango-Vanegas,
• Luan A. Martinho,
• Lucinda J. Bessa,
• Andreanne G. Vasconcelos,
• Alexandra Plácido,
• Alex L. Pereira,
• José R. S. A. Leite and
• Angelo H. L. Machado

Beilstein J. Org. Chem. 2019, 15, 2544–2551, doi:10.3762/bjoc.15.247

• cocktail afforded the resin-free linear peptidomimetics 8. The SN2’ macrocyclization step was performed immediately after the cleavage procedure to avoid the oxidative disulfide dimerization observed when preparative HPLC purification of the resin-free linear peptidomimetics 8 was tried. Thus, a 1 mM

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

• acremines A and B. The dimerization of acremine F to bisacremine E was investigated but could not be achieved, shedding light on the formation of the acremine dimers in nature. Keywords: meroterpenoid; natural product; selective oxidation; total synthesis; Introduction Endophytic fungi grow in a symbiotic

• both secondary allylic alcohols and afforded 2 in good overall yield (Scheme 3). Bisacremine E (7) was proposed to be formed in nature via [4 + 2] cycloaddition involving two acremine F (5) units [4]. Although dimerization of 5 through a Diels–Alder cycloaddition is not electronically favorable, we

• providing a versatile entry into this class of natural products. Furthermore, we investigated the proposed biomimetic dimerization of 5 to bisacremine E. Since these extensive studies were unsuccessful and no dimers could be observed under a variety of biomimetic conditions, it appears that this

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

• interestingly, based on the results and control studies, Li’s group have proposed the ability of macrocycle 15 (triiodide form) to act as a nanoreactor by the photo-driven dimerization of tetracyano-para-quinodimethane (TCNQ). The proposed mechanism consists of 7 steps: the formation of a 1:1 host–guest [15

• nanoreactor because there is an acceleration of the dimerization by two orders of magnitude and the turnover of the catalyst was demonstrated. The synthesis of cyclic carbonates from epoxides and CO2 is an efficient method for CO2 fixation. The development of an effective chiral catalyst for the efficient

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

• and unique range of fused ring and polycyclic scaffolds. In the subsequent sections, the cycloaddition chemistry of fulvenes will be discussed in terms of their dimerization, and intra- and intermolecular reactions. Whereas the high reactivity and poor stability of triafulvenes have limited studies

• cycloaddition proceeds through an ambimodal [6 + 4]/[4 + 6] transition state leading to both of the proposed [6 + 4] adducts, which can interconvert through a Cope rearrangement (Scheme 6) [107]. Dimerisation cycloadditions Generally, dimerization of fulvenes is an undesired process that may occur upon storage

• , or compete during reactions with other substrates. As a result of their structure and reactivity, triafulvene [4] and pentafulvene [31][59][66][108][109][110][111][112][113][114][115][116][117][118] derivatives are susceptible to dimerization. The high ring strain of triafulvenes makes them

Introduction of an isoxazoline unit to the β-position of porphyrin via regioselective 1,3-dipolar cycloaddition reaction

• Xiujun Liu,
• Xiang Ma and
• Yaqing Feng

Beilstein J. Org. Chem. 2019, 15, 1434–1440, doi:10.3762/bjoc.15.143

• dipoles not only react with various dipolarophiles but also undergo spontaneous dimerization to form furoxans. To avoid or minimize this drawback, the substitutents (e.g., Cl or Me) around the CNO group were introduced to stabilize the nitrile oxides even at room temperature [46][47]. Here, the 2,6

• enantiomers of 3a is present, which assembled to a dimeric structure with the fifth chelation of a Zn2+ ion by the carbonyl group of the other molecule. The self-dimerization property of 3a may be utilized in supramolecular chemistry [50][51][52][53]. Experimental 1: Porphyrin phosphonium salt 1 was prepared

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• occurred upon oxygen-directed metalation. The resulting oxiranyllithium probably exists as a dimer in solution, as it has been nicely evidenced by structural characterization and NMR studies of the lithiated o-trifluoromethylstyrene oxide [37]. Such dimerization obviously stabilizes the oxiranyllithium

Insertion of [1.1.1]propellane into aromatic disulfides

• Robin M. Bär,
• Gregor Heinrich,
• Martin Nieger,
• Olaf Fuhr and
• Stefan Bräse

Beilstein J. Org. Chem. 2019, 15, 1172–1180, doi:10.3762/bjoc.15.114

• controlled reactions depend on the concentration of the reaction partners, the dimerization becomes less dominant with a low concentration of the BCP radical. The propagation with the disulfide proceeds faster as the disulfide concentration is higher. The formation of staffanes seems to be less favored than

New terpenoids from the fermentation broth of the edible mushroom Cyclocybe aegerita

• Frank Surup,
• Florian Hennicke,
• Nadine Sella,
• Maria Stroot,
• Steffen Bernecker,
• Sebastian Pfütze,
• Marc Stadler and
• Martin Rühl

Beilstein J. Org. Chem. 2019, 15, 1000–1007, doi:10.3762/bjoc.15.98

• revealed a 3S configuration. The closest known structural relative of 3 is the 3-demethoxy-3-hydroxy derivative of 3, which has been described as a spontaneous dimerization product of psathyrellon B [5]. In addition to disesquiterpenoids 1–3, metabolite 4 with a molecular mass of 250 Da was isolated. 1H

Halogen bonding and host–guest chemistry between N-alkylammonium resorcinarene halides, diiodoperfluorobutane and neutral guests

• Fangfang Pan,
• Mohadeseh Dashti,
• Michael R. Reynolds,
• Kari Rissanen,
• John F. Trant and
• Ngong Kodiah Beyeh

Beilstein J. Org. Chem. 2019, 15, 947–954, doi:10.3762/bjoc.15.91

• inversion, the two conformations show different dimerization modes (Supporting Information File 1, Figure S3). In 1&DIOFB_A, the two hex-NARBrs are linked by two DIOFB molecules via four Br···I halogen bonds with average RXB of 0.86. The two participating bromide anions are on adjacent “arms”; the remaining

• assemblies. In the complex MeOH-MeCN@1&DIOFB, because of the crystallographic disorder, two halogen bonded dimerization modes were found in the crystal lattice. In the complex of Water@2&DIOFB, two water molecules act as inclusion guests, taking up only 33.9% of the cavity, thus the squeezed resorcinarene

• DIOFB, and guests MeCN, MeOH and water. The previously reported halogen-bonded complexes CHCl3@1&DIOFB (a), and MeOH@1&DIOFB (b). (c)The fit of 1,4-dioxane within the cavity of 1 [32]. The two dimerization modes in the MeOH-MeCN@1&DIOFB complex. In both modes, the cavities are shown as transparent

Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells

• Ayato Yamada,
• Manabu Abe,
• Yoshinobu Nishimura,
• Shoji Ishizaka,
• Masashi Namba,
• Taku Nakashima,
• Kiyofumi Shimoji and
• Noboru Hattori

Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84

• counterparts (65.8% vs 85.5%). Keywords: caged compound; nitroxide; photolysis; radical; theranostics; two-photon; Introduction Nitroxides (aminoxyl radicals) possess a delocalized unpaired electron and exhibit negligible dimerization reactivity, making them persistent open-shell species [1][2][3][4]. In

Design, synthesis and spectroscopic properties of crown ether-capped dibenzotetraaza[14]annulenes

• Krzysztof M. Zwoliński and
• Julita Eilmes

Beilstein J. Org. Chem. 2019, 15, 617–622, doi:10.3762/bjoc.15.57

• prepared and their binding properties toward sodium and potassium ions were studied in addition to transition metals. Sakata et al. reported the syntheses and characterization of nickel(II), copper(II) [25] and oxovanadium(IV) [26] complexes of crown ether-annulated DBTAAs, which caused dimerization in the

Gold-catalyzed ethylene cyclopropanation

• Silvia G. Rull,
• Andrea Olmos and
• Pedro J. Pérez

Beilstein J. Org. Chem. 2019, 15, 67–71, doi:10.3762/bjoc.15.7

• diazo reagent must be added in one portion before pressurizing the system. This fact constitutes the main drawback when working with this alkene, and a highly chemoselective catalyst toward cyclopropanation over carbene dimerization is needed to enhance the former transformation. In a first array of

• spectroscopy. It is worth mentioning that when diethyl diazomalonate or ethyl 2-phenyldiazoacetate were employed as the carbene precursor, no cyclopropanes were detected, only olefins formed from carbene dimerization as well as unreacted diazo compounds were identified at the end of the reaction. Conclusion We

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

• -hexene, giving no conversion at room temperature and dimerization at 85 °C. Exchanging the chloride ligands for iodide ligands led to catalysts 80 and 82 with superior latent behavior that allowed for the latent ROMP of norbornene derivatives (e.g., 83, Scheme 9). In order to improve the selectivities in

MoO₃ on zeolites MCM-22, MCM-56 and 2D-MFI as catalysts for 1-octene metathesis

• Hynek Balcar,
• Martin Kubů,
• Naděžda Žilková and
• Mariya Shamzhy

Beilstein J. Org. Chem. 2018, 14, 2931–2939, doi:10.3762/bjoc.14.272

• double bond isomerization followed by cross metathesis and (ii) 1-octene oligomerization (mainly dimerization). The extent of these reactions depends strongly on the support acidity. Highly acidic supports MCM-22(28) and MCM-56(13) delivered a catalyst of rather low selectivity (up to 14% conversion to

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

• , but also on the properties and initiation rates of the most important ruthenium-based metathesis catalysts, including Grubbs, indenylidene, and Hoveyda–Grubbs complexes, as well as carbene dimerization. We also considered two different solvents: dichloromethane, which is a standard solvent for

• , using M06-D3 approach. Previously we have shown that the addition of D3 correction gives very good agreement with the experimental data for Hov and Hoveyda-like systems as well as for investigations of carbenes dimerization [38][49]. As a result we decided to use the M06-D3 functional in calculations of

• Gibbs free energies all system apart from 1st generation Grubbs and indenylidene-like complexes, for which we used pure M06. Results for all systems and both M06 and M06-D3 methods are listed in Supporting Information File 1. Dimerization The tendency of selected NHC to dimerize is a well-known and