Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

• Alexander P. Molchanov,
• Mariia M. Efremova,
• Mariya A. Kryukova and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2020, 16, 2679–2686, doi:10.3762/bjoc.16.218

• for transformations of azomethine imines [37][38][39]. However, only the conversion to pyrazolines and the dimerization were investigated previously for diaziridines under microwave conditions [40][41]. The cycloaddition reactions of unstable azomethine imines generated from diaziridines were

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• monomeric in solution with the small calix[4]arene, while calix[6]arene induces protein dimerization [23], and calix[8]arene even tetramerization [24] in solution as evidenced by SEC-MALS. In the NMR spectra, the assembly of proteins is evident by increased line broadening of most residues due to the

Hierarchically assembled helicates as reaction platform – from stoichiometric Diels–Alder reactions to enamine catalysis

• David Van Craen,
• Jenny Begall,
• Johannes Großkurth,
• Leonard Himmel,
• Oliver Linnenberg,
• Elisabeth Isaak and
• Markus Albrecht

Beilstein J. Org. Chem. 2020, 16, 2338–2345, doi:10.3762/bjoc.16.195

• “Werner-type” triscatecholate titanium(IV) complex. Two of these monomers dimerized in a consecutive step to obtain a non-covalently linked helicate (Scheme 1). The dimerization took place via the coordination of three lithium cations acting as bridges between two monomeric complex units [13][14][15][16

• residue Li[Li3(1)3(6)3Ti2] showed only 16% ee. The yields were higher than 60%. A possible reason for the significant drop in enantioselectivity by switching from ligand 5 to 6 was due to the different dimerization behavior. The homoleptic helicate Li[Li3(6)6Ti2] shows a lower dimerization tendency

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• have attempted various combinations of Ti(IV) and reducing agents but Cp2TiCl2 with Zn powder provided the better results compared to the other combinations [14][40]. Additionally, they prepared benzyl–benzyl coupled sumanene dimer 48 by means of oxidative dimerization via sumanenyl monoanion

Synthesis of 6,13-difluoropentacene

• Matthias W. Tripp and
• Ulrich Koert

Beilstein J. Org. Chem. 2020, 16, 2136–2140, doi:10.3762/bjoc.16.181

• herringbone structure of 1–3. Here, the synthesis and characterization of 6,13-difluoropentacene (5, F2PEN) is reported. Since the central ring of pentacenes is known to be a weak spot (because of light-induced dimerization or oxidation) [2] the effects of fluorination in these positions are of interest

The biomimetic synthesis of balsaminone A and ellagic acid via oxidative dimerization

• Sharna-kay Daley and
• Nadale Downer-Riley

Beilstein J. Org. Chem. 2020, 16, 2026–2031, doi:10.3762/bjoc.16.169

• Sharna-kay Daley Nadale Downer-Riley Department of Chemistry, The University of the West Indies, Mona, Jamaica 10.3762/bjoc.16.169 Abstract The application of oxidative dimerization for the biomimetic synthesis of balsaminone A and ellagic acid is described. Balsaminone A is synthesized via the

• oxidative dimerization of 1,2,4-trimethoxynaphthalene under anhydrous conditions using CAN, PIDA in BF3·OEt2 or PIFA in BF3·OEt2 in 7–8% yields over 3 steps. Ellagic acid is synthesized from its biosynthetic precursor gallic acid, in 83% yield over 2 steps. Keywords: balsaminone A; biomimetic synthesis

• ; ellagic acid; oxidative dimerization; Introduction Over the last century, the formation of an aryl to aryl bond has garnered considerable synthetic attention due to the applications of biaryls as pharmaceutical agents, as well as chiral auxiliaries in asymmetric synthesis [1][2][3]. Methods such as the

Regiodivergent synthesis of functionalized pyrimidines and imidazoles through phenacyl azides in deep eutectic solvents

• Paola Vitale,
• Luciana Cicco,
• Ilaria Cellamare,
• Filippo M. Perna,
• Antonio Salomone and
• Vito Capriati

Beilstein J. Org. Chem. 2020, 16, 1915–1923, doi:10.3762/bjoc.16.158

• formed. The latter was indeed isolated as the main product (68% yield, Scheme 3). A plausible mechanism for the formation of the 2-aroylimidazoles 3/3' is depicted in Scheme 4. A key intermediate may be the in situ generated α-imino ketone 5. The latter is known to undergo dimerization to give 6 followed

• -azide 4a, would undergo either dimerization to give 6a, and then imidazoles 3a/3a' after cyclization and dehydration (see Scheme 5), or trimerization to afford adduct 8a further to an additional attack of 5a to the internal imino group of 6a and dehydration. Consecutive tautomerization, followed by an

• pyrimidines 7b–h in 45–88% yield. Variable amounts of difunctionalized imidazoles 3/3' (20–40%), deriving from a dimerization process, also formed competitively in some cases under the aforementioned conditions. The latter, however, could be easily isolated by column chromatography. The presence of strong

Microwave-assisted efficient one-pot synthesis of N²-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

• Moustafa Sherief Moustafa,
• Ramadan Ahmed Mekheimer,
• Saleh Mohammed Al-Mousawi,
• Mohamed Abd-Elmonem,
• Hesham El-Zorba,
• Afaf Mohamed Abdel Hameed,
• Tahany Mahmoud Mohamed and
• Kamal Usef Sadek

Beilstein J. Org. Chem. 2020, 16, 1706–1712, doi:10.3762/bjoc.16.142

• unequivocally supported by single-crystal X-ray diffraction (Figure 1 and Table 2). A plausible mechanism for the formation of products 4 is postulated in Scheme 3. The dimerization of cyanamide 1 in basic medium to cyanoguanidine 5 and subsequent reaction with 5-aminotetrazole (3) yielded tetrazolylbiguanidine

Pauson–Khand reaction of fluorinated compounds

• Jorge Escorihuela,
• Daniel M. Sedgwick,
• Alberto Llobat,
• Mercedes Medio-Simón,
• Pablo Barrio and
• Santos Fustero

Beilstein J. Org. Chem. 2020, 16, 1662–1682, doi:10.3762/bjoc.16.138

• substitution at the olefinic counterpart. Synthesis of fluorinated enynes 37 [59]. Fluorine-containing substrates in PKR [59]. Pauson Khand reaction for fluorinated enynes by the Fustero group: scope and limitations [59]. Synthesis of chloro and bromo analogues [59]. Dimerization pathway [59]. Synthesis of

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• Raney nickel (Ra-Ni), sometimes as the main product, depending on the activity of the catalyst [10] (Scheme 2). The oxidative dimerization of 1-phenylisoindole (6a) to compound 5a took place under various conditions: when refluxing in benzene in the presence of air [5][11], during an attempted

• dimerization of indole under acidic conditions (Scheme 7) [8]. Electrophilic attack of indole protonated at position 3 toward the position 3 of another indole molecule, followed by deprotonation affords dimer-like derivative 20. The fundamental difference of this transformation from that we observed in the

• -like products 8a,b. Dimerization of indole under acidic conditions. Reaction of o-(pivaloylaminomethyl)benzaldehyde (1e) to give dimer-like products 23a and 23b. Yields of rearranged aldehydes 2 and dimer-like products 3 and 8 in two different solvents. Relative Gibbs free energy values corresponding

A dynamic combinatorial library for biomimetic recognition of dipeptides in water

• Florian Klepel and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2020, 16, 1588–1595, doi:10.3762/bjoc.16.131

• SPPS. Thus one cysteine moiety is left deprotected and can be addressed selectively either by dimerization with another CFC(Acm) or with inversely substituted tripeptide (C(Acm)FC). These linear peptide dimers were subsequently cyclized by oxidative cleavage of the Acm groups to give a(CFC)2 and p(CFC

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

• Shrikant D. Tambe,
• Kwan Hong Min,
• Naeem Iqbal and
• Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

• substituted (E)-N-benzylidene-[1,1'-biphenyl]-2-amines were studied in CH3OH (Scheme 3) [51][52][53][54][55][56]. It is noteworthy that the resulting symmetrical 1,2-diamine compounds are potential ligands for a variety of organic transformations. The dimerization reactions proceeded well, regardless of the

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