Combretastatins D series and analogues: from isolation, synthetic challenges and biological activities

• Jorge de Lima Neto and
• Paulo Henrique Menezes

Beilstein J. Org. Chem. 2023, 19, 399–427, doi:10.3762/bjoc.19.31

• , the authors employed an Ullmann-type condensation [28] between ester 14 and 4-iodobenzaldehyde (15) to give the corresponding diaryl ether 16 in 78% yield. The subsequent demethylation reaction using boron triiodide also promoted the hydrolysis of the ester, and thus a re-esterification step was

• 97% yield. Subsequent intramolecular Ullmann-type reaction using CuMe under high dilution conditions [31] gave macrolide 28 in low yield. Finally, demethylation using boron triiodide [32] led to the formation of combretastatin D-2 (2, Scheme 5). Using this strategy, Boger succeeded to synthesize

Discrimination of β-cyclodextrin/hazelnut (Corylus avellana L.) oil/flavonoid glycoside and flavonolignan ternary complexes by Fourier-transform infrared spectroscopy coupled with principal component analysis

• Nicoleta G. Hădărugă,
• Gabriela Popescu,
• Dina Gligor (Pane),
• Cristina L. Mitroi,
• Sorin M. Stanciu and
• Daniel Ioan Hădărugă

Beilstein J. Org. Chem. 2023, 19, 380–398, doi:10.3762/bjoc.19.30

• ) of the FA glycerides to the corresponding FA methyl esters (FAMEs) [11][13]. The derivatization involved methanol–boron trifluoride (20% BF3), hexane (GC grade) and anhydrous sodium sulfate, all purchased from Merck & Co., Inc., Rahway, NJ, USA. Sodium chloride (reagent grade) used for the separation

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• showed good fluorescence emission; thus, it could be used as a photodynamic therapy application. In 2013, Liu and colleagues [66] used a click chemistry approach to synthesize meso-tetratriazole-bridged Zn(II) porphyrin-boron dipyrromethane conjugates 164 in 85% yield by reacting porphyrin 146 with

Group 13 exchange and transborylation in catalysis

• Dominic R. Willcox and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2023, 19, 325–348, doi:10.3762/bjoc.19.28

• transfer one or more groups from one group 13 element to another, through σ-bond metathesis; where boron is both of the group 13 elements, this is termed transborylation. These redox-neutral processes are increasingly being used to render traditionally stoichiometric group 13-mediated processes catalytic

• in catalysis beyond their typical use as Lewis acids [46]. This strategy has allowed the synthesis of bench-stable boronic ester products, rather than sensitive alkylboranes, and enabled the use of substoichiometric amounts of enantioenriched boron reagents, which can be challenging to prepare. This

• review will explore the use of group 13 exchange reactions as a general method for catalytic turnover, and serves to expand on the previously published review on transborylation-enabled boron catalysis to include a broader range of catalysts and turnover reagents [47]. Review Boron catalysis The borane

Investigation of cationic ring-opening polymerization of 2-oxazolines in the “green” solvent dihydrolevoglucosenone

• Solomiia Borova and
• Robert Luxenhofer

Beilstein J. Org. Chem. 2023, 19, 217–230, doi:10.3762/bjoc.19.21

• for most POx, accordingly, it was used successfully only for the polymerization of EtOx [34]. Correia et al. used supercritical carbon dioxide for the synthesis of 2-oxazoline-based oligomers with antimicrobial properties and applied boron trifluoride etherate as the initiator [35]. However, carbamic

• Dihydrolevoglucosenone (DLG) is prepared by hydrogenation of levoglucosenone in the presence of palladium as a catalyst. Recently, Debsharma et al. reported the CROP of levoglucosenyl alkyl ether in CH2Cl2 at 0 °C and at room temperature using triflic acid or boron trifluoride etherate as initiators [46][47][48]. The 1H

1,4,6,10-Tetraazaadamantanes (TAADs) with N-amino groups: synthesis and formation of boron chelates and host–guest complexes

• Artem N. Semakin,
• Ivan S. Golovanov,
• Yulia V. Nelyubina and
• Alexey Yu. Sukhorukov

Beilstein J. Org. Chem. 2022, 18, 1424–1434, doi:10.3762/bjoc.18.148

• hydrazone groups. The use of N-TAAD derivatives as potential ligands and receptors was showcased through forming boron chelates and host–guest complexes with water and simple alcohols. Keywords: azaadamantanes; cyclotrimerization; hydrazones; inclusion complexes; molecular recognition; Introduction

•  1b) [21][22][23]. In particular, N,N,N-trihydroxy-TAAD derivatives (3O-TAADs) were shown to be chelating ligands for boron [24]. The application of TAAD-boronate complexes was demonstrated by the preparation of conjugates of boronic acids with biomolecules [25][26], COF-like materials [25], and

• of the obtained TAAD derivatives were performed, and the formation of boron chelates and host–guest complexes having an unusual intramolecular H-bonded network was showcased in this work. Results and Discussion Synthesis of 3N-TAADs, 2N,1O-TAADs and 1N,2O-TAADs Our strategy to construct TAAD

B–N/B–H Transborylation: borane-catalysed nitrile hydroboration

• Filip Meger,
• Alexander C. W. Kwok,
• Franziska Gilch,
• Dominic R. Willcox,
• Alex J. Hendy,
• Kieran Nicholson,
• Andrew D. Bage,
• Thomas Langer,
• Thomas A. Hunt and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2022, 18, 1332–1337, doi:10.3762/bjoc.18.138

• of a double B–N/B–H transborylation mechanism. Keywords: boron; catalysis; hydroboration; nitrile; transborylation; Introduction Primary amines are prevalent throughout organic synthesis, finding regular application in materials chemistry, pharmaceuticals, and agrochemicals (Scheme 1a) [1][2][3

• research into the development of new catalytic methodologies, specifically those that use Earth-abundant and low toxicity elements, as an alternative to transition-metal catalysis [9][10]. Using metal-free catalytic systems, including boron-based catalysts, circumvents some of the issues associated with

• strategies [27]. Both of these used non-commercially available catalysts prepared over multiple steps, the first an N-heterocyclic olefin [22], and the second a bicyclic (alkyl)(amino)carbine [23]. Both displayed limited tolerance to reducible functionalities. NaHBEt3 is the only known boron-based catalyst

Mechanochemical bottom-up synthesis of phosphorus-linked, heptazine-based carbon nitrides using sodium phosphide

• Blaine G. Fiss,
• Georgia Douglas,
• Michael Ferguson,
• Jorge Becerra,
• Jesus Valdez,
• Trong-On Do,
• Tomislav Friščić and
• Audrey Moores

Beilstein J. Org. Chem. 2022, 18, 1203–1209, doi:10.3762/bjoc.18.125

• ; Introduction The development of heteroatom-doped graphitic carbon nitrides (g-CN) has been a rapidly growing area of research since their first report towards water splitting in 2009 [1]. Since that time, the addition of elements such as boron [2], phosphorus [3][4][5], sulfur and oxygen [6] have shown to help

Electro-conversion of cumene into acetophenone using boron-doped diamond electrodes

• Mana Kitano,
• Tsuyoshi Saitoh,
• Shigeru Nishiyama,
• Yasuaki Einaga and
• Takashi Yamamoto

Beilstein J. Org. Chem. 2022, 18, 1154–1158, doi:10.3762/bjoc.18.119

• 10.3762/bjoc.18.119 Abstract A straightforward electro-conversion of cumene into acetophenone has been reported using boron-doped diamond (BDD) electrodes. This particular conversion is driven by the addition reaction of a cathodically generated hydroperoxide anion to an anodically generated cumyl cation

• , where the BDD’s wide potential window enables the direct anodic oxidation of cumene into the cumyl cation. Since electricity is directly employed as the oxidizing and reducing reagents, the present protocol is easy to use, suitable for scale-up, and inherently safe. Keywords: aromatic alkyl; boron

• /or cathode. Boron-doped diamond (BDD) is a relatively new electrode material [15][16] and shows a wide potential window, which can be applied to the transformation of compounds with high redox potentials. Therefore, BDD electrodes would enable a straightforward oxidation reaction of aromatic alkyls

Synthetic strategies for the preparation of γ-phostams: 1,2-azaphospholidine 2-oxides and 1,2-azaphospholine 2-oxides

• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 889–915, doi:10.3762/bjoc.18.90

• reaction of 2-imino-2H-chromene-3-carboxamide (228) and diethyl phosphite at 80–90 °C under the catalysis of boron trifluoride, afforded 4-amino-1-ethoxy-9b-hydrochromeno[4,3-c][1,2]azaphosphol-3(2H)-one 1-oxide (229) in 40% yield through the Michael addition and subsequent tautomerization and

Palladium-catalyzed solid-state borylation of aryl halides using mechanochemistry

• Koji Kubota,
• Emiru Baba,
• Tamae Seo,
• Tatsuo Ishiyama and
• Hajime Ito

Beilstein J. Org. Chem. 2022, 18, 855–862, doi:10.3762/bjoc.18.86

• organic materials, typically through Suzuki–Miyaura coupling [1][2][3][4][5][6][7]. The palladium-catalyzed boryl substitution of aryl halides with boron reagents, termed Miyaura–Ishiyama borylation, is an efficient method for synthesizing arylboronates with high functional group compatibility [8][9][10

Post-synthesis from Lewis acid–base interaction: an alternative way to generate light and harvest triplet excitons

• Hengjia Liu and
• Guohua Xie

Beilstein J. Org. Chem. 2022, 18, 825–836, doi:10.3762/bjoc.18.83

• ), DPPPy-Ph-3F (17), and DPPPy-Ph-F (18, Figure 8), and determined the 11B NMR spectra (Figure 9c) [44]. When coordinated with nitrogen atoms, the resonance peak shifted slightly from ca. −10 to 0 ppm, which suggested the interaction between boron and nitrogen atoms. Wang’s group studied the interaction of

• compound 14 respectively with B(C6F5)3 and B(C6H5)3 by X-ray photoelectron spectroscopy (XPS) [29]. The B(1s) signal showed peaks at 190.61 and 191.08 eV, respectively. This is close to the reported characteristic B–N binding energy (190.5 eV) in B–N crystals. Despite the weak signals of boron in these two

Inductive heating and flow chemistry – a perfect synergy of emerging enabling technologies

• Conrad Kuhwald,
• Sibel Türkhan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2022, 18, 688–706, doi:10.3762/bjoc.18.70

• Petasis boron-Mannich (PBM) reaction of glyoxalic acid (30a) or salicylic aldehyde (30b), with morpholine (29) and p-methoxyphenylboronic acid (31) furnished α-aminocarboxylic acid 32a and phenol 32b in excellent yield (98% and 93%), again much higher than the yields found for the batch protocol (77% and

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• ) and excess of triene 53 was carried out using boron trifluoride diethyl etherate or zirconium(IV) tetrachloride to furnish product 54 in good yield (Scheme 15). The same group also explored the Diels–Alder reaction of menadione (10) with trienes 55, 57, and 59 (Scheme 16) [110]. The scandium(III

Unexpected chiral vicinal tetrasubstituted diamines via borylcopper-mediated homocoupling of isatin imines

• Marco Manenti,
• Leonardo Lo Presti,
• Giorgio Molteni and
• Alessandra Silvani

Beilstein J. Org. Chem. 2022, 18, 303–308, doi:10.3762/bjoc.18.34

• -butanesulfinyl ketimine; homocoupling; Introduction As bioisosteres of carboxylic acid derivatives, boronic acids have recently emerged as a novel chemotype in drug design, with a number of boron-containing compounds recently being approved by the FDA [1][2][3][4]. In particular, α- and β-aminoboronic acids are

• commonly utilized as key intermediates for the synthesis of boron-containing peptidomimetics, which have been demonstrated to be efficient covalent ligands and valuable protease inhibitors endowed with various biological activities [5][6]. Going on with our interest in the synthesis of 3,3-disubstituted

• intramolecular transformation [14], the insertion of a boron atom into chiral oxindoles is scarcely reported. Continuing with such previous project, next we looked at the copper-mediated reaction of isatin-derived, optically pure sulfinyl ketimines with bis(pinacolato)diboron, as a potential way to access

Highly stereocontrolled total synthesis of racemic codonopsinol B through isoxazolidine-4,5-diol vinylation

• Lukáš Ďurina,
• Anna Ďurinová,
• František Trejtnar,
• Ľuboš Janotka,
• Lucia Messingerová,
• Jana Doháňošová,
• Ján Moncol and
• Róbert Fischer

Beilstein J. Org. Chem. 2021, 17, 2781–2786, doi:10.3762/bjoc.17.188

• terminal alkenes bearing both an allylic and homoallylic-type hydroxy group, yielding a sole threo isomer, are rare [36]. The cyclization of 5 through an epoxide ring-opening reaction with boron trifluoride etherate in dichloromethane at 0 °C yielded pyrrolidine derivative 12 in 69% isolated yield [37

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

• by Humber et al. [45]. They started with a coupling reaction of (+)-thiolactic acid 3p and 2-benzoyloxyacetaldehyde (3a) using boron trifluoride etherate. A diastereomeric mixture of oxathiolane acids 29 and 30 was prepared in a 1:2 ratio in good yield (Scheme 7). Further separation of the

Synthesis of new bile acid-fused tetrazoles using the Schmidt reaction

• Dušan Đ. Škorić,
• Olivera R. Klisurić,
• Dimitar S. Jakimov,
• Marija N. Sakač and
• János J. Csanádi

Beilstein J. Org. Chem. 2021, 17, 2611–2620, doi:10.3762/bjoc.17.174

• noticeably, while the yield was preserved. Ketone 3 and enone 4 were used for the optimization of reaction conditions. Firstly, the ketone 3 was reacted with hydrazoic acid in the presence of boron trifluoride etherate as a Lewis acid (Table 1, entry 1). The desired tetrazole 13 was obtained after

• for the preparation of tetrazoles with hydrazoic acid Caution: Hydrazoic acid should be handled with care in an efficient fume hood since it is toxic and explosive. In a two-neck round-bottom flask equipped with an addition funnel and argon inlet, a benzene solution of hydrazoic acid (18 mL) and boron

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• , methanesulfonic acid, boron trifluoride etherate) resulted in decomposition if the reactions were left at room temperature overnight, or within ten minutes if the temperature was raised, even to 50 °C (Table 1, entries 6–13). The enaminone appeared to be protonated at room temperature, presumably on the oxygen

• was heated, in which case decomposition took place (Table 1, entry 15). Solutions of 15a in dichloromethane also decomposed rapidly when treated with aluminum trichloride or boron trifluoride at 50 °C, although no reaction was apparent at room temperature even after 18 hours (Table 1, entries 16–19

Facile and innovative catalytic protocol for intramolecular Friedel–Crafts cyclization of Morita–Baylis–Hillman adducts: Synergistic combination of chiral (salen)chromium(III)/BF₃·OEt₂ catalysis

• Karthikeyan Soundararajan,
• Helen Ratna Monica Jeyarajan,
• Raju Subimol Kamarajapurathu and
• Karthik Krishna Kumar Ayyanoth

Beilstein J. Org. Chem. 2021, 17, 2186–2193, doi:10.3762/bjoc.17.140

• -substituted-1H-indenes from unique substrates of Morita–Baylis–Hillman adducts via an easy operating practical procedure. Keywords: boron trifluoride etherate; chiral (salen)chromium(III); intramolecular Friedel–Crafts cyclization; Morita–Baylis–Hillman adducts; substituted-1H-indenes; Introduction

• in MBH adduct 5a (Table 1, entries 14–17). Interestingly among all co-catalysts examined, boron trifluoride etherate was the found to be the suitable co-catalyst in accelerating the proposed reaction. Furthermore on screening the optimized catalytic combination in presence of alternative solvents

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• -dibromo-[2-(3-dodecylthien-2-yl)]azulene (46) by using two successive Suzuki coupling reactions with thiophene boron ester 47 and biphenyl-4,4’-diboronic acid bis(pinacol) ester 49 (Scheme 11), whereas the Suzuki coupling of 46 with 2,1,3-benzothiadiazole-4,7-bis(boronic acid pinacol ester) 51 yielded the

Catalyzed and uncatalyzed procedures for the syntheses of isomeric covalent multi-indolyl hetero non-metallides: an account

• Ranadeep Talukdar

Beilstein J. Org. Chem. 2021, 17, 2102–2122, doi:10.3762/bjoc.17.137

• atom via their C-2 or C-3 positions in a symmetric way. The non-symmetric variety may connect them with C-2 of one with the C-3 of another, via the central atom. Below described are such synthetic strategies which are classified depending on the central tethering atom, largely with boron, carbon

• ]. The reason behind the C-2 attachment of the boron atom rather than at the C-3 position of the indole ring was explained by McGough et al. [37]. They performed a base-free catalytic I2-assisted indole C–H functionalization (electrophilic borylation) using the N-protected indole 1 and NHC·borane 4a that

• excess of the indole reactant. It is seen that in the presence of a base the C-2 deprotonation becomes very fast in 9 (for regaining aromaticity) so the boron at the initial C-3-borylated intermediate 8 (formed via SEAr) cannot migrate fast enough, leading to a C-3 borylation product 10a (unlike Pd) [38

Preparation of mono-substituted malonic acid half oxyesters (SMAHOs)

• Tania Xavier,
• Sylvie Condon,
• Christophe Pichon,
• Erwan Le Gall and
• Marc Presset

Beilstein J. Org. Chem. 2021, 17, 2085–2094, doi:10.3762/bjoc.17.135

• methodology, as illustrated by the preparation of the cyano- (4bn), boron- (4ao), or silicon- (4ap) substituted SMAHOs. The efficiency of the saponification step was also illustrated by the case of α-halomalonates 3aq and 3br. Upon application of the above-mentioned conditions, the useful reagents 4aq and 4br

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

• approach was efficient in solid phase as well as in solution phase synthesis. The participating (S)-(phenylthiomethyl) benzyl chiral auxiliary at the C-2 position of the glucosyl donor permitted the solid phase synthesis of a branched pentaglucan having a α(1–3) branch on an α(1–6) backbone [174]. Boron

• -mediated aglycon delivery (BMAD) with the use of a diboron catalyst allowed for regio-, as well as stereoselective glycosylation to achieve an α(1-3)-pentaglucoside [175]. Regioselective 1,2-cis-glycosylation could also be achieved by boron-catalyzed coupling via a SNi-type mechanism [176]. Hydrogen bond

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• /hemiacetal avoiding undesirable elimination to the enamine, or attack at other electrophilic sites in complex substrates. The presence of a fluorine source like diethylaminosulfur trifluoride (DAST) or the Lewis acid boron trifluoride diethyl etherate (BF3·OEt2) result in the formation of reactive iminium or