Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• 3-amino-2-naphthoic acid (97) to a Sandmeyer reaction and obtained 98. Then, a Curtius rearrangement of 98 by using diphenylphosphoryl azide (DPPA) yielded 3-iodonaphthalen-2-amine, that was subjected to a Suzuki cross-coupling with potassium vinyltrifluoroborate resulting in aminostyrene 99. The

• -dibromo-2,5-dimethylbenzene (101), with subsequent Suzuki cross-coupling of compound 102 with potassium vinyltrifluoroborate, removal of the N-Boc protecting group of 103 with trifluoroacetic acid, and borylative cyclization of precursor aminostyrene 104 [58]. Sparr’s research group developed the 1,5

Regioselective N-alkylation of the 1H-indazole scaffold; ring substituent and N-alkylating reagent effects on regioisomeric distribution

• Ryan M. Alam and
• John J. Keating

Beilstein J. Org. Chem. 2021, 17, 1939–1951, doi:10.3762/bjoc.17.127

• , respectively). Substituting potassium carbonate (K2CO3) for Cs2CO3 did not show any improvement in the regioisomeric distribution of 10 and 11 (ratio N-1 (10)/N-2 (11) = 1.4:1) (Table 1, entry 4). Similarly, the use of sodium carbonate under identical conditions gave a notably lower combined yield of 10 and 11

• , using THF as the reaction solvent with potassium or sodium carbonate bases failed to give the N-alkylated products 10 or 11 (Table 1, entries 7 and 8, respectively). Further variation of the reaction solvent revealed no significant improvement in N-1 regioselectivity, when using acetonitrile (MeCN

• ) positively influenced the regioselectivity, albeit with poor conversion (59–72%) when compared with other inorganic carbonate bases (vide supra). Despite poor conversion (30%), the use of the strong alkoxide base, potassium tert-butoxide, in tetrahydrofuran (THF) gave an appreciably higher degree of N-1

Cationic oligonucleotide derivatives and conjugates: A favorable approach for enhanced DNA and RNA targeting oligonucleotides

• Mathias B. Danielsen and
• Jesper Wengel

Beilstein J. Org. Chem. 2021, 17, 1828–1848, doi:10.3762/bjoc.17.125

• observed (75). The cationic phosphoramidate variant termed DEED was originally tested for its triplex-forming capabilities. The authors found that ONs containing the DEED modification were more capable at forming triplexes under conditions that approximated the magnesium, pH, and potassium levels found in

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• useful electrophilic or radical fluorinating agents by virtue of their easy handling, efficiency, and selectivity. These non-hygroscopic nature and stability make them easier to handle than nucleophilic fluoride reagents. Potassium fluoride (KF) and naked fluoride anion salts are extremely sensitive to

Electron-rich triarylphosphines as nucleophilic catalysts for oxa-Michael reactions

• Susanne M. Fischer,
• Simon Renner,
• A. Daniel Boese and
• Christian Slugovc

Beilstein J. Org. Chem. 2021, 17, 1689–1697, doi:10.3762/bjoc.17.117

• like structures were observed [24]. A more efficient transformation of acrylamide can be obtained with base catalysis. Using activated potassium carbonate, a reaction temperature of 40 °C, and 4 h reaction time give typically better conversions than those reported herein with nucleophiles [25]. Next

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• sterically hindered 1-(2-bromophenyl)-1,2,3-triazole derivatives 130. The target compounds, triazolo[1,5-a]indolones 131, were then obtained from 130 in high yield using catalytic amounts of Pd(OAc)2 and PCy3, carbon monoxide, and potassium carbonate and with heating in toluene at 120 °C. The structure of

Cascade intramolecular Prins/Friedel–Crafts cyclization for the synthesis of 4-aryltetralin-2-ols and 5-aryltetrahydro-5H-benzo[7]annulen-7-ols

• Jie Zheng,
• Shuyu Meng and
• Quanrui Wang

Beilstein J. Org. Chem. 2021, 17, 1481–1489, doi:10.3762/bjoc.17.104

• hydrolysis using 18% aq HCl furnishing the corresponding aldehyde [21]. Without purification, the resultant aldehyde intermediate was then directly reduced using potassium borohydride to the corresponding primary alcohol 11a in 74% yield starting from 9a. Pd-catalyzed cross-coupling of 11a with pinacol

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

Design, synthesis and photophysical properties of novel star-shaped truxene-based heterocycles utilizing ring-closing metathesis, Clauson–Kaas, Van Leusen and Ullmann-type reactions as key tools

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2021, 17, 1374–1384, doi:10.3762/bjoc.17.96

• with CH2Cl2, acetone, and finally with ethyl acetate to give 11 (3.13 g, 92%) as a yellow solid. Synthesis of 2,7,12-tribromo-5,5,10,10,15,15-hexabutyl-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene (5): Compound 11 (1.5 g, 2.59 mmol), dimethyl sulfoxide (20 mL), and potassium tert-butoxide (2.61 g

Photoinduced post-modification of graphitic carbon nitride-embedded hydrogels: synthesis of 'hydrophobic hydrogels' and pore substructuring

• Cansu Esen and
• Baris Kumru

Beilstein J. Org. Chem. 2021, 17, 1323–1334, doi:10.3762/bjoc.17.92

• % aqueous solution, Merck), magnesium chloride (MgCl2, 99%, Merck), melamine (99%, Sigma-Aldrich), poly(ethylene glycol) dimethacrylate (PEGDMA, Mn 550, Sigma-Aldrich), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA, Mn 300, Sigma-Aldrich), potassium chloride (KCl, 99%, Merck), rhodamine B (RhB

• Scan spectrophotometer equipped with an integrating sphere. Thermogravimetric analysis (TGA) was performed via TG 209 Libra from Netzsch under nitrogen atmosphere with a heating rate 10 K min−1 using aluminum crucible for samples. Trace analysis of potassium, calcium and magnesium cations were

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

• different approach was taken in that the two starting materials were combined into a single stream and the base (potassium tert-amyloxide) added via a separate channel. This was presumably established to avoid base-mediated decomposition of the starting material 44 if prepared as a stock solution. The

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• of anti/syn diastereoisomers. Treatment of compounds 24 with potassium hexamethyldisilazide provided vinylaziridines 22 through an intramolecular cyclization step. This intramolecular nucleophilic substitution is a stereospecific process. In the case of aromatic compounds 24, trans-vinylaziridines

• reaction intermediate that was not isolated. Treatment of 115 with potassium hexamethyldisilazide (KHMDS) led to the sulfinyl piperidine derivative 116, and final deprotection under acidic conditions produced enantioenriched 2-allylpiperidine (117) as its hydrochloride (Scheme 32) [121]. Compound 117 has

Recent advances in palladium-catalysed asymmetric 1,4–additions of arylboronic acids to conjugated enones and chromones

• Jan Bartáček,
• Jan Svoboda,
• Martin Kocúrik,
• Jaroslav Pochobradský,
• Alexander Čegan,
• Miloš Sedlák and
• Jiří Váňa

Beilstein J. Org. Chem. 2021, 17, 1048–1085, doi:10.3762/bjoc.17.84

• ]. Specifically, they have dealt with the addition of potassium aryltrifluoroborates to conjugated cyclic enones differing in ring size [32]. The catalysts PdL1a,b exhibited great conversion and enantioselectivities (up to 99% and up to 96% ee) for various combinations of nucleophiles and enones (Table 1). The

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• such as lead tetraacetate, potassium permanganate, or refluxing hydrogen peroxide were shown to produce urea-derived degradation products [3]. Biguanides also possess a remarkable capability to form stable metal complexes, a property that was already noticed by B. Rathke in 1879 [4]. Indeed, he relied

Stereoselective synthesis and transformation of pinane-based 2-amino-1,3-diols

• Ákos Bajtel,
• Mounir Raji,
• Matti Haukka,
• Ferenc Fülöp and
• Zsolt Szakonyi

Beilstein J. Org. Chem. 2021, 17, 983–990, doi:10.3762/bjoc.17.80

• aminohydroxylation process starting from allylic carbamates usually carried out in the presence of potassium osmate [24][25][26][27][28]. In recent years, we have extensively studied the stereoselective synthesis, as well as catalytic and pharmacological applications of monoterpene-based 3-amino-1,2-diols, which are

• synthesize novel, cyclic potentially analogues of sphingosine, incorporating a lipophilic natural pinane skeleton, starting from commercially available monoterpene-based allylic alcohols via a stereoselective hydroxyamination in the presence of a potassium osmate(VI) catalyst. We also planned to explore the

• carbamate 8 in good yield [27][28][36]. In the next step, the aminohydroxylation was accomplished by potassium osmate(VI) as the catalyst and t-BuOCl in the presence of DIPEA affording oxazolidine-2-one 9 [27]. The reaction was found to be highly stereoselective, giving exclusively the diexo-fused tricyclic

Synthesis of bis(aryloxy)fluoromethanes using a heterodihalocarbene strategy

• Carl Recsei and
• Yaniv Barda

Beilstein J. Org. Chem. 2021, 17, 813–818, doi:10.3762/bjoc.17.70

• nucleophiles. The second report, by Scheeren [7], working from a bis(phenoxy)chloromethane synthesis reported by Scheibler [8], described the conversion of phenyl orthoformate to bis(phenoxy)chloromethane with acetyl chloride and anhydrous hydrogen chloride, followed by reaction with potassium

• strategy, we were delighted to observe that the desired compound, 4, was produced as the major product, in 39% yield (72% yield based on recovered starting material) when 6 was reacted with dibromofluoromethane in the presence of excess potassium phosphate in acetonitrile (Scheme 4). Smaller amounts of the

• possible with potassium hydroxide as a base, while potassium carbonate gave only traces of the desired product. DMF was found to be an inferior solvent. All these changes led to larger quantities of the undesired isomer 7, with respect to 4. Attempting to push this reaction to higher conversion of 6 with

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• [32] found a bifunctional group reaction of perfluoroalkylation and β-alkenylation by a perfluoroalkyl radical. Perfluoroalkylation product 93 was synthesized by utilizing (E)-3-methyl-1-phenylhept-1,6-dien-3-ol (92) and perfluorobutyl iodide (28) as substrates and potassium phosphate and DABCO as

• visible-light-mediated synthesis approach of arylphosphonates initiated by an EDA complex. Diethyl phenylphosphonate (165) was given by exploiting diphenyliodonium trifluoromethanesulfonate (163) as electron acceptor, triethylphosphite (164) as electron donor, potassium carbonate as base, and CH3CN as

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• first gave ester 181 and then acid 182 (Scheme 31), the sodium and potassium salts of which are well soluble in water. The compound has antiviral and anticancer activity as well as pronounced antioxidant properties combined with low toxicity. Diarylmethanofullerene 183 was synthesized according to

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• described in detail. Solvolytic depolymerisations can also be promoted by metal-free soluble acid or base catalysts. However, concentrated solutions, quasistoichiometric amounts or strong mineral acids (HNO3, H2SO4, H3PO4) or bases (NaOH, KOH, potassium butoxide) are often required, particularly for

• and a 20:1 excess of strong base potassium tert-butoxide as cocatalyst (Table 1, entry 1) [183]. Although the reaction mechanism was not investigated in detail, it was suggested that cleavage of the ester linkage may occur in a concerted manner through the reported heterolytic route [184][185]. The

• chloride catalyst precursor with potassium butoxide in a 2:1 molar ratio, resulted in a nearly quantitative yield of BDM and EG at a slightly higher reaction temperature (160 °C, 54 bar H2, Table 1, entry 2). Interestingly, PET flakes from postconsumer bottles could be used, showing the catalytic system to

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

• Zbigniew Malinowski,
• Emilia Fornal,
• Agata Sumara,
• Renata Kontek,
• Karol Bukowski,
• Beata Pasternak,
• Dariusz Sroczyński,
• Joachim Kusz,
• Magdalena Małecka and
• Monika Nowak

Beilstein J. Org. Chem. 2021, 17, 558–568, doi:10.3762/bjoc.17.50

• reported by us [30]. It is known that the alkylation of phthalazinones depends on the reaction conditions and can proceed in two ways involving either the nitrogen or the oxygen atom (lactam–lactim tautomerism). It has been proven that potassium salts of phthalazinones or the bromo derivatives are

• In conclusion, we have demonstrated an efficient synthesis of 2-substituted (alkyl, aminoalkyl) 4-aminophthalazinones 5 and 6 via the direct bromination of phthalazin-1(2H)-one (1) with potassium tribromide, followed by the alkylation of 4-bromophthalazinone 2 with methyl iodide, isopropyl iodide or

Synthetic strategies of phosphonodepsipeptides

• Jiaxi Xu

Beilstein J. Org. Chem. 2021, 17, 461–484, doi:10.3762/bjoc.17.41

• nucleophilic esterification of potassium 1-(N-benzyloxycarbonylamino)alkylphosphonates 172 with alkyl halides in the presence of 18-crown-6. They also prepared a phosphonodepsidipeptide 174 with ethyl chloroacetate (173) as an electrophile (Scheme 33) [53]. The macrocyclic peptidyl phosphonodepsipeptide 180

Synthesis of trifluoromethyl ketones by nucleophilic trifluoromethylation of esters under a fluoroform/KHMDS/triglyme system

• Yamato Fujihira,
• Yumeng Liang,
• Makoto Ono,
• Kazuki Hirano,
• Takumi Kagawa and
• Norio Shibata

Beilstein J. Org. Chem. 2021, 17, 431–438, doi:10.3762/bjoc.17.39

• group reported novel DMF-free systems for the nucleophilic trifluoromethylation reaction using HCF3, including the phosphazene base P4-t-Bu (P4-t-Bu), in 2013 (Scheme 1c) [45] and a potassium tert-butoxide (t-BuOK) or potassium hexamethyldisilazide (KHMDS)/glyme combination in 2018 (Scheme 1d) [46]. The

Regioselective chemoenzymatic syntheses of ferulate conjugates as chromogenic substrates for feruloyl esterases

• Olga Gherbovet,
• Fernando Ferreira,
• Apolline Clément,
• Mélanie Ragon,
• Julien Durand,
• Sophie Bozonnet,
• Michael J. O'Donohue and
• Régis Fauré

Beilstein J. Org. Chem. 2021, 17, 325–333, doi:10.3762/bjoc.17.30

• DMF (8 mL) were added potassium carbonate (1.06 g, 7.67 mmol, 1.2 equiv) and homoallylic bromide (670 µL, 6.51 mmol, 1 equiv) at 40 °C. After overnight stirring at 40 °C, the reaction mixture was concentrated under reduced pressure. The residue was redissolved in ethyl acetate, washed with a saturated

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

• Sergey V. Norkov,
• Anton V. Cherkasov,
• Andrey S. Shavyrin,
• Maxim V. Arsenyev,
• Viacheslav A. Kuropatov and
• Vladimir K. Cherkasov

Beilstein J. Org. Chem. 2021, 17, 273–282, doi:10.3762/bjoc.17.26

• yield EPR signals of the same multiplicity as they were observed in the case of spectra of monoreduced species of 6d, but the value of hyperfine splitting constant on protons of the methyl groups of the acetylacetonate fragment (0.17 G for potassium semiquinonate, see Table S4 in Supporting Information

• File 1) is less than that in 6d (0.31 G for potassium semiquinonate). This could be explained by the fact that unlike 6d, the acetylacetonate fragment in 7 lies in an almost orthogonal plane relative to the semiquinone ring that disfavors delocalization of the spin density on the methyl groups. The EPR

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• were increased when potassium fluoride and 18-crown-6 were added to the reaction mixture [20]. Dehydrohalogenation of dichlorodifluoromethane under phase-transfer catalysis: Difluorocarbene can be generated from chlorodifluoromethane by phase-transfer catalysis (PTC) through the reaction with NaOH or