Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• yields and enantioselectivities when subjected to four sequential reactions mediated by a cooperative catalysis of a NHC organocatalyst with LiCl in the presence of DPQ as an oxidant, as shown in Scheme 17. Recently, Chen et al. used a NHC catalyst 59 in γ,δ-difunctionalization of coumarins 56 through an

• together with tetraphenylphosphonium monoperoxysulfate (TPPP) as the stoichiometric oxidant [76]. The authors mentioned that this epoxidation had been previously reported using Jacoben’s (S,S)-(+)-salen-Mn(III) catalyst with 78–83% yield and 95% ee, and via organocatalysis they obtained 98% yield and ≥99

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

• derivatives. Using H2O2 as an oxidant agent, ketones and aldehydes were obtained from hydrocarbons with high yields (85–99%, Scheme 9B and 9C). Although the authors did not explore the biological effects of the obtained products, this class of molecules resembles the basic structure of several important

• -methoxybenzaldehyde imine derivatives with phenyl Grignard reagents as coupling partners. As the catalyst CrCl2 is used and either 2,3-dichlorobutane (DCB) or 1,2-dichloropropane (DCP) are used as oxidant to give 2,5-diarylbenzaldehyde after imine hydrolysis (Scheme 16B). Although benzaldehyde is a basic structure

• reaction was kept at room temperature to avoid the difunctionalization, and the oxidant was added only in the second step. Following this route, six examples were obtained with moderate yields (56–70%, Scheme 16C). Although the use of chromium catalysis is still considered challenging due to the high

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

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• molecules bearing unactivated Csp3–H bonds facilitated by electricity (Scheme 5) [43]. Several pharmaceutically active molecules were committed to the external oxidant-free reaction conditions and were shown to undergo chemoselective azidation. Azidation of ibuprofen methyl ester (14a) was selective for the

Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones

• Girish Suresh Yedase,
• Sumit Kumar,
• Jessica Stahl,
• Burkhard König and
• Veera Reddy Yatham

Beilstein J. Org. Chem. 2021, 17, 1727–1732, doi:10.3762/bjoc.17.121

• , Universitätstraße 31, D-93053 Regensburg, Germany 10.3762/bjoc.17.121 Abstract We have developed a cerium-photocatalyzed aerobic oxidation of primary and secondary benzylic alcohols to aldehydes and ketones using inexpensive CeCl3·7H2O as photocatalyst and air oxygen as the terminal oxidant. Keywords: alcohol

• acting as the terminal oxidant [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Most aerobic oxidation reactions utilize either metal complexes and nanoparticles or persistent radical reagents as catalysts [21]. In the past ten years, visible light-induced

• air as the oxidant (Table 1). The best results were found using 10 mol % CeCl3·7H2O as a photocatalyst and 10 mol % of NaHCO3 as a base in CH3CN under blue LED irradiation at 50 °C for 35 h giving compound 2a in 65% isolated yield (Table 1, entry 1). The product formation was reduced upon employing

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• products instead of reductive ones. Their formation also leads to the generation of Pd(0) species that require the presence of an external oxidant to regenerate the active Pd(II) complex, as well as an additional hydrogenation step, if the hydrofunctionalized product is desired [18]. This particularity

• -substituted β-diketones 2a and 2b (61 and 70% yield, respectively). Notably, the unsaturated carbocycles expected from palladium β-hydride elimination were not observed, indicating that an oxidant was not required in the reaction medium to regenerate the Pd(II) species. Later, deuterium-labeling experiments

• oxidant (Scheme 30) [99]. Bicycle units 82 founded in natural products could be synthetized under Co(II) salen complex 80 catalysis at room temperature with excellent stereoselectivity. Only trans-decalins 82 were observed in the presence of secondary OTBS groups in the substrate backbone; this was not

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

• + antagonist, and exhibits promising anti-oxidant properties. 4-Phenyl-2-propionamidotetralin (4-P-PDOT, 3, Figure 1) [5] is a melatonin MT2 selective antagonist that can be used to map melatonin receptor subtypes in tissue and serves as a chemical biology tool to identify sub-type selective analogues with

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• posthumously in 1919 [35]. In 1894, Guareschi reported the first high-yield synthesis and the structure elucidation of triacetonamine (6, Scheme 3) [35][36][37], the sterically hindered amine that is the starting material for the synthesis of the popular oxidant TEMPO [38]. Triacetonamine had first been

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

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

• depends on the association of eosin Y and oxidant 4 to a donor–acceptor EY–4 ground-system complex (high reactivity). Due to the ability of aryl groups to stabilize the formed alkenyl radical, this protocol could control regioselectivity efficiently with unsymmetrical alkynes. In addition, EPR

Designed whole-cell-catalysis-assisted synthesis of 9,11-secosterols

• Marek Kõllo,
• Marje Kasari,
• Villu Kasari,
• Tõnis Pehk,
• Ivar Järving,
• Margus Lopp,
• Arvi Jõers and
• Tõnis Kanger

Beilstein J. Org. Chem. 2021, 17, 581–588, doi:10.3762/bjoc.17.52

• . Chemical oxidation of 9,11-dihydroxysteroids In the final step, the obtained trans-diols 5 and 6 were subjected to the chemical oxidation of the 9,11 carbon bond. Lead tetraacetate is a classic oxidant for the cleavage of vicinal diols. However, there are serious drawbacks when using Pb(OAc)4. In addition

• to its toxicity, the oxidation rate affording trans-diols was very slow in comparison to that for cis-diols. Using an even longer reaction time and stoichiometric amount of the reagent, diol 5 was not oxidized to the corresponding dicarbonyl compound 8. However, using NaOCl·5H2O as an oxidant [31

• 9α-hydroxylated diol. The following oxidative cleavage of the C–C bond with a mild oxidant leads to the steroid with an appropriately broken steroid skeleton. The method provides the target compound in only two steps, without any manipulations involving protecting groups. The present method features

A new and efficient methodology for olefin epoxidation catalyzed by supported cobalt nanoparticles

• Lucía Rossi-Fernández,
• Viviana Dorn and
• Gabriel Radivoy

Beilstein J. Org. Chem. 2021, 17, 519–526, doi:10.3762/bjoc.17.46

• MgO and tert-butyl hydroperoxide (TBHP) as oxidant is presented. This CoNPs@MgO/t-BuOOH catalytic combination allowed the epoxidation of a variety of olefins with good to excellent yield and high selectivity. The catalyst preparation is simple and straightforward from commercially available starting

• the other hand, the use of supported cobalt nanoparticles as efficient catalysts for the epoxidation of olefins has received increasing attention in the last years. In most cases, a crucial influence of the support (TiO2, HAP, CNTs, SBA, SiO2), the oxidant agent (molecular oxygen or TBHP) and the

• the oxidant agent. Among the reported methods that make use of peroxides as oxidants, cobalt nanoparticles supported on CNTs together with TBHP as oxidant for the epoxidation of styrene, gave good selectivity to styrene oxide but conversions were lower than 40% [41]. More recently, Hutchings et al

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

• found to be a stronger oxidant than 36Q [16]. A very similar redox behavior and shifts of reduction potential values were observed for p-quinone derivatives with attached 1,3-dithiole rings [27][49]. UV–vis spectroscopy Sterically hindered o-quinones are deep-colored compounds. Any changes in their

Facile preparation and conversion of 4,4,4-trifluorobut-2-yn-1-ones to aromatic and heteroaromatic compounds

• Takashi Yamazaki,
• Yoh Nakajima,
• Minato Iida and
• Tomoko Kawasaki-Takasuka

Beilstein J. Org. Chem. 2021, 17, 132–138, doi:10.3762/bjoc.17.14

• trials aimed at optimizing the reaction conditions, the unexpectedly smooth conversion of 1a to 2a was realized. Although it was reported [18][23] that only a small amount of 2a was confirmed after the reaction of 1a with 10 equiv of MnO2 at ambient temperature after 1 day, the same amount of oxidant

• MnO2 oxidation of readily accessible propargylic alcohols 1. In spite of the application of this method only to 1, with an aromatic substituent at the propargylic position and the requirement of an excess amount of this oxidant, the practical convenience, low cost, as well as the clean conversion are

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• 101 could be generated in an oxidative quenching cycle from THIQs 102 using a ruthenium-based photocatalyst and 1,3-dinitrobenzene (DNB) as a sacrificial oxidant (Scheme 13) [51]. These iminium ions could then be intercepted by a Breslow intermediate 103, formed between aldehydes 104 and the NHC

• et al. (Scheme 41) [103]. The proposed mechanism implicates an oxidative quenching cycle using a sacrificial oxidant (TIPS-EBX), followed by a PCET step with hydrogen-bonded complex 260 to give chiral ion pair 260•, which completes the photocatalytic cycle. Subsequent enantioselective radical

Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate

• Mysore Bhyrappa Harisha,
• Pandi Dhanalakshmi,
• Rajendran Suresh,
• Raju Ranjith Kumar and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2020, 16, 2108–2118, doi:10.3762/bjoc.16.178

• unambiguously indicate that the reaction proceeds through a radical pathway. Potassium persulfate helps to generate a thiocyanate radical and in the absence of potassium persulfate the reaction did not proceed. This experiment supports the role of potassium persulfate as an oxidant. Based on these experiments

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

• aqueous conditions to prevent complexation of the reagent and the starting material. Of the Lewis acids used, stannic chloride proved to be the most effective oxidant for dimerization (Table 1). However, the hypervalent iodine reagents PIFA and PIDA gave better results overall, affording dimer 18 in 63

Metal-free synthesis of phosphinoylchroman-4-ones via a radical phosphinoylation–cyclization cascade mediated by K₂S₂O₈

• Qiang Liu,
• Weibang Lu,
• Guanqun Xie and
• Xiaoxia Wang

Beilstein J. Org. Chem. 2020, 16, 1974–1982, doi:10.3762/bjoc.16.164

• motifs were conveniently synthesized from readily available diphenylphosphine oxides and alkenyl aldehydes via a metal-free tandem phosphinoylation/cyclization protocol. The reaction utilizes K2S2O8 as oxidant and proceeds in DMSO/H2O at environmentally benign conditions with a broad substrate scope and

•  1a). Besides, in 2016 Li’s group [28] reported a silver-catalyzed straightforward approach for the synthesis of phosphonate-functionalized chroman-4-ones via a phosphoryl radical-initiated cascade cyclization of 2-(allyloxy)arylaldehydes using K2S2O8 as an oxidant, however, diphenylphosphine oxide

• employing 2-(allyloxy)benzaldehyde (1a) and diphenylphosphine oxide (DPPO, 2a) as the model substrates with K2S2O8 as the oxidant, which is a cheap, readily available, and versatile oxidant. On the basis of literature reports [29][30] and our continuing interest in green chemistry [31][32], we set the

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• activation, a catalytic amount of a transition metal (generally Pd, Rh and Ru) is frequently used in combination with a stoichiometric amount of an external oxidant (typically Cu or Ag salts). Such additional oxidants are required if transiently produced low-valent metal complexes need to be reoxidized by

• , together with a metal hydride or a low-valent metal complex. Hence, in order to reoxidize the metal catalyst, excess of an external oxidant, such as Cu(II) or Ag(I) salts, was frequently used. On the other hand, photoredox catalysis has been mainly employed for electron-transfer reactions and, remarkably

• selecting judiciously a PC with adequate redox potentials, the ground state of the latter could be regenerated by means of a mild and abundant oxidant such as molecular oxygen. The overall process thus allowed the replacement of stoichiometric amounts of external oxidants with a suitable PC. Following this

Fluorohydration of alkynes via I(I)/I(III) catalysis

• Jessica Neufeld,
• Constantin G. Daniliuc and
• Ryan Gilmour

Beilstein J. Org. Chem. 2020, 16, 1627–1635, doi:10.3762/bjoc.16.135

• organocatalyst, Selectfluor® was employed as the terminal oxidant, and an amine/HF complex enlisted as the fluoride source (please see Supporting Information File 1 for full details). The reaction was performed in CHCl3 at ambient temperature and the crude reaction mixtures were analysed by 19F NMR spectroscopy

• (50% yield), ground Oxone® or N-pyridine oxide proved to be ineffective (Table 1, entries 9–11). Increasing the reaction temperature to 50 °C led to the same outcome as at ambient temperature (64% yield, Table 1, entry 12). Finally, the control reactions in the absence of catalyst, oxidant and HF

Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach

• Rhys A. Lippa,
• John A. Murphy and
• Tim N. Barrett

Beilstein J. Org. Chem. 2020, 16, 1617–1626, doi:10.3762/bjoc.16.134

• occur via a radical pathway. When iodide 29 was replaced by a superior oxidant in 1,2-dibromoethane, formation of dimer 32 increased (17% isolated yield). This supports the previously reported proposals that dimerisation occurs via single-electron oxidation of the 2-picolyl anion by the halide

• /pseudohalide oxidant followed by recombination of the resulting picolyl radical [28][29][30]. Whilst trace oxygen may be involved, as indicated by the presence of alcohol 31, no dimerisation or alcohol formation was seen in the absence of a halide/pseudohalide-based oxidant, during C-phosphorylation or

NHC-catalyzed enantioselective synthesis of β-trifluoromethyl-β-hydroxyamides

• Alyn T. Davies,
• Mark D. Greenhalgh,
• Alexandra M. Z. Slawin and
• Andrew D. Smith

Beilstein J. Org. Chem. 2020, 16, 1572–1578, doi:10.3762/bjoc.16.129

• ][44][45] in the presence of an oxidant. As representative examples of the use of azolium enolates in reactions with trifluoroacetophenone derivatives, Ye and co-workers have shown that using disubstituted ketenes as azolium enolate precursors and NHC precatalyst 1 allowed access to trifluoromethyl

• enantioselectivity but requiring superstoichiometric quantities of quinone as an oxidant (Figure 2B) [47]. In our previous work, we have developed α-aroyloxyaldehydes as reactive, bench-stable precursors of azolium enolates [48][49][50][51][52][53], which can be synthesized in a single step from the desired aldehyde

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• –C bonds gave P(=O)Ph2-containing phenanthridines 7.5a–c (Scheme 7, path c), which occurred in the presence of a base (CsF or Cs2CO3) and an external oxidant (K2S2O8). Notably, the presence of electron-withdrawing groups on the biphenyl unit inhibited the process in some instances [67]. Starting from

• exploited for the construction of phenanthridine 6-carboxylates (Scheme 12). Notably, the process occurred in water under metal-free conditions in the presence of rose bengal (5 mol %) and made use of molecular oxygen as the terminal oxidant. Thus, N-biarylglycine esters 12.1a–d promoted the reductive

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• electron-rich aryl disulfides as the photocatalyst and oxygen as the oxidant [16]. At room temperature, bis(4-methoxyphenyl) disulfide was employed as the metal-free photocatalyst under visible-light and 1 bar of O2 to realize the aerobic oxidative cleavage of the C=C bonds. Under these mild conditions

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116