Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• the presence of the acid, it is protonated and collapses into the corresponding alkoxy radical. This radical carries out a 1,5-HAT to generate a carbon-centered radical. Finally, this radical recombines with the α-amino radical generated from the above-mentioned pathway. 2.3 Oxidation reactions In

• present on the pypzs ligand, and activates the carbonyl group. The PCET occurs, furnishing a ketyl radical that can react with another molecule (ketone or aldehyde), delivering the pinacol product. A final HAT with another equivalent of HEH or HEH+ delivers the product, and the resulting radical cation of

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• . This system is being used in C–C, C–N, C–O, C–S, and C–X bond-breaking and -forming processes [55]. Similarly, photoinduced direct hydrogen atom transfer (HAT) catalysis also plays a major role in the functionalization of intricate molecules. Photocatalysts that can undergo this process are uranyl

• cations, polyoxometallates, and benzophenones [9][80], but a major drawback is the limited availability of photocatalysts that can perform direct HAT. Therefore, there is a high demand for a direct-HAT catalyst that is accessible, metal-free, allows no side reactions, and can be activated by visible light

• oxidation via HAT or SET/deprotonation, generates the desired product 97 (Figure 15). The oxidation of the persulfate anion generates a sulfate radical anion, which acts as an oxidant in the aromatization step. In the absence of light and photoredox catalyst, no product was obtained. C–H phosphonylation

Dirhodium(II)-catalyzed [3 + 2] cycloaddition of N-arylaminocyclopropane with alkyne derivatives

• Wentong Liu,
• Yi Kuang,
• Zhifan Wang,
• Jin Zhu and
• Yuanhua Wang

Beilstein J. Org. Chem. 2019, 15, 542–550, doi:10.3762/bjoc.15.48

• radical cation C resulting from cyclopropane ring opening reacts with alkyne substrate 2a generating radical D. The intermediate radical D yielded E through intramolecular radical addition. After hydrogen atom transfer (HAT) from complex A, the desired product is obtained with regeneration of the N

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• -workers also reported the first silver-catalyzed ring-opening and acylation of cyclopropanols 91 with aldehydes 48 for the synthesis of 1,4-diketones 144 (Scheme 39) [119]. They proposed that the involvement of an uncommon water-assisted 1,2-HAT process was strongly exothermic and it promoted the addition

Cobalt bis(acetylacetonate)–tert-butyl hydroperoxide–triethylsilane: a general reagent combination for the Markovnikov-selective hydrofunctionalization of alkenes by hydrogen atom transfer

• Xiaoshen Ma and
• Seth B. Herzon

Beilstein J. Org. Chem. 2018, 14, 2259–2265, doi:10.3762/bjoc.14.201

• transfer (HAT) to the alkene substrate, followed by interception of the resulting alkyl radical intermediate with a SOMOphile. In addition, we report the first reductive couplings of unactivated alkenes and aryldiazonium salts by an HAT pathway. The simplicity and generality of the Co(acac)2–TBHP–Et3SiH

• reagent combination suggests it as a useful starting point to develop HAT reactions in complex settings. Keywords: HAT; hydrogen atom transfer; hydrofunctionalization; Introduction Many powerful methods to effect alkene hydrogenation [1][2][3][4] and Markovnikov-selective hydroheterofunctionalization (H

• –X addition, X = O [5][6][7][8][9], I [3], Br [3], Se [3], S [8][9][10], Cl [8][11], F [12][13], and N [8][14][15][16][17]) by metal-mediated hydrogen atom transfer (HAT) [18][19][20][21] are now known. Additionally, methods to achieve carbon–carbon bond formation to alkenes by HAT have been

Synthesis and photophysical studies of a multivalent photoreactive Ru^II-calix[4]arene complex bearing RGD-containing cyclopentapeptides

• Sofia Kajouj,
• Lionel Marcelis,
• Alice Mattiuzzi,
• Adrien Grassin,
• Damien Dufour,
• Pierre Van Antwerpen,
• Didier Boturyn,
• Eric Defrancq,
• Mathieu Surin,
• Julien De Winter,
• Pascal Gerbaux,
• Ivan Jabin and
• Cécile Moucheron

Beilstein J. Org. Chem. 2018, 14, 1758–1768, doi:10.3762/bjoc.14.150

• amino acids (type II photosensitization). In particular, it was shown that RuII complexes containing at least two highly π-deficient polyazaaromatic ligands such as 1,4,5,8-tetraazaphenanthrene (TAP) [12][13][14] or 1,4,5,8,9,12-hexaazatriphenylene (HAT) [15] are able to oxidize the guanine base (G) of

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• -butoxide anion to CBrCl3, forming the tert-butoxy radical [94]. This radical attacks the α-hydrogen of 2a via hydrogen atom transfer (HAT), to form intermediate A with a radical at the α-carbon. A then undergoes α-bromination to form the intermediate 6 [95]. Attack at the α-carbon of 6 by 2

• •CCl3 radicals are quenched to CHCl3 via HAT [93]. The proposed catalytic cycle for the synthesis of benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones is as follows. The Lewis acidic InIII metal center coordinates to the more nucleophilic benzothiazole N atom, forming an adduct A [98]. This activates the N–H

Cp₂TiCl/D₂O/Mn, a formidable reagent for the deuteration of organic compounds

• Antonio Rosales and
• Ignacio Rodríguez-García

Beilstein J. Org. Chem. 2016, 12, 1585–1589, doi:10.3762/bjoc.12.154

• -ordination of water to Cp2TiCl might weakens the strength of the O–H bond. In this way a single electron transfer from titanium to oxygen might facilitate the HAT from the titanocene aqua-complex to the free radicals. Theoretical calculations supported that the coordination of water to Cp2TiIIICl weakens the

• bond in water. Although more theoretical and experimental studies should be performed to determine the mechanism of reduction of radicals using Cp2TiCl and water, it can be stated that tertiary and hindered radicals are normally reduced via HAT from water in a process mediated by Cp2TiIIICl. Primary

• and unhindered radicals are normally reduced via hydrolysis of an organometallic alkyl-TiIV intermediate [37]. This HAT or protonation mechanism by Cp2TiCl/D2O/Mn, compared with the single-electron-transfer conditions using SmI2/D2O in the synthesis of α,α-dideuterated alcohols from carboxylic acids

Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations

• Adriana K. Slavova-Kazakova,
• Silvia E. Angelova,
• Timur L. Veprintsev,
• Petko Denev,
• Davide Fabbri,
• Maria Antonietta Dettori,
• Maria Kratchanova,
• Vladimir V. Naumov,
• Aleksei V. Trofimov,
• Rostislav F. Vasil’ev,
• Giovanna Delogu and
• Vessela D. Kancheva

Beilstein J. Org. Chem. 2015, 11, 1398–1411, doi:10.3762/bjoc.11.151

• up does not exert any influence on the antioxidant efficiency and reactivity of the two dimers. The presence of the keto–enol moiety is not of significance for the hydrogen-atom-transfer (HAT) reactions and the classical chain-breaking antioxidant activity. The presence of two longer unsaturated keto

• the antioxidant action. However, the ORAC assay is a method for the detection of radical-scavenging activity based on the HAT mechanism [31][32]. From the results obtained (see Table 1) in aqueous medium there are no considerable differences in the antioxidant activities between the monomers and

• dimers in terms of the HAT reaction mechanism. This could be explained by the solvent effect of water, blocking OH groups by H bonds and thus decreasing their antioxidant capacity. Another reason for the similar results obtained for the studied monomers/dimers is the fact that the process is monitored by

Damage of polyesters by the atmospheric free radical oxidant NO₃^•: a product study involving model systems

• Catrin Goeschen and
• Uta Wille

Beilstein J. Org. Chem. 2013, 9, 1907–1916, doi:10.3762/bjoc.9.225

• transformation processes at night. NO3•, which is formed through reaction of the atmospheric pollutants nitrogen dioxide, NO2•, with ozone, O3 (Scheme 1a) [7][8], reacts with organic compounds through various pathways, such as hydrogen abstraction (HAT) and addition to π systems. Most importantly, NO3• is one of

• the adipic acid derivatives 2. In the case of the former this could be explained by the fact that the aromatic ring is very deactivated due to the two electron-withdrawing ester substituents, so that oxidative electron transfer (ET) by NO3• is not possible. Also, NO3• induced HAT from the ester

• base [23]. It is important to note that the formation of radical intermediate 7 could principally also occur in one step through NO3•-induced benzylic HAT in 3 (not shown). However, it appears from the outcome of the reactions with the neopentyl derivatives of 1 and 2 that HAT by NO3• is not

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• laccase-ABTS follows an electron transfer (ET) mechanism, NHPI, VLA, HBT, and NHAmediators promote a hydrogen atom transfer (HAT) route through the formation of the corresponding N-oxyl radicals as NHDs-Medox species (Scheme 11). The same research group also emphasized the specialization of mediators

• morphology and the molecular weight of the starting material [48]. Moreover, this catalytic system could be employed with dioxygen in place of NaClO as the ultimate oxidizing agent [49]. In this case, the mechanism follows a radical chain via classical HAT by PINO abstraction (Scheme 17). Aldehydes and the

• of molecular bromine as a co-catalyst [68] (Scheme 24). According to the proposed mechanism, Br2 generates ET processes by oxidizing the o-phenanthroline to the corresponding cation radicals. The latter promote in turn ET and HAT processes with NHPI, leading to the formation of PINO. In 2009 the same

From discovery to production: Scale- out of continuous flow meso reactors

• Peter Styring and
• Ana I. R. Parracho

Beilstein J. Org. Chem. 2009, 5, No. 29, doi:10.3762/bjoc.5.29

• become deposited on the catalyst beads on standing between studies and that the initial linear increase in yield was a consequence of the salts being washed off in the continuous flow and adsorption of the organobromide on to the newly freed reactive sites. It is seen from Figure 6 hat the production of