Recent developments and trends in the iron- and cobalt-catalyzed Sonogashira reactions

• Surendran Amrutha,
• Sankaran Radhika and
• Gopinathan Anilkumar

Beilstein J. Org. Chem. 2022, 18, 262–285, doi:10.3762/bjoc.18.31

• 69% and 66% yield, respectively. The mechanistic scenario begins with the reduction of cobalt(II/III) complex B to form cobalt(I) complex A in the Sonogashira reaction system. The cobaloxime derivative Co(C9H9NO2)3 complex is used as a radical precursor. The reaction of preformed cobalt(I) complex A

• with an electrophile results in the formation of a cobalt(III) intermediate. Subsequent homolytic cleavage and generation of cobalt(II) complex C and radical D the radical undergoes addition to phenylacetylene to provide cobalt(III) intermediate E. The targeted compound 1-methyl-4-(2-phenylethynyl

Synthesis and late stage modifications of Cyl derivatives

• Phil Servatius and
• Uli Kazmaier

Beilstein J. Org. Chem. 2022, 18, 174–181, doi:10.3762/bjoc.18.19

• should undergo a wide range of addition reactions. Ozonolysis, on the other hand, should generate a carbonyl functionality. Radical additions towards the double unsaturated side chain of the Cyl-1 derivative might also allow cyclizations. To get access to the desired double unsaturated cyclopeptide, we

• , we treated 11 with thioacetic acid and BEt3/air in THF to give 82% of the thiol-ene click product (Scheme 4). Careful analysis of the NMR spectra revealed that the intermediately formed radical cyclized in an intramolecular 5-exo-trig fashion with the internal double bond to form a tetrahydrofuran

High-speed C–H chlorination of ethylene carbonate using a new photoflow setup

• Takayoshi Kasakado,
• Takahide Fukuyama,
• Tomohiro Nakagawa,
• Shinji Taguchi and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2022, 18, 152–158, doi:10.3762/bjoc.18.16

• chlorination, which is consistent with the requirement of photoirradiation for the purpose of radical initiation. Near-complete selectivity for single chlorination required the low conversion of ethylene carbonate such as 9%, which was controlled by limited introduction of chlorine gas. At a higher conversion

• ; ethylene carbonate; photo flow reactor; vinylene carbonate; Introduction The C–H chlorination by molecular chlorine is a highly exothermic reaction that proceeds via a radical chain mechanism as illustrated in Scheme 1 [1][2][3][4][5][6]. Frequently, photoirradiation is used for radical initiation through

• homolysis of the Cl–Cl bond to generate chlorine radicals. In a subsequent step, a SH2 reaction by chlorine radicals at C–H bonds generates alkyl radicals and HCl. The second SH2 reaction between alkyl radicals and molecular chlorine then occurs to give the C–H chlorinated product and a chlorine radical

Efficient synthesis of ethyl 2-(oxazolin-2-yl)alkanoates via ethoxycarbonylketene-induced electrophilic ring expansion of aziridines

• Yelong Lei and
• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 70–76, doi:10.3762/bjoc.18.6

• alcohols [13][14][15] (Scheme 1a); (3) oxidative condensation of aldehydes with vicinal amino alcohols [16] (Scheme 1b); (4) cyclization of N-allylamides in the presence of electrophilic reagents or radical initiators or catalysts [17] (Scheme 1c); (5) direct synthesis from alkenes and amides or nitriles

• diastereomeric products 3 were obtained. Compared with previously reported methods, our current method is more convenient and low cost without any activators (such as thionyl chloride, sulfonyl chlorides, NBS, electrophiles, and radical initiators) and catalysts. The current synthetic strategy is a clean

1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• electrons through a redox cycle promoted by the 1,2- or 1,4-naphthoquinone system. In this cycle, transient reactive oxygen (ROS) and nitrogen (RNS) species are formed as free radicals, peroxides, superoxide anions, radical anions, or dianions. These species generated inside cells accelerate hypoxia and

DABCO-promoted photocatalytic C–H functionalization of aldehydes

• Bruno Maia da Silva Santos,
• Mariana dos Santos Dupim,
• Cauê Paula de Souza,
• Thiago Messias Cardozo and
• Fernanda Gadini Finelli

Beilstein J. Org. Chem. 2021, 17, 2959–2967, doi:10.3762/bjoc.17.205

• a reactive species, often used in catalytic amounts, capable of promoting a highly selective homolytic cleavage of the C–H bond that results in a carbon-centered radical [5][6]. Nitrogenated structures are easily oxidized under mild conditions into their radical or radical cation forms [7], being

• a common inexpensive organic base with two nitrogen atoms in a bicyclic cage structure. The interaction between these two nitrogen atoms makes DABCO easier to oxidize and improves the lifetime of the radical cation species when compared to quinuclidine [7]. Investigation of DABCO as a hydrogen

• abstractor in photocatalytic strategies could expand the catalyst combinations, as illustrated in Figure 1, to create new and exciting methodologies and improve the understanding on theoretical aspects of the HAT process with nitrogen radical cations. However, despite its promising chemical properties and

A two-phase bromination process using tetraalkylammonium hydroxide for the practical synthesis of α-bromolactones from lactones

• Yuki Yamamoto,
• Akihiro Tabuchi,
• Kazumi Hosono,
• Takanori Ochi,
• Kento Yamazaki,
• Shintaro Kodama,
• Akihiro Nomoto and
• Akiya Ogawa

Beilstein J. Org. Chem. 2021, 17, 2906–2914, doi:10.3762/bjoc.17.198

• the α-position relative to the carbonyl group, is the most versatile synthetic intermediate [19][20][21][22][23][24][25][26][27][28]. α-Bromolactones are widely used as synthetic intermediates for functional materials and pharmaceuticals, as well as initiators in atom-transfer living radical

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• which will react further. However, reactions catalyzed by the Lewis-acidic character of iron salts are beyond the scope of this review. Iron also has the ability to transfer one or two electrons to a substrate. This opens the possibility for radical reactions via a single electron transfer (SET). Once

• initiated, the reaction will propagate, which typically involves the insertion of a π-system (carbometallation of alkenes/alkynes) in the case of organoiron species (Scheme 2). Alternatively, the generated radical species may undergo radical addition to alkenes, alkynes, or aromatic arenes. The final step

• is the termination of the reaction through the trapping of the reactive intermediate. Organoiron complexes have been shown to undergo electrophilic trapping with external species or proceed through cross-coupling eventually undergoing reductive elimination. Radical addition will typically conclude

Selective sulfonylation and isonitrilation of para-quinone methides employing TosMIC as a source of sulfonyl group or isonitrile group

• Chuanhua Qu,
• Run Huang,
• Yong Li,
• Tong Liu,
• Yuan Chen and
• Guiting Song

Beilstein J. Org. Chem. 2021, 17, 2822–2831, doi:10.3762/bjoc.17.193

• important C1 synthon. Its special reactivity, such as the ability to react with electrophilic, nucleophilic, and radical reagents [25][26][27][28], determines that it can participate in many types of reactions such as multicomponent reactions [29][30][31][32], tandem reactions [33][34], and insertion

• decompose to a Ts anion and formaldehyde, possibly accompanied by the formation of a cyanide ion [54]. The previous reports on the reaction mechanism of TosMIC as a source of Ts are mainly a radical mechanism [19][20][21][22][23]. To assess the possibility of radical intermediates, a stoichiometric amount

• of the radical inhibitor 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was subjected to the model reaction system, however, the reaction was not inhibited (Scheme 6B). This result suggests that no radical pathway is involved in this transformation. Based on the above experiments, a proposed mechanism

Photophysical, photostability, and ROS generation properties of new trifluoromethylated quinoline-phenol Schiff bases

• Inaiá O. Rocha,
• Yuri G. Kappenberg,
• Wilian C. Rosa,
• Clarissa P. Frizzo,
• Nilo Zanatta,
• Marcos A. P. Martins,
• Isadora Tisoco,
• Bernardo A. Iglesias and
• Helio G. Bonacorso

Beilstein J. Org. Chem. 2021, 17, 2799–2811, doi:10.3762/bjoc.17.191

• possible reactive oxygen species in DMSO solution (e.g., hydroxyl and superoxide radical species) that are not identified by the type of photooxidation assay employed in this work. The good photostability and tendency of these Schiff base derivatives to generate 1O2 under light irradiation demonstrated

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

• Ilya A. P. Jourjine,
• Lukas Zeisel,
• Jürgen Krauß and
• Franz Bracher

Beilstein J. Org. Chem. 2021, 17, 2668–2679, doi:10.3762/bjoc.17.181

• radical cyclizations [22], Pschorr reactions [23], and diverse cycloaddition protocols [24][25]. Especially transition-metal-catalyzed cross-coupling reactions starting from benzophenones, benzoic acids, dihalogenated benzene building blocks and others have emerged as new approaches in recent years [26

• of oxidizing agents, oxidizing systems, and radical initiators on a set of model molecules 2 (see Table 1) in a preliminary screening for suitable oxidants for the intramolecular ring-closure reaction. The set of model molecules 2 bears different benzylic N-containing functional groups, including

• adverse effect on the yield of fluorenone (3). Addition of TBAI (Table 2, entry 10) in particular looked promising, as TBAI/TBHP-mediated radical cyclizations and cross-dehydrogenative coupling (CDC) reactions are not only well established [57], but addition of TBAI has been shown to increase the yield of

Cryogels: recent applications in 3D-bioprinting, injectable cryogels, drug delivery, and wound healing

• Luke O. Jones,
• Leah Williams,
• Tasmin Boam,
• Martin Kalmet,
• Chidubem Oguike and
• Fiona L. Hatton

Beilstein J. Org. Chem. 2021, 17, 2553–2569, doi:10.3762/bjoc.17.171

• -polymerised precursors can cause free radical damage or react with proteins in the human body containing thiols and amino groups [84]. Further toxicity research would be required for all of these cryogels to fully understand how they react in the human body as opposed to animal substitutes. However, the use

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• homolysis to produce CuI species and radical intermediates. These intermediates can initiate productive organic transformations [39]. 2.1 Visible-light-mediated Cu(I) catalytic cycle Upon the absorption of a photon (Scheme 4), CuILn forms a singlet MLCT state, which subsequently yields the excited triplet

• state CuI*Ln via rapid ISC. The excited CuI*Ln species has a lifetime to finish the chemical processes. A radical mechanism is proposed in Scheme 4. In path a (a ligand transfer cycle), CuI* is oxidized by an electrophilic reagent (haloalkane) to form CuII and the radical species R• in a single-electron

• transfer (SET) process. Subsequently, CuII undergoes ligand exchange with a nucleophilic reagent (Nu) to produce the CuII−Nu species. The reorganization of CuII–Nu is trapped by the radical intermediate R• to generate the final product (R–Nu) with concomitant regeneration of the CuI catalyst. Alternatively

Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation

• Azra Kocaarslan,
• Zafer Eroglu,
• Önder Metin and
• Yusuf Yagci

Beilstein J. Org. Chem. 2021, 17, 2477–2487, doi:10.3762/bjoc.17.164

• photocatalysts have been successfully applied in both small- and large-scale synthesis such as organic reactions [16][17], free radical polymerization (FRP) [18][19][20], controlled radical polymerization (CRP) [21][22], CuAAC chemistry [23][24][25], and thiol–ene chemistry [26][27]. However, most of the

• [34][38][39][40]. The use of 2D materials for the photoinitiated electron transfer reactions with CuII catalysts for the photoinduced atom transfer radical polymerization (ATRP) and CuAAC reactions prompted us to develop a new photoredox system that works under NIR irradiation for the CuAAC reaction

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

• Yi Liu,
• Puying Luo,
• Yang Fu,
• Tianxin Hao,
• Xuan Liu,
• Qiuping Ding and
• Yiyuan Peng

Beilstein J. Org. Chem. 2021, 17, 2462–2476, doi:10.3762/bjoc.17.163

• -annulation reaction may undergo a free-radical addition pathway. Firstly, NFSI oxidizes Cu(I) to form bissulfonylamidyl radical 10. Secondly, intermolecular nitrogen free-radical addition to the alkyne provides the vinyl radical 11. Then, there may be two possible pathways. Path a: vinyl radical 11 is

• trapped by Cu(II) to deliver the Cu(III) species 12, which undergoes intramolecular annulation and reductive elimination to afford the desired product 8 and regenerate the Cu(I) catalyst. Path b: vinyl radical intermediate 11 is oxidized by Cu(II) to give the cationic vinyl species 14. Finally, the

• trace amount of the desired product was observed. Control experiments indicated that the possible reaction mechanism may proceed through a Cu(II)/Rh(III)-promoted radical process. Aryl azides are versatile intermediates, which were widely used in synthetic and medicinal chemistry as well as material and

Strategies for the synthesis of brevipolides

• Yudhi D. Kurniawan and
• A'liyatur Rosyidah

Beilstein J. Org. Chem. 2021, 17, 2399–2416, doi:10.3762/bjoc.17.157

• brevipes Poit., furthermore, exhibited free radical scavenging and potential antitumor activities [2]. The ethnomedicinal background and preliminary biological studies triggered researchers to further examine the chemical constituents of the plant. In 2009, Kinghorn and co-workers reported the first study

• folk medicines [2][3][5][6][7][8][9][10] to pest management [2][3]. These traditional applications stimulated researchers to conduct biological studies with these plant extracts. A variety of bioactivities were then evidenced, such as antifungal, antibacterial [4][9] insecticidal [7], and radical

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• synthesis of trisphaeridine to afford the product in four linear steps in an overall yield of 6.5% from 1-bromo-2,4,5-trimethoxybenzene. Keywords: aromatic compounds; cyclization; iminyl radical; phenanthridines; radical cation; synthesis; UV irradiation; Introduction Phenanthridine derivatives have

• intramolecular cyclization of O-acetyloximes to afford phenanthridines. (Figure 2, reaction 2) [8][9]. For these transformations, the reaction is thought to go via the transient iminyl radical [10]. More recently, Yu has reported the use of in situ-derived O-acyl oximes from benzaldehydes that when subjected to

• hypothesized that oxime 7 undergoes a homolytic cleavage of the N–O bond giving the iminyl radical 11 [14] followed by an intramolecular cyclization with concomitant expulsion of the ortho-methoxy group, liberating phenanthridine 9. To the best of our knowledge, such a reaction in which the aromatic methoxy

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• be a challenging endeavor. As conventional methods, e.g., the Heck reaction are incompatible with quinones [15], a large subset of research recently focused on radical-based CH-arylation reactions. In 2011, Baran published a seminal paper that relied on using a AgNO3/K2S2O8 induced homolytic

• splitting of boronic acids in a useful radical CH mono-arylation of benzoquinones [16]. Later research demonstrated that the metal catalyst can be replaced by a less expensive iron catalyst [17][18] or even be omitted at higher temperatures [19]. Despite their reputation as unstable intermediates

• , aryldiazonium salts have long played an essential role as radical precursors [20]. Their use in CH-arylation reactions of olefins, catalyzed by copper salts, was first published by Meerwein in 1939 [21]. Recently, we published a Meerwein arylation/cyclization sequence to benzofuropyridine derivatives in this

Photoredox catalysis in nickel-catalyzed C–H functionalization

• Lusina Mantry,
• Rajaram Maayuri,
• Vikash Kumar and
• Parthasarathy Gandeepan

Beilstein J. Org. Chem. 2021, 17, 2209–2259, doi:10.3762/bjoc.17.143

• combined with radical species [41][42][43], a wide variety of reactions have been discovered. Within a remarkable renaissance of photoredox dual catalysis, nickel/photoredox catalysis has recently been identified as a viable C‒H functionalization tool under milder reaction conditions [40][44][45][46][47

• were found to be suitable to achieve the transformation in satisfactory yields under visible light irradiation (Scheme 2). The authors hypothesized that the key α-nitrogen carbon-centered radical 5 could be generated via a photoredox-driven N-phenyl oxidation and α-C–H deprotonation sequence from

• nickel(II) species 2-VI and radical species 2-IV forms a nickel(III) intermediate 2-VII, which undergoes a reductive elimination to afford the desired product 7 and the nickel(I) species 2-VIII. The SET reduction of 2-VIII by the iridium(II) species 2-III regenerates the nickel(0) catalyst 2-V and the

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

• better stabilization of cation radicals, di-, and polycations by the unique dipolar nature of azulene, and in the case of iodine doping, it was attributed to the strengthened spin–spin interaction arising due to a high radical concentration. Recently, it was also established that the water-dispersible

• contrast. Azulene-methacrylate copolymers Emrick and co-workers [45] reported the synthesis of azulene-substituted methacrylate polymers derived from a free radical polymerization strategy, where azulenes were used as pendants. The key starting points to make these polymers were azulene-2-yl methacrylate

• free radical polymerization by using azobis(isobutyronitrile) (AIBN) to obtain the polymers 151 and 152 in 73 and 82% yields, respectively (Scheme 26A and B). The Mn and PDI for these polymers 151 and 152 were 13500 Da, 2.5 and 13600 Da, 2.2, respectively, and their solubility was good in organic

Constrained thermoresponsive polymers – new insights into fundamentals and applications

• Patricia Flemming,
• Alexander S. Münch,
• Andreas Fery and
• Petra Uhlmann

Beilstein J. Org. Chem. 2021, 17, 2123–2163, doi:10.3762/bjoc.17.138

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

• silylation of N-methylindole (1) with observed H2 evolution [54]. Here the di(indol-2-yl)silane (31) was found as a minor product though (Scheme 5a). The reaction has a high turnover number of 92 and it was halted in the presence of radical scavengers. However, the mechanism was unidentified, although it was

• proved to not going via a Minisci-type silyl radical addition [55], as the reaction with pyridine did not afford any product. Bell studied the properties of such molecules which are similar to those used in OLED devices (organic light emitting diodes) in 2017. The molecule 34 was synthesized by base

• 10% yield when chloranil was used as the oxidant (Scheme 25) [115]. The high electrophilicity of 178 at the C7 position resulted in this product formation. The reaction proceeds through the radical intermediate 181. Sulfides Reddy synthesized the di(indol-5-yl)sulfide (183) via a cascade strategy

An initiator- and catalyst-free hydrogel coating process for 3D printed medical-grade poly(ε-caprolactone)

• Jochen Löblein,
• Thomas Lorson,
• Miriam Komma,
• Tobias Kielholz,
• Maike Windbergs,
• Paul D. Dalton and
• Robert Luxenhofer

Beilstein J. Org. Chem. 2021, 17, 2095–2101, doi:10.3762/bjoc.17.136

• demonstrate this surface modification using a hydrogel, poly(2-hydroxyethyl methacrylate) (PHEMA) [19]. However, this approach should have broad utility for a spectrum of monomers and macromonomers susceptible to radical polymerization onto (almost) any surface featuring C–H bonds. This hydrogel coating is

• scaffolds, which may be required for suitable interaction with cells or other materials. SIPGP does not require special equipment other than a UV lamp or special reagents. As a proof-of-concept, we demonstrated the feasibility using HEMA as monomer, but essentially any monomer polymerizable by free radical

Towards new NIR dyes for free radical photopolymerization processes

• Haifaa Mokbel,
• Guillaume Noirbent,
• Didier Gigmes,
• Frédéric Dumur and
• Jacques Lalevée

Beilstein J. Org. Chem. 2021, 17, 2067–2076, doi:10.3762/bjoc.17.133

• filled samples can be potentially used for composite materials and/or adhesives. Both photochemical and photothermal NIR approaches were proposed to initiate polymerization, e.g., for free-radical processes, interpenetrating polymer network (IPN) synthesis, or photopolyaddition reactions [3][4][6][7][8

• combination with an amine and an iodonium salt, iod, for the free radical polymerization of a benchmark acrylate monomer and compared to a reference initiating system based on IR 813 (Scheme 2) [7]. As the different dyes presented above exhibit good absorption properties at 785 nm, the photoinitiating

• depicted in Figure 2 and Figure 3. The NIR dyes proposed have strong abilities to initiate the free radical polymerization. Indeed, the polymers obtained are tack-free after only a few seconds of irradiation (Scheme 6). Without NIR dyes, no polymerization occurs. At 785 nm, in most cases, the final

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

• sequential modifications [30], photocyclization of divinylterphenyl derivatives [31], tandem radical cyclization of (Z,Z)-1,4-bis(2-iodostyryl)benzene derivatives [32], and ring-closing olefin metathesis of tetravinylterphenyls [33] as the best-known synthetic routes. Herein, we have classified the synthetic