Carbonylative synthesis and functionalization of indoles

• Alex De Salvo,
• Raffaella Mancuso and
• Xiao-Feng Wu

Beilstein J. Org. Chem. 2024, 20, 973–1000, doi:10.3762/bjoc.20.87

• what we have just written, Li’s group performed the reaction by a Rh-catalysis using [Rh(COD)Cl]2 and re-oxidizing it with K2S2O8. The reactions led to the products in toluene after 24–48 hours at 110 °C under 1 bar of CO (Scheme 36). Another example to obtain indole-3-carboxylates, was again reported

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• adjacent C=C bond, various conjugated alkenyl C–H bonds can also be activated to construct functionalized ethers. In 2013, Wang et al. achieved a mild Cu(OTf)2-catalyzed CDC of (benzo)thiazoles with cyclic ethers in the presence of K2S2O8 (Scheme 9) [59]. The catalytic system is also suitable for

• methodologies involving ether α-C(sp3)–H and aromatic C(sp2)–H bonds were investigated and these are shown in Scheme 43. Shah et al. reported a catalyst-free CDC method using only 2 equivalents of K2S2O8 in H2O under irradiation with a 27 W CFL (Scheme 43a) [123]. In this reaction, both water and the light

Sulfate radical anion-induced benzylic oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines

• Joydev K. Laha,
• Pankaj Gupta and
• Amitava Hazra

Beilstein J. Org. Chem. 2023, 19, 771–777, doi:10.3762/bjoc.19.57

• synthesis of synthetically useful N-arylsulfonylimines from N-(arylsulfonyl)benzylamines using K2S2O8 in the presence of pyridine as a base is reported herein. In addition, a “one-pot” tandem synthesis of pharmaceutically relevant N-heterocycles by the reaction of N-arylsulfonylimines, generated in situ

• -aryl(benzyl)amines to N-arylimines using K2S2O8 is reported to be problematic, the oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines using K2S2O8 has been achieved for the first time. The dual role of the sulfate radical anion (SO4·−), including hydrogen atom abstraction (HAT) and

• single electron transfer (SET), is proposed to be involved in the plausible reaction mechanism. Keywords: arylsulfonylimine; benzylic oxidation; benzyl sulfonamide; K2S2O8; sulfate radical anion; Introduction Among various imine compounds [1], N-arylsulfonylimines are perhaps the most prominent due to

Transition-metal-catalyzed C–H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

• Louis Monsigny,
• Floriane Doche and
• Tatiana Besset

Beilstein J. Org. Chem. 2023, 19, 448–473, doi:10.3762/bjoc.19.35

• described the selective palladium-catalyzed ortho-2,2,2-trifluoroethoxylation of a series of benzaldehydes (Scheme 22, 35 examples) using the amino acid ʟ-valine in the presence of K2S2O8 and TFA at 80 °C [153]. This reaction proved to be highly tolerant to various substituents including a CF3 group at the

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

• Péter Kisszékelyi,
• Tibor Peňaška,
• Klára Stankovianska,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 1195–1202, doi:10.3762/bjoc.18.124

• successfully prepared [32]. The protocol, using NaI as a catalyst and K2S2O8 as an oxidant, tolerated a broad range of substrates with good stereoselectivity. Interestingly, structurally related benzothiazine derivatives with a carboxylic function in the C-3 position are only seldomly described in the

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

• an interesting artifice to track the dimerization reaction path: they synthesized 2-(methyl-13C)-1,4-naphthoquinone (10) (Scheme 1) [81]. For that, sodium acetate-2-13C was used as the source of the methyl radical, generated by its treatment with K2S2O8 and AgNO3. After 3 hours at 60 °C, the 13C

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

• group (Scheme 2) [33]. In contrast to transition-metal-mediated approaches [27], metal-free oxidative methods are attractive not only from an ecological point of view, but also due to the typically low cost of the applied oxidants. Biarylcarboxaldehydes were cyclized to fluorenones using K2S2O8 [34

• nitrate (CAN) [41], 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO)/CuCl [51], K2S2O8 [36], dimethyl sulfoxide (DMSO)/O2 [52], PhI(OAc)2/benzoyl peroxide (BPO) [47], Dess-Martin periodinane, N-bromosuccinimide (NBS), N-hydroxyphthalimide (NHPI)/Co(OAc)2/O2 [53], H2O2/tetrabutylammonium iodide (TBAI) [43], CBr4

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

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

• and the subsequent aerobic oxidation by an amine. Single-electron oxidants such as cerium ammonium nitrate or K2S2O8 were used for the regiospecific ring opening of the simple gem-difluorocyclopropanes 134 (Scheme 58). The brominative ring-opening reactions of compounds 134 gave good yields of the

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

• thiocyanate 2 in the presence of several oxidants and metal salts (Table 1). The initial attempts employing iodine, CAN and ZnCl2 upon refluxing in acetonitrile for 6 hours did not yield any product (Table 1, entries 1, 2 and 4). When potassium persulfate (K2S2O8) is employed, highly substituted oxazole 3i

• synthesis of 2,4,5-trisubstituted oxazole from azirine. a) I2, PPh3; b) NaH, 1H-pyrazole; c) 2-bromoacetyl bromide, NaN3; d) heating; e) t-BuOK; f) Ph-CHO, visible light; g) KSCN, K2S2O8. Scope of the α-azidochalcones. The reactions were carried out at reflux temperature, using 1 (1 mmol), 2 (3 mmol

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

• a mild and efficient protocol for the remote C4–H sulfonylation of 1-naphthylamine derivatives with sodium sulfinates in the presence of K2S2O8 as the oxidant (Figure 35) [99]. This strategy was based on the use of a bidentate picolinamide DG promoting the direct C–H functionalization of the

• the naphthyl ring after an intramolecular electron transfer. In the meantime, the sulfonyl radical is generated by oxidation of the sulfinate substrate via the photocatalytic cycle with the Ru(bpy)3 catalyst and K2S2O8 (the direct oxidation of sulfinate by persulfate could also be envisioned

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

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• nitrones (products 150a–d). A similar cyanation reaction was realized using TMSCN as a cyanide source and the oxidative system Cu(NO3)2/K2S2O8 (Scheme 51) [140]. Both aromatic (products 152a–c) and aliphatic (products 152d–f) β,γ-unsaturated oximes undergo this transformation. Oximes substituted at the α

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

• Ming-Xi Bi,
• Shuai Liu,
• Yangen Huang,
• Xiu-Hua Xu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2020, 16, 657–662, doi:10.3762/bjoc.16.62

• surprise, the reaction of 1a and AgSCF3 in the presence of K2S2O8 and KHCO3 in DMSO at 80 °C gave bis(trifluoromethylthiolated) product 2a in 28% yield (Table 1, entry 1). Only trace of mono(trifluoromethylthiolated) product was detected, and most of the substrate 1a was not converted. To the best of our

• knowledge, the combination of bis(trifluoromethylthiolation) [36][39][40][41] and cascade cyclization reactions has not been reported before. Thus, the amounts of AgSCF3 and K2S2O8 were increased to deliver 2a in 52% yield (Table 1, entry 2). Other oxidants including Na2S2O8 and (NH4)2S2O8 afforded 2a in

Construction of trisubstituted chromone skeletons carrying electron-withdrawing groups via PhIO-mediated dehydrogenation and its application to the synthesis of frutinone A

• Qiao Li,
• Chen Zhuang,
• Donghua Wang,
• Wei Zhang,
• Rongxuan Jia,
• Fengxia Sun,
• Yilin Zhang and
• Yunfei Du

Beilstein J. Org. Chem. 2019, 15, 2958–2965, doi:10.3762/bjoc.15.291

• = 5.3 nM) properties [90][91][92]. Treating the obtained chromene-3-carboxylate 2l with LiOH [93] led to the formation of the chromene-3-carboxylic acid G. Heating compound G overnight in the presence of AgNO3 and K2S2O8 afforded frutinone A in an isolated yield of 45% (Scheme 5). Conclusion In summary

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• decarboxylative trifluoromethylation of various primary and secondary aliphatic carboxylic acids. With AgNO3 as a catalyst, (bpy)Cu(CF3)3 (bpy = 2,2’-bipyridine) as a CF3 source and K2S2O8 as an oxidant, aliphatic carboxylic acids were converted to the corresponding trifluoromethylated products in good yields

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

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

• AgNO3 and K2S2O8. The radical 98 undergoes a ring-opening to give the alkyl radical 99. Finally, the radical 99 is intercepted by NCS 118 to furnish the chlorinated ketone 119. The generated imidyl radical 120 can also participate in hydrogen abstraction of cyclopropanol 91 to form the radical 98. In

• ring-opening and difluoromethylthiolation of cyclopropanols 91 with PhSO2SCF2H 142 for the synthesis of difluoromethylthioethers 143 was reported by Shen and co-workers (Scheme 38) [118]. AgNO3 was utilized as catalyst, K2S2O8 as oxidant, and SDS (sodium dodecyl sulfate) as addictive in water. The SDS

DABCO- and DBU-promoted one-pot reaction of N-sulfonyl ketimines with Morita–Baylis–Hillman carbonates: a sequential approach to (2-hydroxyaryl)nicotinate derivatives

• Soumitra Guin,
• Raman Gupta,
• Debashis Majee and
• Sampak Samanta

Beilstein J. Org. Chem. 2018, 14, 2771–2778, doi:10.3762/bjoc.14.254

• as the requirement of high temperatures or use of strong oxidants (H2O2, oxone, K2S2O8, TBHP, PIDA, NHPI etc.) that are not much compatible with functionality, precluding late-stage functionalization. Moreover, the scope of substitution on the pyridine ring is limited which in turn hampers the

One-pot preparation of 4-aryl-3-bromocoumarins from 4-aryl-2-propynoic acids with diaryliodonium salts, TBAB, and Na₂S₂O₈

• Teppei Sasaki,
• Katsuhiko Moriyama and
• Hideo Togo

Beilstein J. Org. Chem. 2018, 14, 345–353, doi:10.3762/bjoc.14.22

• addition–cyclization reactions of aryl 2-alkynoates with RC(=O)CO2H/AgNO3(cat.)/K2S2O8 at 60 °C [24], with Cu(OAc)2/1-trifluoromethyl-3,3-dimethyl-1,2-benziodoxole (Togni reagent) at 60 °C [25], with R2P(=O)H/Ag2CO3(cat.)/Mg(NO3)2 at 100 °C [26], with BrCF2CO2Et/fac-Ir(ppy)3(cat.) under irradiation at rt

• [27], with R-CH=O/(n-Bu)4NBr (TBAB, cat.)/K2S2O8 at 90 °C [28], with ArSO2H/Eosin Y(cat.)/tert-butyl hydrogen peroxide (TBHP) at rt [29], and with ArSO2NHNH2/n-Bu4NI(cat.)/TBHP at 80 °C [30]. In addition, the formation of coumarins via the bromine-radical-mediated reaction of aryl 2-alkynoates with

• TBAB/K2S2O8 at 90 °C [31], the cyanomethyl-radical-mediated reaction of aryl 2-alkynoates with tert-butyl peroxybenzoate (TBPB)/acetonitrile at 130 °C [32], the sunlight-promoted reaction of aryl 2-alkynoates with N-iodosuccinimide (NIS) at rt [33], and the visible-light-mediated reaction of aryl 2

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• CF3SO2Na by means of an oxidative system comprising catalytic amounts of silver(I) nitrate and potassium persulfate K2S2O8. Both atmospheric oxygen and K2S2O8 can be the source of the oxygen atom of the ketone moiety. A series of experiments that include the formation of TEMPO–CF3 (TEMPO: 2,2,6,6

• using 18O2; no reaction occurred under N2 instead of O2; K2S2O8 rather than O2 served as initiator; the radical CF3SO2• could either extrude SO2 to CF3• or react with O2 to re-initiate the radical chain process (Scheme 7). Vinyl azides were used by Liu and co-workers as precursors of α

• reactions with K2S2O8, I2O5 or a hypervalent iodine reagent, and (iii) photochemical activation. Most of the works concerned cascade intramolecular reactions in which a C–C bond is formed after the initial trifluoromethylation. Therefore, Lipshutz and co-workers reported a copper-catalysed intramolecular

Chemoselective synthesis of diaryl disulfides via a visible light-mediated coupling of arenediazonium tetrafluoroborates and CS₂

• Jing Leng,
• Shi-Meng Wang and
• Hua-Li Qin

Beilstein J. Org. Chem. 2017, 13, 903–909, doi:10.3762/bjoc.13.91

• undesired diphenyl polysulfides (Table 2, entry 4). Switching to DMSO as the solvent for the reaction afforded exclusively the desired product 3a in excellent yield (88%, Table 2, entry 6). Next, other sulfur sources were also examined, such as S8, NaSH, Na2S, Na2S2O3, Na2S2O4 and K2S2O8, however, none of

Transition-metal-catalyzed synthesis of phenols and aryl thiols

• Yajun Liu,
• Shasha Liu and
• Yan Xiao

Beilstein J. Org. Chem. 2017, 13, 589–611, doi:10.3762/bjoc.13.58

• ]. Rao and co-workers found that both biaryl ketone and aryl alkyl ketones could be regioselectively hydroxylated in satisfying yields. The reaction proceeded in TFA/TFAA in the presence of Pd(OAc)2 as catalyst and several type of oxidants including selectfluor, PhI(OAc)2 and K2S2O8, respectively (Scheme

• reaction conditions for the hydroxylation of aryl alkyl ketones. The conditions using PhI(TFA)2 as oxidant and DCE as the solvent were milder and more selective, while the conditions using K2S2O8 as oxidant and TFA as solvent were more reactive (Scheme 42). Interestingly, although the reaction gave the

• ketones. The Rao group developed a catalytic system of [RuCl2(p-cymene)]2 and K2S2O8 in TFA/TFAA, which promoted the hydroxylation of ethyl benzoates, benzamides and carbamates (Scheme 49). They reported the first ortho-hydroxylation of ethyl benzoates in 2012 [79]. Both electron-rich and electron

Cascade alkylarylation of substituted N-allylbenzamides for the construction of dihydroisoquinolin-1(2H)-ones and isoquinoline-1,3(2H,4H)-diones

• Ping Qian,
• Bingnan Du,
• Wei Jiao,
• Haibo Mei,
• Jianlin Han and
• Yi Pan

Beilstein J. Org. Chem. 2016, 12, 301–308, doi:10.3762/bjoc.12.32

• -methylallyl)benzamide (4a) and cyclohexane (2a) as model compounds (Table 1). As shown in Table 1, we found that the reactions did not happen or gave only a trace amount of the desired product with K2S2O8, AIBN, BPO and TBHP as oxidants (Table 1, entries 1, 3–5). PhI(OAc)2 and DCP could be used as oxidants