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

• converted to fused sultams (Scheme 30) [56]. Anand et al. reported a Cu-catalyzed one-pot method for the preparation of 1,2,3-triazole-fused tricyclic heterocycles 106 via an intramolecular [3 + 2]-annulation. This strategy includes the 1,6-conjugate addition of Me3SiN3 to o-alkynylated p-quinone methides

• 105, followed by an intramolecular Click annulation to provide rapid access to a wide range of desired 1,2,3-triazole-fused isoindolines 108 with a reasonable yield. The reaction was carried out well by using o-alkynylated p-quinone methides 105 and TMSN3 in the presence of a catalytic amount of CuOTf

• ⋅PhMe in DCE at 60 °C. A series of o-alkynylated p-quinone methides containing electron-donating, electron-withdrawing, halogen, and alkyl groups was treated with Me3SiN3 under the optimized reaction conditions and produced the desired fused 1,2,3-triazole derivatives (Scheme 31) [57]. Two mechanisms

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

• hydroalkylation cascades. In 2016, the Cui group reported the hydroalkylation of olefins 59 using p-quinone methides 60 as electrophilic partners (Scheme 24A) [91]. Alkenyl alcohols could be employed without needing to protect the hydroxy functional group, and the acidity of the phenolic hydrogen present in the

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• naphthoquinone-derived products and low-intensity bands in the visible region (≈400 nm) for the anthraquinone series. Keywords: [3 + 2]-cycloadditions; fluorinated compounds; fused pyrazoles; N-heterocycles; nitrile imines; 1,4-quinones; Introduction The 1,4-quinone scaffold belongs to the most important

• fluorine-containing organic molecules combined with the 1,4-quinone moiety can be considered as a challenging problem of current organic synthesis. Thus, the main goal of the present study was to check the course of [3 + 2]-cycloaddition reactions of electron-deficient CF3-substituted nitrile imines 7 with

• ]-cycloaddition more efficiently than fluorinated nitrile imines 7 generated under basic conditions. It seems likely that in the presence of a base, sequential reactions of the conjugated C–H-acidic quinone 1c occur, which lead to a complex mixture of products. In contrast, the reaction of the same nitrile imine

Organocatalytic asymmetric Michael/acyl transfer reaction between α-nitroketones and 4-arylidenepyrrolidine-2,3-diones

• Chandrakanta Parida and
• Subhas Chandra Pan

Beilstein J. Org. Chem. 2021, 17, 1447–1452, doi:10.3762/bjoc.17.100

• the keto group [11][12][13]. Consequently, our group developed an organocatalytic asymmetric Michael–acyl transfer reaction of α-nitroketones with unsaturated pyrazolones, 2-hydroxycinnamaldehydes, γ/δ-hydroxyenones, o-quinone methides, etc. [14][15][16][17][18]. Other groups also contributed

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

• by the basic treatment of chloroform electrophilically attacks phenol, generating a chloromethylene quinone methide. Under wet conditions, this is attacked by water, eventually leading to a formylated phenol. In the absence of water, the quinone methide is attacked by a molecule of unreacted phenate

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

Application of the Meerwein reaction of 1,4-benzoquinone to a metal-free synthesis of benzofuropyridine analogues

• Rashmi Singh,
• Tomas Horsten,
• Rashmi Prakash,
• Swapan Dey and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 977–982, doi:10.3762/bjoc.17.79

• , various metal-based approaches for arylation of quinone involving electrochemical [32], oxidative [33], and photochemical methods [34][35][36] are also available in the literature [37]. Langer and co-workers reported the synthesis of benzofuropyridines based on a domino reaction of 3-chlorochromones with

• aminoheterocycles [38]. Alternatively, the classical Meerwein reaction can be applied starting from 3-amino-2-chloropyridine (10), which was transformed into the diazonium salt and coupled in situ with 1,4-benzoquinone, forming arylated quinone 11 without an additional reducing agent [39]. The quinone was reduced

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• with alcohol 307 to obtain 309 (Scheme 71) [113]. The introduction of electron-withdrawing nitro groups on the BINOL backbone in the catalysts significantly enhanced the reactivity and enantioselectivity. Zhou et al. reported an asymmetric Prins cyclization of in situ-generated quinone methides from

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• inverse electron-demand Diels–Alder cycloaddition reactions between a dibenzosuberenone and tetrazines that bear various substituents. The pyridazines were synthesized in high yields by oxidation of dihydropyridazine-appended dibenzosuberenones with PIFA or NO. p-Quinone derivatives of pyridazines were

• also obtained by H-shift isomerization following the inverse electron-demand Diels–Alder reaction of tetrazines with p-quinone dibenzosuberenone. Then these pyridazines were converted to the corresponding pyrroles by reductive treatment with zinc. It was observed that all the dihydropyridazines

• obtained gave absorbance and emission at long wavelengths. Keywords: dibenzosuberenone; inverse electron-demand Diels–Alder cycloaddition reactions; p-quinone methide; polycyclic π-conjugated dihydropyridazines; pyridazines; pyrroles; Inroduction Dibenzosuberone and dibenzosuberenone derivatives are

[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

• the synthesis of various spiromethanofullerenes. For example, spiro derivatives 73–75 were obtained in one of the first works on this subject (Figure 7). The authors obtained quinone-derived [6,6]-closed spiromethanofullerenes 76–78 by reactions of C60 with the corresponding diazo compounds upon

• ]. Subsequently, the scope of quinone-substituted methanofullerenes was expanded by derivatives 82 and 83, and the scope of indanedione-substituted derivatives by compound 84. All of them were synthesized under conditions similar to those indicated in Scheme 24 (Figure 8) [112]. Synthesis of methanofullerenes

• . Structures of complexes 63–65. Structures of spiromethanofullerenes 73–75. Quinone-substituted spiromethanofullerenes 82–84. Structures of 4-C61-phenylorganofullerenes 159 and 160. Structures of methanofullerenes containing aromatic polycyclic systems. 4,4-Diphenylfullerene derivatives 31, 32, 167, and 168

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

• activity. An effective method for the synthesis of sterically hindered o-quinones containing 1,3-diketonate, dinitrile and p-quinone-methide functional groups at the periphery of the ligand has been developed. The novel compounds have rigid and conjugated structures and exhibit properties typical of o

• -quinones. A study of their monoreduced semiquinone derivatives reveal that the spin density is delocalized across the whole molecule, including peripheral fragments. The first stable o-quinone derivative bearing an annulated thiete heterocycle has been isolated and characterized. Keywords: dioxolene

• ligand; 1,3-dithiole; ditopic ligand; o-quinone; thiete; Introduction There are a number of methods which may be used for the synthesis of new o-quinones in order to vary their redox properties and coordination abilities. The key features of o-quinones are redox activity as well as chelating

Construction of pillar[4]arene[1]quinone–1,10-dibromodecane pseudorotaxanes in solution and in the solid state

• Xinru Sheng,
• Errui Li and
• Feihe Huang

Beilstein J. Org. Chem. 2020, 16, 2954–2959, doi:10.3762/bjoc.16.245

• 450001, P. R. China 10.3762/bjoc.16.245 Abstract We report novel pseudorotaxanes based on the complexation between pillar[4]arene[1]quinone and 1,10-dibromodecane. The complexation is found to have a 1:1 host–guest complexation stoichiometry in chloroform but a 2:1 host–guest complexation stoichiometry

• in the solid state. From single crystal X-ray diffraction, the linear guest molecules thread into cyclic pillar[4]arene[1]quinone host molecules in the solid state, stabilized by CH∙∙∙π interactions and hydrogen bonds. The bromine atoms at the periphery of the guest molecule provide convenience for

• new pseudorotaxanes based on the pillar[4]arene[1]quinone H and 1,10-dibromodecane (G, Scheme 1). The pillar[4]arene[1]quinone H, which is composed of four 1,4-diethoxybenzene subunits and one benzoquinone subunit, was prepared by partial oxidation of perethylated pillar[5]arene according to previous

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• sumanene provided the covalent adduct 171 with Cl atoms attached onto the Te atoms, confirmed by an X-ray analysis (Scheme 44). Having the quinone derivatives 166 and 167 in hands, they were next subjected to the condensation reaction with a variety of aryl-1,2-diamines 168 in the presence of AcOH to

Synthesis of 6,13-difluoropentacene

• Matthias W. Tripp and
• Ulrich Koert

Beilstein J. Org. Chem. 2020, 16, 2136–2140, doi:10.3762/bjoc.16.181

• subsequent reduction step using NaBH4 to diol 13 was performed without further purification of the quinone. The low yield for the formation of 13 seems to be an intrinsic instability of its ortho-fluorobenzylic alcohol moiety. Moreover, the compound quantitatively decomposes to 6,13-pentacenequinone 15 in

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

• ) [17] and violet-quinone (3) [18] (Figure 1). Similar to those natural products, the biomimetic synthesis of balsaminone A (4) and ellagic acid (5) can be attained using oxidative dimerization reactions, based on their proposed biosynthesis (Scheme 1 and Scheme 2) [19][20]. These pathways, which start

• which undergoes reduction to the dihydroxynaphthalene 8. This is then dimerized by the copper-rich enzyme to quinone arenol 9, which, following intramolecular cyclization, affords balsaminone A (4, Scheme 1). Similarly, the biosynthetic precursor of ellagic acid (5), gallic acid (10), undergoes

• 16 in 29, 34, and 19% yields, respectively (Table 1). As anticipated, the reaction of naphthalene 17 with CAN under aqueous conditions resulted in preferential oxidative demethylation to give quinone 7, as opposed to oxidative dimerization. The elimination of water from the reaction posed a few

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

• 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

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• –OCO), phenolic groups (R–OH) and carbonyl or quinone groups (R=O). Differentiation is possible by titration with different basic solutions NaHCO3, Na2CO3, NaOH, NaOC2H5, respectively. Titration of the samples with hydrochloric acid determines the basic properties on activated carbon surface in form of

• gases were determined by mass spectrometry. In general, each type of surface group decomposes to a defined product such as CO2 from carboxylic acid or lactones and CO from carbonyl, hydroxide, phenol, ether or quinone groups and thus, information on the amounts of oxygen-containing surface groups are

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• an enol system, as in the case of unsaturated ketones which is not easy to isolate, could be modified in such way that the resultant intermediate is highly stable. For example, Tortosa [65] showed that this type of catalytic system could be applied to the quinone methide system 162, which is

• cyclobutyl boronates in high yields and with excellent stereocontrol [101]. This work followed on the heels of earlier studies on the borylation of 2,6-disubstituted p-quinone methides en route to enantioenriched mono- and dibenzylic boronates [102]. An efficient regio-divergent method starting from a single

The interaction between cucurbit[8]uril and baicalein and the effect on baicalein properties

• Xiaodong Zhang,
• Jun Xie,
• Zhiling Xu,
• Zhu Tao and
• Qianjun Zhang

Beilstein J. Org. Chem. 2020, 16, 71–77, doi:10.3762/bjoc.16.9

• , baicalein contains three phenolic hydroxy groups, which are easily oxidized to the quinone derivative and appear green, therefore, it has limited use in pharmaceuticals on account of its poor aqueous solubility and stability [31]. The cucurbit[n]urils (Q[n]s n = 5–8, 10, …) are macrocyclic hosts with a

• study BALE has three phenolic hydroxy groups, which are easily oxidized to a quinone-type structure. The time-resolved UV–vis absorption spectra of BALE showed that the stability of BALE in water was poor in the absence of Q[8], whereas the stability of BALE was greatly improved in the presence of Q[8

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• reaction, causing the formation of complex products. Examples of dienes that have previously been used include cyclic diketones (o-benzoquinones) (Scheme 15, reaction pathways (i)) [60][89][156][157][158][160][161][162][163][164][165][211][215][226], o-quinone methides [87], o-xylylenes [125][153

Mechanochemical Friedel–Crafts acylations

• Mateja Đud,
• Anamarija Briš,
• Iva Jušinski,
• Davor Gracin and
• Davor Margetić

Beilstein J. Org. Chem. 2019, 15, 1313–1320, doi:10.3762/bjoc.15.130

• naphthalene were less reactive under the same ball milling conditions and reactions stopped at the stage of formation of product 3 and 15. One-step preparation of quinone 30 [39], was achieved by melting reactants at 140 °C for 10 min. Under these conditions, a mixture of adducts 3 and 30 (1.5:1 ratio) was

• obtained. The product ratio was established by 1H NMR analysis of the characteristic H-10 proton signal of product 3 (peak resonance doublet at δ 9.2 ppm), which is shifted towards lower magnetic field in quinone 30 (δ 10.0 ppm), and concurrent appearance of singlet for H-3 at δ 9.1 ppm. These experiments

Heck- and Suzuki-coupling approaches to novel hydroquinone inhibitors of calcium ATPase

• Robert J. Kempton,
• Taylor A. Kidd-Kautz,
• Soizic Laurenceau and
• Stefan Paula

Beilstein J. Org. Chem. 2019, 15, 971–975, doi:10.3762/bjoc.15.94

• -step sequence of oxidation employing ammonium cerium(IV) nitrate (CAN) [20] to afford the corresponding quinone (not shown), followed by reduction with sodium hydrosulfite [21]. With the nitrile in hand, we next attempted to reduce that functional group to an amine to which a leucine moiety could be

• Na2S2O4 or H2/Pd). What finally proved effective was the two step sequence of oxidation of 12a with CAN followed by treatment of the resulting quinone 13 with sodium borohydride in dry methanol – a sequence that gave 14 (which upon standing readily re-oxidizes back to 13) in 34% overall yield from 12a. A

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• was developed based on a Stille coupling to install the C-linked sugar residue [3]. Moreover, the addition of lithiated glycals to quinone derivatives followed by a rearrangement was also studied for the synthesis of kidamycin according to a “reverse polarity” strategy [4][5]. Considering that the

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

• Piotr Pomarański,
• Piotr Roszkowski,
• Jan K. Maurin,
• Armand Budzianowski and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2018, 14, 2384–2393, doi:10.3762/bjoc.14.214

• auxiliaries. Therefore, the atropselective synthesis is an important synthetic approach pursued by many research groups [22][23][24][25][26]. In 2015 the first phosphoric acid-catalysed asymmetric reactions of 2-naphthols with quinone analogues were described, allowing an access to a class of sterically

The enzymes of microbial nicotine metabolism

• Paul F. Fitzpatrick

Beilstein J. Org. Chem. 2018, 14, 2295–2307, doi:10.3762/bjoc.14.204

• oxidative demethylation of 4-(methoxymethyl)phenols via a quinone methide intermediate [28][29]. Based on this precedent and the assumption that DHNO oxidizes the C2–C3 bond, Koetter and Schultz [27] proposed the mechanism shown in Scheme 5 for DHNO. However, members of the p-cresol methylhydroxylase

• more consistent with the simple mechanism of Scheme 4 (Fitzpatrick et al., manuscript in preparation). The proposed quinone methide is not detected during stopped-flow analyses of either the wild-type enzyme or the E352Q variant, (R)-6-chloronicotine and (R)-nicotine, which would not form the quinone