First thia-Diels–Alder reactions of thiochalcones with 1,4-quinones

• Grzegorz Mlostoń,
• Katarzyna Urbaniak,
• Paweł Urbaniak,
• Anna Marko,
• Anthony Linden and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2018, 14, 1834–1839, doi:10.3762/bjoc.14.156

• cycloadduct was isolated in 37% yield. Keywords: hetero-Diels–Alder reactions; quinone dyes; quinones; sulfur heterocycles; thiochalcones; Introduction Hetero-Diels–Alder reactions are considered to be a powerful methodology widely explored for the synthesis of six-membered heterocycles [1][2] with numerous

• all other initially formed cycloadducts, further oxidative conversion to the quinone structure was not possible in this case. Conclusion The present study demonstrates that 1,4-quinones are prone dienophiles in reactions with aryl/hetarylthiochalcones. These thia-Diels–Alder reactions led to a new

• class of 4H-thiopyran derivatives. The presence of a quinone system is an important structural aspect of this class as it is common in many naturally occurring compounds, e.g., dyes such as alizarin, carminic acid, and isoprenoid dyes, as well as drugs such as doxorubicin. In addition, the presence of

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• anomeric aci-nitroester 131 is formed, which is converted into the corresponding gluconolactone 133 under elimination of a quinone monoxime 132 (Scheme 28). Conclusion In this account, 15 years after Professor Mitsunobu has passed away, we have surveyed the literature on the Mitsunobu reaction for anomeric

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• -benzotropone (12) was also performed (Scheme 36). This condensation followed by incipient oxidation gave the quinone 223 (15%), the bridged bicyclic product 224 (7%), and 225 (28%) [152]. 4. Chemistry of 3,4-benzotropone (13) 4.1. Generation, characterization, and reaction 3,4-Benzotropone (13) is of

• reactions were carried out at various quinone/BF3.OEt2/CH2N2 molar ratios in a different solvent under an atmosphere of nitrogen and with cooling in an ice bath and 3,4-benzotropolonoboron difluoride 281 was obtained in 2–25.5% yield. The hydrolysis of chelate compound 281 was performed with dilute sulfuric

On the design principles of peptide–drug conjugates for targeted drug delivery to the malignant tumor site

• Eirinaios I. Vrettos,
• Gábor Mező and
• Andreas G. Tzakos

Beilstein J. Org. Chem. 2018, 14, 930–954, doi:10.3762/bjoc.14.80

• . Furthermore, they stabilize the topoisomerase II DNA complex preventing the transcription. They may also increase quinone type free radical production, however, this plays a role rather in their cytotoxic side effects. Daunorubicin is mainly used in the treatment of leukemia [95] while doxorubicin in the cure

Nanoreactors for green catalysis

• M. Teresa De Martino,
• Loai K. E. A. Abdelmohsen,
• Floris P. J. T. Rutjes and
• Jan C. M. van Hest

Beilstein J. Org. Chem. 2018, 14, 716–733, doi:10.3762/bjoc.14.61

• of glucose oxidase (GOx) to convert glucose into D-glucono-δ-lactone and hydrogen peroxide was the first step of the reaction (Scheme 3A); subsequently, myoglobin (Myo) employed the hydrogen peroxide produced to oxidize guaiacol to quinone and water (Scheme 3B). When the pH was below 7, the

Mannich base-connected syntheses mediated by ortho-quinone methides

• Petra Barta,
• Ferenc Fülöp and
• István Szatmári

Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43

• Mannich reactions where the process involves an ortho-quinone methide (o-QM) intermediate. The reactions are classified on the basis of the o-QM source followed by the reactant, e.g., the dienophile partner in cycloaddition reactions (C=C or C=N dienophiles) or by the formation of multicomponent Mannich

• adducts. Due to the important pharmacological activities of these reactive o-QM intermediates, special attention is paid to the biological activity of these compounds. Keywords: aminophenols; [4 + 2] cycloaddition; dienophile; Mannich reaction; ortho-quinone methide; Review Introduction The Mannich

• and the aldehyde yields a Schiff base and then the latter reacts with 2-naphthol in the second nucleophilic addition step. The other theory assumes the formation of an ortho-quinone methide (o-QM) intermediate by the reaction of 2-naphthol and benzaldehyde. Re-aromatization, the driving force of the

Quinone-catalyzed oxidative deformylation: synthesis of imines from amino alcohols

• Xinyun Liu,
• Johnny H. Phan,
• Benjamin J. Haugeberg,
• Shrikant S. Londhe and
• Michael D. Clift

Beilstein J. Org. Chem. 2017, 13, 2895–2901, doi:10.3762/bjoc.13.282

• Xinyun Liu Johnny H. Phan Benjamin J. Haugeberg Shrikant S. Londhe Michael D. Clift Department of Chemistry, The University of Kansas, 2010 Malott Hall, 1251 Wescoe Hall Drive, Lawrence, KS, 66045, United States 10.3762/bjoc.13.282 Abstract A new method for imine synthesis by way of quinone

• synthetic versatility of quinone-catalyzed oxidative C–C bond cleavage. Keywords: catalysis; deformylation; organic synthesis; organocatalysis; Introduction Imines are extremely versatile intermediates in organic chemistry [1][2][3]. Consequently, many synthetic methods have been developed for the

• high-value imine products under catalytic conditions has the potential to be broadly useful. Herein, we report a new method that utilizes quinone catalysis to enable the synthesis of imines via oxidative deformylation of amino alcohols. Our group has recently reported the quinone-catalyzed

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

• conditions tolerated a broad range of functional groups and the yields ranged from 31 to 68% (Scheme 50). During the process, the quinone was converted into hydroquinone and a regeneration process was established by passing through a cartridge of MnO2. A mechanism for this transformation was proposed as a

Main group mechanochemistry

• Agota A. Gečiauskaitė and
• Felipe García

Beilstein J. Org. Chem. 2017, 13, 2068–2077, doi:10.3762/bjoc.13.204

• ) directly from germanium metal or germanium dioxide (GeO2) was recently reported [87]. Milling of germanium powder or GeO2 with quinone or catechol, respectively, in the presence of a Lewis base under LAG conditions, produced a series of germanium complexes (see Scheme 5). These complexes are inherently

Oxidative dehydrogenation of C–C and C–N bonds: A convenient approach to access diverse (dihydro)heteroaromatic compounds

• Santanu Hati,
• Ulrike Holzgrabe and
• Subhabrata Sen

Beilstein J. Org. Chem. 2017, 13, 1670–1692, doi:10.3762/bjoc.13.162

• , ammonium acetates, o-aminothiophenols and various aldehydes, respectively (Scheme 18). In another example an ortho-quinone-based bioinspired catalyst was used in the oxidative dehydrogenation of tetrahydroisoquinolines 67 to dihydroisoquinoline 68 in acetonitrile at 60 °C under oxygen atmosphere (Scheme 19

• , phd = 1,10-phenanthroline-5,6-dione. Oxidative dehydrogenation with Flavin mimics. o-Quinone based bioinspired catalysts for the synthesis of dihydroisoquinolines. Cobalt-catalyzed aerobic dehydrogenation of Hantzch 1,4-DHPs and pyrazolines. Mechanism of cobalt-catalyzed aerobic dehydrogenation of

Nitration of 5,11-dihydroindolo[3,2-b]carbazoles and synthetic applications of their nitro-substituted derivatives

• Roman A. Irgashev,
• Nikita A. Kazin,
• Gennady L. Rusinov and
• Valery N. Charushin

Beilstein J. Org. Chem. 2017, 13, 1396–1406, doi:10.3762/bjoc.13.136

• 6,12-dinitro-ICZs, giving the ICZ-quinone diimine A. Then the intermediate A is hydrolyzed under acidic conditions into ICZ-quinone B, which is reduced into 6,12-unsubstituted ICZ derivatives (Scheme 6). The suggested mechanism is only a hypothesis, which is based on a similar reduction of

Total synthesis of elansolids B1 and B2

• Liang-Liang Wang and
• Andreas Kirschning

Beilstein J. Org. Chem. 2017, 13, 1280–1287, doi:10.3762/bjoc.13.124

• elansolids B1 (2) and B2 (3) along with A3 (4) bearing the unusual p-quinone methide unit were isolated from the fermentation broth. All elansolids belong to the group of trans-polyketides type I [3][4][5][6]. For the first generation total synthesis of elansolid B1 (2) we utilized an endo-selective

• saponification of all ester groups in the presence of isopropanol successfully yielded elansolid B1 (2). When isopropanol was exchanged by methanol, elansolid B2 (3) was generated. Its formation can be rationalized by formation of the intermediate p-methide quinone which selectively trapped methanol, exclusively

• configured trienes present in polyketides [12][13][14][15]. Furthermore, we show how the intermediate p-methide quinone can be exploited to also prepare elansolid B2 (3). The improved synthesis allows more easily preparing analogues of the elansolids for further biological evaluation. Experimental General

Ultrasound-promoted organocatalytic enamine–azide [3 + 2] cycloaddition reactions for the synthesis of ((arylselanyl)phenyl-1H-1,2,3-triazol-4-yl)ketones

• Gabriel P. Costa,
• Natália Seus,
• Juliano A. Roehrs,
• Raquel G. Jacob,
• Ricardo F. Schumacher,
• Thiago Barcellos,
• Rafael Luque and
• Diego Alves

Beilstein J. Org. Chem. 2017, 13, 694–702, doi:10.3762/bjoc.13.68

• -(phenylselanylmethyl)-1,2,3-triazole A (Se-TZ) demonstrated an antidepressant-like effect (Figure 1) [60]. In another example, 5-phenyl-1-(2-(phenylselanyl)phenyl)-1H-1,2,3-triazole-4-carbonitrile B (Se-TZCN) was reported to exhibit antioxidant activities in different in vitro assays (Figure 1) [36]. Selenanyl-quinone

A versatile route to polythiophenes with functional pendant groups using alkyne chemistry

• Xiao Huang,
• Li Yang,
• Rikard Emanuelsson,
• Jonas Bergquist,
• Maria Strømme,
• Martin Sjödin and
• Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 2682–2688, doi:10.3762/bjoc.12.265

• quinone moieties are vulnerable in nucleophilic and acidic environments. Furthermore, the viologen moiety, available from 4,4’-bipyridine (BP) has potential for energy storage and electrochromic applications [35][36], but it has previously been anchored to a polymer backbone only by oxidative coupling via

Protonated paramagnetic redox forms of di-o-quinone bridged with p-phenylene-extended TTF: A EPR spectroscopy study

• Nikolay O. Chalkov,
• Vladimir K. Cherkasov,
• Gleb A. Abakumov,
• Andrey G. Starikov and
• Viacheslav A. Kuropatov

Beilstein J. Org. Chem. 2016, 12, 2450–2456, doi:10.3762/bjoc.12.238

• State University, Gagarina av., 23, Nizhny Novgorod, Russia Southern Scientific Center of Russian Academy of Science, 344006, Chekhov str., 41, Rostov-on-Don, Russia 10.3762/bjoc.12.238 Abstract The chemical oxidation and reduction processes of deprotonated, direduced o-quinone-exTTF-o-quinone in

• protic solvents were studied by EPR spectroscopy. The formation of relatively stable paramagnetic protonated redox forms of the parent triad was very surprising. The character of spin-density distribution in the semiquinone–quinone and semiquinone–catechol redox forms indicates that the p-phenylene

• -extended tetrathiafulvalene connector provides a quite effective electronic communication channel between dioxolene coordination sites. It was found that the deprotonated, direduced o-quinone-exTTF-o-quinone is capable to reduction of the metal copper in solution. The radical anion species formed in this

Bridgehead vicinal diallylation of norbornene derivatives and extension to propellane derivatives via ring-closing metathesis

• Sambasivarao Kotha and
• Rama Gunta

Beilstein J. Org. Chem. 2016, 12, 1877–1883, doi:10.3762/bjoc.12.177

• %) by using our earlier reported method [38]. Next, diallyl compound 2a on RCM using Grubbs first generation (G-I) catalyst in CH2Cl2 at room temperature (rt) gave the desired propellane derivative 1a (61%) along with a minor amount of quinone derivative 4 (17%) (Scheme 1). The formation of quinone 4

• gave the ring-closing product 1b with retention of the configuration. Similarly, staring with substrate 2bb', another propellane derivative 1bb' was synthesized using the same catalyst (i.e., G-I) in CH2Cl2 at rt. Here, along with the desired propellane 1bb' (79%) a minor amount of quinone derivative

• 16 (13%) was also generated due to a one-pot RCM-rDA sequence of 2bb' which is similar to the substrate 2a (Scheme 6). Compound 1bb' was characterized based on the 1H and 13C NMR, DEPT-135 and further supported by HRMS data. However, spectroscopic data of quinone 16 were identical with the literature

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

• nucleophilic migrating groups prefer TS2 (Scheme 5). The dependence of the course of the Baeyer–Villiger oxidation on the type of O−O-bond cleavage in the Criegee intermediate was studied in the oxidation reaction of 1,2-quinone 18 with perbenzoic acid [221]. The reaction gave two oxidation products

Cyclisation mechanisms in the biosynthesis of ribosomally synthesised and post-translationally modified peptides

• Andrew W. Truman

Beilstein J. Org. Chem. 2016, 12, 1250–1268, doi:10.3762/bjoc.12.120

• pyrroloquinoline quinone (PQQ, Figure 2) has a ribosomal origin [17] but has been modified so that no peptide bonds remain. This demonstrates that a huge amount of structural diversity can be introduced into RiPPs, despite an intrinsic requirement to be assembled from the 20 regular proteinogenic amino acids

• –4S] cluster along with simultaneous loss of a proton to rearomatise. An analogous reaction takes place in the biosynthesis of the bacterial cofactor pyrroloquinoline quinone (PQQ), where the SPASM protein PqqE was proposed to catalyse the oxidative cross-linking of carbon bonds on glutamate and

• the biosynthesis of pyrroloquinoline quinone (PQQ). RiPPs with uncharacterised mechanisms of cyclisation. Unusual heterocycles in ComX and methanobactin are indicated in red. RTD-1 is formed by the head-to-tail dimerisation of precursor peptides encoded on two separate genes. Acknowledgements The

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• review, Lou and co-workers reported an additional example of conjugate addition–enantioselective protonation involving an α,β-unsaturated ketone. In the new report, a chiral primary amine catalyzed conjugate addition of a 1,3-diketone nucleophile into an in situ generated ortho-quinone methide was

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

• Bin Yu,
• Hui Xing,
• De-Quan Yu and
• Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

• superior to quinone. The cinnamaldehyde was proved to be more efficient and selective than other aldehydes for the reaction. 3-Hydroxyoxindole-based further transformations Apart from aforementioned asymmetric construction of biologically important 3-hydroxyoxindoles, their use as versatile precursors has

Regiodefined synthesis of brominated hydroxyanthraquinones related to proisocrinins

• Joyeeta Roy,
• Tanushree Mal,
• Supriti Jana and
• Dipakranjan Mal

Beilstein J. Org. Chem. 2016, 12, 531–536, doi:10.3762/bjoc.12.52

• cyanophthalide 12 with acceptor 36 formed hydroquinone 37, which was directly treated with bromine in DCM to give tribrominated quinone 38 in 58% yield (over two steps) (Scheme 6). The structure of bromo compound 38 was proposed on the basis of the high chemical shift (δ = 7.63 ppm) of the proton attached to the

Hydroquinone–pyrrole dyads with varied linkers

• Hao Huang,
• Christoffer Karlsson,
• Maria Strømme,
• Martin Sjödin and
• Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 89–96, doi:10.3762/bjoc.12.10

• : conjugation; heterocycles; hydroquinone; linker effect; pyrrole; Introduction Quinone–pyrrole dyads have attracted interest in various applications due to the possibility of modulating the electronic interaction between the two subunits, with porphyrin–quinone dyads being well-known examples [1][2][3

• ]. Recently, we have shown the suitability of the quinone–hydroquinone redox couple (Figure 1) as the redox active and capacity carrying component in conducting redox polymers (CRPs) [4][5]. To further investigate the interaction between the molecular components in these systems, a series of compounds with

• procedures for the synthesis of quinone–pyrrole dyads with a variety of linkers between the two subunits. The target compounds thus consist of a pyrrole unit as well as a hydroquinone group (protected as dimethyl ether, i.e., dimethoxybenzene, DMB), connected by different linkers, resulting in varying

Recent highlights in biosynthesis research using stable isotopes

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2015, 11, 2493–2508, doi:10.3762/bjoc.11.271

• units, five methyl groups from SAM and one L-tyrosine [53]. Two possible mechanisms for the cyclization of the linear precursor 21 were hypothesized. In route A, an oxidation of the aromatic ring would lead to an electrophilic center at the quinone moiety in 22, which can be attacked by the C-6 hydroxy

2-Hetaryl-1,3-tropolones based on five-membered nitrogen heterocycles: synthesis, structure and properties

• Yury A. Sayapin,
• Inna O. Tupaeva,
• Alexandra A. Kolodina,
• Eugeny A. Gusakov,
• Vitaly N. Komissarov,
• Igor V. Dorogan,
• Nadezhda I. Makarova,
• Anatoly V. Metelitsa,
• Valery V. Tkachev,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2015, 11, 2179–2188, doi:10.3762/bjoc.11.236

• convenient approach to the construction of seven-membered rings of 1,3-tropolone derivatives has been afforded by the acid-catalyzed reaction of o-quinones with methylene active compounds that proceeds with the expansion of the quinone six-membered ring [17][18][19][20]. The study of the reaction had been

• -tetrachloro-1,3-tropolone [25][26], but no comprehensive study of the mechanism of the expansion of the o-quinone rings in this reaction has yet been undertaken. Therefore, one of the purposes of the present work was to gain insight into the major details of the mechanism of the formation of 5,6,7-trichloro

• -chloranil affords the intermediate adducts, 6-(2-hetarylmethylene)-6-hydroxy-2,4-cyclohexadiene-1-ones 7. Such type intermediates were isolated and structurally characterized in the reactions of 2-methylquinoline with 3,5-di-tert-butyl-o-quinone [19] and benzophenones with o-chloranil [22]. The addition of

Total synthesis of panicein A₂

• Lili Yeung,
• Lisa I. Pilkington,
• Melissa M. Cadelis,
• Brent R. Copp and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 1991–1996, doi:10.3762/bjoc.11.215

• cytotoxicity against a number of tumour cell lines. Keywords: modified Claisen rearrangement; sesquiterpene; chromenol; total synthesis; Introduction The panicein family is an unusual family of natural products, which generally consist of an aromatic sesquiterpene group linked to a quinone (as seen in