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

Fe(II)/Et₃N-Relay-catalyzed domino reaction of isoxazoles with imidazolium salts in the synthesis of methyl 4-imidazolylpyrrole-2-carboxylates, its ylide and betaine derivatives

• Ekaterina E. Galenko,
• Olesya A. Tomashenko,
• Alexander F. Khlebnikov,
• Mikhail S. Novikov and
• Taras L. Panikorovskii

Beilstein J. Org. Chem. 2015, 11, 1732–1740, doi:10.3762/bjoc.11.189

• ][27] and coenzyme pyrroloquinoline quinone [28]. The synthesis of 4-imidazolylpyrrole-2-carboxylic acid derivatives usually involves the corresponding pyrrole with a functional group allowing the formation of a imidazole ring [8][9]. Recently we developed a new approach to 3-(1H-pyrrol-3-yl)-1H

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• -acetyldopamine (B) into an O-quinone derivative which reacted itself with the arylamine (A) through a Michael addition mechanism and the acridine core was formed via a nucleophilic condensation process. The addition step was also facilitated by CeCl3 used here as a Lewis acid. The last step, characterized by the

• converted into an amide in the presence of methylaminoacetaldehyde dimethylacetal. A ring closure occurs by treating the amide with a strong acid. The reaction gave a mixture of a quinone and a dimethoxy intermediate that were first reduced to amine products. Furthermore, the dimethoxy intermediate was

• subjected to cerium ammonium nitrate for oxidative demethylation and the amino quinone formed cyclized to afford neoamphimedine (12, Scheme 4) [62]. Two synthetic routes, illustrated in Scheme 2 and Scheme 3, were used to prepare neoamphimedine (12) where the second description was shorter and more

A facile synthetic route to benzimidazolium salts bearing bulky aromatic N-substituents

• Gabriele Grieco,
• Olivier Blacque and
• Heinz Berke

Beilstein J. Org. Chem. 2015, 11, 1656–1666, doi:10.3762/bjoc.11.182

• much as possible. In addition to the 1,3-benzoimidazolium salts prepared by Chianese and co-workers, polycyclic diaminocarbenes were reported possessing mesityl substituents in the N1,N2-positions and in addition benzoquinone [39][40] or quinone [41] imidazole annulated systems or those with an

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

• macrocycle 211 (39%, Scheme 33). Kotha and Shirbhate [169] have reported the longithorone framework by using RCM as a key step. Dibromo compound 212 was reacted with monoalkylated ethyl acetoacetate 213 in the presence of NaH to deliver bis-alkyated product 214, followed by an oxidation the quinone

• derivative 215 (67%) was obtained. Next, the quinone 215 was subjected to RCM to generate the cyclized product 216 (71%, Scheme 34). Nicolaou and Xu [170] assembled the floresolide B 219 via RCM as a key step. Compound 217 underwent cyclization in the presence of G-II (13) in DCM heated under reflux to

• -workers [195]. This unusual heptacyclic marine natural product is a cytotoxic agent. Its synthesis is considered difficult due to the stereocenters present in the ring system of longithorone A and E. Moreover, hindered rotation around the quinone moiety adds even more complexity to its synthesis. Recently

Glycoluril–tetrathiafulvalene molecular clips: on the influence of electronic and spatial properties for binding neutral accepting guests

• Yoann Cotelle,
• Marie Hardouin-Lerouge,
• Stéphanie Legoupy,
• Olivier Alévêque,
• Eric Levillain and
• Piétrick Hudhomme

Beilstein J. Org. Chem. 2015, 11, 1023–1036, doi:10.3762/bjoc.11.115

• a glycoluril-based framework possessing quinone moieties for developing a Diels–Alder cycloaddition strategy. Thus compound 12 [33] was prepared in 73% yield by treatment with an excess of hydroquinone in 1,2-dichloroethane using a Friedel–Crafts alkylation as an electrophilic aromatic substitution

Adsorption mechanism and valency of catechol-functionalized hyperbranched polyglycerols

• Stefanie Krysiak,
• Qiang Wei,
• Klaus Rischka,
• Andreas Hartwig,
• Rainer Haag and
• Thorsten Hugel

Beilstein J. Org. Chem. 2015, 11, 828–836, doi:10.3762/bjoc.11.92

• –quinone. Similar to the measurement of Lee et al., the higher forces in our measurement occurred at the beginning of the measurement and the lower forces at the end. This is consistent with longer term oxidation as in the measurements by Wilke et al. [13]. An increasing pH shifted the equilibrium between

• DOPA and DOPA–quinone towards the oxidized quinone. While the lower force peak values were roughly comparable (290 pN vs 210 pN), our high force peak was considerably smaller than that of Lee et al. (410 pN vs 760 pN). The reasons for this could be differences in experimental parameters like the force

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

• Danielle L. Paterson and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 265–270, doi:10.3762/bjoc.11.29

• aryl group and arylethyl substituent at C-8 adopt an anti relationship (Figure 6). Loss of stereochemistry at C-10 is most likely due to the formation of a quinone methide, such as 24, which upon attack by the C-11 alcohol gives a mixture of isomers with the isomer 7a being favoured over the more

Natural phenolic metabolites with anti-angiogenic properties – a review from the chemical point of view

• Qiu Sun,
• Jörg Heilmann and
• Burkhard König

Beilstein J. Org. Chem. 2015, 11, 249–264, doi:10.3762/bjoc.11.28

• synthesis of 4-amino-2-sulfanylphenol compounds (Scheme 6) [53] starts from the 4-aminophenol hydrochloride salt (25), which reacted with various substituted sulfonyl chlorides in pyridine, yielding compound 26 that differs in the substituent R1. Oxidation by NaIO4/SiO2 gives the quinone-type structures 27