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

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• quinone 116 afforded esters 117. This method was also applied to the synthesis of esters 117a–c from amino alcohols (Scheme 25) [115][116]. Different conditions were proposed for the cross-dehydrogenative C–O coupling of aldehydes with alcohols and phenols catalyzed by N-heterocyclic carbenes (118, 129

Design and synthesis of novel bis-annulated caged polycycles via ring-closing metathesis: pushpakenediol

• Sambasivarao Kotha and
• Mirtunjay Kumar Dipak

Beilstein J. Org. Chem. 2014, 10, 2664–2670, doi:10.3762/bjoc.10.280

• the corresponding 2,5-diallyl-1,4-benzoquinone (18) was obtained in good yield (67%). Since the quinone 18 is prone to polymerization (it gave a long streak on TLC when exposed to air at rt), it was immediately subjected to the [4 + 2] cycloaddition reaction with freshly prepared 1,3-cyclopentadiene

Oxidative phenylamination of 5-substituted 1-hydroxynaphthalenes to N-phenyl-1,4-naphthoquinone monoimines by air and light “on water”

• Julio Benites,
• Juan Meléndez,
• Cynthia Estela,
• David Ríos,
• Luis Espinoza,
• Iván Brito and
• Jaime A. Valderrama

Beilstein J. Org. Chem. 2014, 10, 2448–2452, doi:10.3762/bjoc.10.255

• phenylamines “on water” [8] represent two valuable examples on the scope of green methodologies in the field of quinone synthesis. 1,4-Naphthoquinones possessing a substituted amino group in the 2-position have been the subject of study for many years due to their use in a variety of medical and biological

• concluded that the oxidative arylamination of 1,5-DHN (1) is favorable with arylamines containing electron-donor substituents. Bearing in mind that the formation of the quinone monoimines 6–10 under the above experimental conditions requires aerial oxidation reactions, most likely mediated by oxygen species

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• the 5- and 8-positions by H–D exchange [19]. Furthermore, dehydration of 5-(1-hydroxyethyl)-1-naphthol (34) is very efficient, leading to quinone methide 35 which is trapped by solvent MeOH (Scheme 8). The corresponding 4-(1-hydroxyethyl)-1-naphthol, however, is unreactive. Comparisons of the two

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• relatively high [35]. It must be noted that IIc contains additional substitution at the ortho-dihydroxyphenol moiety, which probably further decreases the possibilities for resonance stabilization compared to unsubstituted α-hydroxychalcone (quinone methide formation is disabled). Interestingly, the course

Flexible synthesis of anthracycline aglycone mimics via domino carbopalladation reactions

• Markus Leibeling and
• Daniel B. Werz

Beilstein J. Org. Chem. 2013, 9, 2194–2201, doi:10.3762/bjoc.9.258

• -Diels–Alder reaction of an aryldiacetylene system (Scheme 2) [15]. Compound 7 reacts at high temperature in a mixture consisting of toluene and triethylamine to an inseparable mixture of cyclized diol (52%) and quinone 8 (36%). Quantitative oxidation of the diol by MnO2 provided the desired tetracycle 8

• carbopalladation sequence generating both, the B and the C-ring of the system in a single step. Further derivatisation included the cleavage of the silyl ether and two-fold benzylic oxidation to the quinone moiety. We believe that these natural product mimics might be of interest as useful candidates for drug

Anodic coupling of carboxylic acids to electron-rich double bonds: A surprising non-Kolbe pathway to lactones

• Robert J. Perkins,
• Hai-Chao Xu,
• John M. Campbell and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2013, 9, 1630–1636, doi:10.3762/bjoc.9.186

• originating from 19i benefited from the use of more base. It appears that the use of base reduced the formation of a quinone methide from the product. For example, when a full equivalent of base was used for the reaction, the desired product was obtained in 74% isolated yield. It is clear that the success of

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• hydrocarbons, Xu and co-workers developed other redox initiators in addition to the NHPI/quinone systems previously described. In 2005 they reported the selective oxygenation of ethylbenzene to the corresponding acetophenone by means of a NHPI/o-phenanthroline-mediated organocatalytic system, in the presence

Methylidynetrisphosphonates: Promising C₁ building block for the design of phosphate mimetics

• Vadim D. Romanenko and
• Valery P. Kukhar

Beilstein J. Org. Chem. 2013, 9, 991–1001, doi:10.3762/bjoc.9.114

• prepared in good yield by the Arbuzov reaction of trimethylsilyl esters of trivalent phosphorus acids with the easily accessible 2,6-di-tert-butyl-4-(dichloromethyl)phenol. In the next step, the bisphosphonate 16 was oxidized with K3Fe(CN)6 into quinone methide 17 in 91% yield. Further addition of diethyl

• interactions of quinone methide 17 with diphenylphosphinite and quinone methide 19 with diethyl phosphite (Scheme 10) [33]. However, when the same researchers tried to obtain triphosphorus derivatives with one phosphono and two phosphinoxido groups using quinone methides 19 and 21 as starting materials

• , phosphonylation of the aromatic nucleus via splitting off a tert-butyl group as isobutene and formation of bisphosphonates 22 and 23 was observed. The same happened when quinone methide 21 was treated with diphenylphosphinite (Scheme 11). The primary step of this reaction, which proceeds under mild alkaline

Asymmetric synthesis of a highly functionalized bicyclo[3.2.2]nonene derivative

• Toshiki Tabuchi,
• Daisuke Urabe and
• Masayuki Inoue

Beilstein J. Org. Chem. 2013, 9, 655–663, doi:10.3762/bjoc.9.74

• -dimethylbenzene-1,4-diol (3) and maleic anhydride lead to the construction of bicyclo[2.2.2]octene 4, which was then transformed into racemic 2 through electrolysis [11]. Alternatively, the Diels–Alder reaction between 3,6-dimethyl-o-quinone monoacetal 5 and 1,1-diethoxyethylene provided bicyclo[2.2.2]octene 6

Synthesis of 2,3-dihydronaphtho[2,3-d][1,3]thiazole-4,9-diones and 2,3-dihydroanthra[2,3-d][1,3]thiazole-4,11-diones and novel ring contraction and fusion reaction of 3H-spiro[1,3-thiazole-2,1'-cyclohexanes] into 2,3,4,5-tetrahydro-1H-carbazole-6,11-diones

• Lidia S. Konstantinova,
• Kirill A. Lysov,
• Ljudmila I. Souvorova and
• Oleg A. Rakitin

Beilstein J. Org. Chem. 2013, 9, 577–584, doi:10.3762/bjoc.9.62

• containing nitrogen in position 2 are the most promising ones for furthering clinical applications [1]. Meanwhile, in terms of further structural and chemical system modifications, the introduction of other heteroatoms (e.g., sulfur) through the heterocyclic ring incorporation to the quinone system has been

• group remained intact whereas three protons of the methyl group and one of the quinone ring disappeared. These observations are in agreement with the thiazole-2-thione structure 10a (Scheme 5). The 13C NMR spectrum confirmed this structure by a characteristic C=S signal at 189.8 ppm. The reaction was

• ) and anthraquinonothiazoles (2) are generated by the same route. The most plausible mechanism is shown in Scheme 7. The key step is assumed to be the insertion of two sulfur atoms of complex 8 between two activated CH groups, the first one being adjacent to the carbonyl group of the quinone ring and

Hydrophobic analogues of rhodamine B and rhodamine 101: potent fluorescent probes of mitochondria in living C. elegans

• Laurie F. Mottram,
• Safiyyah Forbes,
• Brian D. Ackley and
• Blake R. Peterson

Beilstein J. Org. Chem. 2012, 8, 2156–2165, doi:10.3762/bjoc.8.243

• the corresponding dialkyaminophenol with o-tolualdehyde (12) [39]. Oxidative cyclization of triarylmethanes with the quinone oxidant chloranil provided 9 and 10 in modest yield. 8-Hydroxyjulolidine (14) for synthesis of HR101 10 was either purchased commercially or prepared as previously described [40

Bioactive selaginellins from Selaginella tamariscina (Beauv.) Spring

• Chao Yang,
• Yutian Shao,
• Kang Li and
• Wujiong Xia

Beilstein J. Org. Chem. 2012, 8, 1884–1889, doi:10.3762/bjoc.8.217

• [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In the past five years, more than 10 selaginellins (novel pigments with a unique para-quinone methide and alkynylphenol carbon skeleton) have been isolated from several Selaginella species in China [13][14][15][16][17][18][19][20

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• nucleophiles are characterized by two solvent-dependent parameters, the nucleophilicity parameter N and the sensitivity parameter sN [1][2][3]. By defining benzhydrylium ions, structurally related quinone methides, and arylidenemalonates as reference electrophiles, which cover a reactivity range of 32 orders

• responsible for the higher intrinsic barrier and subsequently the lower nucleophilicity of DMAP (39) [94]. The upper part of Figure 23 compares the relative rates for the reactions of various organocatalysts (in THF) with the benzhydrylium ion 18e and the structurally related quinone methide 18k. This

• NHCs, 41, 42, and 43, react quantitatively with the quinone methide 18k, while none of the other Lewis bases, despite their similar nucleophilicities, gives an adduct. The resulting conclusion, that all NHCs are significantly stronger Lewis bases than PPh3 (10b), DMAP (39), and DABCO (38), is confirmed

Organocatalytic asymmetric Michael addition of unprotected 3-substituted oxindoles to 1,4-naphthoquinone

• Jin-Sheng Yu,
• Feng Zhou,
• Yun-Lin Liu and
• Jian Zhou

Beilstein J. Org. Chem. 2012, 8, 1360–1365, doi:10.3762/bjoc.8.157

• of the catalyst to activate quinone 2a and the tertiary amine to deprotonatively activate oxindole 1. The reaction generally proceeded slowly, and only the oxidation product, 1,4-naphthoquinone derivative 3a, was obtained in moderate yield after five days. No hydroquinone product 4 was detected by

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• undergo phototropism with a given direction. The enantiomerically pure 2- and 3-sulfinyl azo compounds are obtained with excellent regioselectivities by using a new and simple method for the synthesis of aromatic azobenzenes based on the treatment of quinone bisacetals 17 and 19 with different

Enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinones to nitroalkenes catalyzed by binaphthyl-derived organocatalysts

• Saet Byeol Woo and
• Dae Young Kim

Beilstein J. Org. Chem. 2012, 8, 699–704, doi:10.3762/bjoc.8.78

• ; Introduction Quinone and naphthoquinone structures exist in a large number of natural products and biologically active molecules [1][2][3][4]. Many of these naturally occurring naphthoquinones and their synthetic analogues are important precursors for the synthesis of natural products and pharmaceuticals [5][6