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

Synthesis of mesomeric betaine compounds with imidazolium-enolate structure

• Nina Gonsior,
• Fabian Mohr and
• Helmut Ritter

Beilstein J. Org. Chem. 2012, 8, 390–397, doi:10.3762/bjoc.8.42

• ) with different halide-containing quinone derivatives and subsequent hydrolysis [11]. Since the quaternization reaction is very common for imidazole chemistry, e.g., synthesis of ionic liquids, we investigated the quaternization reaction of three different imidazole compounds with tetrabromo-1,4

Self-assembly of Ru₄ and Ru₈ assemblies by coordination using organometallic Ru(II)₂ precursors: Synthesis, characterization and properties

• Sankarasekaran Shanmugaraju,
• Dipak Samanta and
• Partha Sarathi Mukherjee

Beilstein J. Org. Chem. 2012, 8, 313–322, doi:10.3762/bjoc.8.34

• , 4H, H4-quinone), 5.75 (d, J = 6.0 Hz, 16H, Hβ-cymene), 2.86–2.79 (septet, 8H, H2-cymene), 2.22 (s, 24H, H3-cymene), 1.31 (d, 48H, H1-cymene); 19F NMR (376.5 MHz, CD3CN) δ −79.08; 13C NMR (100 MHz, CD3NO2) δ 183.92, 140.62, 134.75, 131.45, 124.09, 122.92, 119.74, 103.76, 99.10, 84.88, 83.65, 79.47

Predicting the UV–vis spectra of oxazine dyes

• Scott Fleming,
• Andrew Mills and
• Tell Tuttle

Beilstein J. Org. Chem. 2011, 7, 432–441, doi:10.3762/bjoc.7.56

• ; oxazine; TD-DFT; UV–vis; Introduction Oxazine dyes are a subclass of quinone imines, which are all based upon the p-benzoquinone imine or -diimine scaffold. Other important subclasses within the quinone imines include, the azine dyes and thiazine dyes. The structural relationships described are

• Gaussian 09 program [47]. Finally, we have also employed the orbital overlap diagnostic of Tozer et al. in order to assess the CT character in the principal excited states [27]. Quinone imine structural relationships. Numbering and structure of oxazine dyes studied in this work (counterions not shown

Surfactant catalyzed convenient and greener synthesis of tetrahydrobenzo[a]xanthene-11-ones at ambient temperature

• Pravin V. Shinde,
• Amol H. Kategaonkar,
• Bapurao B. Shingate and
• Murlidhar S. Shingare

Beilstein J. Org. Chem. 2011, 7, 53–58, doi:10.3762/bjoc.7.9

• surfactant was sufficient for catalyzing the reaction effectively. In accordance with the literature [15], a plausible mechanistic path for the formation of tetrahydrobenzo[a]xanthen-11-ones can be outlined as follows: nucleophilic addition of 2-naphthol to the aldehyde to give an intermediate ortho-quinone

Synthesis of 2a,8b-Dihydrocyclobuta[a]naphthalene-3,4-diones

• Kerstin Schmidt and
• Paul Margaretha

Beilstein J. Org. Chem. 2010, 6, No. 76, doi:10.3762/bjoc.6.76

• ; quinone monoacetals; Introduction The behaviour of excited 1,2- and 1,4-quinones towards ground-state molecules differs greatly. Whereas the former typically react via H-abstraction by an excited carbonyl group [1], the latter smoothly undergo [2 + 2] cycloaddition to alkenes to afford cyclobutane-type

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

• are deprotonated, which leads to lactone ring opening and the formation of a colored quinone conjugated carboxylate structure. The chemosensor discriminated terminal diamines by length: 1,8-diaminooctane (Kass = 1270 M−1) and 1,9-diaminononane (Kass = 2020 M−1) showed the highest binding constants in

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• twist angles ranging between 42° and 43° for 1–4 and a slightly lower angle, around 40°, for 5. A larger twist angle of 50.1° is found in dihydro[4]helicene quinones 7 and 8, whereas a wider value, 81.7°, is allowed in tetrahydro[4]helicene quinone 6, because of the higher flexibility arising from the

• different behavior is exhibited by derivative 5, which has bulkier TBDMS substituents; one of them is constrained by the proximity of the quinone ring, whereas the other is pointing towards the molecular periphery and is more free. Three structures with similar energy were obtained, differing essentially in

• the larger dimensions of the [4]helicene quinone derivatives, which possess a wider extension of aromatic rings, capable of establishing stronger dispersion interactions with the host molecules. As to the effect of substituents, we can compare the results obtained for the pairs 1–2, 3–4, and 7–8

Studies on polynuclear furoquinones. Part 1: Synthesis of tri- and tetra- cyclic furoquinones simulating BCD/ABCD ring system of furoquinone diterpenoids

• Faruk H. Shaik and
• Gandhi K. Kar

Beilstein J. Org. Chem. 2009, 5, No. 47, doi:10.3762/bjoc.5.47

• of aryl-furyl C–C bond via Suzuki reaction [35] and the generation of the quinone functionality by oxidation of a phenolic intermediate (Figure 2). Retrosynthesis of the molecule showed that the required phenolic compound can easily be achieved in 7–8 steps starting from 2-bromo-3,4-dihydro-1

• acid (TFA) and trifluoroacetic anhydride (TFAA) at room temperature in 71% yield. The phenol 12 was finally oxidized (with Fremy’s salt) [36][37][38] to the o-quinone 13 to complete the synthesis of phenanthro[1,2-b]furan-10,11-dione. The compounds were characterized by usual spectroscopic and

• ), 7.49 (1H, d, J = 2.0 Hz), 7.45 (1H, m), 6.86 (1H, d, J = 2.0 Hz)]. Some biologically active tetra cyclic furoquinone derivatives (isolated from Dan Shen) and synthetic tricyclic furoquinones. Key strategies for development of C-ring with quinone functionality. Retro synthesis of tetra cyclic