Functionalization of imidazole N-oxide: a recent discovery in organic transformations

• Koustav Singha,
• Imran Habib and
• Mossaraf Hossain

Beilstein J. Org. Chem. 2022, 18, 1575–1588, doi:10.3762/bjoc.18.168

• presence of 1.0 mmol AcCl as eliminating agent (EA) in dry THF as solvent at −78 °C; (II) in case of path B, the mixture of 1.0 mmol of 2,2-dimethyl-4-phenyl-2H-imidazole 1-oxide (9a) and 1.0 mmol of pentafluorobenzene (12), 1.1 mmol of n-BuLi as base, 1.5 equiv DDQ as oxidant in dry THF as solvent was

• leaving groups. The eliminating agent (AcCl) led to O-acylation of the intermediate 14 and resulted in deoxygenation through the release of AcOH giving 2H-imidazole derivatives. On the other hand, in case of “addition–oxidation” (SNH AO, path B), the oxidant DDQ picked up a proton from intermediate 14 to

Dissecting Mechanochemistry III

• Lars Borchardt and
• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1454–1456, doi:10.3762/bjoc.18.150

• ) from an initial mechanical treatment of trichloroheptazine and Na3P, once again highlighting the importance of halogenated organic molecules as building blocks for graphitic heptazine materials (Scheme 4) [8]. Another halogenated molecule, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), proved to be

• intermolecular C–N coupling reactions using DDQ as an oxidant.

Synthesis of meso-pyrrole-substituted corroles by condensation of 1,9-diformyldipyrromethanes with pyrrole

• Baris Temelli and
• Pinar Kapci

Beilstein J. Org. Chem. 2022, 18, 1403–1409, doi:10.3762/bjoc.18.145

• the bilane intermediate by using DDQ (Scheme 2). Pyrrole was used as both reagent and solvent in these reactions. The desired product was not observed in the reaction medium when various catalysts (TFA, I2, AlCl3, InCl3, FeCl3, H2SO4, p-TsOH, Mont. KSF, Mont. K-10, and AgOTf) were used at different

• further increase in the amount of catalyst did not affect the yield (Table 1, entries 11–13). In order to determine the effect of the oxidant type and the oxidant amount, reactions were carried out with 3 and 4 equivalents of DDQ and p-chloranil. While more than 2 equivalents of DDQ did not have a

• positive effect on the reaction yield (Table 1, entries 14 and 15), p-chloranil formed a product with a lower yield than DDQ (Table 1, entries 16–18). The activities of different copper catalysts were also tested in the model reaction. Only CuCl2 formed the product in 5% yield and the other salts did not

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

• Péter Kisszékelyi,
• Tibor Peňaška,
• Klára Stankovianska,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 1195–1202, doi:10.3762/bjoc.18.124

• . The use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in 1,4-dioxane afforded the dimer 11a in a slightly better yield of 46% (Scheme 2). For all the prepared benzothiazine derivatives 10 we observed some degree of instability. The derivatives were reasonably stable in the solid state but usually

Facile and diastereoselective arylation of the privileged 1,4-dihydroisoquinolin-3(2H)-one scaffold

• Dmitry Dar’in,
• Grigory Kantin,
• Alexander Bunev and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2022, 18, 1070–1078, doi:10.3762/bjoc.18.109

• the exclusive isolable product when benzene was eliminated from the reaction mixture (Table 1, entry 6). Interestingly, the formation of byproduct 15 (which could be, in principle, obtained by DDQ oxidation of 11 [25]) via the elimination of a diazo group has not been reported. Having identified the

Copper-catalyzed multicomponent reactions for the efficient synthesis of diverse spirotetrahydrocarbazoles

• Shao-Cong Zhan,
• Ren-Jie Fang,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2022, 18, 796–808, doi:10.3762/bjoc.18.80

• -arylidene-1,3-dimethylbarbituric acid and 4-methylbenzaldehyde under the standard reaction conditions and further oxidation with DDQ generated the final aromatized product 3a in 75% yield. Under the same reaction conditions, similar aromatized products 3b and 3c were also produced in good yields with

• . On the other hand, the tetrahydrospiro[carbazole-3,5'-pyrimidine] 4 can be converted to aromatized spiro[carbazole-3,5'-pyrimidine] 3 through the oxidation of DDQ. In the absence of the effective dienophile, the normal Friedel–Crafts alkylation of 2-methylindole with aromatic aldehyde gives the well

• reduced pressure, the mixture of the above obtained product and DDQ (1.0 mmol, 0.227 g, 2.0 equiv) in dry acetonitrile (10.0 mL) was stirred at room temperature for about four hours. After removing the solvent by evaporating at reduced pressure, the residue was subjected to column chromatography with

DDQ in mechanochemical C–N coupling reactions

• Shyamal Kanti Bera,
• Rosalin Bhanja and
• Prasenjit Mal

Beilstein J. Org. Chem. 2022, 18, 639–646, doi:10.3762/bjoc.18.64

• -Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a commonly known oxidant. Herein, we report that DDQ can be used to synthesize 1,2-disubstituted benzimidazoles and quinazolin-4(3H)-ones via the intra- and intermolecular C–N coupling reaction under solvent-free mechanochemical (ball milling) conditions. In

• the presence of DDQ, the intramolecular C(sp2)–H amidation of N-(2-(arylideneamino)phenyl)-p-toluenesulfonamides leads to 1,2-disubstituted benzimidazoles and the one-pot coupling of 2-aminobenzamides with aryl/alkyl aldehydes resulted in substituted quinazolin-4(3H)-one derivatives in high yields

• . Keywords: ball mill; 1H-benzo[d]imidazole; C(sp2)–H amidation; DDQ; mechanochemistry; quinazolin-4(3H)-one; Introduction The reawakening approaches to use solvent-free and environmentally benign conditions in organic synthesis have facilitated new opportunities [1][2][3][4]. The research area of

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• -rich phenols, as well as those bearing halogen substituents, were suitable substrates under these reaction conditions. In Lei’s report, the reaction shuts down in the presence of TEMPO and in the absence of DDQ; thus, the formation of a phenoxy radical was proposed. In 2018, Zhong and co-workers

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• diastereoselectivity and 99% ee in the presence of the chiral phosphoric acid CPA 2. Subsequently, using the chiral phosphoric acid-catalyzed [3 + 2] formal cycloaddition and a moderate DDQ oxidation method over 34, enantiomerically enriched 2,3-diarylbenzoindoles 35 were successfully prepared by performing a central

• accelerating imine formation (I-19), and under the catalysis of a chiral phosphoric acid, intramolecular nucleophilic addition occurs to form I-20, followed by oxidative dehydrogenation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). In the presence of 10 mol % chiral phosphoric acid CPA 7, the axially

• to provide stable atropisomeric quinolines after oxidation by DDQ [86]. 3. Enantioselective synthesis of axially chiral arylalkene and N-arylamines Although many elegant strategies have been developed to enable the atroposelective construction of axially chiral biaryls and heterobiaryls [87][88][89

Electrocatalytic C(sp³)–H/C(sp)–H cross-coupling in continuous flow through TEMPO/copper relay catalysis

• Bin Guo and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2021, 17, 2650–2656, doi:10.3762/bjoc.17.178

• the oxidation of the tetrahydroisoquinoline to an iminium intermediate with various chemical oxidants such as peroxides and DDQ followed by reaction with the copper acetylide species to deliver the 2-substituted tetrahydroisoquinoline product (Scheme 1A). These methods usually require elevated

• electrochemical microreactors can be a viable tool for developing efficient transition-metal electrocatalysis. C(sp3)–H alkynylation of tetrahydroisoquinolines. L* = chiral ligand. TEMPO = 2,2,6,6-tetramethylpiperidine 1-oxyl. DDQ = 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. BPO = benzoyl peroxide. Substrate

Efficient synthesis of polyfunctionalized carbazoles and pyrrolo[3,4-c]carbazoles via domino Diels–Alder reaction

• Ren-Jie Fang,
• Chen Yan,
• Jing Sun,
• Ying Han and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2021, 17, 2425–2432, doi:10.3762/bjoc.17.159

• diastereoisomers of tetrahydropyrrolo[3,4-c]carbazoles, which can be dehydrogenated by DDQ oxidation in acetonitrile at room temperature to give the aromatized pyrrolo[3,4-c]carbazoles in high yields. On the other hand, the one-pot reaction of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones with chalcones or

• benzylideneacetone in acetonitrile in the presence of p-TsOH and DDQ resulted in polyfunctionalized carbazoles in satisfactory yields. The reaction mechanism included the DDQ oxidative dehydrogenation of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones to the corresponding 3-vinylindoles, their acid-catalyzed Diels–Alder

• efficient domino reactions for the synthesis of biologically important carbazole derivatives [48][49][50][51][52][53], herein we wish to report the DDQ-mediated dehydrogenative Diels–Alder reaction of 3-(indol-3-yl)maleimides and benzoyl-substituted 3-ethylindoles with readily available chalcones for the

Strategies for the synthesis of brevipolides

• Yudhi D. Kurniawan and
• A'liyatur Rosyidah

Beilstein J. Org. Chem. 2021, 17, 2399–2416, doi:10.3762/bjoc.17.157

• using DDQ to form alcohol 40. At this point, the stereogenic center at the C6’ carbon required an inversion to match the target molecule. Thus, a standard Mitsunobu procedure followed by basic methanolysis were conducted. The desired inverted product 16, however, did not form. The authors hypothesized a

• -closing metathesis of this compound installed the 5,6-dihydro-α-pyrone moiety, and TBS removal followed by esterification with 4-methoxycinnamic acid provided compound 92. After removal of the PMB group using DDQ, the natural brevipolide H (8) was successfully achieved. Sabitha’s strategy to brevipolide M

• furnish the terminal epoxide 115 in 85% from 109. Then, the epoxide ring was opened with deprotonated propargylic ether 116. Global removal of the PMB functionality with DDQ gave triol 117. The partial reduction of the triple bond in 117 to the (Z)-olefin derivative was achieved using Lindlar catalyst and

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• corresponding cyclotrimerization products 18 or 19 (Scheme 4). The subsequent DDQ oxidation step yielded anthracenes 20 or azaanthracenes 21 in good yields (see the representative examples 20a–d and 21a–d) [38]. Recently, in a related approach, Bunz, Freudenberg, and co-workers described a useful route to

• products 24. Next, the key step was introducing chlorine, bromine, or iodine substituents by halodesilylation of 24. With the halogenated products 25 in hands, the authors employed DDQ in the oxidation/aromatization step, to obtain the di- and tetrahaloanthracenes 26 in good yields (61–85%) [39]. This

• 138. Then, an oxidative cyclization of 138 in the presence of FeCl3 afforded dibenzo[a,c]anthracenes 139a and 139b in moderate yields (58–68%). On the other hand, they obtained dibenzo[a,c]anthracenes 139c–e in low to moderate yields (15–54%) when they used DDQ/MeSO3H instead of FeCl3 [66]. In a study

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• and B) [145]. The authors successfully applied a manganese salt in catalytic amounts, allied with the use of an electrical current in combination with blue LED lights and an organic photocatalyst (DDQ), affording azidated alkyl moieties in excellent yields and chemoselectivity through alkyl C–H bonds

Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones

• Girish Suresh Yedase,
• Sumit Kumar,
• Jessica Stahl,
• Burkhard König and
• Veera Reddy Yatham

Beilstein J. Org. Chem. 2021, 17, 1727–1732, doi:10.3762/bjoc.17.121

• thermal conditions. Significant advances were made for the oxidation of benzylic alcohols by using metal-based photocatalysts [38][39][40][41][42][43][44][45][46] and metal-free photocatalysis [47][48][49][50][51][52][53] in combination with various oxidants, such as TBHP and DDQ [54][55]. However, the

Structural effects of meso-halogenation on porphyrins

• Keith J. Flanagan,
• Maximilian Paradiz Dominguez,
• Zoi Melissari,
• Hans-Georg Eckhardt,
• René M. Williams,
• Dáire Gibbons,
• Caroline Prior,
• Gemma M. Locke,
• Alina Meindl,
• Aoife A. Ryan and
• Mathias O. Senge

Beilstein J. Org. Chem. 2021, 17, 1149–1170, doi:10.3762/bjoc.17.88

• addition, the cold bath was removed and stirring was continued for an additional 45 min. Subsequently, pre-dried DDQ (291 mg, 1.28 mmol, 6.4 equiv) was added, resulting in a color change from green/brown to dark purple/brown. Stirring was continued for 1 h, and the solvent was removed under reduced

• atom during the study being DCM [56]. Another study suggests that the chlorinated product may be formed from a Cl radical generated during the reaction, although it was not stated if the origin of the radical was DCM or DDQ [57]. Here, it was shown that the source of Cl to yield the meso-chlorinated

• porphyrin was DDQ, given the absence of DCM. Investigations into why similar compounds as 4 were not frequently observed in previous research, and into the targeted synthesis of species 4 by DDQ are currently ongoing. Alternative methods to achieve the chloro derivatives of porphyrins have been reported by

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

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

• converted to novel oxazole-fused derivatives 19 and 20, respectively, by condensation with benzaldehyde and subsequent 2,3-dichloro-5.6-dicyano-p-benzoquinone (DDQ)-mediated oxidation (Scheme 3). Aldehyde building block 16 was a versatile starting material for further cyclization reactions. Synthesis of

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

• activation via DDQ oxidation, followed by nucleophilic attack of an unactivated olefin to obtain all-cis-trisubstituted Prins products with high stereochemical precision [111]. A single-electron transfer (SET) mechanism was proposed for the above transformation (Scheme 69). A SET from an arene or alkene to

• DDQ and the subsequent abstraction of hydride from the benzylic or allylic position generated a charge-transfer complex 298. The complex 298 formed a tin-containing ate oxocarbenium ion complex 299 with SnBr4, and then rapid C–C bond formation took place to generate the cyclic intermediate 300. The

• cyclopropane carbaldehydes and propargyl alcohol. Mullen and Gagné's (R)-[(tolBINAP)Pt(NC6F5)2][SbF6]2-catalyzed asymmetric Prins cyclization strategy to chromans. Yu and co-workers’ DDQ-catalyzed asymmetric Prins cyclization strategy to trisubstituted THPs. Lalli and Weghe’s chiral-Brønsted-acid- and achiral

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

• mmol DDQ, 20 mL CH2Cl2, room temperature, 30 min. Proposed mechanism for the formation of 13. Synthesis of cycloadducts 3a–l. Some photophysical properties of cycloadducts 3c–3f and 3k. Supporting Information Supporting Information File 52: Experimental procedures, copies of 1H NMR, 13C NMR, and HRMS

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

• ′-tetramethylethylenediamine (TMEDA) as shown in the Scheme 1. Having the compound 4 in hand, it was subjected to the cyclization in the presence of boron trifluoride to provide the tricyclohexyl-fused benzene derivative which on further dehydrogenation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) afforded 1,5,9

• accessible compound, namely norbornadiene (10) by involving oxidative aromatization in the presence of DDQ via an intermediate 17, as displayed in Scheme 2. As can be seen from an inspection of Scheme 2, they first performed a single step cyclotrimerization of 10 using n-BuLi and t-BuOK in 1,2-dibromoethane

• hexahydrosumanene 17 which on subsequent aromatization using DDQ furnished the desired molecule sumanene (2) in good yield. To their surprise, tandem metathesis for achieving compound 17 from 13 (anti) was fruitless may be because of the endothermic reaction by 37.4 kcal/mol as compared to the exothermic (51.4 kcal

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• ). However, the use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) at 25 °C for 48 h led to the aromatized compound 21a in high yield (Table 4, entry 3). Under similar reaction conditions, the series of pyrrolo[3,4-e]indole-1,3-diones 21b–g was resulted in high yields (Table 4, entries 4 and 6–10

• using manganese oxide or DDQ as the oxidizing reagents, or even including Pd/C at high temperatures (250 °C) [45], failed to obtain the series of indoles 23. It is likely that the electron withdrawing effect of the formyl group at the C-7 position counterbalance the delocalization direction of the

• aromatization of pentacycles 11 was explored. Although the use of DDQ under the oxidative reaction conditions shown in Table 4 was efficient for the preparation of derivatives 21, the conversion of 11a into 12 was unsuccessful (Scheme 7). The action of active MnO2 in toluene at high temperature was able to

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• quinazolinone 73a (Scheme 27) [118]. The method for oxidative cyclization of thiohydroximic acids 75 under the action of DDQ and p-TsOH with the formation of the corresponding 1,4,2-oxathiazoles 76 was developed (Scheme 28) [119]. The authors noted that reaction in the absence of p-TsOH proceeded with lower

• yield of 76. A radical mechanism was proposed in which the oxime moiety is oxidized by DDQ to the iminoxyl radical 77, which undergoes 1,5-HAT to give a C-centered radical 78 stabilized by a sulfur atom. 78 is oxidized by DDQ to a carbocation 79, followed by the closure of the oxathiazole ring (Scheme

•  29). Later, DDQ-mediated oxidative cyclization of amidoximes with the formation of 1,2,4-oxadiazoles (analogous transformation with K3PO4/O2 system was shown above in Scheme 26) was realized without the addition of TsOH [120]. Isoxazolines 82 were synthesized by a one-pot sequence, which included the

Synthesis and properties of tetrathiafulvalenes bearing 6-aryl-1,4-dithiafulvenes

• Aya Yoshimura,
• Hitoshi Kimura,
• Kohei Kagawa,
• Mayuka Yoshioka,
• Toshiki Itou,
• Dhananjayan Vasu,
• Takashi Shirahata,
• Hideki Yorimitsu and
• Yohji Misaki

Beilstein J. Org. Chem. 2020, 16, 974–981, doi:10.3762/bjoc.16.86

• ion complexes with DDQ or iodine were reported [17][18][19][20][21][22][23][24]. Peripherally thiophene-functionalized TTFs, as potential precursors to conducting polymers, and organic metals were also prepared and characterized [25][26][27][28][29]. To design more tempting molecules, the attachment