An unusual thionyl chloride-promoted C−C bond formation to obtain 4,4'-bipyrazolones

• Gernot A. Eller,
• Gytė Vilkauskaitė,
• Algirdas Šačkus,
• Vytas Martynaitis,
• Ashenafi Damtew Mamuye,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2018, 14, 1287–1292, doi:10.3762/bjoc.14.110

• prepared. Moreover, the structure of a representative 5,5'-dioxo-4,4'-bipyrazole-4,4'-dicarboxylate was confirmed by X-ray crystal structure analysis. Keywords: dimerization; NMR (1H; 13C; 15N); pyrazolones; thionyl chloride; X-ray structure analysis; Introduction Many biologically active substances

• corresponding dimers of type 3 were obtained in moderate to good yields (Scheme 3). In order to check if these dimerization reactions also occur with other 5-hydroxypyrazoles carrying a C=O function at pyrazole C4 we subjected ketone 4 and hydrazide 5 to the same reaction conditions. In both cases, a plethora

• → 3 is unclear. Dimerization by air oxidation can be ruled out as performing the reaction under N2 atmosphere provided the same result. It should be mentioned that for the oxovanadium(V)-mediated dimerization of 4-aroyl-5-hydroxypyrazoles mentioned above a radical mechanism was postulated [32

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• spirocyclization of naphthol carboxylic acid [34]. Later Birman et al. reported a new variation of a chiral I(V) reagent, namely 2-(o-iodoxyphenyl)oxazoline derivative 28 [35]. The reagent was applied to an asymmetric [4 + 2] Diels–Alder dimerization of phenolic derivatives 29 to construct tricyclic derivatives 30

• . Asymmetric oxidation of sulfides by chiral hypervalent iodine reagents. Oxidative dearomatization of naphthol derivatives by Kita et al. [4 + 2] Diels–Alder dimerization reported by Birman et al. m-CPBA guided catalytic oxidative naphthol dearomatization. Oxidative dearomatization of phenolic derivatives by

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

• substantial contribution of 13B to 13A in the ground state. Moreover, it was found that the photochemical behavior of 230 depended on the state of the irradiation medium. For example, the smooth [π10 + π10] dimerization of 13 to give dimeric product 233 was realized with the irradiation (>420 nm) of 13 in a

An overview of recent advances in duplex DNA recognition by small molecules

• Sayantan Bhaduri,
• Nihar Ranjan and
• Dev P. Arya

Beilstein J. Org. Chem. 2018, 14, 1051–1086, doi:10.3762/bjoc.14.93

• ). This has been attributed to strong self-association (dimerization) in an antiparallel, head-to-tail orientation in aqueous solution during complex formation with duplex DNA oligomers verified via NOE experiments [61]. They further reported several structurally diverse MGBs, derived from distamycin, in

Cross-coupling of dissimilar ketone enolates via enolonium species to afford non-symmetrical 1,4-diketones

• Keshaba N. Parida,
• Gulab K. Pathe,
• Shimon Maksymenko and
• Alex M. Szpilman

Beilstein J. Org. Chem. 2018, 14, 992–997, doi:10.3762/bjoc.14.84

• path to 1,4-dicarbonyl compounds. However, while oxidative dimerization of enolates is fairly straightforward [6][7], the coupling of two dissimilar enolates is contrastingly highly challenging. The more similar in steric and electronic properties the two dissimilar enolates become, the more difficult

• ) with 4 (R1 = Ph, R2 =H) afforded 20 in 51% yield. Since both meso-23 and rac-23 are well-described in the literature [33], we chose to study the diastereoselectivity of the reaction using the dimerization of enol ether 21. The geometry of the TMS enol ether 21 was established as being exclusively Z

Local energy decomposition analysis of hydrogen-bonded dimers within a domain-based pair natural orbital coupled cluster study

• Ahmet Altun,
• Frank Neese and
• Giovanni Bistoni

Beilstein J. Org. Chem. 2018, 14, 919–929, doi:10.3762/bjoc.14.79

• publications [23][24][25][26][27][28][29][30][31][32][33]. We thus only recall here the main features of this technique. Within a supramolecular approach, the energy of a molecular adduct XY relative to the total energies of noninteracting fragments X and Y, i.e, dimerization energy (ΔE), can be written as

• CCSD(T) result of 2.737 Å with a quintuple−ζ basis [71]. The equilibrium ΔEe and zero-point corrected ΔE0 dimerization energies of water and HF dimers are given in Table 1. These correspond to the equilibrium De and zero-point D0 dissociation energies with opposite sign, respectively. The ΔEe value of

• kcal/mol) values at the CCSD(T)/CBS level [74]. It was shown [74] that the effects of quadruple excitations Q (−0.008 ± 0.004 kcal/mol), relativity (0.016 ± 0.001 kcal/mol), and the diagonal Born–Oppenheimer correction (−0.012 ± 0.000 kcal/mol) to the dimerization energy of the HF dimer are negligible

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

Investigating radical cation chain processes in the electrocatalytic Diels–Alder reaction

• Yasushi Imada,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 642–647, doi:10.3762/bjoc.14.51

• the catalytic cycle (Figure 1). The concentration of substrates must be balanced to lengthen the chain process, since a higher concentration of trans-anethole (1) is effective for the bulk SET, but it can also cause undesired self-dimerization. We intentionally stopped the reaction at 0.01 F/mol in

• ). However, some dimerization of trans-anethole (1) via the trapping of the radical cation (1·+) by neutral trans-anethole was also detected in both cases (Scheme 2). Since the undesired dimerization can decrease the current efficiency, we raised the amount of isoprene (2) from 3 to 10 equivalents in order

• efficiency of 3167% (Table 2, entry 4). Under these conditions, the undesired dimerization of trans-anethole (1) took place to give the dimer 4. However, we found that the electrochemical radical cation Diels–Alder reaction was also possible from the dimer, whose photochemical version was reported by Yoon

An air-stable bisboron complex: a practical bidentate Lewis acid catalyst

• Longcheng Hong,
• Sebastian Ahles,
• Andreas H. Heindl,
• Gastelle Tiétcha,
• Andrey Petrov,
• Zhenpin Lu,
• Christian Logemann and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 618–625, doi:10.3762/bjoc.14.48

• procedure for the synthesis of bisboron compound A via a dimerization requires a high reaction temperature (Scheme 3, top). Due to the use of volatile BCl3, the dimerization reaction is usually carried out in a sealed pressure tube. Using Schlenk technique, the procedure affords compound A in good yield

• optimized procedure, BBr3 was used to replace BCl3 and the dimerization reaction can be carried out in a normal Schlenk tube without any solvent. The methylation reagent, AlMe3 can be added in situ followed by the complexation with pyridazine. The one-pot procedure is also applicable to the synthesis of

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

• dimers formed in a Diels–Alder dimerization process by heating the corresponding Mannich bases under reflux in dichloromethane for 2 hours. In the synthesis of 3,4-dihydro-2-aryl-2H-benzo[f]chromenes and 2-aryl-6,7-dimethylchromans starting from substituted styrenes and 1-dimethylaminomethyl-2-naphthol

• unexpected side products. As mentioned above [71], Osyanin et al. reported the synthesis of Uvaria scheffleri alkaloid (±)-schefflone. In this publication, the dimerization of the o-QM resulting in intermediate 41 is a key step in the synthesis of the final natural trimer compound. Reactions with C=N

• various conditions applied in the synthesis of amidoalkylnaphthols 4. Formation and substrate scope of phenolic Mannich bases. Reactions of o-QMs with different dienophile species. Dimerization of o-QMs. Acknowledgements The authors thank the Ministry of National Economy, National Research Development

Oxidative cycloaddition of hydroxamic acids with dienes or guaiacols mediated by iodine(III) reagents

• Hisato Shimizu,
• Akira Yoshimura,
• Keiichi Noguchi,
• Victor N. Nemykin,
• Viktor V. Zhdankin and
• Akio Saito

Beilstein J. Org. Chem. 2018, 14, 531–536, doi:10.3762/bjoc.14.39

• of 1a with simple dienes or guaiacols, benzoyl anhydride was detected as a byproduct. Since benzoyl anhydride is known to be formed via the dimerization of benzoylnitroso compounds [35], these results suggest that acylnitroso species would be generated from 1a by iodine(III) reagents. Therefore, the

Progress in copper-catalyzed trifluoromethylation

• Guan-bao Li,
• Chao Zhang,
• Chun Song and
• Yu-dao Ma

Beilstein J. Org. Chem. 2018, 14, 155–181, doi:10.3762/bjoc.14.11

• catalytic amount of copper salt was required in this reaction. The hydrogens on the ortho and para positions of phenols have higher reactivity. Thus, undesired side reactions were often involved in the trifluoromethylation of less substituted phenols, including oxidative dimerization and oligomerization

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• -inflammatory signaling cascade. The lipid A portion of hexaacyl LPS (e.g., in E. coli LPS) is recognized and bound by a co-receptor protein MD-2 which is physically asssociated with TLR4. The binding of lipid A initiates dimerization of two copies of the TLR4∙MD-2–LPS complexes which results in the formation

• -inflammatory signaling and activation of the host innate immunity (Figure 3B) [42][45][46]. Compounds which compete with LPS in binding to the same site on MD-2 are capable of inhibiting the induction of the signal transduction pathway by preventing the LPS-induced receptor complex dimerization (Figure 3C

•  4B) [42][64]. Thus, lipid A directly participates in the formation of an active multimeric ligand–receptor complex, whereas the tightness and efficiency of dimerization strongly depends on specific structural characteristics such as the acylation pattern and the number of negative charges (e.g

From dipivaloylketene to tetraoxaadamantanes

• Gert Kollenz and
• Curt Wentrup

Beilstein J. Org. Chem. 2018, 14, 1–10, doi:10.3762/bjoc.14.1

• and phenyl-substituted tetraoxaadamantanes 1a and 1b were obtained by Arnold [1] and Almqvist [2] through the dimerization of β-ketoaldehydes (reactions 1 and 2 in Scheme 1). This was confirmed by Opitz et al., but the attempted synthesis of further analogs by these procedures failed [3]. Takeda et al

• . performed the dimerization of β-ketoaldehydes with SO2Cl2 (reaction 3 in Scheme 1) [4], and the X-ray crystal structure of 1b was reported [5]. Chekalov et al. described the preparation of the tetramethyl derivative 1d by dimerization of acetylacetone induced by SiF4 (reaction 4 in Scheme 1) [6] and also

• dimerization of dipivaloylketene (2), itself obtained in high yield by FVP of furan-2,3-dione 6 (Scheme 3). Ketene 3 reacts with a variety of nucleophiles in an addition reaction to the ketene function, thereby transforming the ketene to enol derivatives 14 or 9 of 1,3-dioxin-4-ones. Subsequently, these enols

A Brønsted base-promoted diastereoselective dimerization of azlactones

• Danielle L. J. Pinheiro,
• Gabriel M. F. Batista,
• Pedro P. de Castro,
• Leonã S. Flores,
• Gustavo F. S. Andrade and
• Giovanni W. Amarante

Beilstein J. Org. Chem. 2017, 13, 2663–2670, doi:10.3762/bjoc.13.264

• Brønsted base system for the diastereoselective dimerization of azlactones using trichloroacetate salts and acetonitrile has been developed. Desired products were obtained in good yields (60–93%) and with up to >19:1 dr after one hour of reaction. Additionally, the relative stereochemistry of the major

• analogue of streptopyrrolidine was accomplished in 65% overall yield. Keywords: azlactones; dimerization; diasteoreselective synthesis; kinetics; streptopyrrolidine analogue; Findings Azlactones have been acknowledged as a common nucleophilic reagent to introduce a quaternary carbon stereocenter in the α

• azlactone dimer, which is a versatile heterocycle containing two stereogenic centers (Figure 1). Kobayashi and co-workers demonstrated the rich reactivity of azlactones conducting the dimerization reaction using strong bases as catalysts; however, higher temperatures and long reaction times were required

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• . The dimerization of the same carbene leading to a mixture of E- and Z-1a was observed when ethyl dibromocyanoacetate was treated with equimolar amounts of LiI in DMF at room temperature with the highest reported yield of 83% [12]. The dimethyl ester E-1b was also obtained selectively by treatment of

A mechanochemical approach to access the proline–proline diketopiperazine framework

• Nicolas Pétry,
• Hafid Benakki,
• Eric Clot,
• Pascal Retailleau,
• Farhate Guenoun,
• Fatima Asserar,
• Chakib Sekkat,
• Thomas-Xavier Métro,
• Jean Martinez and
• Frédéric Lamaty

Beilstein J. Org. Chem. 2017, 13, 2169–2178, doi:10.3762/bjoc.13.217

• a scaffold for the preparation of small compound libraries [15]. The Pro–Pro diketopiperazine can be prepared directly by dimerization of unprotected proline in a one-pot transformation, generally under harsh conditions [16]. Good results were indeed reported, although this procedure gives access

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• -catalyzed dimerization of isoprene is a practical approach of synthesizing monoterpenes. Though several highly selective methods have been reported, most of them still required pressure or costly ligands for attaining the active system and desired selectivity. Herein, we present a simple and economical

• heterocyclic terpenes by subsequent (hetero)-Diels–Alder or [4 + 1]-cycloadditions with nitrenes is also depicted. Keywords: dimerization; heterocycles; isoprene; monoterpene; palladium catalysis; Introduction The dimerization of conjugated dienes represents a useful, highly atom economic and straightforward

• reaction for the construction of important olefinic substituted synthetic building blocks [1][2]. Despite the high value of this type of compounds, there are only few robust methodologies that have led to commercial processes such as the Kuraray telomerization – dimerization with a nucleophile – of 1,3

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C–S cross-coupling reaction

• Debasish Sengupta,
• Koushik Bhowmik,
• Goutam De and
• Basudeb Basu

Beilstein J. Org. Chem. 2017, 13, 1796–1806, doi:10.3762/bjoc.13.174

• and Ni/RGO-60) were also tested (Table 1). All reactions were carried out under a N2 atmosphere to avoid oxidative dimerization of thiols to disulfide [50]. Solvent optimization was started with water (Table 1, entry 1) followed by toluene (Table 1, entry 2) and isolating diaryl sulfide only 6–8

• suppressing the overall yield of the thioether (Table 1, entries 5 and 6). Without using any base, the yield was 74%, while the use of KOH as a base afforded the thioether in 83% yield (Table 1, entries 7 and 8). Formation of the diphenyl disulfide via oxidative dimerization of benzenethiol was noticed (15

1-Imidoalkylphosphonium salts with modulated C_α–P⁺ bond strength: synthesis and application as new active α-imidoalkylating agents

• Jakub Adamek,
• Roman Mazurkiewicz,
• Anna Węgrzyk and
• Karol Erfurt

Beilstein J. Org. Chem. 2017, 13, 1446–1455, doi:10.3762/bjoc.13.142

• side reactions (for example Kolbe-dimerization), the yields were only poor (10–35%) [33][34]. According to our previously reported procedure for the electrochemical decarboxylative α-methoxylation of N-acyl-α-amino acids [18], amino acid derivatives 6 were converted to N-(1-methoxyalkyl)imides 7. The

Aqueous semisynthesis of C-glycoside glycamines from agarose

• Juliana C. Cunico Dallagnol,
• Alexandre Orsato,
• Diogo R. B. Ducatti,
• Miguel D. Noseda,
• Maria Eugênia R. Duarte and
• Alan G. Gonçalves

Beilstein J. Org. Chem. 2017, 13, 1222–1229, doi:10.3762/bjoc.13.121

• , enolization and dimerization are among the drawbacks that can be encountered during the transformation of mono- or oligosaccharides directly into glycamines. Considering (a) the potential of AnGal as starting material for the synthesis of glycamines structurally related to muscarine, (b) the suitability of

Chemoselective synthesis of diaryl disulfides via a visible light-mediated coupling of arenediazonium tetrafluoroborates and CS₂

• Jing Leng,
• Shi-Meng Wang and
• Hua-Li Qin

Beilstein J. Org. Chem. 2017, 13, 903–909, doi:10.3762/bjoc.13.91

• of a carbon sulfide [11]. The active radical intermediate III can transform into three types of products through different pathways. Firstly, diaryl disulfide 3 is obtained through a dimerization of radical intermediates III, whereas the reaction of radical III with phenyl radical I is leading to

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

• Carmen Moreno-Marrodan,
• Francesca Liguori and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2017, 13, 734–754, doi:10.3762/bjoc.13.73

• . Selectivity in partial hydrogenation is ruled by the relative rates of the first and second hydrogenation steps, as well as by the adsorption strengths of alkyne and alkene over the metal catalyst surface. Other side-products may include those due to dimerization and isomerization reactions, depending on the

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• Meldrum’s acids 70 have been used for the synthesis of 1-indanones 71 [48]. The reaction was catalyzed by Sc(OTf)3 and proceeded in very good yields (up to 94%) (Scheme 24). 1.1.4 From aldehydes and dialdehydes: The stereoselective dimerization reaction of phthalaldehydes 72, catalyzed by a N-heterocyclic

Dimerization reactions of aryl selenophen-2-yl-substituted thiocarbonyl S-methanides as diradical processes: a computational study

• Michael L. McKee,
• Grzegorz Mlostoń,
• Katarzyna Urbaniak and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 410–416, doi:10.3762/bjoc.13.44

• , Winterthurerstrasse 190, CH-8057 Zurich, Switzerland 10.3762/bjoc.13.44 Abstract An intriguing stepwise diradical mechanism of the dimerization of the reactive intermediate (thiocarbonyl S-methanide) appearing in the reaction of phenyl selenophen-2-yl thioketone with diazomethane was studied by means of

• computational methods. The preferred formation of the unusual macroheterocycle, competitive with the 1,3-ring closure leading to a thiirane and the head-to-head dimerization yielding a 1,4-dithiane derivative, respectively, was explained based on the analysis of the structure of the favored conformer of the

• located at the terminal C-atoms of the 1,3-dipole. In the case of polar groups, such as sulfonyl or phosphonyl moieties, the dimerization leads to five-membered 1,3-dithiolane derivatives 4 (sulfoniumylides) [7][8]. Diaryl-substituted thiocarbonyl S-methanides 1 react in the absence of a dipolarophile