A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• naphthoquinone-derived products and low-intensity bands in the visible region (≈400 nm) for the anthraquinone series. Keywords: [3 + 2]-cycloadditions; fluorinated compounds; fused pyrazoles; N-heterocycles; nitrile imines; 1,4-quinones; Introduction The 1,4-quinone scaffold belongs to the most important

Co-crystallization of an organic solid and a tetraaryladamantane at room temperature

• Fabian Rami,
• Jan Nowak,
• Felix Krupp,
• Wolfgang Frey and
• Clemens Richert

Beilstein J. Org. Chem. 2021, 17, 1476–1480, doi:10.3762/bjoc.17.103

• and thermodynamic aspects. Kinetically, when crystallizing from a solvent, the solvent may be more likely to be encapsulated than the second solid-forming compound, as the solvent will be smaller and more abundant, making it the more likely molecule to be entrapped in cavities left by the scaffold

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

• complementary DNA strands were studied. The analysis of the melting temperature of the resulting duplex revealed that the synthesized double-headed nucleotide behaved as a compressed dinucleotide and combination of all natural nucleobases on compressed scaffold can form Watson–Crick base pairs with

Design, synthesis and photophysical properties of novel star-shaped truxene-based heterocycles utilizing ring-closing metathesis, Clauson–Kaas, Van Leusen and Ullmann-type reactions as key tools

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2021, 17, 1374–1384, doi:10.3762/bjoc.17.96

• , superior solubility, improve morphological, optical, electrical and film-forming properties because of the involvement of extra dimensionality. Amongst them, the heptacyclic truxene scaffold possessing three overlapping fluorene units and its congeners are of archetypal interest due to their potential

• synthetic strategies and also novel truxene-based functional materials with unique properties. Bearing in mind the importance of the truxene framework, herein, we report diverse C3-symmetric heterocyclic systems possessing the truxene scaffold in their structures by means of cyclotrimerization, ring-closing

• -containing five-membered aromatic pyrrole scaffold will continue to play a significant role in the development of novel anionic receptors [33][34]. Therefore, as outlined in Scheme 2, our synthetic strategy towards the construction of the target pyrrole-based truxene derivative 6 initiated with the acid

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• scaffold [4]. The Guareschi–Lustgarten reaction is at the basis of the pharmacopoeia assay of thymol (3) [5], and investigation on the color associated with the reaction eventually led to the discovery of the Reimer–Tiemann formylation of phenols [6]. Conversely, the third Guareschi eponymic reaction, the

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• for their synthesis, work-up, and purification. In this context, the aim of the next part of this review is to propose a generalized and comparative overview of the synthetic methods to access this particular scaffold. We chose to sort the synthetic routes by reaction types, from the most general and

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

• of the THP key scaffold and its application towards the total synthesis of natural products. Many advancements were also taking place in Prins cyclization methodologies over that period of time. This appraisal aims to bring together the work of many research groups in the area of the development of

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

• diseases. Oligonucleotides with alterations to their scaffold, prepared with modified nucleosides and solid-phase synthesis, have yielded molecules with interesting biophysical properties that bind to their targets and are tolerated by the cellular machinery to elicit a therapeutic outcome. Structural

• arguably the most radical alternative nucleic acid pairing system, peptide nucleic acid (PNA), the sugar-phosphate backbone is replaced by an amide-based, neutral and achiral scaffold that allows cross-pairing with both DNA and RNA as well as formation of double- and triple-stranded species [57]. Despite

• [148], and in the use of antisense oligonucleotides for splice modulation through the induction of Dmd exon-23 skipping in mice in vitro [149]. Recently, a lot of attention has been paid to modifying the LNA scaffold to incorporate various heteroatoms, modify the bicyclic framework, and to change the

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• donor. Furthermore, due to the commercially available material and wide range of substrates, this approach has major significance for drug scaffold methodologies, providing useful strategy for the synthesis of spiropyrrolines. In 2019, Yu and colleagues [23] reported the utilization of

DNA with zwitterionic and negatively charged phosphate modifications: Formation of DNA triplexes, duplexes and cell uptake studies

• Yongdong Su,
• Maitsetseg Bayarjargal,
• Tracy K. Hale and
• Vyacheslav V. Filichev

Beilstein J. Org. Chem. 2021, 17, 749–761, doi:10.3762/bjoc.17.65

• the nuclear DNA, confirmed that the Ts-ON foci are present within the cytoplasm as shown in Figure 4. Discussion Chemical modification provides an effective and efficient way of obtaining therapeutic antigene/antisense agents based on the nucleic acid scaffold. To regulate transcription or translation

β-Lactamase inhibition profile of new amidine-substituted diazabicyclooctanes

• Zafar Iqbal,
• Lijuan Zhai,
• Yuanyu Gao,
• Dong Tang,
• Xueqin Ma,
• Jinbo Ji,
• Jian Sun,
• Jingwen Ji,
• Yuanbai Liu,
• Rui Jiang,
• Yangxiu Mu,
• Lili He,
• Haikang Yang and
• Zhixiang Yang

Beilstein J. Org. Chem. 2021, 17, 711–718, doi:10.3762/bjoc.17.60

• , Jinfeng District, Yinchuan, Ningxia 750002, P.R. China College of Pharmacy, Ningxia Medical University, Shengli Street, Xingqing District, Yinchuan, Ningxia 750004, P.R. China 10.3762/bjoc.17.60 Abstract The diazabicyclooctane (DBO) scaffold is the backbone of non-β-lactam-based second generation β

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

• Mikhail K. Klychnikov,
• Radek Pohl,
• Ivana Císařová and
• Ullrich Jahn

Beilstein J. Org. Chem. 2021, 17, 688–704, doi:10.3762/bjoc.17.58

• γ-lactam scaffold [40][41][42][43][44]. The pyrrolidinone fragment is often synthesized by transition metal- [45][46][47][48][49][50] or Lewis acid-catalyzed cyclization reactions [51][52][53][54]. The Diels–Alder reaction can also be used for the preparation of functionalized γ-lactams in a single

Effective microwave-assisted approach to 1,2,3-triazolobenzodiazepinones via tandem Ugi reaction/catalyst-free intramolecular azide–alkyne cycloaddition

• Maryna O. Mazur,
• Oleksii S. Zhelavskyi,
• Eugene M. Zviagin,
• Svitlana V. Shishkina,
• Vladimir I. Musatov,
• Maksim A. Kolosov,
• Elena H. Shvets,
• Anna Yu. Andryushchenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2021, 17, 678–687, doi:10.3762/bjoc.17.57

• complex scaffold in just two steps. Unusually, the azide–alkyne cycloaddition for both terminal and non-terminal alkynes was effective under catalyst-free conditions while normally for non-terminal alkynes a ruthenium-based catalysis is required. Using the developed method, a library of 22 target

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

• Zbigniew Malinowski,
• Emilia Fornal,
• Agata Sumara,
• Renata Kontek,
• Karol Bukowski,
• Beata Pasternak,
• Dariusz Sroczyński,
• Joachim Kusz,
• Magdalena Małecka and
• Monika Nowak

Beilstein J. Org. Chem. 2021, 17, 558–568, doi:10.3762/bjoc.17.50

• 5i in a lower yield as compared with aliphatic amines. Moreover, it turned out that an aminoalkyl substituent attached to the lactam scaffold did not disturb its functionalization at the 4 position by a simple amine. The corresponding product 5j was obtained in 89% yield. It was found that also

The synthesis of chiral β-naphthyl-β-sulfanyl ketones via enantioselective sulfa-Michael reaction in the presence of a bifunctional cinchona/sulfonamide organocatalyst

• Deniz Tözendemir and
• Cihangir Tanyeli

Beilstein J. Org. Chem. 2021, 17, 494–503, doi:10.3762/bjoc.17.43

• a low (1 mol %) catalyst loading, to obtain enantiomerically enriched β-naphthyl-β-sulfanyl ketones with up to 96% ee. The target adducts are the core structure of seco-raloxifene derivatives, which are potent anti-breast cancer agents [32]. In addition, the same scaffold has also shown urease

Diels–Alder reaction of β-fluoro-β-nitrostyrenes with cyclic dienes

• Savva A. Ponomarev,
• Roman V. Larkovich,
• Alexander S. Aldoshin,
• Andrey A. Tabolin,
• Sema L. Ioffe,
• Jonathan Groß,
• Till Opatz and
• Valentine G. Nenajdenko

Beilstein J. Org. Chem. 2021, 17, 283–292, doi:10.3762/bjoc.17.27

• ratios similar to those of the starting mixture 2. We believe that this is a result of an exo-epoxidation which is preferred in norbornene systems [78][79]. Such a functionalization is very attractive to produce new reactive building blocks bearing the norbornane scaffold. This approach can pave a

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

Novel library synthesis of 3,4-disubstituted pyridin-2(1H)-ones via cleavage of pyridine-2-oxy-7-azabenzotriazole ethers under ionic hydrogenation conditions at room temperature

• Romain Pierre,
• Anne Brethon,
• Sylvain A. Jacques,
• Aurélie Blond,
• Sandrine Chambon,
• Sandrine Talano,
• Catherine Raffin,
• Branislav Musicki,
• Claire Bouix-Peter,
• Loic Tomas,
• Gilles Ouvry,
• Rémy Morgentin,
• Laurent F. Hennequin and
• Craig S. Harris

Beilstein J. Org. Chem. 2021, 17, 156–165, doi:10.3762/bjoc.17.16

• Roche and Genentech researchers have described the first route to this scaffold for their FAK and EGFR mutant programs, respectively [1][2]. Both processes started from the versatile 4-iodo-2-methoxynicotinaldehyde (3). Oxidation to the carboxylic acid followed by chlorodehydration afforded the key

• the C-2–OAt ether presumably due to the lower basicity of 26 compared to 8, therefore, activation via protonation of the pyridine was not occurring. With a view to capitalize on our knowledge acquired so far on this scaffold, we decided to force the transformation to the OBt ether by SNAr under basic

• hydrogenation conditions at just room temperature. Retrosynthetic disconnection of our privileged kinase scaffold 1. Reagents and conditions: (a) MeOH, DIPEA, reflux, 70%; b) TBTU, DIPEA, DMF, rt, 91%. Proposed mechanistic explanation for the liberation of the Pd catalytic cycle after addition of sacrificial Cu

Supramolecular polymerization of sulfated dendritic peptide amphiphiles into multivalent L-selectin binders

• David Straßburger,
• Svenja Herziger,
• Katharina Huth,
• Moritz Urschbach,
• Rainer Haag and
• Pol Besenius

Beilstein J. Org. Chem. 2021, 17, 97–104, doi:10.3762/bjoc.17.10

• trimesic acid scaffold by PyBOP coupling in DMF and NMM as weak base. After subsequent size exclusion chromatography, the ready to use azide-functional monomer 7 was isolated in high purity. The peptide amphiphile was finally conjugated to the propargylated sulfated [G2] oligoglycerol dendron 8 via a

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• organometallic enantiomeric scaffold for an asymmetric construction of a wide variety of heterocyclic systems. The synthetic precursor 66 was obtained from furfurylamine (65), as previously published by the authors [52]. 66 was converted to the (E)-(−)-6-alkylidene-5-oxo 68 through a sequence of Mukayama aldol

• in terms of common intermediaries. Therefore, it’s a new synthesis of (−)-adaline (1) and might eventually be applied to related homotropanes. In conclusion, (−)-adaline (1) was obtained in 14 steps from 66 using a new scaffold-based semipinacol/1,5-Michael-like strategy. The enantiomeric excess for

Molecular basis for protein–protein interactions

• Brandon Charles Seychell and
• Tobias Beck

Beilstein J. Org. Chem. 2021, 17, 1–10, doi:10.3762/bjoc.17.1

• formation. This theoretical approach is backed up by experimental results from hepatitis B virus (HBV), where the homodimeric core protein assembles in vitro without any biological scaffold [82]. Nonetheless, HBV is a relatively simple system where the viral capsid is only made up of the homodimer [83]. In

• more complicated systems, such as in cowpea chlorotic mottle virus (CCMV), the viral capsid is made up of different assembly units. In vivo, viral nucleic acids may serve as biological scaffold to attract free assembly units [84] and organise on the surface [85]. Assembly with viral RNA present can be

• that a nucleic acid scaffold aids the assembly by concentrating assembly units and providing additional association energy. Some viral capsids can self-assemble around other scaffolds that mimic the viral genome in charge and size [89] or can also assemble without any scaffold to form empty capsid

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• active compound is a common practice in medicinal chemistry [1][2][3]. In particular, the biaryl moiety is a privileged scaffold largely present in the skeleton of natural substances [4][5][6][7] and in useful chiral ligands [8][9][10]. The synthesis of biaryl derivatives remains, however, a considerable

Chiral anion recognition using calix[4]arene-based ureido receptors in a 1,3-alternate conformation

• Tereza Horáčková,
• Jan Budka,
• Vaclav Eigner,
• Wen-Sheng Chung,
• Petra Cuřínová and
• Pavel Lhoták

Beilstein J. Org. Chem. 2020, 16, 2999–3007, doi:10.3762/bjoc.16.249

• basic conformations (cone, partial cone, 1,3-alternate, and 1,2-alternate) offers the combination of a precisely defined 3D structure, with functional groups being introduced at exactly defined mutual positions. This makes calix[4]arenes an ideal molecular scaffold [25][26] for the construction of

• exemplified by our previously published receptors C1 based on a calix[4]arene moiety or by C2 using thiacalix[4]arene as the core scaffold [44][45]. Moreover, the introduction of the tert-butyl groups into the 1,3-alternate conformer should lead to the overall increase rigidity of the molecule, possibly

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• motif [20][21][22][23], the development of cost-effective methods to access functionalized pyrrole skeletons has remained an ongoing challenge. N-(Hetero)aryl-4,5-unsubstituted pyrroles are one of the most important types of pyrroles, which are frequently used as a core scaffold in pharmaceuticals

• synthesis, we also observed an unexpected reaction in which the pyrazolo[3,4-b]pyridine scaffold was constructed under analogous conditions. As shown in Scheme 6, In the presence of a catalytic amount of AlCl3 and 1.2 equiv of KI, 3-methyl-1-phenyl-1H-pyrazol-5-amine (1b) reacted smoothly with 2a and 3a