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

• acids are widely used in stereoselective oxidative/cross-coupling of two aryl counterparts, asymmetric control of aromatic ring formation, atroposelective functionalization of biaryl compounds, and so on [17][29][30]. In this context, Akiyama (2004) described that chiral phosphoric acids (CPAs) have

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

• give the 1,3-oxathiolane sugar ring. Herein, the research on 1,3-oxathiolane sugar ring formation strategies, mainly starting from oxygen- and sulfur-containing substrates, is summarized. In 1989, Belleau and co-workers [38] produced the first oxathiolane nucleoside as a racemic mixture, popularly

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• total syntheses of many natural products [34]. Despite its wide application in ring formation reactions, only a few review articles on Hg(II)-salt-mediated cyclization reactions are available in the literature [35]. This review describes the intramolecular cyclization of unsaturated compounds in the

• -ribose derivative 16 at room temperature (Scheme 7). They had confirmed the formation of the α-isomer of ᴅ-C-ribofuranosyl 16 predominantly over the β-isomer (α/β 95:5) [44]. In contrast, when Reitz and co-workers carried out a ring formation of benzylated C-arabinofuranoside derivative 17 in presence of

• in a diastereomeric pair of cyclized products 69 and 71, respectively. It was observed that the cis-isomer was predominant in the case of the five-membered ring while the trans-isomer was predominant in the case of the six-membered ring formation (Scheme 24) [72]. Cyclization involving alkynes (-C≡C

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• of this kind of reaction is the catalytic use of the hydride donor, in this case phenylsilane (PhSiH3), due to the regeneration of the active metal hydride species in the cycloisomerization mechanism pathway (Scheme 18). The lower cyclization constant for the six-membered ring formation, in

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

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

• ion intermediate in a stereoselective manner for THP ring formation as shown in Scheme 3. The outcome of exclusive cis-stereoselectivity in the Prins cyclization might be attributed to the most favorable conformation adopted by 12 with equatorial orientation of the 2,6-substituents (R1 and R2). Alder

Menthyl esterification allows chiral resolution for the synthesis of artificial glutamate analogs

• Kenji Morokuma,
• Shuntaro Tsukamoto,
• Kyosuke Mori,
• Kei Miyako,
• Ryuichi Sakai,
• Raku Irie and
• Masato Oikawa

Beilstein J. Org. Chem. 2021, 17, 540–550, doi:10.3762/bjoc.17.48

• conversion of oxanorbornene (rac)-13 to heterotricycle (rac)-16 through the eight-membered-ring formation would be owing to the cis-relationships of the pentenyl and vinyl groups on the ring B of (rac)-15, which allows the proximal arrangement of the reacting sites in the RCM. The N-Boc derivatization of

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

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• that a specific geometry of the tethered alkene is required, as no 6-membered ring formation was observed. Interestingly, Cárdenas’ precursor 35 [30] led, after a cascade of reactions, to the formation of compound 36. Computational as well as experimental studies suggested that the ligand and

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• catalyst 2 with (NH4)2S2O8, which acted as a cost-efficient and environmentally friendly oxidant (Scheme 14) [139]. In the mechanism, the excited photocatalyst generates the benzoyloxy radical 98, and the cyclization of 98 is completed via 6-endo-trig ring formation to form the intermediate 99, which, upon

Combining the Ugi-azide multicomponent reaction and rhodium(III)-catalyzed annulation for the synthesis of tetrazole-isoquinolone/pyridone hybrids

• Gerardo M. Ojeda,
• Prabhat Ranjan,
• Pavel Fedoseev,
• Lisandra Amable,
• Upendra K. Sharma,
• Daniel G. Rivera and
• Erik V. Van der Eycken

Beilstein J. Org. Chem. 2019, 15, 2447–2457, doi:10.3762/bjoc.15.237

• activation of the N-benzamidomethyltetrazole core followed by isoquinolone-ring formation to furnish 4a. We endeavored two catalytic systems based on ruthenium and rhodium, which in our laboratory have proven success in this type of cyclization [32][48]. First, the alkynylation protocol was attempted using

Sugar-derived oxazolone pseudotetrapeptide as γ-turn inducer and anion-selective transporter

• Sachin S. Burade,
• Sushil V. Pawar,
• Tanmoy Saha,
• Navanath Kumbhar,
• Amol S. Kotmale,
• Manzoor Ahmad,
• Pinaki Talukdar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2019, 15, 2419–2427, doi:10.3762/bjoc.15.234

• functionalities are apart from each other. However, an individual intramolecular coupling reaction of 8 and 9 using CMPI as a coupling reagent, in the presence of Et3N in dichloromethane, afforded pseudodipeptide 1 and pseudotetrapeptide 2a, respectively, with oxazolone ring formation at the C-terminal of the

In water multicomponent synthesis of low-molecular-mass 4,7-dihydrotetrazolo[1,5-a]pyrimidines

• Irina G. Tkachenko,
• Sergey A. Komykhov,
• Vladimir I. Musatov,
• Svitlana V. Shishkina,
• Viktoriya V. Dyakonenko,
• Vladimir N. Shvets,
• Mikhail V. Diachkov,
• Valentyn A. Chebanov and
• Sergey M. Desenko

Beilstein J. Org. Chem. 2019, 15, 2390–2397, doi:10.3762/bjoc.15.231

• starting material and subsequent dihydropyrimidine ring formation. The first approach [6][7] represents a two-component cyclocondensation of 5-aminotetrazole (1) as binucleophilic component and bielectrophilic α,β-unsaturated carbonyl compounds 2 (Scheme 1, reaction 1). The second method [8][9][10][11][12

• several times [5][6]. A third approach (Scheme 1, reaction 3) is completely different and consists of the tetrazole ring formation through cyclization of dihydropyrimidinethiones with sodium azide [14]. Generally, all three approaches allow for the preparation of a broad range of compounds 3 with a wide

Inherent atomic mobility changes in carbocation intermediates during the sesterterpene cyclization cascade

• Hajime Sato,
• Takaaki Mitsuhashi,
• Mami Yamazaki,
• Ikuro Abe and
• Masanobu Uchiyama

Beilstein J. Org. Chem. 2019, 15, 1890–1897, doi:10.3762/bjoc.15.184

• 5/6/8/5 tetracyclic intermediate. This, in turn, is transformed to a 4/6-membered ring in quiannulatene biosynthesis, whereas 5/5 ring formation proceeds in sesterfisherol biosynthesis (Scheme 1, Scheme 2, and Scheme 3). Based on our DFT calculations, this regioselectivity is determined by the

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• disease [99]. Synthesis of enantiomerically pure (3R,5S)-168 could be accomplished from the aziridine aldehyde (2S,1'R)-6 because the butyrolactone ring formation would proceed with inversion of configuration at C2 in the aziridine ring (Scheme 43) [100]. Thus, condensation of the aldehyde (2S,1'R)-6 with

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• -Hydrazinylpyridines (a) and pyridinylhydrazones (b), as well as their acylated derivatives (c), are versatile scaffolds for the preparation of triazolopyridines (Scheme 1). The known methods for the [1,2,4]triazolopyridine ring formation use various condensation agents such as HCOOH, orthoesters, Lawesson’s reagent

Polyaminoazide mixtures for the synthesis of pH-responsive calixarene nanosponges

• Antonella Di Vincenzo,
• Antonio Palumbo Piccionello,
• Alberto Spinella,
• Delia Chillura Martino,
• Marco Russo and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2019, 15, 633–641, doi:10.3762/bjoc.15.59

• . Formation of the 1,3-oxazinan-2-one ring. Formation of the product at m/z 382.2765 u. Formation of the components of mixture I. Percent of absorbed guest in the sequestration tests.a Supporting Information Supporting Information File 332: Possible structures of the components present in the mixtures

Protein–protein interactions in bacteria: a promising and challenging avenue towards the discovery of new antibiotics

• Laura Carro

Beilstein J. Org. Chem. 2018, 14, 2881–2896, doi:10.3762/bjoc.14.267

• multiplication and viability of bacteria, and second, they are highly conserved in many bacterial species [85]. Various studies have shown that Z interaction protein A (ZipA) is one of the essential components that stabilize the Z-ring formation and that it binds to FtsZ with high affinity. The interaction

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• stereoselectivity of the ring-formation step can be explained by the suprafacial addition of the allene to the double bond of the α,β-unsaturated compound 4, the diastereoselectivity being sterically controlled by the methyl group on the β-face. The transformation of the vinylsilane moiety in 5 into the

DFT calculations on the mechanism of copper-catalysed tandem arylation–cyclisation reactions of alkynes and diaryliodonium salts

• Tamás Károly Stenczel,
• Ádám Sinai,
• Zoltán Novák and
• András Stirling

Beilstein J. Org. Chem. 2018, 14, 1743–1749, doi:10.3762/bjoc.14.148

• in the order of the oxazoline ring formation and the aryl transfer steps. In our model transformation, it was found that the reaction generally features the aryl transfer–ring closing sequence and this sequence shows very limited sensitivity to the variation of the substituent of the reactants. On

• Scheme 2 and Scheme 3) the ring formation takes place with an activation free barrier of 22.6 kcal/mol (TSrcA). Along this path this is the rate determining step. The calculations revealed that once the ring is formed, the aryl transfer spontaneously occurs and a significant amount of free energy is

• amount free energy to arrive at the same state as postulated for path A. Comparison of the two free energy profiles indicates that the preferred route is the one where the aryl transfer precedes the oxazoline ring formation. On the other hand, the calculated activation free energy barriers are compatible

Recent advances in synthetic approaches for medicinal chemistry of C-nucleosides

• Kartik Temburnikar and
• Katherine L. Seley-Radtke

Beilstein J. Org. Chem. 2018, 14, 772–785, doi:10.3762/bjoc.14.65

• (compound 23) is shown in Figure 9, which involves installing an allyl group at C1' (20) and converting the C2'–CN to an aldehyde (21) followed by a Wittig reaction to install a second allyl group at C2' (22). Second generation Grubb’s catalyst was used for the ring formation, followed by hydrogenation to

A concise flow synthesis of indole-3-carboxylic ester and its derivatisation to an auxin mimic

• Marcus Baumann,
• Ian R. Baxendale and
• Fabien Deplante

Beilstein J. Org. Chem. 2017, 13, 2549–2560, doi:10.3762/bjoc.13.251

• precursors in a multistep sequence prior to indole ring formation [7]. In order to address these potential shortcomings we set out to develop a benign process relying on inexpensive substrates and non-toxic reagents that would rapidly deliver the desired indole in a readily scalable and continuous fashion

• looked at telescoping the final two steps of the process; substitution of the ethoxy group by hydrazine and then ring formation to the 3H-[1,3,4]oxadiazol-2-one unit [32][33]. In this procedure a 0.95 M THF solution of compound 12 was united with a solution of hydrazine (1.0 M in THF) and directed into a

Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz–Fritsch–Bobbitt reaction with non-activated and moderately-activated systems

• Marco Mottinelli,
• Mathew P. Leese and
• Barry V. L. Potter

Beilstein J. Org. Chem. 2017, 13, 1871–1878, doi:10.3762/bjoc.13.182

• -ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4

• function of the water content of the reaction mixture. An acetal concentration of 0.3 M proved optimal to minimize the ether formation. The PF reaction conditions could possibly lead to a competition between 6-membered and 5-membered ring formation in systems such as 9a,o,p (Scheme 6). For this study

• cyclized into the indole 16p. It is thus possible to infer that indole formation is highly disfavored and only the presence of a great number of activating groups can make this outcome competitive. We then decided to expand our analysis to include competition between 6- and 7-membered ring formation

Photocatalyzed synthesis of isochromanones and isobenzofuranones under batch and flow conditions

• Manuel Anselmo,
• Lisa Moni,
• Hossny Ismail,
• Davide Comoretto,
• Renata Riva and
• Andrea Basso

Beilstein J. Org. Chem. 2017, 13, 1456–1462, doi:10.3762/bjoc.13.143

• , selective synthesis of benzo-fused six- or five-membered rings can be achieved. We have demonstrated that the 5-membered ring formation is favored, when the two processes are competitive, and we have also shown that acetonitrile can act as a third component in the cyclization to oxazepinones. By employing

Studies directed toward the exploitation of vicinal diols in the synthesis of (+)-nebivolol intermediates

• Runjun Devi and
• Sajal Kumar Das

Beilstein J. Org. Chem. 2017, 13, 571–578, doi:10.3762/bjoc.13.56

• formation. Further we speculated that compound 26, in the presence of a base, might undergo a simultaneous epoxidation–intramolecular epoxide-ring opening to produce 27 (Scheme 7) as the corresponding benzoxepin ring formation via intramolecular displacement of –OTs group by ArO− is unresponsive [23]. To

• , may produce traces to significant amounts of side-products via hydrogenolysis. Thus, we decided to modify Panda’s synthetic route to significantly increase the overall yield. We hypothesized that this problem might be circumvented by performing the debenzylation reaction prior to the epoxide-ring