A cyclopeptide and three oligomycin-class polyketides produced by an underexplored actinomycete of the genus Pseudosporangium

• Shun Saito,
• Kota Atsumi,
• Tao Zhou,
• Keisuke Fukaya,
• Daisuke Urabe,
• Naoya Oku,
• Md. Rokon Ul Karim,
• Hisayuki Komaki and
• Yasuhiro Igarashi

Beilstein J. Org. Chem. 2020, 16, 1100–1110, doi:10.3762/bjoc.16.97

• six-membered ring and the axial orientations of H-31 and the H-41 methyl group. Therefore, the relative configuration of the spiroacetal ring was established to be (23S*,24R*,25S*,27R*,30S*,31S*) (Figure 7). The molecular formula of pseudosporamicin B (3) was determined to be C41H70O9 based on a

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• -membered ring B. The large difference between the LUMO and HOMO leads to an intramolecular charge transfer, resulting in broad absorption bands in the UV–vis spectrum (Figure 3a) [36]. In addition, the LUMO energy of 1 (−2.98 eV) is significantly lower than that of 6 (−2.38 eV), which is responsible for

• aromatic core. In contrast to 6, compound 1 presents a significant difference in the shape of its molecular orbitals. The LUMO of 1 is mainly localized on the core, whereas the HOMO keeps a line of high electron density along the fused five-membered rings (rings A and C in Figure 2d) and the central six

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

• Svetlana V. Amosova,
• Andrey A. Filippov,
• Nataliya A. Makhaeva,
• Alexander I. Albanov and
• Vladimir A. Potapov

Beilstein J. Org. Chem. 2020, 16, 515–523, doi:10.3762/bjoc.16.47

• group in the six-membered ring 5 are not equivalent. As consequence they are observed in the 1H NMR spectrum as two doublets of doublets with geminal and vicinal coupling constants with the SCH-proton in the same ring (3.79 ppm, 2JН,Н = 12.4 Hz, 3JН,Н = 2.1 Hz; 3.33 ppm, 2JН,Н = 12.4 Hz, 3JН,Н = 6.6 Hz

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• imposed by the adjacent phenyl and cyclohexyl rings [59]. The treatment of compound 5 under Schmidt reaction conditions with sodium azide in TFA [60] resulted in the conversion to the corresponding six-membered ring lactam 39 in 41% yield, demonstrating the reactivity of the enone 5 at the carbonyl group

Functionalization of the imidazo[1,2-a]pyridine ring in α-phosphonoacrylates and α-phosphonopropionates via microwave-assisted Mizoroki–Heck reaction

• Damian Kusy,
• Agata Wojciechowska,
• Joanna Małolepsza and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 15–21, doi:10.3762/bjoc.16.3

• halogen substituent in the imidazo[1,2-a]pyridine ring on its reactivity in the Mizoroki–Heck reaction. We confined our studies to the analogs bearing substituents at positions 6, 7, and 8 of the six-membered ring of the imidazo[1,2-a]pyridine (1a–f, in Figure 1) [24]. We found that the reaction occurred

Photochromic diarylethene ligands featuring 2-(imidazol-2-yl)pyridine coordination site and their iron(II) complexes

• Andrey G. Lvov,
• Max Mörtel,
• Anton V. Yadykov,
• Frank W. Heinemann,
• Valerii Z. Shirinian and
• Marat M. Khusniyarov

Beilstein J. Org. Chem. 2019, 15, 2428–2437, doi:10.3762/bjoc.15.235

• comparison with 4. The expansion of the five-membered carbocyclic bridge to a six-membered ring in 7 leads to a slight hypsochromic shift. The presence of a CO2Et group in the cyclohexenone bridge in 6 results in further minor hypsochromic shift. Thus, the absorption maxima of the closed-ring ligands are

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• five and six-membered ring β-ketoesters were converted to the corresponding products in high yields and enantioselectivities (Scheme 56). In 2018, the first example for the copper-catalyzed stereospecific trifluoromethylation of secondary propargyl sulfonates was described by the group of Zhang [116

Genome mining in Trichoderma viride J1-030: discovery and identification of novel sesquiterpene synthase and its products

• Xiang Sun,
• You-Sheng Cai,
• Yujie Yuan,
• Guangkai Bian,
• Ziling Ye,
• Zixin Deng and
• Tiangang Liu

Beilstein J. Org. Chem. 2019, 15, 2052–2058, doi:10.3762/bjoc.15.202

• precursor FPP via sesquiterpene synthase have been described. Nearly 75% of these structures have at least one six-membered ring; 69% of these contain five-membered rings, occupying a large portion. Three- and seven-membered ring structures account for just 21% and 24% of these structures, respectively

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

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• species E1 (δ 53 ppm) and E2 (δ 43 ppm). This difference may reveal that phosphorus in cation E4 is bound to a carbon atom, rather than to a heteroatom O or N, like in E1 and E2. Structurally close six-membered ring cations, having the C–P bond, resonate at 30.5–31.9 in 31P NMR [16], that is close to the

Hoveyda–Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring. Synthesis of stable, industrially scalable, highly efficient ruthenium metathesis catalysts and 2-vinylbenzylamine ligands as their precursors

• Kirill B. Polyanskii,
• Kseniia A. Alekseeva,
• Pavel V. Raspertov,
• Pavel A. Kumandin,
• Eugeniya V. Nikitina,
• Atash V. Gurbanov and
• Fedor I. Zubkov

Beilstein J. Org. Chem. 2019, 15, 769–779, doi:10.3762/bjoc.15.73

• has the greatest industrial importance [3][9][29][30][31]. Noteworthy, there are only rare and sporadic publications describing the synthesis and properties of the Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring [32][33][34][35][36][37][38]. Thus, the present work opens a series

• ruthenium atom. The ruthenium-containing six-membered ring has a slightly distorted envelope conformation with a ca. 51° to 54° deviation of the nitrogen atom from the mean plane of other five atoms. The most important feature of the catalyst structure is the length of the ruthenium–nitrogen bond, which

• synthesis of 2-(N,N-dialkylaminomethyl)styrenes. The resultant vinyl benzenes are excellent precursors for the synthesis of a new type of Hoveyda–Grubbs catalysts bearing an N→Ru coordinate bond in a six-membered ring. This process does not require the use of complex equipment, extremely expensive or toxic

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• formation of the metallacyclobutane intermediate. The modest activities of butenyl and pentenyl sulfides were rationalized by the formation of five and six-membered ring chelates. The aqueous CM with allyl sulfides was also exploited by Hunter et al. for the generation of a metathesis-based dynamic

Synthesis, biophysical properties, and RNase H activity of 6’-difluoro[4.3.0]bicyclo-DNA

• Sibylle Frei,
• Adam K. Katolik and
• Christian J. Leumann

Beilstein J. Org. Chem. 2019, 15, 79–88, doi:10.3762/bjoc.15.9

• denaturation experiments with complementary RNA displayed a duplex stabilization for FHNA and a duplex destabilization for Ara-FHNA. The reason for the stabilization of the former was accounted to a combination of the increased rigidity of the six-membered ring and the positioning of the axial oriented

6’-Fluoro[4.3.0]bicyclo nucleic acid: synthesis, biophysical properties and molecular dynamics simulations

• Sibylle Frei,
• Andrei Istrate and
• Christian J. Leumann

Beilstein J. Org. Chem. 2018, 14, 3088–3097, doi:10.3762/bjoc.14.288

• orientation and the six-membered ring in a twist-boat conformation (Figure 3b). Approximately 1 kJ/mol higher in energy was the second conformer where the furanose unit adopted a C3’-exo arrangement and the cyclohexene unit a half-chair conformation (Figure 3c). The C(5’) hydroxy group adopted in both

Copper(I)-catalyzed tandem reaction: synthesis of 1,4-disubstituted 1,2,3-triazoles from alkyl diacyl peroxides, azidotrimethylsilane, and alkynes

• Muhammad Israr,
• Changqing Ye,
• Munira Taj Muhammad,
• Yajun Li and
• Hongli Bao

Beilstein J. Org. Chem. 2018, 14, 2916–2922, doi:10.3762/bjoc.14.270

• excellent yields. Phenylacetylene with an electron-withdrawing bromo-, chloro-, or fluoro substituent afforded the corresponding products 3h–n in up to 92% yield, while phenylacetylenes with electron-donating groups gave the corresponding products 3b–g and 3o–q in up to 86% yield. Instead of a six-membered

• ring, five-membered heteroaromatics (ethynylthiophenes) have also been used, and afforded the desired products 3s and 3t in up to 76% yield. Terminal aliphatic alkynes were then examined and it was found that they could smoothly deliver the corresponding 1,2,3-triazoles 3u–z with high yields

Ring-opening metathesis of some strained bicyclic systems; stereocontrolled access to diolefinated saturated heterocycles with multiple stereogenic centers

• Zsanett Benke,
• Melinda Nonn,
• Márton Kardos,
• Santos Fustero and
• Loránd Kiss

Beilstein J. Org. Chem. 2018, 14, 2698–2707, doi:10.3762/bjoc.14.247

• that unsaturated bicyclic β-lactams (±)-2 and (±)-8, bearing the fused four-membered and six-membered ring system, have a lower ring strain than bicyclic, unsaturated γ-lactones (±)-3, (±)-4 and (±)-9. Because of their higher constraint, the latter compounds underwent ring opening providing the

• carbene-based catalysts (G-2 and HG-2) were effective in case of bridged lactones with a six-membered ring part in their framework, with O-functionalities (±)-3, (±)-4, (±)-9 and (±)-14. In case of isoxazoline-fused derivative (±)-16 G-1 gave the best result, while in case of lactam (±)-18 HG-1 was the

• -membered ring system thus possessing ring strain, did not afford any ROM products. Interestingly, lactone (±)-3 in the presence of second generation catalysts (G-2 and HG-2) provided the corresponding ring-opened compound (±)-5 albeit with modest yields (Scheme 3, Table 1). In the presence of G-2 and HG-2

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• of bicyclic diterpenoids sharing the eunicellane skeleton. Closure of the ten-membered ring by pinacol cyclization proved to be possible, if the six-membered ring is either aromatic or a 1,3-cyclohexadiene, but failed for systems with two sp3 centers as bridgeheads. The ten-membered ring of benzene

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• six-membered-ring transition state similar to that described earlier by Feng et al. [69]. Epoxidation In 2014 Sciotto et al. reported the synthesis of two novel calix[4]arene–salen ligands 105a,b in 1,3-alternate conformation. Reaction of the salen ligands with appropriate metal acetate salt according

Stepwise radical cation Diels–Alder reaction via multiple pathways

• Ryo Shimizu,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 704–708, doi:10.3762/bjoc.14.59

• one of the most powerful methods to construct six-membered ring systems. A “normal” Diels–Alder reaction must consider an electronic matching of the substrates, with an electron-rich diene and electron-deficient dienophile as the general combination. Although having both an electron-rich diene and

• cation 1·+ is then trapped by 2,3-dimethyl-1,3-butadiene (2) to construct the acyclic radical cation intermediate A·+, which is potentially converted into the aromatic radical cation with a six-membered ring (3·+) or a four-membered ring (4·+) via rapid intramolecular SET processes. It can be

• rationalized that the six-membered ring closure of the acyclic radical cation intermediate (A·+) would be a stepwise process, leading to the Diels–Alder adduct 3 as an approximately cis/trans = 1:1 mixture. However, since the oxidative SET-triggered rearrangement of the vinylcyclobutane 4 gives the Diels–Alder

Liquid-assisted grinding and ion pairing regulates percentage conversion and diastereoselectivity of the Wittig reaction under mechanochemical conditions

• Kendra Leahy Denlinger,
• Lianna Ortiz-Trankina,
• Preston Carr,
• Kingsley Benson,
• Daniel C. Waddell and
• James Mack

Beilstein J. Org. Chem. 2018, 14, 688–696, doi:10.3762/bjoc.14.57

• mechanism of the E selectivity is similar. The intermediate (Scheme 1) allows for a reaction pathway involving the formation of a six-membered ring instead of the traditional four-membered oxaphosphetane ring of the Wittig reaction. This six-membered ring may account for the higher E selectivity due to the

• present, its dielectric constant will be the determining factor in diastereoselectivity, consistent with our previous observations. Counter-ion pairing We further hypothesized that, if the benzyl benzoate is formed through a six-membered ring intermediate to give (E)-stilbene as the major product, then

• cation into the mechanism, a six-membered ring, similar to that proposed in Scheme 2, would result (Figure 3). Based on this hypothesis, in addition to the oxygen and phosphorous forming a stable bond, the alkali metal and halide must form a stable contact ion pair as well. These interactions and the

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• , reactions of 5-aminopyrazoles with various reagents to construct a six membered ring with pyrazole are discussed. The synthetic methods have been arranged in order of the ascending number of heteroatoms in the azine ring. The systematic arrangement in this review explores the possibility of providing

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• trifluoromethylation of (hetero)arenes under photoredox catalysis. Direct C–H trifluoromethylation of five- and six-membered ring (hetero)arenes using heterogeneous catalysis. Trifluoromethylation of terminal olefins. Trifluoromethylation of enamides. (E)-Selective trifluoromethylation of β-nitroalkenes under

Ring-size-selective construction of fluorine-containing carbocycles via intramolecular iodoarylation of 1,1-difluoro-1-alkenes

• Takeshi Fujita,
• Ryo Kinoshita,
• Tsuyoshi Takanohashi,
• Naoto Suzuki and
• Junji Ichikawa

Beilstein J. Org. Chem. 2017, 13, 2682–2689, doi:10.3762/bjoc.13.266

• -difluoroallylic moiety, which might perturb cationic charge distribution in the corresponding cyclic iodonium intermediates. The aryl group in the 2-position (at the carbon atom in β-position to the fluorine substituents) promoted a six-membered-ring closure, most likely because of the localization of cationic

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

• shown in Figure 3. Furthermore, a six-membered ring involving the salt cation, the azlactone ring and the enolate might be involved in the addition step. Irreversible intramolecular cyclization of 4 gave 5 (for a reaction reversibility study of product 2h, see Supporting Information File 1), eventually

What contributes to an effective mannose recognition domain?

• Christoph P. Sager,
• Deniz Eriş,
• Martin Smieško,
• Rachel Hevey and
• Beat Ernst

Beilstein J. Org. Chem. 2017, 13, 2584–2595, doi:10.3762/bjoc.13.255

• the six-membered ring counterpart, effectively increasing the entropic cost of binding to FimHLD (I), while the enthalpic fingerprint observed for both ligands was identical. However, depending on its needs, UPEC can vary the conformational state of FimH. In the unbound state, FimH exhibits the low