Recent advances in total synthesis of illisimonin A

• Juan Huang and
• Ming Yang

Beilstein J. Org. Chem. 2025, 21, 2571–2583, doi:10.3762/bjoc.21.199

• NaOH facilitated a retro-Claisen reaction, yielding the intermediate 106, which subsequently underwent an intramolecular aldol reaction to form the five-membered ring. The resulting carboxylic acid was then esterified with TMSCHN2 to furnish ester 107, which possesses the characteristic tricyclo

Total syntheses of highly oxidative Ryania diterpenoids facilitated by innovations in synthetic strategies

• Zhi-Qi Cao,
• Jin-Bao Qiao and
• Yu-Ming Zhao

Beilstein J. Org. Chem. 2025, 21, 2553–2570, doi:10.3762/bjoc.21.198

• of (+)-ryanodol (4) in just 15 steps, highlighting the Pauson–Khand cyclization and a selenium dioxide-mediated selective oxidation as key transformations [48] (Scheme 7). To construct the multi-substituted five-membered ring in the target molecule, the authors strategically employed the Pauson–Khand

The intramolecular stabilizing effects of O-benzoyl substituents as a driving force of the acid-promoted pyranoside-into-furanoside rearrangement

• Alexey G. Gerbst,
• Sofya P. Nikogosova,
• Darya A. Rastrepaeva,
• Dmitry A. Argunov,
• Vadim B. Krylov and
• Nikolay E. Nifantiev

Beilstein J. Org. Chem. 2025, 21, 2456–2464, doi:10.3762/bjoc.21.187

• five-membered ring due to the formation of an intramolecular hydrogen bond (Figure 2A). It has been shown that furanoside is preferentially formed in nonpolar solvents such as toluene. This form was successfully fixed and purified as benzoate derivative. Bulky substituents can also stabilize the

Synthetic study toward vibralactone

• Liang Shi,
• Jiayi Song,
• Yiqing Li,
• Jia-Chen Li,
• Shuqi Li,
• Li Ren,
• Zhi-Yun Liu and
• Hong-Dong Hao

Beilstein J. Org. Chem. 2025, 21, 2376–2382, doi:10.3762/bjoc.21.182

• alkylidene carbene. Therefore, we modified the synthetic sequence and opted to construct the five-membered ring prior to β-lactone formation, identifying intermediate 19 as a potentially suitable precursor. From 19, after treatment with lithiotrimethylsilyldiazomethane [45], only tetrahydrofuran 22 was

• 1,3-diol intermediate was transformed into acetonide 25 (Scheme 5). Subsequently, the desired five-membered ring was successfully constructed through the in situ-generated alkylidene carbene 26 followed by C–H insertion; herein lies a significant electronic effect influencing this crucial step. With

Recent advances in Norrish–Yang cyclization and dicarbonyl photoredox reactions for natural product synthesis

• Peng-Xi Luo,
• Jin-Xuan Yang,
• Shao-Min Fu and
• Bo Liu

Beilstein J. Org. Chem. 2025, 21, 2315–2333, doi:10.3762/bjoc.21.177

• conditions (300 W Xe lamp, MeOH/CH3CN = 3:1, −78 °C) induced the formation of the five-membered ring, forming spiroacetal (−)-107 in 68% yield with nearly complete configurational integrity (98% ee). This high stereoselectivity is attributed to three factors: (1) polar solvents enhance yields by accelerating

Pathway economy in cyclization of 1,n-enynes

• Hezhen Han,
• Wenjie Mao,
• Bin Lin,
• Maosheng Cheng,
• Lu Yang and
• Yongxiang Liu

Beilstein J. Org. Chem. 2025, 21, 2260–2282, doi:10.3762/bjoc.21.173

• polycyclic aromatic heterocycles (Scheme 15) [23]. Catalysts bearing the strong σ-donating IPr ligand exhibited a marked preference for the 5-exo-dig cyclization pathway, affording five-membered ring product 70 (Scheme 15, path a). When a bulky Me4XPhos ligand was employed, the reaction favored 6-endo-dig

Electrochemical cyclization of alkynes to construct five-membered nitrogen-heterocyclic rings

• Lifen Peng,
• Ting Wang,
• Zhiwen Yuan,
• Bin Li,
• Zilong Tang,
• Xirong Liu,
• Hui Li,
• Guofang Jiang,
• Chunling Zeng,
• Henry N. C. Wong and
• Xiao-Shui Peng

Beilstein J. Org. Chem. 2025, 21, 2173–2201, doi:10.3762/bjoc.21.166

• reaction mechanisms are disclosed if available. Keywords: alkyne; catalysis; cyclization; electrochemistry; five-membered ring; Introduction Organic five-membered rings, an essential class of organic compounds, not only are frequently used as important starting materials, intermediates or ligands in

The application of desymmetric enantioselective reduction of cyclic 1,3-dicarbonyl compounds in the total synthesis of terpenoid and alkaloid natural products

• Dong-Xing Tan and
• Fu-She Han

Beilstein J. Org. Chem. 2025, 21, 2085–2102, doi:10.3762/bjoc.21.164

• -cyclopentanedione derivative was adopted as one of the key reactions, which facilitated the construction of the five-membered ring bearing an all-carbon quaternary center as the key chiral building block. Their synthesis began with 1,3-dione 40 (Scheme 2) [31][32], allylation of this substrate with allylic bromide

Approaches to stereoselective 1,1'-glycosylation

• Daniele Zucchetta and
• Alla Zamyatina

Beilstein J. Org. Chem. 2025, 21, 1700–1718, doi:10.3762/bjoc.21.133

Formal synthesis of a selective estrogen receptor modulator with tetrahydrofluorenone structure using [3 + 2 + 1] cycloaddition of yne-vinylcyclopropanes and CO

• Jing Zhang,
• Guanyu Zhang,
• Hongxi Bai and
• Zhi-Xiang Yu

Beilstein J. Org. Chem. 2025, 21, 1639–1644, doi:10.3762/bjoc.21.127

• annulation to construct the C ring (cyclohexenone ring), and an intramolecular SN2 reaction to build the D ring (five-membered ring) [15][16][17][18]. In 2013, Wallace and co-workers disclosed the second route for this molecule (Scheme 2B) [19], in which the five-membered ring B was formed by utilizing

Facile synthesis of hydantoin/1,2,4-oxadiazoline spiro-compounds via 1,3-dipolar cycloaddition of nitrile oxides to 5-iminohydantoins

• Juliana V. Petrova,
• Varvara T. Tkachenko,
• Victor A. Tafeenko,
• Anna S. Pestretsova,
• Vadim S. Pokrovsky,
• Maxim E. Kukushkin and
• Elena K. Beloglazkina

Beilstein J. Org. Chem. 2025, 21, 1552–1560, doi:10.3762/bjoc.21.118

• in the formation of two new carbon–heteroatom bonds and the formation of a five-membered ring. Thus, the aryl attached to the nitrogen atom from the dipolarophile fragment is brought closer to the substituent from the C-end of the dipole. This proximity in the presence of ortho-substituents in the

Wittig reaction of cyclobisbiphenylenecarbonyl

• Taito Moribe,
• Junichiro Hirano,
• Hideaki Takano,
• Hiroshi Shinokubo and
• Norihito Fukui

Beilstein J. Org. Chem. 2025, 21, 1454–1461, doi:10.3762/bjoc.21.107

• nucleophilic substitution of the thus generated alkoxide to form an oxygen-containing five-membered ring. At least, density functional theory (DFT) calculations support that the nucleophilic attack of methylenetriphenylphosphorane to the exo-methylene unit is slightly favorable over reaction with the carbonyl

Development and mechanistic studies of calcium–BINOL phosphate-catalyzed hydrocyanation of hydrazones

• Carola Tortora,
• Christian A. Fischer,
• Sascha Kohlbauer,
• Alexandru Zamfir,
• Gerd M. Ballmann,
• Jürgen Pahl,
• Sjoerd Harder and
• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2025, 21, 755–765, doi:10.3762/bjoc.21.59

• -state structure, two bonds (Ca–O and Si–C) are broken, while a Si–O bond is simultaneously formed, in a concerted step implying a cyclic flow of six electrons in a five-membered ring. The isocyanide Ca–N–C bond angle in TS 11-12 lies between that of 7 and 9. While the replacement step is slow, and hence

Origami with small molecules: exploiting the C–F bond as a conformational tool

• Patrick Ryan,
• Ramsha Iftikhar and
• Luke Hunter

Beilstein J. Org. Chem. 2025, 21, 680–716, doi:10.3762/bjoc.21.54

• rate and the β-stereoselectivity of the glycosylation reaction (e.g., 63 → 65 vs 64 → 66, Figure 9) [129]. Of course, the fluorine substituent remains in the product, which may or may not be advantageous depending on the particular biological context. Let us now consider furanoses (i.e., five-membered

• ring sugars). Five-membered rings are inherently more flexible than six-membered rings, so there is more scope for fluorine to influence the pucker. When fluorine is introduced anywhere across C-1–C-3 as a replacement for a hydroxy group (e.g., 67 and 68, Figure 9), the preferred ring pucker is

Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• also applied to o-carboranes fused with five-membered ring systems [39][40]. The positioning of the heteroatom in these exo rings governs bonding, leading to restricted conjugation and, consequently, no aromatic stabilization. Importantly, the magnetic field generated by the 3D cluster influences the

• the carborane and the pyrazole, i.e., B–B, C–B and C–C decrease from 1.760, to 1.674 and to 1.605 Å, respectively (Figure 2). Thus, the longer the length of the fusing bond, the lower the tension of the formed five-membered ring and the more stable the complex. The stronger strength of the C–B bond

• , although 2-pyrazoline presents a shorter 1.40 Å distance (Figure 2). Thus, and based on the above geometrical data, compared to either pyrazole or indazole molecules, can the pyrazole fused to o-carborane be referred as pyrazole? Or otherwise, should we refer to this five-membered ring as pyrazoline due to

Synthesis, characterization, antimicrobial, cytotoxic and carbonic anhydrase inhibition activities of multifunctional pyrazolo-1,2-benzothiazine acetamides

• Ayesha Saeed,
• Shahana Ehsan,
• Muhammad Zia-ur-Rehman,
• Erin M. Marshall,
• Sandra Loesgen,
• Abdus Saleem,
• Simone Giovannuzzi and
• Claudiu T. Supuran

Beilstein J. Org. Chem. 2025, 21, 348–357, doi:10.3762/bjoc.21.25

• dry DMF. The five-membered ring of this esterified benzisothiazole 2 was then expanded to form a six-membered cycle via a ring-expansion reaction in anhydrous conditions. In this reaction, the benzisothiazole scaffold was converted into a benzothiazine backbone 3 followed by N-methylation to obtain

Streamlined modular synthesis of saframycin substructure via copper-catalyzed three-component assembly and gold-promoted 6-endo cyclization

• Asahi Kanno,
• Ryo Tanifuji,
• Satoshi Yoshida,
• Sota Sato,
• Saori Maki-Yonekura,
• Kiyofumi Takaba,
• Jungmin Kang,
• Kensuke Tono,
• Koji Yonekura and
• Hiroki Oguri

Beilstein J. Org. Chem. 2025, 21, 226–233, doi:10.3762/bjoc.21.14

• , was obtained in one-pot, presumably via generation of the aminonitrile 17 and subsequent nucleophilic attack of the phenolic hydroxy group to form the five-membered ring. Our efforts to optimize this one-pot sequence led to the best results, affording 11 in 73% isolated yield, when acetone cyanohydrin

Emerging trends in the optimization of organic synthesis through high-throughput tools and machine learning

• Pablo Quijano Velasco,
• Kedar Hippalgaonkar and
• Balamurugan Ramalingam

Beilstein J. Org. Chem. 2025, 21, 10–38, doi:10.3762/bjoc.21.3

Synthesis, structure and π-expansion of tris(4,5-dehydro-2,3:6,7-dibenzotropone)

• Yongming Xiong,
• Xue Lin Ma,
• Shilong Su and
• Qian Miao

Beilstein J. Org. Chem. 2025, 21, 1–7, doi:10.3762/bjoc.21.1

• -membered ring, and one seven-membered ring, and the third one containing three benzene rings and two seven-membered rings. The crystal structure of 3·CH2Cl2 reveals that each unit cell contains a pair of enantiomers, (M,P,M)-3 and (P,M,P)-3, co-crystallized with two molecules of CH2Cl2. Here P and M

• than the colorless crystal of Cs-1. Slow evaporation of solvent from a solution of 3 in CH2Cl2/CH3OH resulted in the formation of single crystals suitable for X-ray crystallography [27]. Compound 3 consists of three [5]helicenoid moieties, with two of them containing three benzene rings, one five

Recent advances in transition-metal-free arylation reactions involving hypervalent iodine salts

• Ritu Mamgain,
• Kokila Sakthivel and
• Fateh V. Singh

Beilstein J. Org. Chem. 2024, 20, 2891–2920, doi:10.3762/bjoc.20.243

Synthesis of tricarbonylated propargylamine and conversion to 2,5-disubstituted oxazole-4-carboxylates

• Kento Iwai,
• Akari Hikasa,
• Kotaro Yoshioka,
• Shinki Tani,
• Kazuto Umezu and
• Nagatoshi Nishiwaki

Beilstein J. Org. Chem. 2024, 20, 2827–2833, doi:10.3762/bjoc.20.238

• acid amides and acetylides, respectively. When adduct 4 was treated with a base or ammonium acetate, ring closure proceeded to form a five-membered ring, accompanied by the elimination of the ethoxycarbonyl group. 2,5-Disubstituted oxazole-4-carboxylic acid derivatives are frequently found in

Computational design for enantioselective CO₂ capture: asymmetric frustrated Lewis pairs in epoxide transformations

• Maxime Ferrer,
• Iñigo Iribarren,
• Tim Renningholtz,
• Ibon Alkorta and
• Cristina Trujillo

Beilstein J. Org. Chem. 2024, 20, 2668–2681, doi:10.3762/bjoc.20.224

• this FLP is situated within a five-membered ring. Using this structural insight, an asymmetric catalyst was subsequently designed by strategically modifying the pyrrolidine substituent (C5 in Figure 4) based on the most efficient FLP. The coupling reaction proposed in Scheme 3 was studied. In order to

Anion-dependent ion-pairing assemblies of triazatriangulenium cation that interferes with stacking structures

• Yohei Haketa,
• Takuma Matsuda and
• Hiromitsu Maeda

Beilstein J. Org. Chem. 2024, 20, 2567–2576, doi:10.3762/bjoc.20.215

• 2+-B(C6F5)4−, the distance between the boron of B(C6F5)4− and the central carbon of TATA+ was 7.32 Å, with an offset angle of 47.1° (Figure 3d, Figure 7a, and Figures S14 and S20 in Supporting Information File 1). On the other hand, in 2+-PCCp−, the PCCp− unit (centroid of the five-membered ring

Photoredox-catalyzed intramolecular nucleophilic amidation of alkenes with β-lactams

• Valentina Giraldi,
• Giandomenico Magagnano,
• Daria Giacomini,
• Pier Giorgio Cozzi and
• Andrea Gualandi

Beilstein J. Org. Chem. 2024, 20, 2461–2468, doi:10.3762/bjoc.20.210

• stereocenter in the five-membered ring was attributed by 1H NMR analysis for 11c. Moreover, the configuration was also confirmed by NOE studies on the two isolated diastereoisomers, which confirmed the preferred trans-isomer formation (see Supporting Information File 1). Analysis of the dr values revealed that

Hypervalent iodine-mediated cyclization of bishomoallylamides to prolinols

• Smaher E. Butt,
• Konrad Kepski,
• Jean-Marc Sotiropoulos and
• Wesley J. Moran

Beilstein J. Org. Chem. 2024, 20, 2455–2460, doi:10.3762/bjoc.20.209

• amide at both the oxygen and the nitrogen, however, the ΔG‡ value for the latter was lower by 2.5 kcal·mol−1. This demonstrates a clear kinetic preference for formation of the five-membered ring over the seven-membered one [19]. Subsequent deprotonation of 11 leads to tertiary amide 12. Upon cyclization

• atoms separating the functional groups, cyclization at the amide oxygen occurs to generate five- and six-membered rings, respectively. However, when there is a three-carbon atom link, the corresponding seven-membered ring is not formed. Instead, cyclization at nitrogen occurs to generate a five-membered

• ring. We have performed DFT calculations to support the proposed change in mechanism and developed superior reaction conditions to effect this transformation. Finally, we have explored the substrate scope of this cyclization. Functional molecules containing a substituted pyrrolidine core. A) Our