Formaldehyde surrogates in multicomponent reactions

• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Bernhard Westermann

Beilstein J. Org. Chem. 2025, 21, 564–595, doi:10.3762/bjoc.21.45

Synthesis, structure, ionochromic and cytotoxic properties of new 2-(indolin-2-yl)-1,3-tropolones

• Yurii A. Sayapin,
• Eugeny A. Gusakov,
• Inna O. Tupaeva,
• Alexander D. Dubonosov,
• Igor V. Dorogan,
• Valery V. Tkachev,
• Anna S. Goncharova,
• Gennady V. Shilov,
• Natalia S. Kuznetsova,
• Svetlana Y. Filippova,
• Tatyana A. Krasnikova,
• Yanis A. Boumber,
• Alexey Y. Maksimov,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2025, 21, 358–368, doi:10.3762/bjoc.21.26

• contraction and the formation of 2-azabicyclic products and pyridino[1,2-a]benzo[e]indol-10,11-diones [24]. o-Chloranil was found to be the most efficient 1,2-benzoquinone, which engages in o-quinone ring-expansion reactions with 2,3,3-trimethylindolenines to form hard-to-reach polychlorinated derivatives of

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

Antibiofilm and cytotoxic metabolites from the entomopathogenic fungus Samsoniella aurantia

• Rita Toshe,
• Syeda J. Khalid,
• Blondelle Matio Kemkuignou,
• Esteban Charria-Girón,
• Paul Eckhardt,
• Birthe Sandargo,
• Kunlapat Nuchthien,
• J. Jennifer Luangsa-ard,
• Till Opatz,
• Hedda Schrey,
• Sherif S. Ebada and
• Marc Stadler

Beilstein J. Org. Chem. 2025, 21, 327–339, doi:10.3762/bjoc.21.23

• (2) and B (3) [8] together with three cyclodepsipeptides beauvericins A–C (4–6) [14][15]. Farinosones (1–3) belong to a class of tetramic acid metabolites related to tenellin congeners that are prone to oxidative ring expansion affording their corresponding 2-pyridone derivatives. Based on a

• -ketoheptaketide that would in turn combine to a tyrosine moiety bound to NRPS to afford the first tetramic acid derivative. Then, oxygenation at C-2’ of the afforded first product followed by tautomerization would yield farinosone D (1), whereas oxidative ring expansion instead of tautomerization would produce

Radical reactivity of antiaromatic Ni(II) norcorroles with azo radical initiators

• Siham Asyiqin Shafie,
• Ryo Nozawa,
• Hideaki Takano and
• Hiroshi Shinokubo

Beilstein J. Org. Chem. 2024, 20, 1967–1972, doi:10.3762/bjoc.20.172

• ]. Moreover, the ring-expansion or ring-opening reactions of Ni(II) norcorroles are induced by an activated zwitterionic intermediate [22], oxidants [23][24], and carbenes [25][26]. During the last decade, the various reactivities of Ni(II) norcorroles have been elucidated. However, the reaction with radical

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• . Jung and Shinde, on the other hand, synthetized a supramolecular acid catalyst 14 combining β-cyclodextrins with succinic acid and tested it in a GBB reaction between isatin (15), indazol-3-amine (16) and pentyl isocyanide (17), yielding, after a ring expansion triggered by a retro-aza-ene reaction via

(Bio)isosteres of ortho- and meta-substituted benzenes

• H. Erik Diepers and
• Johannes C. L. Walker

Beilstein J. Org. Chem. 2024, 20, 859–890, doi:10.3762/bjoc.20.78

• (±)-30. In a related strategy, Procter and co-workers prepared 1,2-BCHs (±)-33a–e from BCBs 32 via a SmI2-catalysed radical relay alkene insertion (Scheme 3C) [35]. This approach relied on single-electron reduction of the ketone moiety and ring-expansion from the ketyl radical anion. Electron-deficient

• catalytic system of B2cat2 and 4-phenylpyridine to form pyridine-boryl radicals which initiated ring expansion. The method was shown to be similarly tolerable of functional groups as Procter’s synthesis. Intramolecular crossed [2 + 2] cycloadditions offer an alternative approach to 1,2-disubstituted BCHs

Chemical and biosynthetic potential of Penicillium shentong XL-F41

• Ran Zou,
• Xin Li,
• Xiaochen Chen,
• Yue-Wei Guo and
• Baofu Xu

Beilstein J. Org. Chem. 2024, 20, 597–606, doi:10.3762/bjoc.20.52

• enzymatic ring-expansion process in their respective fungi. Both shentonins A (1) and B (2) also feature a reduction of a carbonyl to a hydroxy group within the succinimide ring. All isolated compounds were subjected to antimicrobial evaluations, and compound 12 was found to have moderate inhibitory

Synthesis of π-conjugated polycyclic compounds by late-stage extrusion of chalcogen fragments

• Aissam Okba,
• Pablo Simón Marqués,
• Kyohei Matsuo,
• Naoki Aratani,
• Hiroko Yamada,
• Gwénaël Rapenne and
• Claire Kammerer

Beilstein J. Org. Chem. 2024, 20, 287–305, doi:10.3762/bjoc.20.30

• naphthyl substituents carrying each an alkyne moiety on the ortho position. Ring expansion of both thiophene units in 19 was then triggered by platinum catalysis to generate the corresponding thiopyrans, and finally the bromine atoms located on the latter rings were exploited for the ring closure of the

Synthesis of spiropyridazine-benzosultams by the [4 + 2] annulation reaction of 3-substituted benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes

• Wenqing Hao,
• Long Wang,
• Jinlei Zhang,
• Dawei Teng and
• Guorui Cao

Beilstein J. Org. Chem. 2024, 20, 280–286, doi:10.3762/bjoc.20.29

• bond under basic conditions. Finally, the ring expansion led to intermediate C which was then hydrolyzed to 4aa. Conclusion In conclusion, we have developed a [4 + 2] annulation reaction of 3-substituted benzo[d]isothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes for the efficient preparation of

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• , which underwent a ring expansion and 1,2-sulfur migration and subsequent deprotonation/aromatization to deliver product 16. Another work in the use of AlCl3 for cyclization of N‑arylpropynamides 17 with N‑sulfanylsuccinimides 1 was described by Gao and Zhou et al. (Scheme 12) [51]. Annulation in the

Synthesis of imidazo[4,5-e][1,3]thiazino[2,3-c][1,2,4]triazines via a base-induced rearrangement of functionalized imidazo[4,5-e]thiazolo[2,3-c][1,2,4]triazines

• Dmitry B. Vinogradov,
• Alexei N. Izmest’ev,
• Angelina N. Kravchenko,
• Yuri A. Strelenko and
• Galina A. Gazieva

Beilstein J. Org. Chem. 2023, 19, 1047–1054, doi:10.3762/bjoc.19.80

• esters are also suitable substrates for the reaction. In this case hydrolysis and thiazole ring expansion were accompanied with the change of the thiazolotriazine junction type from thiazolo[3,2-b][1,2,4]triazine to thiazino[2,3-c][1,2,4]triazine. Keywords: N,S-heterocycles; ring expansion; skeletal

• ][1,3]thiazino[2,3-c][1,2,4]triazines 3a–i as a result of ester group hydrolysis and thiazolidine ring expansion to the corresponding thiazine (Scheme 3). The potassium salts 3a,b were isolated in 81 and 63% yield, respectively. Compounds 3c–i were used in further transformations without isolation. 1H

First synthesis of acylated nitrocyclopropanes

• Kento Iwai,
• Rikiya Kamidate,
• Khimiya Wada,
• Haruyasu Asahara and
• Nagatoshi Nishiwaki

Beilstein J. Org. Chem. 2023, 19, 892–900, doi:10.3762/bjoc.19.67

• , but a dihydrofuran, so the cyclopropane 1b’ reported in the literature [12][13][19] is presumably incorrect [22]. In the cases of donor–acceptor cyclopropanes possessing an electron-donating group such as an alkoxy or amino group, ring expansion caused by an intramolecular attack of nitro oxygen

• elimination of nitrous acid, accompanied by aromatization, yielded furan 13. In addition to the stepwise mechanism, a concerted ring-expansion can be also acceptable [25]. Conclusion Although nitrocyclopropanedicarboxylic acid esters 1a have been used in organic syntheses, nitrocyclopropanes possessing an

• ). A plausible mechanism for formation of cyclopropane 1 and dihydrofuran 8. Tin(II)-mediated ring expansion of nitrocyclopropane 1e. Michael addition of 1,3-dicarbonyl compounds 3b–g to nitrostyrene 2a. Comparison of the 1H NMR data of ring protons for compounds 1a, 1b’, and product 8b. Cyclization of

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• compound 12. Meanwhile, Campaña, Morcillo, and co-workers converted the eight-membered ring 11 to nonagon-containing carbohelicene 14 through a single ring expansion reaction by treating 11 with TMSCHN2 (Scheme 2). By reacting with Tebbe’s reagent, compound 14 could be converted to all-carbon analogue 15

Strategies in the synthesis of dibenzo[b,f]heteropines

• David I. H. Maier,
• Barend C. B. Bezuidenhoudt and
• Charlene Marais

Beilstein J. Org. Chem. 2023, 19, 700–718, doi:10.3762/bjoc.19.51

• Ring expansion through rearrangement Several methods utilise ring expansion to prepare the required 7-membered azepine and oxepine rings of 1a and 1b. 2.1 Ring expansion of acridin-9-ylmethanols In 1960, Bergmann and Rabinovitz [43] reported a simple ring expansion of acridin-9-ylmethanol (23) to 1a in

• unsubstituted as well as chloro-substituted derivatives of 1a. Storz et al. [44] have reported on an analogous method to prepare dibenzo[b,f]oxepines 1b through the rearrangement of 9-(α-hydroxyalkyl)xanthenes. 2.2 Ring expansion of 2-(9-xanthenyl)malonates Oxidative ring expansion of 2-(9-xanthenyl)malonates

• the enol carboxylate and subsequent 1,2 radical rearrangement and decarboxylation. Moderate to good yields of dibenzo[b,f]oxepine carboxylates 25 were achieved (63–85%). Stopka et al. [46] reported on tandem C–H functionalisation and ring expansion as an alternative to the Wagner–Meerwin rearrangement

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

• -positive and Gram-negative bacteria (Scheme 31B). 4.4 Photocatalyzed oxidative ring expansion: alternative radical chemistry for pleuromutilin scaffold construction Following the advent of photoredox catalysis in ring-opening and ring-expansion chemistry [75], a new route was proposed by Foy and Pronin to

• articulated around a ring expansion of a fused cyclobutane/perhydroindanone fragment, leading to the cyclooctane motif. Interestingly, and unlike the previously reported strategies, the perhydroindanone precursor was prepared starting from achiral building blocks 157 and 158. They were engaged in a selective

• formation of the fused cyclobutane acid 162 as the desired precursor for the cyclooctane formation. The ring expansion was achieved in the presence of an iridium catalyst and under blue LED irradiation, via the trapping by TEMPO or O2 of the cyclobutyl radical resulting from decarboxylation, which allowed a

1,4-Dithianes: attractive C2-building blocks for the synthesis of complex molecular architectures

• Bram Ryckaert,
• Ellen Demeyere,
• Frederick Degroote,
• Hilde Janssens and
• Johan M. Winne

Beilstein J. Org. Chem. 2023, 19, 115–132, doi:10.3762/bjoc.19.12

• pioneered by Parham and co-workers to be the most suited (Scheme 4, 12 → 2) [28][29][30]. Parham described a ring expansion of 1,3-dithiolanes derived from α-halocarbonyls into the 1,4-dithianes which then dehydrohalogenate to afford dihydrodithiins. The ring expansion involves a 1,2-sulfur migration of a β

• -haloalkylsulfide via a cyclic sulfonium intermediate, which then ring opens and eliminates the halide to give the unsaturated 1,4-dithiane ring. We have found this Parham ring expansion to be the most practical preparatory procedure for 2 on large scale [30]. Thus, a simple condensation of ethane-1,2-dithiol (10

• then brominated with an excess of bromination reagent, which effects the 1,2-sulfur-migratory ring expansion, followed by bromination-induced dehydrogenation to the aromatic ring [31]. At the time of writing this review, the resulting benzoannelated dithiane 5 is also commercially available in small

Catalytic aza-Nazarov cyclization reactions to access α-methylene-γ-lactam heterocycles

• Bilge Banu Yagci,
• Selin Ezgi Donmez,
• Onur Şahin and
• Yunus Emre Türkmen

Beilstein J. Org. Chem. 2023, 19, 66–77, doi:10.3762/bjoc.19.6

• enantioselective organocatalytic aza-Nazarov cyclization affording six-membered heterocycles after a ring expansion of the cyclization products [22]. Rasapalli and co-workers recently developed an efficient aza-Nazarov cyclization of quinazolinonyl enones promoted by TfOH or MsOH (methanesulfonic acid) for the

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

• Péter Kisszékelyi,
• Tibor Peňaška,
• Klára Stankovianska,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 1195–1202, doi:10.3762/bjoc.18.124

• -3(4H)-ones were also prepared by cyclization of 1,2-diaryldisulfanes with dialkyl but-2-ynedioates [24][25]. N-Substituted benzo-1,4-thiazine-2-carboxylates 4 (Figure 1) were prepared by m-CPBA-mediated oxidative ring expansion of substituted benzothiazoles [26], or via copper-catalyzed

An isoxazole strategy for the synthesis of 4-oxo-1,4-dihydropyridine-3-carboxylates

• Timur O. Zanakhov,
• Ekaterina E. Galenko,
• Mikhail S. Novikov and
• Alexander F. Khlebnikov

Beilstein J. Org. Chem. 2022, 18, 738–745, doi:10.3762/bjoc.18.74

• -aryl-, 2-aryl-6-aryl and 2,6-diaryl-5-aryl/hetaryl-substituted methyl 4-oxo-1,4-dihydropyridine-3-carboxylates by Mo(CO)6-mediated ring expansion of methyl 2-(isoxazol-5-yl)-3-oxopropanoates. The high reactivity of 4-oxo-1,4-dihydropyridine-3-carboxylates synthesized provide easy access to 2,4,6

• -triaryl-substituted and 1,2,5,6-tetrasubstituted nicotinates. Keywords: isoxazole; methyl nicotinate; molybdenum hexacarbonyl; 4-pyridone; ring expansion; Introduction Pyridine moieties are present in many natural products, drugs, pesticides and industrial materials. Pyridine fragments are used in drugs

Unusual highly diastereoselective Rh(II)-catalyzed dimerization of 3-diazo-2-arylidenesuccinimides provides access to a new dibenzazulene scaffold

• Anastasia Vepreva,
• Alexander S. Bunev,
• Andrey Yu. Kudinov,
• Grigory Kantin,
• Mikhail Krasavin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2022, 18, 533–538, doi:10.3762/bjoc.18.55

• intermediate D into cycloheptadiene E is an example of a relatively rare reaction of the cyclopropane-ring expansion through a 1,5-C‒C bond migration [15][16][17]. This concerted process is followed by yet another 1,5-migration of the hydrogen atom, leading to the final dimer 2a. The formation of a single

Efficient synthesis of ethyl 2-(oxazolin-2-yl)alkanoates via ethoxycarbonylketene-induced electrophilic ring expansion of aziridines

• Yelong Lei and
• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 70–76, doi:10.3762/bjoc.18.6

• alkoxycarbonylketenes, which undergo an electrophilic ring expansion with aziridines to afford alkyl 2-(oxazolin-2-yl)alkanoates in good to excellent yields under microwave heating. The method is a convenient and clean reaction without any activators and catalysts and can be also applied in the synthesis of 2-(oxazolin

• -2-yl)alkanamides and 1-(oxazolin-2-yl)alkylphosphonates. Keywords: aziridine; diazooxoester; diazo compound; ketene; oxazoline; ring expansion; Introduction Oxazoline derivatives are an important class of nitrogen and oxygen-containing five-membered unsaturated heterocycles [1] and widely exist in

• -diazo-3-oxoalkanoates first generate alkoxycarbonylketenes, which undergo an electrophilic ring expansion with aziridines to afford alkyl 2-(oxazolin-2-yl)alkanoates in good to excellent yields under microwave heating. The current method is an activator- and catalyst-free, and clean synthetic strategy

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• use of aldehydes (R′ = H), which are usually less stable than their ketone counterparts; (2) ring expansion (Z, R = cyclic) or contraction (Z, R′ = cyclic) of strained cyclic α-ketols; (3) the use of α-dicarbonyl compounds (R′ = acyl, ester, amide, etc.), which lead to more stable β-dicarbonyl

• excellent yields (>85%), but the two most strongly electron-withdrawing, para-CF3 and meta-CH3, had lower yields (59% and 67%, respectively). Instead of a ring expansion driving the rearrangement, the authors also tested a series of α,α-diaryl-α-hydroxyaldehydes 12 and their corresponding aldimines 14

• concept by application to isolated reactions, while in the following section, examples of tandem reactions in total syntheses are given. Inspired by the direct ring expansion of 1-alkynylcyclobutanols to α-methylenecyclopentanones catalyzed by gold reported by Toste and co-workers [9], Kim et al

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