Electrosynthetic access to unsymmetrical oxaza[8]helicenes with high chiral stability and strong circularly polarized luminescence (CPL)

• Tin Zar Aye,
• Rubal Sharma,
• Muthu Karuppasamy,
• Daiya Suzuki,
• Haruka Nakajima,
• Yoshitane Imai,
• Mitsuhiro Arisawa,
• Mohamed S. H. Salem and
• Shinobu Takizawa

Beilstein J. Org. Chem. 2026, 22, 372–382, doi:10.3762/bjoc.22.25

• characteristic transformations of the organosulfur functionality [32][33]. In 2024, Badani, Karnik, and co-workers accessed one member of this class, 7,12-dioxa[8]helicene I, through a sequence featuring photochemical E–Z isomerization, electrocyclization, and oxidative aromatization [34]. In parallel, Liu and

Reactivity umpolung of the cycloheptatriene core in hexa(methoxycarbonyl)cycloheptatriene

• Dmitry N. Platonov,
• Alexander Yu. Belyy,
• Rinat F. Salikov,
• Kirill S. Erokhin and
• Yury V. Tomilov

Beilstein J. Org. Chem. 2026, 22, 64–70, doi:10.3762/bjoc.22.2

• aryldiazonia involved electrophilic attacks onto the α-position. The azo compounds formed do not undergo a direct electrocyclization into norcaradienes 6h–k but through a preliminary 1,5-arylazo shift which proceeds in a single direction of the seven-membered ring (clockwise for the structure in Scheme 2) into

• further transformation in the case of allylation. Reactions with diazonium salts mainly involve a vicinal addition of the reagent to the anion and subsequent 1,5-sigmatropic shift, 6π-electrocyclization, and azocyclopropane rearrangement into dihydroindazole derivatives. Analysis of the reaction

Rotaxanes with integrated photoswitches: design principles, functional behavior, and emerging applications

• Jullyane Emi Matsushima,
• Khushbu,
• Zuliah Abdulsalam,
• Udyogi Navodya Kulathilaka Conthagamage and
• Víctor García-López

Beilstein J. Org. Chem. 2025, 21, 2345–2366, doi:10.3762/bjoc.21.179

• ). However, the cis isomer may undergo a 6π-electrocyclization, forming dihydrophenanthrene intermediates that further oxidize into phenanthrene derivatives, thereby irreversibly deactivating the photoswitch [75]. The first stilbene-based rotaxane was reported by Anderson and co-workers in 2001, featuring a

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

• reaction pathway. Tautomerization of intermediate 117 produced an aza-triene species, which underwent a 6π-aza-electrocyclization to afford 1,2-dihydropyridine derivatives 119 (Scheme 24, path b). This work established a divergent cycloisomerization of N-propargyl-N-vinyl sulfonamides governed by catalyst

Ambident reactivity of enolizable 5-mercapto-1H-tetrazoles in trapping reactions with in situ-generated thiocarbonyl S-methanides derived from sterically crowded cycloaliphatic thioketones

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Marcin Palusiak,
• Heinz Heimgartner,
• Marta Denel-Bobrowska and
• Agnieszka B. Olejniczak

Beilstein J. Org. Chem. 2025, 21, 1508–1519, doi:10.3762/bjoc.21.113

• regioselectivity in high yields. Upon heating to 65 °C in toluene solution, in analogy to the well-known compounds 2a and 2b, they extruded N2 and the in situ-generated reactive thiocarbonyl S-methanides 1c and 1d, in absence of any trapping reagent, underwent 1,3-dipolar electrocyclization yielding the

• crowded thioketones 7b [28], as well as 7c,d derived from cyclobutanedione. The in situ generation of sterically crowded thiocarbonyl S-methanides 1c,d (via a 1,3-dipolar cycloreversion) in absence of any trapping reagent and their electrocyclization (ring closure) leading to thiiranes 8a,b. Reactions of

Recent advances in synthetic approaches for bioactive cinnamic acid derivatives

• Betty A. Kustiana,
• Galuh Widiyarti and
• Teni Ernawati

Beilstein J. Org. Chem. 2025, 21, 1031–1086, doi:10.3762/bjoc.21.85

Recent advances in controllable/divergent synthesis

• Jilei Cao,
• Leiyang Bai and
• Xuefeng Jiang

Beilstein J. Org. Chem. 2025, 21, 890–914, doi:10.3762/bjoc.21.73

• different substituents and polysubstituted annular boronic acids 98, a Suzuki coupling was employed to synthesize advanced isoquinoline intermediates 100. Following this, a 6π electrocyclization reaction and nucleophilic reaction were developed to achieve C–C and C–N bond constructions, respectively

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

• rearrangement under mild conditions [6], and the Nazarov-type electrocyclization of alkenyl aryl carbinols [7]. Exploiting the ease with which calcium forms hydrides, hydrogenation of aldimines, transfer hydrogenation of alkenes, and even deuteration of benzene by an SNAr mechanism, have been recently achieved

Effect of substitution position of aryl groups on the thermal back reactivity of aza-diarylethene photoswitches and prediction by density functional theory

• Misato Suganuma,
• Daichi Kitagawa,
• Shota Hamatani and
• Seiya Kobatake

Beilstein J. Org. Chem. 2025, 21, 242–252, doi:10.3762/bjoc.21.16

• family of photochromic compounds. This study explores the photochromic properties and thermal back reactivities of various aza-diarylethene regioisomers (N1–N4 and I1–I4) in n-hexane. These molecules exhibit fast thermally reversible photochromic reactions driven by 6π aza-electrocyclization. Kinetic

Efficacy of radical reactions of isocyanides with heteroatom radicals in organic synthesis

• Akiya Ogawa and
• Yuki Yamamoto

Beilstein J. Org. Chem. 2024, 20, 2114–2128, doi:10.3762/bjoc.20.182

• electrocyclization reaction, the aza-Bergmann cyclization, takes place, selectively yielding nitrogen-containing 6-membered cyclization products (Scheme 19) [67]. The aza-Bergmann cyclization of ortho-alkynyl isocyanides proceeds under milder conditions than the Bergmann cyclization of endiynes, forming quinoline

A fiber-optic spectroscopic setup for isomerization quantum yield determination

• Anouk Volker,
• Jorn D. Steen and
• Stefano Crespi

Beilstein J. Org. Chem. 2024, 20, 1684–1692, doi:10.3762/bjoc.20.150

• reactant. This isomerization can be reversed by light of a different wavelength or thermal stimuli. Depending on the nature of the reactant, different classes of photoreactions can be utilized: double bond isomerizations, electrocyclization, cycloadditions, and electron-, hydrogen-, or group transfer [1

Bismuth(III) triflate: an economical and environmentally friendly catalyst for the Nazarov reaction

• Manoel T. Rodrigues Jr.,
• Aline S. B. de Oliveira,
• Ralph C. Gomes,
• Amanda Soares Hirata,
• Lucas A. Zeoly,
• Hugo Santos,
• João Arantes,
• Catarina Sofia Mateus Reis-Silva,
• João Agostinho Machado-Neto,
• Leticia Veras Costa-Lotufo and
• Fernando Coelho

Beilstein J. Org. Chem. 2024, 20, 1167–1178, doi:10.3762/bjoc.20.99

• [15], and the Nazarov reaction [16][17][18][19][20]. The Nazarov cyclization is one of the most versatile and simple methods for preparing indanones from aryl vinyl ketone derivatives [16][17][18][19][20]. The Nazarov reaction is classically formulated as a 4π conrotatory electrocyclization of a

• electrocyclization reaction could be mediated by weaker Lewis acids, and consequently a catalytic amount of them could be used. The first example of a catalytic version of the Nazarov cyclization was reported by Denmark and Jones [25][26][27][28][29][30][31]. They found that a substoichiometric amount of FeCl3 (40

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

• , this class of compounds is prone to valence isomerization via 6π-electrocyclization leading to the formation of heteroatom-containing norcaradiene, and oxepine has been shown to exist in equilibrium with its valence isomer benzene oxide [37]. In contrast with the parent oxepine, which is isolable at

Trifluoromethylated hydrazones and acylhydrazones as potent nitrogen-containing fluorinated building blocks

• Zhang Dongxu

Beilstein J. Org. Chem. 2023, 19, 1741–1754, doi:10.3762/bjoc.19.127

• conditions [38] (Scheme 2). Moreover, a chiral Brønsted acid-catalyzed asymmetric 6π electrocyclization of trifluoroacetaldehyde hydrazones for the synthesis of enantiomerically enriched 3-trifluoromethyl-1,4-dihydropyridazines was first developed by Rueping et al. [39]. The strategy involves chiral ion

Synthesis of substituted 8H-benzo[h]pyrano[2,3-f]quinazolin-8-ones via photochemical 6π-electrocyclization of pyrimidines containing an allomaltol fragment

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Mikhail E. Minyaev and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2023, 19, 778–788, doi:10.3762/bjoc.19.58

• shown that for the hydroxy derivatives the main pathway of phototransformation is a 6π-electrocyclization of the 1,3,5-hexatriene system and subsequent [1,9]-H sigmatropic shift leading to dihydrobenzo[h]pyrano[2,3-f]quinazolines. At the same time, for methylated analogues the photoreaction proceeds in

• proposed. Keywords: allomaltol; dihydrobenzo[h]pyrano[2,3-f]quinazolines; 6π-electrocyclization; photocyclization; pyrimidines; Introduction Photochemical processes involve absorption of UV light leading to the generation of molecules in the excited state and subsequent chemical transformations [1][2

• [16][17][18][19][20]. The photochemical behavior of terarylenes containing an allomaltol fragment deserves special attention. In this case, two types of photoprocesses are possible: a 6π-electrocyclization of the 1,3,5-hexatriene system and the aforementioned ESIPT-induced transformation to α-hydroxy

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

Synthetic study toward tridachiapyrone B

• Morgan Cormier,
• Florian Hernvann and
• Michaël De Paolis

Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183

• feature a bicyclo[3.1.0]hexene core which photochemically arises from 1,3-cyclohexadiene precursors, tridachiapyrone A or 9,10-deoxytridachione, as demonstrated by Ireland [16][17]. In turn, the ring system arises from α-tetraenyl-α’-methoxy-γ-pyrone precursor 1a upon heating through 6π-electrocyclization

• electrocyclization of compounds 1a and b [19][20][21][22]. Interestingly, Baldwin and Moses demonstrated the irradiation or sunlight-promoted cycloisomerization of a similar tetraenyl framework into the bicyclo[3.1.0]hexane core through a 6π-conrotatory stereocontrol [23][24]. To date, the known strategies to

• install a quaternary carbon center connected to α’-methoxy-γ-pyrone therefore rely exclusively on the electrocyclization of tetraenes. With recently demonstrated potent antitumoral [25] and anti-HIV properties [26], aureothin is a natural product featuring the α’-methoxy-γ-pyrone motif connected to a

Dienophilic reactivity of 2-phosphaindolizines: a conceptual DFT investigation

• Nosheen Beig,
• Aarti Peswani and
• Raj Kumar Bansal

Beilstein J. Org. Chem. 2022, 18, 1217–1224, doi:10.3762/bjoc.18.127

• -electrocyclization of the initially formed pyridinium alkoxycarbonyl-dichlorophosphinomethylide followed by 1,2-elimination affording 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines [5]. After having access to a good number of differently substituted derivatives of these four classes of 2-phosphaindolizines, we were

A study of the photochemical behavior of terarylenes containing allomaltol and pyrazole fragments

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2022, 18, 588–596, doi:10.3762/bjoc.18.61

• -pyranone containing terarylenes with a pyrazole bridge fragment were studied. It was shown that UV-induced 6π-electrocyclization of the 1,3,5-hexatriene system was not observed for the considered objects molecules. At the same time, the phototransformation of such systems proceeds exclusively in the

• processes used in organic synthesis, 6π-electrocyclization of 1,3,5-hexatriene systems is attracting considerable attention [10][11][12][13][14][15][16][17]. The photocyclization of terarylenes leading to the formation of polyheterocyclic compounds is one of the most widely studied processes of this type

• two stages: 6π-electrocyclization of 1,3,5-hexatriene systems and subsequent aromatization of the central benzene ring. Among the significant diversity of terarylenes, compounds containing a 5-hydroxy-2-methyl-4H-pyran-4-one (allomaltol) fragment are of particular interest. For such systems two types

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

• analysis (see Supporting Information File 1). A plausible mechanism of the observed transformations of DAS (shown for 1a) is presented in Scheme 2. The initially formed rhodium carbene A undergoes 1,5-electrocyclization to form intermediate B which turns into indene C as the result of a 1,5-suprafacial

Synthesis of piperidine and pyrrolidine derivatives by electroreductive cyclization of imine with terminal dihaloalkanes in a flow microreactor

• Yuki Naito,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2022, 18, 350–359, doi:10.3762/bjoc.18.39

• . Furthermore, piperidine and pyrrolidine derivatives could be obtained on preparative scale by continuous electrolysis for approximately 1 hour. Keywords: electrochemical synthesis; electrocyclization; flow microreactor; heterocyclic amines; imine; Introduction Heterocycles are a very important class of

Regioselectivity of the S_EAr-based cyclizations and S_EAr-terminated annulations of 3,5-unsubstituted, 4-substituted indoles

• Jonali Das and
• Sajal Kumar Das

Beilstein J. Org. Chem. 2022, 18, 293–302, doi:10.3762/bjoc.18.33

• V. Electrocyclization of V followed by loss of proton from the intermediate VI afforded the corresponding cyclopenta[e]indol-6-ones 35a,b. While involved in the synthesis of 9H-fluorenes and 9,10-dihydrophenanthrenes through intramolecular arylative ring-opening of indole-tethered donor–acceptor

A photochemical C=C cleavage process: toward access to backbone N-formyl peptides

• Haopei Wang and
• Zachary T. Ball

Beilstein J. Org. Chem. 2021, 17, 2932–2938, doi:10.3762/bjoc.17.202

• unstable under basic conditions, readily forming aldehyde products 3. However, related hemi-aminal compounds are quite stable under non-basic conditions, and the motif is even contained in some natural products, such as zampanolide [21] and spergualin [22]. We propose a competing electrocyclization pathway

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• with concomitant aromatization yields the desired products 142. A 6π-electrocyclization reaction was efficiently explored by Jiang and co-workers [128] for the construction of pyrazolo[3,4-b]pyridines 143a. This approach consists of four-component reactions involving substituted pyrazolylamine 140, two

• the allene intermediate D. Finally, an intramolecular 6π-electrocyclization and tautomerism results in the desired products 143a. The authors proposed a mechanism for azepinoindoles (Scheme 59) [128] wherein acid-catalyzed protonation of arylglyoxal monohydrate followed by dehydration and addition of

Total synthesis of pyrrolo[2,3-c]quinoline alkaloid: trigonoine B

• Takashi Nishiyama,
• Erina Hamada,
• Daishi Ishii,
• Yuuto Kihara,
• Nanase Choshi,
• Natsumi Nakanishi,
• Mari Murakami,
• Kimiko Taninaka,
• Noriyuki Hatae and
• Tominari Choshi

Beilstein J. Org. Chem. 2021, 17, 730–736, doi:10.3762/bjoc.17.62

• ]quinoline framework via electrocyclization of 2-(pyrrol-3-yl)benzene containing a carbodiimide moiety as a 2-azahexatriene system. The employed six-step sequence afforded trigonoine B (1) in 9.2% overall yield. The described route could be employed for the preparation of various N-substituted 4

• -aminopyrroloquinolines with various biological activities. Keywords: 2-azahexatiriene system; carbodiimide; electrocyclization; pyrrolo[2,3-c]quinoline; trigonoine B; Introduction In 2011, two novel alkaloids, namely trigonoine A and B, were isolated from the leaves of Trigonostemon lii by Hao and co-workers [1]. The

• heterocyclic compounds by constructing fused pyridine ring systems based on a thermal electrocyclization of an azahexatriene moiety [14][15]. It has been hoped that the development of compounds with enhanced biological activity would be possible using these natural products and their derivatives [16][17][18