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

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

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

Click chemistry towards thermally reversible photochromic 4,5-bisthiazolyl-1,2,3-triazoles

• Chenxia Zhang,
• Kaori Morinaka,
• Mahmut Kose,
• Takashi Ubukata and
• Yasushi Yokoyama

Beilstein J. Org. Chem. 2019, 15, 2161–2169, doi:10.3762/bjoc.15.213

• ] or the introduction of two aromatic rings to the central aromatic ring [11]. If the construction of three contiguous aromatic-ring arrays can be easily achieved, a new and facile synthesis method for the photochromic family which undergoes 6π-electrocyclization can be realized [13]. Early in the 21st

Oxidative and reductive cyclization in stiff dithienylethenes

• Michael Kleinwächter,
• Ellen Teichmann,
• Lutz Grubert,
• Martin Herder and
• Stefan Hecht

Beilstein J. Org. Chem. 2018, 14, 2812–2821, doi:10.3762/bjoc.14.259

• Diarylethenes (DAEs) are a rich family of organic photoswitches formally derived from stilbene [1][2]. Upon irradiation they are able to undergo reversible photoisomerization based on 6π-electrocyclization and -cycloreversion, respectively, between two thermally stable states, which make them interesting

• derivatives with 6-membered rings undergo efficient cyclization upon two-electron oxidation. Notably, both E- and Z-isomers undergo 6π-electrocyclization because rotation about the central bond is possible in the dication. Furthermore, we discovered three examples undergoing cyclization upon two-electron

A strategic approach to [6,6]-bicyclic lactones: application towards the CD fragment of DHβE

• Tue Heesgaard Jepsen,
• Emil Glibstrup,
• François Crestey,
• Anders A. Jensen and
• Jesper Langgaard Kristensen

Beilstein J. Org. Chem. 2017, 13, 988–994, doi:10.3762/bjoc.13.98

• effective synthetic protocol to access [6,6]-bicyclic lactone moieties through a regio- and stereoselective intramolecular Mizoroki–Heck cross-coupling reaction followed by a 6π-electrocyclization. This method enabled the first synthesis of the elusive CD fragment of the Erythrina alkaloid DHβE. Preliminary

• pharmacological evaluations support the notion that the key pharmacophores of DHβE are located in the A and B rings. Keywords: DhβE; Mizoroki–Heck cross-coupling reaction; 6π-electrocyclization; [6,6]-bicyclic lactone; vinyl halide; Introduction The neuronal nicotinic acetylcholine receptors (nAChRs) have been

• intramolecular Mizoroki–Heck cross-coupling reaction and a 6π-electrocyclization as key steps. Results and Discussion First strategy with Ts and Cbz protecting groups As depicted in Scheme 1, our first strategy featured a late stage installation of the lactonic D ring by a 6π-electrocyclization and formation of

Rapid regio- and multi-coupling reactivity of 2,3-dibromobenzofurans with atom-economic triarylbismuths under palladium catalysis

• Maddali L. N. Rao,
• Jalindar B. Talode and
• Venneti N. Murty

Beilstein J. Org. Chem. 2016, 12, 2065–2076, doi:10.3762/bjoc.12.195

• the synthesis of 2,3-dialkenylbenzofurans and functionalized dibenzofurans with domino “twofold Heck/6π-electrocyclization” of 2,3-di- and 2,3,5-tribromobenzofuran substrates [34]. In this regard, the cross-coupling studies of triarylbismuth reagents in regioselective studies with functionalized

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• electrocyclization of the benzodivinyl moiety to intermediate C followed by 1,5-H shift and rearomatization of the benzene ring. Analogue electrocyclization was not detected in phenyl or furyl-substituted o-divinylbenzenes but instead stilbene-like 6π electrocyclization and formation of 1-vinylphenanthrene [42] or 6

• detected. The 1,6-ring closure of the biradicals A/A’ occurs stereoselectively giving the major products rel-(2S)-8a/rel-(2S)-10 in which the hydrogen on C-2 is oriented toward the methano bridge. The formation of dihydronaphthalene derivative 9, found only on irradiation of 1, is explained by 6π

Isoxazolium N-ylides and 1-oxa-5-azahexa-1,3,5-trienes on the way from isoxazoles to 2H-1,3-oxazines

• Alexander F. Khlebnikov,
• Mikhail S. Novikov,
• Yelizaveta G. Gorbunova,
• Ekaterina E. Galenko,
• Kirill I. Mikhailov,
• Viktoriia V. Pakalnis and
• Margarita S. Avdontceva

Beilstein J. Org. Chem. 2014, 10, 1896–1905, doi:10.3762/bjoc.10.197

• synthetic approach to derivatives of 2H-1,3-oxazines via a Rh2(OAc)4-catalyzed reaction of diazo esters with 2-acyl-2H-azirines F. This reaction involves the intermediate formation of azirinium ylides G, their transformation into 1-oxa-5-azahexa-1,3,5-triene D, and finally the 6π-electrocyclization of the

• diazo esters B involved an isoxazolium N-ylide intermediate C formed by an attack of the rhodium carbenoid onto the isoxazole nitrogen. Furthermore, ylide C could undergo either a 1,2-shift to directly generate oxazine E or a ring opening to 1-oxa-5-azahexa-1,3,5-triene D, followed by a 6π

• -electrocyclization to give oxazine E (Scheme 1). At the same time, the third mechanism of the reaction, involving a one-step formation of 1-oxa-5-azahexa-1,3,5-triene D, cannot be excluded. The reaction of a carbenoid with isoxazoles is the only known one-step intermolecular reaction which can in principle produce

Flexible synthesis of anthracycline aglycone mimics via domino carbopalladation reactions

• Markus Leibeling and
• Daniel B. Werz

Beilstein J. Org. Chem. 2013, 9, 2194–2201, doi:10.3762/bjoc.9.258

• delivered the best results with yields of up to 89%. For the reaction mechanism we assume that the palladium(0) inserts into the C(sp2)–Br bond to form a Pd(II) species. A sequence of two carbopalladation reactions form a triene system which is able to cyclize by a Heck-type reaction, a 6π

• -electrocyclization [39] or a direct CH-activation to the respective anthracycline precursor 13. The design of the dialkyne provides a simultaneous formation of the linear ring system. All four cycles were annulated in a single step, in which the B and C-ring were formed as a consequence of the reaction cascade

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• unsaturated bridge in the cyclization step and points towards a 6π-electrocyclization rather than to a simple nucleophilic aromatic displacement mechanism. Among the triazinium salts prepared in this work is the hydroxymethyl derivative 1e, which, in principle, can be incorporated into more complex molecular

Synthesis of a novel chemotype via sequential metal-catalyzed cycloisomerizations

• Bo Leng,
• Stephanie Chichetti,
• Shun Su,
• Aaron B. Beeler and
• John A. Porco Jr.

Beilstein J. Org. Chem. 2012, 8, 1338–1343, doi:10.3762/bjoc.8.153

• with the Pt-activated alkyne, the resulting metal-“ate” intermediate 28 may undergo preferential elimination and proto-demetallation to afford 1,5-diene 29. A second elimination results in the ring-opened triene 30. Subsequent 6π-electrocyclization affords alcohol 31, which aromatizes through loss of

A practical two-step procedure for the preparation of enantiopure pyridines: Multicomponent reactions of alkoxyallenes, nitriles and carboxylic acids followed by a cyclocondensation reaction

• Christian Eidamshaus,
• Roopender Kumar,
• Mrinal K. Bera and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2011, 7, 962–975, doi:10.3762/bjoc.7.108

• , we reported a new synthesis of pyridines based on the trimethylsilyl trifluoromethanesulfonate (TMSOTf) induced cyclocondensation reaction of β-ketoenamides [29][30][31][32][33][34]. This cyclocondensation step can be rationalized as a 6π-electrocyclization of the disilylated intermediate 5 to

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

• Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

• can be induced by chloromethylethers. Loss of HCl from B (presumably to A, which is a monobasic species)[13] gives an imino-azomethin-ylide 1,5-dipole C (only one mesomeric structure shown), which will undergo 1,5-dipolar cyclization (6π electrocyclization) [18][19][20] to an oxy-imidazoline D

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• phenylcarbenes to isobenzofurans. Ring opening of 2-furylcarbenes to alk-2-en-4-yn-1-ones. Coupled coarctate cyclization and 6π electrocyclization. Supporting Information Supporting Information File 26: bisfuran-supportinginfo.doc 100 Kb Acknowledgements Financial support from the National Science Foundation