Novel library synthesis of 3,4-disubstituted pyridin-2(1H)-ones via cleavage of pyridine-2-oxy-7-azabenzotriazole ethers under ionic hydrogenation conditions at room temperature

• Romain Pierre,
• Anne Brethon,
• Sylvain A. Jacques,
• Aurélie Blond,
• Sandrine Chambon,
• Sandrine Talano,
• Catherine Raffin,
• Branislav Musicki,
• Claire Bouix-Peter,
• Loic Tomas,
• Gilles Ouvry,
• Rémy Morgentin,
• Laurent F. Hennequin and
• Craig S. Harris

Beilstein J. Org. Chem. 2021, 17, 156–165, doi:10.3762/bjoc.17.16

• -opening of the triazole moiety through a Dimroth rearrangement process affording 20 (reaction becomes instantly bright red); c) reduction of diazonium species to afford intermediate 21, observed by UV-LC–MS; and finally d) reductive cleavage of the -O–NH- bond, usually carried out under catalytic

Tuning the solid-state emission of liquid crystalline nitro-cyanostilbene by halogen bonding

• Subrata Nath,
• Alexander Kappelt,
• Matthias Spengler,
• Bibhisan Roy,
• Jens Voskuhl and
• Michael Giese

Beilstein J. Org. Chem. 2021, 17, 124–131, doi:10.3762/bjoc.17.13

• after one heating/cooling cycle reveal the impact of the alkoxy chain length and a significant rearrangement of the solid-state packing upon heating/cooling the sample (diameter of sample ≈ 0.8 cm). Temperature-dependent fluorescent images of NO2-C9∙∙∙F4St showing the enhancement of emission upon

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• those experiments resulted in a rearrangement in the tetrazole ring, as shown in Scheme 4, upper path. We were able to obtain the desired aminotetrazole 9 by treating 3g with dry HCl at elevated temperature (Scheme 4, lower path). The resulting compound is particularly appealing, as similar scaffolds are

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• stereospecific semipinacol rearrangement in 78% yield over two steps. The resulting terminal alkene (−)-70 was submitted to Vacker's conditions to produce methyl ketone (−)-71 in 93% yield. The treatment of this ketone with potassium trimethylsilanolate induced a 1,5-Michael type reaction, via attack of tethered

• approach consisted of a 3,3-sigmatropic rearrangement to give an all-carbon quaternary center, a ring-closing alkene metathesis to give an 8-membered ring, and the use of a single enantiomer of p-menthane-3-carboxaldehyde to make two natural alkaloids of opposite configuration. Firstly, (+)-euphococcinine

• in a 9:1 ratio. After chromatographic separation, alcohol (−)-77a, isolated in 67% yield and >99% de was subjected to a Claisen rearrangement, leading to aldehyde (−)-78 in 79% yield (96% de determined by 1H NMR). (−)-78 was treated with vinylmagnesium bromide to give a mixture of allyl alcohols

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• Studi di Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Florence, Italy 10.3762/bjoc.16.255 Abstract The tandem gold(I)-catalyzed rearrangement/Nazarov reaction of enynyl acetates in which the double bond is embedded in a piperidine ring was computationally and experimentally studied. The

• of a triple bond, which has ultimately led to the total synthesis of several natural compounds [2][8]. The gold-catalyzed rearrangement of suitably substituted propargylic esters in particular provides a platform for cascade processes that involve a cationic or an allene intermediate generated in the

• first step [1][9][10][11][12]. In the framework of our studies on gold(I)-catalyzed reactions of propargyl alcohol derivatives [13][14][15], we have recently reported that the pentannulation of N-heterocycles [16] can be efficiently achieved by a cascade gold-catalyzed [3,3]-rearrangement/Nazarov

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• tetracyclic compound 56. Dihydroxylation of freshly prepared 56 with OsO4 and then selective tosylation afforded 57 in 39% yield over two steps. Exposure of 57 to DBU upon heating gave the elimination product 58, which was subjected to an oxidative rearrangement with PDC to give enone 59 in 68% yield. Copper

• rearrangement product 99 in 85% yield. The synthesis of daphenylline (11) was completed by a seven-step synthesis from benzofuran 99. Phosphine-catalyzed enantioselective [3 + 2] annulation In 2019, Lu and co-workers disclosed a novel chiral-phosphine-catalyzed enantioselective [3 + 2] annulation of allenes and

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• Truce–Smiles rearrangement in aryl sulfonamides and aryl phenylsulfonates [44][45][46] or the [3,3]-sigmatropic rearrangement of sulfonium salts arising from the reaction of aryl sulfoxides and phenols [47]. To overcome this problem, the use of a metal catalyst (mainly Ni) was mandatory as reported for

Regioselective synthesis of heterocyclic N-sulfonyl amidines from heteroaromatic thioamides and sulfonyl azides

• Vladimir Ilkin,
• Vera Berseneva,
• Tetyana Beryozkina,
• Tatiana Glukhareva,
• Lidia Dianova,
• Wim Dehaen,
• Eugenia Seliverstova and
• Vasiliy Bakulev

Beilstein J. Org. Chem. 2020, 16, 2937–2947, doi:10.3762/bjoc.16.243

• thioamides with alkyl- and arylsulfonyl azides. For each type of thioamides a reliable procedure to prepare N-sulfonyl amidines in good yields was found. Reactions of 1-aryl-1,2,3-triazole-4-carbothioamides with azides were shown to be accompanied with a Dimroth rearrangement to form 1-unsubstituted 5

• -arylamino-1,2,3-triazole-4-N-sulfonylcarbimidamides. 2,5-Dithiocarbamoylpyridine reacts with sulfonyl azides to form a pyridine bearing two sulfonyl amidine groups. Keywords: amidines; Dimroth rearrangement; isoxazoles; sulfonyl thiazoles; thioamides; 1,2,3-triazoles; Introduction The biological activity

• Beckmann reaction of oximes with p-toluenesulfonyl azide [34], the sulfonyl ynamide rearrangement by treatment with amines [35], the sodium iodide catalyzed reaction of sulfonamide with formamide [36], and the condensation of sulfonamide derivatives with DMF–DMA [37]. A few representatives of N-sulfonyl

Fluorine effect in nucleophilic fluorination at C4 of 1,6-anhydro-2,3-dideoxy-2,3-difluoro-β-D-hexopyranose

• Danny Lainé,
• Vincent Denavit,
• Olivier Lessard,
• Laurie Carrier,
• Charles-Émile Fecteau,
• Paul A. Johnson and
• Denis Giguère

Beilstein J. Org. Chem. 2020, 16, 2880–2887, doi:10.3762/bjoc.16.237

• core, would be suitable for the C4 deoxyfluorination of intermediates 2–5. However, it is well documented that undesired rearrangement products with 1,2-aglycone migration [26][27][28] or skeletal rearrangements [29] have been observed during fluorodeoxygenation of glycopyranosides with DAST

• fluorine electron density to attack equatorially. Although we propose an oxiranium intermediate for the C4 deoxyfluorination of 13, we did not observe any ring rearrangement, typically as a result of ring contraction (for example, compound 19, step d) [26][29][38]. Also, we did not observe any 1,2-alkyl

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• rearrangement after the protonation of 1 and 2 furnished exclusively the two complexes [(1•H+)(3)] and [(2•H+)(4)] (Figure 3). The reduced affinity of the cucurbit[7]uril toward the protonated diethylamino-substituted guest in combination with the concomitant increased binding for the dimethylammonium

• hydrogen-bonded octameric and tetrameric tubes. (c) A representation of the complex mixture after combining the monomers 5 and 6 in CDCl3. (d) The partial separation of the mixture upon the selective C60 complexation by monomer 5. The guest-induced rearrangement results in an incomplete self-sorted mixture

• (2019) American Chemical Society. Cyclic metallosupramolecular transformations. Fully reversible multiple-state rearrangement of metallosupramolecular architectures depending upon copper(I) stoichiometry. Reproduced from [65]. The selective encapsulation and sequential release of guests in a self-sorted

On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A–C

• Anwei Hou and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2020, 16, 2807–2819, doi:10.3762/bjoc.16.231

• through reactions that are classified as σ-bond cleavages, α-fragmentations, inductive cleavages, McLafferty rearrangements [11], retro-Diels–Alder fragmentations [12][13], and the recently observed unusual radical-induced retro-Cope rearrangement (herein, “retro” indicates that the mass spectrometric

• energetically more feasible process may be represented by an inductive cleavage leading to b1•+, a hydrogen rearrangement to c1•+, and an α-cleavage to d1+ (Scheme 1B). The formation of the fragment ion at m/z = 312 proceeds through a highly specific loss of the C8–9 portion of 1. This is explainable from b1

• group C23 results in j1+ (Scheme 1E). The fragmentation of the C25–3–4 portion can be explained starting from 1•+ by a hydrogen rearrangement to k1•+ and α-cleavage to l1•+ (Scheme 1F). Another hydrogen rearrangement combined with an α-fragmentation then leads to the allyl cation m1•+ which may undergo

3-Acetoxy-fatty acid isoprenyl esters from androconia of the ithomiine butterfly Ithomia salapia

• Florian Mann,
• Daiane Szczerbowski,
• Lisa de Silva,
• Melanie McClure,
• Marianne Elias and
• Stefan Schulz

Beilstein J. Org. Chem. 2020, 16, 2776–2787, doi:10.3762/bjoc.16.228

• formed from hedycaryol (7) during GC/MS analysis by a Cope-rearrangement [20][21], indicating that 7 might be originally present in the hairpencils. That said, we cannot disprove that this rearrangement could also occur in the androconia. Hedycaryol is an early product of sesquiterpene biosynthesis

• in the region around the acylium ions. Monounsaturated prenyl esters show the elimination of C5H10 (M − 70, m/z 280 in A), likely formed by rearrangement of an allylic H to the carbonyl group, followed by H-transfer (Figure 3C). Furthermore, the prenyl group can be lost (M − 69, m/z 281) and the

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• rearrangement of the pseudo[2]rotaxane into a non-threaded complex as discussed above. As dethreading is impossible in NDIRot, the electrochemical data are significantly different from those of the non-threaded complexes formed from the pseudorotaxane and the (CH3)2NH2PF6 complex of NDIC8. The optoelectronic

Synthesis of novel fluorinated building blocks via halofluorination and related reactions

• Attila Márió Remete,
• Tamás T. Novák,
• Melinda Nonn,
• Matti Haukka,
• Ferenc Fülöp and
• Loránd Kiss

Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208

• involved a rearrangement, providing the isomeric products (rac)-20a and (rac)-21a (Scheme 12). We also observed the formation of the dibrominated compound 22, which became the sole product when the reaction was performed under reflux conditions. Iodofluorination was much less effective: even after repeated

• isomeric halofluorination products can be explained by the preferred formation of the halonium ions T6a–c, respectively, since the halogen cation attacks the C=C bond of the imide 19 from the less hindered side, followed by rearrangement into the intermediates (rac)-T7a–c, respectively. For epoxides and

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• ]. Bach et al. also found that alkenes 198 can undergo a light-induced rearrangement to cyclopropane 199 in the presence of 185 (Scheme 30b) [88]. They discovered that 199 is configurationally unstable under the reaction conditions and propose that a similar deracemisation mechanism is responsible for the

• enantioselectivity via triplet state intermediate 200, rather than proceeding via an enantioselective rearrangement. Bifunctional hydrogen bonding photocatalysts have been developed by other groups as well. Sivaguru developed an atropisomeric thiourea-based catalyst 201 and used it for the intramolecular

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

• Asitanga Ghosh

Beilstein J. Org. Chem. 2020, 16, 2297–2303, doi:10.3762/bjoc.16.190

• distribution of these photoproducts may be wavelength dependent [7]. In order to investigate the photoreaction of such enones, we observed a complete 1,2-acyl shift (1,2-AS) photoproduct formation when 1a–h have been irradiated (Scheme 1) [14][16]. We also observed that such a rearrangement took place very

• , the photorearrangement route is selectively from the α,β-enone part and we confirmed that the irradiation follows a type B rearrangement (Scheme 2) [16]. Another interesting set of competitive 1,5-(C–O) acyl shift rearrangements (formation of vinyl ketene) with that of 1,2-AS were observed when

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• analogous to 21 could be isolated [56]. A cationic 1,5-cylization converts 21 into cyclopentene 22, from which fulvene 19 is formed by deprotonation and a formal 1,4-shift of the NMe2 group. The details of this rearrangement are not known, an N,N-dimethyldihydropyrrolium intermediate may be involved

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• ] was followed by a 3-O-vinylation. A thermal 3,3-sigmatropic Claisen rearrangement of 62 gave the cis-2,6-disubstituted dihydropyran 63, which upon sequential Wittig olefination with 2-(triphenylphosporanylidene)propanal and then methylenetriphenylphosphorane yielded the diene 64. The removal of the di

• with a 6:1 diastereoselectivity. The Red-Al reduction of 94, protection of the 2° alcohol, and reduction of the enoate to an allylic alcohol were prerequisites for the stereoselective 2,3-sigmatropic selenoxide rearrangement to generate 95. Further protecting group manipulation and Johnson–Lemieux

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• olefination or defluorination reactions or a sigmatropic rearrangement, but these approaches are limited and do not allow the synthesis of tetrasubstituted fluoroalkenes with good control of their geometry [18][19][20][21]. In order to develop a selective synthesis for tetrasubstituted fluoroalkenes we

• Smiles rearrangement occurred leading to fluoroethylene and benzothiazolone. Therefore, its benzylation was explored under acidic conditions with benzyl trichloroacetimidate (1.5 equiv) and a catalytic amount of trifluoromethanesulfonic acid. This gave benzyl ether 7 as a 2.5:1 mixture with N

• already reported in the literature from oxetane-containing α,β-unsaturated carbonyl derivatives through a Lewis acid-catalyzed rearrangement [31]. When the previous conditions (HBr/AcOH) were tried (3.5 h, 0 °C to 20 °C), hydroxymethyllactone 14 (87%, Table 4, entry 1) was the main product with traces of

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides

• Vladimir P. Rybalkin,
• Sofiya Yu. Zmeeva,
• Lidiya L. Popova,
• Valerii V. Tkachev,
• Andrey N. Utenyshev,
• Olga Yu. Karlutova,
• Alexander D. Dubonosov,
• Vladimir A. Bren,
• Sergey M. Aldoshin and
• Vladimir I. Minkin

Beilstein J. Org. Chem. 2020, 16, 1820–1829, doi:10.3762/bjoc.16.149

• undergo an irreversible transformation leading to decoloration of their solutions. This rearrangement with the formation of the dihydronaphthalene core appeared to be by 2–3 orders of magnitude more efficient than for the known diphenylmethylene(aryl(hetaryl))fulgides. The molecular structures of E- and Z

• -isomers and of products of the photoinduced rearrangement completed by 1,5-H shift reaction, 3a,4-dihydronaphtho[2,3-c]furans(pyrroles) C, were established based on the data of 1H and 13C NMR spectroscopy and X-ray diffraction studies. Keywords: benzo[b]thiophene; fulgide; fulgimide; photorearrangement

• photochromic properties of 2-benzo[b]thienylfulgides [22]. UV irradiation of acetonitrile solutions of these compounds results in the electrocyclic hexatriene–cyclohexadiene rearrangement of the ring-opened isomers O into the colored ring-closed ones C (Scheme 1) which exhibit enhanced spectral characteristics

Microwave-assisted efficient one-pot synthesis of N²-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

• Moustafa Sherief Moustafa,
• Ramadan Ahmed Mekheimer,
• Saleh Mohammed Al-Mousawi,
• Mohamed Abd-Elmonem,
• Hesham El-Zorba,
• Afaf Mohamed Abdel Hameed,
• Tahany Mahmoud Mohamed and
• Kamal Usef Sadek

Beilstein J. Org. Chem. 2020, 16, 1706–1712, doi:10.3762/bjoc.16.142

• the synthesis of 6-substituted-N2-aryl-1,6-dihydro-1,3,5-triazine-2,4-diamines via the reaction of aromatic amines, cyanoguanidine, and ketones which afforded the corresponding 1-aryl-1,6-dihydro-6-substituted-1,3,5-triazine-2,4-diamines in 21–56% yields followed by Dimroth rearrangement utilizing

• cyanoguanidine 5 to the formed Schiff’s base (route c). Product 4 was the sole isolable product as under reflux in pyridine as base, compound 8 well undergoes a Dimroth rearrangement forming the more thermodynamically stable product 4 [33]. We established route c, as the formation of the Schiff base is more

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• , and to explain the observed product distributions and structural variances in the dimer-like products. Studies on the transformation of unsubstituted o-(pivaloylaminomethyl)benzaldehyde under similar conditions were presented as well. Keywords: DFT calculations; NMR; reaction mechanism; rearrangement

• case of isoindoles is that the attack of water at cation 19 and subsequent ring opening did not happen here. DFT calculations The proposed mechanism of the 1→2 rearrangement (Scheme 4) was investigated in detail by DFT level quantum chemical computations using the Gaussian 09 program package [19

• ), respectively, was also investigated by DFT level quantum chemical calculations with the same parameters as in the case of the 1→2 rearrangement. The racemic RS and RR forms were taken into consideration, and the computations showed that the formation of the RS compound required an energy investment of ΔG#4e

Azidophosphonium salt-directed chemoselective synthesis of (E)/(Z)-cinnamyl-1H-triazoles and regiospecific access to bromomethylcoumarins from Morita–Baylis–Hillman adducts

• Soundararajan Karthikeyan,
• Radha Krishnan Shobana,
• Kamarajapurathu Raju Subimol,
• J. Helen Ratna Monica and
• Ayyanoth Karthik Krishna Kumar

Beilstein J. Org. Chem. 2020, 16, 1579–1587, doi:10.3762/bjoc.16.130

• initiates the allylic rearrangement and thereby facilitates the removal of the crucial phosphonium oxide. The outcome of this process is the structurally relevant azido moiety IIIa, which then undergoes a 1,3-dipolar cycloaddition with the copper acetylide IVa to furnish the 1,4-disubstituted 1,2,3

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125