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

Synthesis of functionalized imidazo[4,5-e]thiazolo[3,2-b]triazines by condensation of imidazo[4,5-e]triazinethiones with DMAD or DEAD and rearrangement to imidazo[4,5-e]thiazolo[2,3-c]triazines

• Alexei N. Izmest’ev,
• Dmitry B. Vinogradov,
• Natalya G. Kolotyrkina,
• Angelina N. Kravchenko and
• Galina A. Gazieva

Beilstein J. Org. Chem. 2021, 17, 1141–1148, doi:10.3762/bjoc.17.87

• ]triazine derivatives. In this regard, the possibility of prepearing esters 5 with an angular structure on the basis of directed isomerization of linear imidazo[4,5-e]thiazolo[3,2-b]triazines 4a–n in basic media has been studied. Indeed, boiling ethyl ester 4h in methanol in the presence of 0.5 equiv of a

• 1,3-diethylimidazo[4,5-e]thiazolo[3,2-b]triazines 4a,b,h,i upon treatment with an equivalent amount of triethylamine in corresponding alcohols proceeded without hydrolysis of ester groups and led to the formation of the corresponding regioisomeric derivatives 5a,b,h,i (Scheme 4). The isomerization of

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles

• Ramazan Koçak and
• Arif Daştan

Beilstein J. Org. Chem. 2021, 17, 719–729, doi:10.3762/bjoc.17.61

• also obtained by H-shift isomerization following the inverse electron-demand Diels–Alder reaction of tetrazines with p-quinone dibenzosuberenone. Then these pyridazines were converted to the corresponding pyrroles by reductive treatment with zinc. It was observed that all the dihydropyridazines

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

• Mikhail K. Klychnikov,
• Radek Pohl,
• Ivana Císařová and
• Ullrich Jahn

Beilstein J. Org. Chem. 2021, 17, 688–704, doi:10.3762/bjoc.17.58

• lactam 13nA (Scheme 3, insert). The relative configuration of the compounds 12m,n was determined by analogy, by ROESY investigations for the keto lactams 13m,n, and by isomerization experiments for 12n (vide infra). Amides 9o,p with cycloalkenyl substituents on the nitrogen were transformed to fused

• also occurred exclusively at the convex face of the bicyclic system. The configurations of the fused lactams were assigned by chemical derivatization and NOE experiments (vide infra). Functionalization reactions of lactams 12 Base-mediated isomerization reactions Lactams 12 are mixtures of two, four

• trans-12b can be also easily deprotected by a rhodium-catalyzed isomerization to the corresponding N-propenyl lactam followed by osmium tetroxide-catalyzed oxidative cleavage, providing lactam trans-17 in 62% yield. Additionally, the diastereomeric mixture of lactam 12o was subjected to oxidative N–O

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• . This observation suggests that lutidine allows the isomerization of 90 into 93, followed by a nucleophilic attack of the solvent at the sulfur atom (Scheme 25). The reactivity of analogous monotrifluoromethyl-substituted allyl derivatives 94, bearing an aryl group in the vinylic position was also

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• isomerization [36]. Several nitrogen nucleophiles have been evaluated as catalysts to promote the difluorocarbene formation from TFDA in order to bring about the cyclopropanation of a 2-siloxybuta-1,3-diene derivative; 1,8-bis(dimethylamino)naphthalene (proton sponge) was found to be particularly effective [37

• isomerization of trans-1,2-dichloro-3,3-difluorocyclopropane (84) (Scheme 37) [82]. Further research in this area was performed by the groups of Jefford [83] and Dolbier [84], who studied the 1,1-difluoro-2,3-dimethylcyclopropanes 86 and 87 (Scheme 38). Dolbier found that geminal fluorine substituents lowered

• the activation energies for both cis–trans-isomerization and for the transformation of vinylcyclopropanes into cyclopentenes. Both processes could occur by a C–C-bond homolysis to form a diradical. Computational studies by Gety, Hrovat, and Borden indicated that there would be a preference for

Progress in the total synthesis of inthomycins

• Bidyut Kumar Senapati

Beilstein J. Org. Chem. 2021, 17, 58–82, doi:10.3762/bjoc.17.7

• triene system, which is susceptible to cis–trans isomerization, have been longstanding problems in the area of inthomycins. The problems are more acute for the construction of enantioenriched β-hydroxycarbonyl units as evident from the recent reports [19][20][21]. Since the pioneering works of Henaff and

• )-(+)-54 to overcome the problems of isomerization of the (Z,E,E)-triene unit of the desired products. Finally, PdCl2(CH3CN)2 (1 mol %) in DMF was found to smoothly deliver the required triene (+)-55 in quantitative yield. After many unsuccessful attempts of direct conversion of methyl ester (+)-55 into

• . Stille coupling of (Z,Z)-(rac)-62 with vinyl iodide 48 in the presence of Pd(CH3CN)2Cl2 in DMF proceeded smoothly to give the corresponding ester (triene isomerization was less than 20% during coupling), which was then converted into acid derivative (rac)-63 by saponification. Finally, the acid

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

• Daria I. Tonkoglazova,
• Anna V. Gulevskaya,
• Konstantin A. Chistyakov and
• Olga I. Askalepova

Beilstein J. Org. Chem. 2021, 17, 11–21, doi:10.3762/bjoc.17.2

• acid as a cyclizing agent [72]. Unfortunately, only in the case of compound 9c, heating in trifluoroacetic acid led to isomerization into the required carbazole-based [6]helicene 10c (Table 5, entry 3). Under these conditions, alkynes 9a and 9b produced an unseparable mixture of some products. To our

• . Sonogashira coupling of compounds 7 with p-tolylacetylene. Acid-induced isomerization of compounds 9 into carbazole-based [6]helicenes 10. Comparison of X-ray data of the carbazole-based [6]helicenes (atomic numbering does not correspond to IUPAC nomenclature). Photophysical properties of carbazole-based [6

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

• XII and XV is hardly reversible due to the high exergonic character, and thus the equilibration of both final isomers through the previous intermediate IV is very unlikely. Our hypothesis is that an isomerization between XII and XV must be operative under these reaction conditions through a nonstudied

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

• tricyclic compound 25, which led to the synthesis of (±)-hirsutene (14) [22] (Scheme 1A). Refluxing azo compound 22 in acetonitrile generated the proposed biradical intermediate 23 through nitrogen extrusion. This intermediate underwent isomerization to 24 and intramolecular diyl trapping through a [3 + 2

• cycloaddition adduct (not shown) [39] (Scheme 4B). Subsequent treatement with t-BuOLi resulted in the isomerization of the exo-olefin followed by exposure to n-butyllithium and Davis‘ oxaziridine 76 to give 77 in 60% yield with 89% ee. A three-step synthesis from 77 gave α,β-unsaturated amide 78, which

• of aldehyde 163 and isoprene (164) with Ni(acac)2 and diethylzinc [78] and then Dess–Martin oxidation gave a diene (not shown, 94% yield over two steps), which was subjected to ring-closing metathesis to give enone 165 in 85% yield. Isomerization of the freshly prepared 165 to more stable α,β

Naphthalonitriles featuring efficient emission in solution and in the solid state

• Sidharth Thulaseedharan Nair Sailaja,
• Iván Maisuls,
• Jutta Kösters,
• Alexander Hepp,
• Andreas Faust,
• Jens Voskuhl and
• Cristian A. Strassert

Beilstein J. Org. Chem. 2020, 16, 2960–2970, doi:10.3762/bjoc.16.246

• , internal conversion, intermolecular electron transfer, as well as excimer or exciplex formation and isomerization. These phenomena significantly limit the usability of luminogens for the abovementioned purposes. Several attempts were already made to prevent or restrict these non-radiative pathways by

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

• Alexander P. Molchanov,
• Mariia M. Efremova,
• Mariya A. Kryukova and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2020, 16, 2679–2686, doi:10.3762/bjoc.16.218

• 3a–l are formed as single diastereomers mostly in good yields (up to 70%). In some cases, the pyrazolines 4a–d are obtained in small quantities (Scheme 2). Pyrazolines are typical byproducts observed in transformations of 6-aryldiazabicyclo[3.1.0]hexanes and are formed during the isomerization of

• formation of adduct 3m and pyrazoline 4b (Scheme 3). Thus, the azomethine imine A, formed by heating of DABCH 1a, either reacts with propenone 2f giving the adduct 3m or undergoes isomerization affording pyrazoline 4a. On the basis of this observation we suppose that the reaction products undergo

Vicinal difluorination as a C=C surrogate: an analog of piperine with enhanced solubility, photostability, and acetylcholinesterase inhibitory activity

• Yuvixza Lizarme-Salas,
• Alexandra Daryl Ariawan,
• Ranjala Ratnayake,
• Hendrik Luesch,
• Angela Finch and
• Luke Hunter

Beilstein J. Org. Chem. 2020, 16, 2663–2670, doi:10.3762/bjoc.16.216

• to undergo facile E/Z isomerization upon the absorption of UV photons, leading rapidly to a mixture of all four possible geometric isomers of 1 [15][16][17]. In the present work, this phenomenon was confirmed by exposing an ethanolic solution of 1 to sunlight for 2.5 h (Figure 3). The analysis of the

Activation of pentafluoropropane isomers at a nanoscopic aluminum chlorofluoride: hydrodefluorination versus dehydrofluorination

• Maëva-Charlotte Kervarec,
• Thomas Braun,
• Mike Ahrens and
• Erhard Kemnitz

Beilstein J. Org. Chem. 2020, 16, 2623–2635, doi:10.3762/bjoc.16.213

• dehydrofluorination product 2,3,3,3-tetrafluoropropene (HFO-1234yf, 1) and the isomerization product 1,1,1,2,2-pentafluoropropane (HFC-245cb, 10b) in a 1:2 ratio (Scheme 2, top) with almost full conversion. The group of Kemnitz previously showed that 1 and 10b can be in an equilibrium when HF is present in the

Anion exchange resins in phosphate form as versatile carriers for the reactions catalyzed by nucleoside phosphorylases

• Julia N. Artsemyeva,
• Ekaterina A. Remeeva,
• Tatiana N. Buravskaya,
• Irina D. Konstantinova,
• Roman S. Esipov,
• Anatoly I. Miroshnikov,
• Natalia M. Litvinko and
• Igor A. Mikhailopulo

Beilstein J. Org. Chem. 2020, 16, 2607–2622, doi:10.3762/bjoc.16.212

• isomerization of dIno into 7-(2-deoxy-β-ᴅ-ribofuranosyl)hypoxanthine (2'd-N7-inosine) through reversal condensation of dRib-1P and hypoxanthine. The formation of dRib-1P and 2'd-N7-inosine in yields of 29% and 49%, respectively, was estimated in the reaction mixture starting from dIno (100 IU of PNP per 1 mmol

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• . Photoisomerization of the azo unit between cis and trans is achieved upon irradiation with 505 nm (trans→cis) and 435 nm (cis→trans). Concurrently with the isomerization and coordination/decoordination, the spin state of the Ni ion switches between singlet (low-spin) and triplet (high-spin). Previous studies have

• under air to form the disulfide. Investigation on the spin switching performance of the Ni(II)-porphyrins The spin switching performance of a record player molecule depends on different parameters: 1. the coordination strength of the axial ligand, 2. the effectivity of the cis–trans isomerization, since

• NMR experiments. For 1f and 1i the cis/trans ratio was obtained from integration of the signals of H-11, which differ in cis and trans configuration. (Supporting Information File 1, Figure S14). However, NMR spectroscopy was not suitable to determine the cis–trans isomerization yields of 1e, 1g, 1h

A new method for the synthesis of diamantane by hydroisomerization of binor-S on treatment with sulfuric acid

• Rishat I. Aminov and
• Ravil I. Khusnutdinov

Beilstein J. Org. Chem. 2020, 16, 2534–2539, doi:10.3762/bjoc.16.205

• diamondoid homologous series, which is produced on an industrial scale (prepared by AlBr3 or AlCl3-induced skeletal isomerization of a petrochemical monomer, hydrogenated dicyclopentadiene) [1], have been studied rather extensively, the chemical behavior of diamantane, the second member of the diamandoid

• homologous series, has been poorly studied. The main cause of this situation is the lack of facile methods for its synthesis. In the literature, diamantane (1) is prepared by skeletal isomerization of strained С14Н20 polycyclic hydrocarbons [2][3][4][5][6][7]. In particular, the most suitable initial

• ), 60.05 (C6), 133.69 (C4), 133.75 (C3); EIMS (70 eV, m/z): 184 [M]+ (40), 169 (21), 155 (45), 141 (45), 129 (51), 117 (100), 115 (53), 91 (88), 78 (43), 65 (21), 41 (20) %. Isomerization of 3а–с to diamantane (1). Reaction conditions: (a) CoBr2·2PPh3–BF3·OEt2, 110 °C, 12 h; (b) Pt, H2 (200 psi), 70 °C, 3

A proposed sustainability index for synthesis plans based on input provenance and output fate: application to academic and industrial synthesis plans for vanillin as a case study

• John Andraos

Beilstein J. Org. Chem. 2020, 16, 2346–2362, doi:10.3762/bjoc.16.196

• ] and other cellulosic biomass feedstocks, respectively. Isoeugenol and eugenol were chosen to originate from the natural product clover oil since 80% by weight of this essential oil is eugenol [48], and isoeugenol is directly obtained from eugenol by base-catalyzed isomerization. (5) Oxygen from air

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

Azo-dimethylaminopyridine-functionalized Ni(II)-porphyrin as a photoswitchable nucleophilic catalyst

• Jannis Ludwig,
• Julian Helberg,
• Hendrik Zipse and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2119–2126, doi:10.3762/bjoc.16.179

• shielded in the cis configuration and therefore catalytically inactive. The basicity was restored by isomerization to the trans state leading to a rapid conversion to the β-nitroalcohol, the product of the Henry reaction [10][11][12]. We now present a photoswitchable catalyst whose basicity is controlled

• influence of the solvent on the switching efficiency was evaluated by UV–vis (Figure S2, Supporting Information File 1) and NMR experiments (Figure 2). It is important to note that there are two ways to define the switching efficiency of record player molecules: 1. the cis–trans isomerization of the

• coordination. On this account, isomerization and coordination were investigated separately by 1H NMR spectroscopy. The protons meta to the azo group in the azopyridine unit (H-11) are responsive to the configuration of the azo group (cis or trans) and the chemical shifts of the pyrrole protons of the porphyrin

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

• extent (13c) or not at all (13b) (Scheme 4). A remarkable stereochemical aspect accompanied the reaction of 1a with (E)-1-phenyl-1-propene leading to 2-((E)-1-phenylprop-1-enyl)indene 12d, where trans(Ph,Me)→cis isomerization at the olefinic bond has occurred. The E-configuration was assigned based on

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

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

• in a high yield and enantioselectivity (Scheme 5) [17][18]. The Rubottom oxidation [28] of 43 gave a separable mixture of the desired 44 and its C-14 epimer (≈7:1 ratio). The reductive deoxygenation of 44 proceeded via the tosylhydrazone to afford 45, which upon desilylation and alkyne isomerization

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

• Vladimir Kubyshkin

Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151

• probing of the molecular sites with relatively small dipoles of the solvent. This is why here it seems more reasonable to adhere to simple schematic descriptions such as the one shown in Figure 7. Amide-bond rotation: thermodynamics Isomerization of the amide (peptide) bond is an important issue in

• transition state would explain the energy penalty in the rotation barriers (Figure 9D). In 3,3-dimethylprolines, the isomerization into the C4-exo envelope would lead to a steric clash between one of the methyl groups and the backbone carbonyl (k decreases by a factor of 2–6) [99]; in 3,4-dehydroprolines

• , the ring is unable to adopt an envelope conformation due to an endocyclic double bond (k decreases by factor 3) [72]. Overall, the conclusions regarding the ring conformation preference in the transition state provides an entirely new insight onto the peptide-bond isomerization, and can be helpful for

One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• minimized by decreasing the reaction temperature to 210 °C, improving the hydrogenation capacity by optimization of the concentration of Ru/C and decreasing the solvent volume to 40 mL. A formation of isomerization products of isohexides was observed as the isomerization of glucose is acid-catalyzed, and

• the isomerization of alditols is catalyzed by Ru/C. An isosorbide yield of 52% was obtained after 1 h at 210 °C and 50 bar of H2 from 10 wt % of cellulose and a catalyst/cellulose ratio of 1:4 in the presence of 1 g of Ru/C (5 wt % of Ru). It was also shown that a longer reaction time led to an

Synthesis of Streptococcus pneumoniae serotype 9V oligosaccharide antigens

• Sharavathi G. Parameswarappa,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2020, 16, 1693–1699, doi:10.3762/bjoc.16.140

• via a two-step process of triflation and azide substitution to produce the desired trisaccharide 24 [29]. Removal of the allyl group using iridium-catalyzed isomerization and subsequent treatment with iodine in the presence of water yielded trisaccharide acceptor 25 for the late stage [2 + 3