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 β-triazolylenones via metal-free desulfonylative alkylation of N-tosyl-1,2,3-triazoles

• Soumyaranjan Pati,
• Renata G. Almeida,
• Eufrânio N. da Silva Júnior and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2021, 17, 762–770, doi:10.3762/bjoc.17.66

• many bioactive heterocycles [36]. These are also important precursors of diazo adducts which are used in insertion, cyclopropanation, and various rearrangements to construct various cyclic as well as acyclic moieties under metal-catalysed conditions [37][38]. On the contrary, under basic conditions

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

• -containing skeletons of the general structure IX or XI, respectively (Scheme 1A). Recently, we became interested in merging sigmatropic rearrangements with radical oxygenation reactions since profound changes in the connectivity patterns during both reaction modes will potentially significantly simplify the

Unexpected rearrangements and a novel synthesis of 1,1-dichloro-1-alkenones from 1,1,1-trifluoroalkanones with aluminium trichloride

• Beatrice Lansbergen,
• Catherine S. Meister and
• Michael C. McLeod

Beilstein J. Org. Chem. 2021, 17, 404–409, doi:10.3762/bjoc.17.36

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

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

• methylenecyclopropanes are of interest as Michael acceptors and as substrates for thermal rearrangements. As they are not readily available by difluorocarbene addition to allene derivatives, Taguchi et al. developed an alternative route to these compounds by selenoxide elimination (Scheme 30) [75]. Later, this approach

• isopropanol as reductant, in conjunction with a Noyori–Ikariya ruthenium-based homogeneous catalyst (Scheme 36) [73]. 2 Reactions of difluorocyclopropane and its derivatives Difluorocyclopropanes are synthetically useful substrates for a variety of reactions such as thermal rearrangements, carbocation

• , carbanion, and radical chemistry. Furthermore, gem-difluorocyclopropanes readily go through carbonylation, dehalogenation, and annulation, resulting in various useful materials. 2.1 Thermal rearrangements The substitution of hydrogen with fluorine in cyclopropane leads to a significant weakening of the C–C

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

• interesting building blocks in organic synthesis [17][18][19][20] (Figure 1). An N-sulfonyl amidine was recently found to be a key group in acid–base-induced rearrangements of 1,2,3-triazoles and thiadiazoles [22]. A variety of methods have been developed for the synthesis of N-sulfonyl amidines. The most

• various ring transformations and rearrangements [48][49][50][51], we decided to study reactions of 1-alkyl-1,2,3-triazole-4-carbothioamides 1a–d with aryl- and alkylsulfonyl azides 2a–f with, with the goal of affecting a “iminosulfonylation” (Scheme 1). The thioamides 1a–d were prepared from the

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

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

• was a strain release upon opening the dimeric species 60. The multiple rearrangements as discussed so far are complex and fascinating but in most of the cases they represent irreversible transformations which prevent a use in reversible switching processes. A multistate reversible transformation

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

• originating from the isopropyl group C20–19–21 or, by involving multiple C–C bond cleavages and hydrogen rearrangements, from the C25–3–4 portion. Alternatively, a combined loss of the C8–9 moiety and one methyl group (C22, C23, C24, or C25) is possible which basically combines the fragmentations of Scheme 1A

• C25, while the fragmentation of C20 or C21 does not make a significant contribution. Notably, even from the olefinic methylene group C23 a methyl group can be cleaved off, which requires hydrogen rearrangements prior to the fragmentation. A possible mechanism starts from 2•+ by the hydrogen

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

• bromonium ions of norbornene systems, such rearrangements are not uncommon [38][39][40]. Then, the carbenium ion motif of (rac)-T7a–c can be attacked from both sides to give the products (rac)-20a–c and (rac)-21a–c (Scheme 13). The formation mechanism of the product 22, however, is still an open question

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

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

• position; ketene; mixed chromophores; Introduction Enones exhibit a rich and diverse photochemistry. The deep-seated photochemical rearrangements found in these systems have attracted numerous mechanistic studies. In this context, the photochemistry of α,β-enones A and β,γ-enones B (Figure 1) has become

• an actively researched area for more than two decades [1][2][3][4][5][6], particularly because of their fascinating photochemical rearrangements. In view of their rich photochemistry, it may be expected that incorporation of both enones into the same molecule C would lead to a variety of more

• interesting reactions. Indeed, this type of mixed enone photochemistry is also an attractive field [7][8] for chemists because the photochemistry of such substrates can feature the intramolecular competition of different photochemical rearrangements. For several years, our laboratory (S. Lahiri et al.) is

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

• properties and high quantum efficiencies of their light-induced pericyclic rearrangements constitute one of the most prospective and amply studied photochromic families [5][6][7][8][9][10][11][12]. A general approach to the synthesis of fulgides is based on a Stobbe condensation [13] of aromatic or

• moiety, usually demonstrate positive photochromism as the result of conversion to their deeply colored cyclic isomers. However, fulgides containing a diphenylmethylene group are capable of negative photoinduced rearrangements [14][15][16][17]. Comparison of the photochromic properties of aromatic and

• investigation of their photoinduced rearrangements. Results and Discussion Fulgides 3E, 3Z, 7E and fulgimides 4E, 4Z, 8E were synthesized as shown in Scheme 2 and Scheme 3. The Stobbe condensation of dimethyl 2-(diphenylmethylene)succinate with 1-methoxy- and 1-chlorobenzo[b]thiophene-2-carbaldehydes was used

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• antibacterial, antifungal, anticancer, or anti-inflammatory agents or even on the central nervous system [7][12][13]. Several routes have been reported to access these key compounds, the most developed being for the indole [14] derivatives using the Fischer indole synthesis involving sigmatropic rearrangements

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

• transformations employed quaternary phosphonium salts as favourable catalysts [36]. Their synthetic utility was not only confined to catalysis, but they were also used as intermediates for the synthesis of 1H-indazoles [37], as promoters for stereoselective rearrangements [38], and as temporary protectors of O,P

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• improved protocol when using continuous conditions. Subsequently, we reported a comprehensive methodology involving photooxygenations of conjugated dienes and rearrangements, thus leading to relevant oxidized products (Scheme 37) [87]. In this methodology, we developed in both batch and continuous-flow

• . Synthesis of artemisinin using TPP and supercritical CO2. Synthesis of artemisinin using chlorophyll a. Quercitol stereoisomer preparation. Photocatalyzed preparation of naphthoquinones. Continuous endoperoxidation of conjugated dienes and subsequent rearrangements leading to oxidized products. The Opatz

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• rearrangements, are frequently observed [8]. The use of oxidative couplings is further limited for the synthesis of strained [9][10], electron-deficient, or sterically congested aromatics [11][12][13][14]. Some of these limitations can be overcome by using prefunctionalized precursors [11], as exemplified by

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

• Svetlana V. Amosova,
• Andrey A. Filippov,
• Nataliya A. Makhaeva,
• Alexander I. Albanov and
• Vladimir A. Potapov

Beilstein J. Org. Chem. 2020, 16, 515–523, doi:10.3762/bjoc.16.47

• rearrangements occurred by a nucleophilic attack of the selenocyanate anion at two different carbon atoms of the seleniranium intermediate. The efficient regioselective synthesis of alkyl, allyl, 2-propynyl, benzyl, 4-fluorobenzyl, and 2-pyridinylmethyl 1,3-thiaselenol-2-ylmethyl selenides was developed based on

• , we are observing a new manifestation of this effect, consisting in the promotion of new rearrangements leading to the selective formation of various selenium-containing unsaturated linear and heterocyclic compounds. This effect works in 2-(bromomethyl)-1,3-thiaselenole (1) – a unique reagent, which

• potassium selenocyanate led to the six-membered thiaselenine 5 (kinetic product), which underwent a rearrangement to a five-membered thiaselenole selenocyanate 4 (thermodynamic product). These rearrangements proceeded by a nucleophilic attack of the selenocyanate anion on two different carbon atoms of the

Aerobic synthesis of N-sulfonylamidines mediated by N-heterocyclic carbene copper(I) catalysts

• Faïma Lazreg,
• Marie Vasseur,
• Alexandra M. Z. Slawin and
• Catherine S. J. Cazin

Beilstein J. Org. Chem. 2020, 16, 482–491, doi:10.3762/bjoc.16.43

• : catalysis; copper; copper catalysis; N-heterocyclic carbene; solvent-free; sulfonylamidines; Introduction Amide derivatives represent a ubiquitous molecular construct in chemistry [1][2][3]. This structural motif favours rearrangements that lead to high reactivity and associated bioactivity [4][5]. Indeed

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• -quinolyhydrazine (112) at a molar ratio of 2:1 in the presence of a base gave compound 113 in very good yield. Heating of compound 113 in toluene induced isomerization where the pendant arm is shifted to the quinoline ring via a P–C migration to obtain compound 114. The corresponding P–N and P–P rearrangements

Synthesis and herbicidal activities of aryloxyacetic acid derivatives as HPPD inhibitors

• Man-Man Wang,
• Hao Huang,
• Lei Shu,
• Jian-Min Liu,
• Jian-Qiu Zhang,
• Yi-Le Yan and
• Da-Yong Zhang

Beilstein J. Org. Chem. 2020, 16, 233–247, doi:10.3762/bjoc.16.25

• substituted 1,3-dimethyl-1H-pyrazole-5-ol, using DMAP as the catalyst. Subsequently, the key enol ester E and M were respectively obtained. Finally, Fries-type rearrangements were performed in anhydrous DCM at room temperature to afford the title compounds I and III [31]. As shown in Scheme 4, the title

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some

• control experiments and DFT calculations. Keywords: Brønsted and Lewis acids; DFT; mechanistic studies; rearrangement; stereochemistry; sulfur atom migration; Introduction Among all organic reactions, rearrangements are an exciting class of transformations where unusual or even unexpected products can

• be obtained. Many rearrangements are of practical use in synthetic organic chemistry, including Beckmann [1][2][3][4], Claisen [5][6][7][8], pinacol [9][10][11][12], Wagner–Meerwein [13][14][15][16], Curtius [17][18][19][20], Hofmann [21][22][23][24], Overmann [25][26][27][28] rearrangements, and

Terpenes

• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 2966–2967, doi:10.3762/bjoc.15.292

• generate a highly reactive cationic intermediate that can be subject to a cascade reaction through typical carbocation chemistry, including cyclisation reactions, hydride migrations and Wagner–Meerwein rearrangements [1][2]. The cascade is usually terminated by deprotonation or attack of water. The

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• rearrangements. Furthermore, these organocatalysts slowed down the Ireland–Claisen rearrangement in comparison to an uncatalyzed reaction. The catalyst-free reaction proceeded well in green solvents or without any solvent. DFT calculations showed that the activation barriers are higher for reactions involving

• acid, catalyzed by in situ-generated copper hydride with diethoxymethylsilane as a reductive agent gave the γ,δ-unsaturated acid with good to excellent diastereoselectivities [27]. Various asymmetric organocatalyzed rearrangements are known [28]. However, the catalysis of sigmatropic rearrangements is

• difficult due to their rather nonpolar transition states, which are difficult to be addressed by catalysts [29]. Several stereoselective [3,3]-sigmatropic rearrangements are realized with chiral Brønsted acids [30][31][32][33][34]. Jacobsen reported guanidinium-catalyzed enantioselective Claisen