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

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• rearrangements, creating the basic hydrocarbon skeleton of a terpene [10][11]. This basic hydrocarbon skeleton is then modified to generate a large number of terpenoid structures, which can be further modified by addition of other building blocks, like sugars, amino acids, or fatty acids [12]. Terpenes are named

• electrostatic interactions [54]. Moreover, TCs also assist intramolecular atom transfer and rearrangements including hydride or proton transfer and carbon shifts [10]. Eventually, the carbocation is quenched by deprotonation (E1-like) or nucleophilic attack (SN1-like) of water [45]. In contrast to

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• arenium ions in which a proton is attached at the same carbon as the migrating substituent. Interconversions among the six quaterphenyl isomers have been studied here as a model for rearrangements of linear polyphenyls. All reactions were carried out in 1 M CF3SO3H (TfOH) in dichloroethane at 150 °C in a

• displays such a complex and fascinating collection of molecular rearrangements. Building on a long history, new synthetic applications [1][2] and explanations of carbocation reaction mechanisms [3][4][5][6] continue to be discovered. Chemistry in superacid solutions has played a major role in this field [7

• arenium ions, like many other types of carbocations, often rearrange by 1,2-shifts. This leads to a fascinating collection of rearrangements that can migrate hydrogen, halogens or more complex substituents around the ring and even modify the carbon skeleton. Early reports by Baddeley [18] helped to

Inherent atomic mobility changes in carbocation intermediates during the sesterterpene cyclization cascade

• Hajime Sato,
• Takaaki Mitsuhashi,
• Mami Yamazaki,
• Ikuro Abe and
• Masanobu Uchiyama

Beilstein J. Org. Chem. 2019, 15, 1890–1897, doi:10.3762/bjoc.15.184

• 2609 plots for quiannulatene formation and 2640 plots for sesterfisherol formation. We divided the whole biosynthetic process into three phases; (I) 5/12/5 tricycle formation, (II) conformational changes and hydrogen shifts, and (III) ring rearrangements (Scheme 2 and Scheme 3). Then, we computed the

• in the following ring rearrangement reactions. Phase III: ring rearrangements While C23 is still static in phase III, C20 is relatively flexible, which might serve to decrease the affinity for the enzyme’s binding pocket. Interestingly, although different types of ring rearrangement reactions occur

• diphosphate, IM: intermediate. Quiannulatene is formed by the deprotonation of IM11. Phase (I): 5/12/5 tricycle formation is highlighted in blue. Phase (II): conformational changes and hydrogen shifts are highlighted in orange. Phase (III): ring rearrangements are highlighted in yellow. Reaction mechanisms of

Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• the aza-Piancatelli and related rearrangements. Experimental General procedure for the rearrangement: Furylcarbinol 1 and aniline 2 were dissolved in DCM. At 23 °C, 5 mol % of the catalyst 8 was added to the reaction mixture and the reaction mixture was stirred for 5 days. The reaction was then

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• ] transferring the non-oxygenated boron substituent and promoting oxirane ring opening [39]. The group’s migratory aptitude cannot be directly compared to that known from cationic rearrangements, because the nature of the other boron substituents plays a key role in migration, as revealed by calculations [40][41

Selective detection of DABCO using a supramolecular interconversion as fluorescence reporter

• Indrajit Paul,
• Debabrata Samanta,
• Sudhakar Gaikwad and
• Michael Schmittel

Beilstein J. Org. Chem. 2019, 15, 1371–1378, doi:10.3762/bjoc.15.137

• machinery [22]. In contrast, the actual contribution seeks to explore the utility of supramolecular rearrangements [23] for sensing and detection, in particular with an emphasis on high selectivity. As a notable example of the latter category, Nitschke recently reported the guest-induced transformation of

• integrity of complex 6. In sum, the clean formation of complexes 5 and 6 provides a reliable base for the elaboration of completive and incomplete double self-sorted guest-induced structural rearrangements. In order to verify the forward conversion shown in Scheme 1, ligands 1 and 2 as well as [Cu(CH3CN)4

Robust perfluorophenylboronic acid-catalyzed stereoselective synthesis of 2,3-unsaturated O-, C-, N- and S-linked glycosides

• Madhu Babu Tatina,
• Xia Mengxin,
• Rao Peilin and
• Zaher M. A. Judeh

Beilstein J. Org. Chem. 2019, 15, 1275–1280, doi:10.3762/bjoc.15.125

• results obtained using boron trifluoride diethyl etherate [32]. We then applied the perfluorophenylboronic acid catalyst to promote the reaction between 2,3,4,6-tetra-O-acetyl-D-glucal (4a) and O- and S-nucleophiles (Figure 2). The Ferrier-catalyzed rearrangements of 2-substituted sugars such as 2,3,4,6

Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2019, 15, 789–794, doi:10.3762/bjoc.15.75

• enzymatic step [1][2][3]. With this approach, nature makes perfect use of the versatile chemistry of carbocations with its hydride or proton shifts and Wagner–Meerwein rearrangements leading to a large variety of possible structures. Among terpenoid natural products, achiral compounds are rarely found, but

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• pyrimidine N-oxides PO30–33 derived from β-ketoenamides KE43, KE45, KE78 and KE80. Reduction of PO4 to PM5 and Boekelheide rearrangements of PO13, PO14, PO4 and PO30 to 4-acetoxymethyl-substituted pyrimidine derivatives; Ad = 1-adamantyl. Deprotection of 4-acetoxymethyl-substituted pyrimidine derivatives

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• through different strategies, this review is focusing specifically on the use of [2,3]- and [3,3]-sigmatropic rearrangements involving cyclopropenylcarbinol derivatives as substrates. These sigmatropic rearrangements, which have been developed in recent years, allow a remarkably efficient and

• stereoselective access to a wide variety of heterosubstituted and/or functionalized alkylidenecyclopropanes which would not be readily accessible by other strategies. The different [2,3]- and [3,3]-sigmatropic rearrangements of cyclopropenylcarbinol derivatives disclosed to date, as well as the analysis of their

• substrate scope and some applications of the products arising from those reactions, are presented in this review. Keywords: alkylidenecyclopropanes; cyclopropanes; cyclopropenes; sigmatropic rearrangements; strained rings; Introduction Among the ever expanding diversity of chemical transformations

Synthesis of 1,2-divinylcyclopropanes by metal-catalyzed cyclopropanation of 1,3-dienes with cyclopropenes as vinyl carbene precursors

• Jesús González,
• Alba de la Fuente,
• María J. González,
• Laura Díez de Tejada,
• Luis A. López and
• Rubén Vicente

Beilstein J. Org. Chem. 2019, 15, 285–290, doi:10.3762/bjoc.15.25

• allows sigmatropic rearrangements leading to odd-numbered carbocyclic derivatives [8]. In this sense, seven-membered carbocycles, namely 1,4-cycloheptadienes, can be forthrightly prepared from cis- or trans-1,2-divinylcyclopropanes through a Cope rearrangement [8][9]. The potential of this type of

• stereoselective reaction. Once more, simple ZnCl2 was particularly effective for this reaction in sharp contrast to the incompetence of [Rh2(OAc)4]. It should be noticed that 1,2-divinylcyclopropanes 3a–l did not undergo [3,3]-Cope rearrangements under the reaction conditions. Moreover, when pure endo-3e was

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• homolytic cleavage of the Co(III)–C bonds. The carbon-skeleton rearrangements were achieved in the vesicle due to cage effects in the apoenzyme model. Conversely, such reactions hardly proceeded in homogenous solutions. The yields of the migration products increased in order of CN ~ CO2C2H5 < COCH3. A

• cyclophane-type B12 artificial enzyme also mediated similar carbon-skeleton rearrangements [32]. We developed another artificial enzyme composed of human serum albumin (HSA) and heptapropyl cobyrinate [34]. It is known that HSA acts as a carrier for in vivo hydrophobic molecules. Hydrophobic B12 model

One-pot synthesis of epoxides from benzyl alcohols and aldehydes

• Edwin Alfonzo,
• Jesse W. L. Mendoza and
• Aaron B. Beeler

Beilstein J. Org. Chem. 2018, 14, 2308–2312, doi:10.3762/bjoc.14.205

• alcohols and aldehydes. Keywords: Corey–Chaykovsky; epoxide; heterocycle; one-pot; ylide; Introduction Epoxides have historically served as strategic functional groups in target-oriented synthesis [1][2][3][4]. Common examples of their utility include stereospecific ring opening [5][6][7], rearrangements

Revisiting ring-degenerate rearrangements of 1-substituted-4-imino-1,2,3-triazoles

• James T. Fletcher,
• Matthew D. Hanson,
• Joseph A. Christensen and
• Eric M. Villa

Beilstein J. Org. Chem. 2018, 14, 2098–2105, doi:10.3762/bjoc.14.184

• and bioactive molecules, but depending on the substituent identity, it can be inherently unstable due to Dimroth rearrangements. This study examined parameters governing the ring-degenerate rearrangement reactions of 1-substituted-4-imino-1,2,3-triazoles, expanding on trends first observed by L’abbé

• analogs have been reported to display an inherent instability at elevated temperatures due to the propensity to undergo Dimroth rearrangements [40], as originally described by L’abbé et al. for this motif [41][42][43], as shown in Figure 1. This study demonstrated that such compounds are prone to

• than originally reported are lacking. With an emerging interest in the 4-imino-1,2,3-triazole motif as coordination chemistry synthon, motivation for revisiting the ring degenerate rearrangements first described by L’abbe is twofold. A better understanding of parameters suppressing this rearrangement

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• driven by cleavage of the N–O bond is an ideal approach to selectively synthesize O-protected 2-aminophenols 2 while maintaining the oxidation state during the transformation (Scheme 2a) [4][5][6][7][8][9][10][11]. However, there is a significant drawback, these [3,3]-rearrangements of carboxylic acyloxy

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• ]. Oxyarylation of alkenes [71]. Asymmetric oxidative rearrangements of alkenes [72]. Bromolactonization of alkenes [75]. Bromination of alkenes [77][78]. Cooperative strategy for the carbonylation of alkenes [79]. Acknowledgements We are grateful for financial support from the National Nature Science Foundation

Synthesis of spirocyclic scaffolds using hypervalent iodine reagents

• Fateh V. Singh,
• Priyanka B. Kole,
• Saeesh R. Mangaonkar and
• Samata E. Shetgaonkar

Beilstein J. Org. Chem. 2018, 14, 1778–1805, doi:10.3762/bjoc.14.152

• ][34][35][36][37][38] and electrophilic nature of different iodine(III) reagents has been explored to developed various synthetic transformation including rearrangements [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62]. Hypervalent iodine chemistry has

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• , C–C, C–O, or C–N couplings, dearomatization of phenols, rearrangements, to name but a few, have been reported using these compounds thereby reflecting their versatility. A survey of the general structure of polyvalent organoiodine compounds reveals that they are prepared mostly from iodoarene

• to the triple bond of 22 to give the intermediate 26, followed by the reductive elimination of the trivalent iodine motif to afford the palladium-vinylidene 27. This would undergo a nucleophilic addition of the imine and a subsequent proto-demetallation to give enamine 29. A series of rearrangements

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• αvβ5 integrins. Benzo[7]annulenylidenes 73–75 and their rearrangements have attracted much interest due to their thermal and photochemical transformations (Figure 5) [74][75][76]. For the first time, Jones reported the chemical trapping of thermal and photochemical decomposition of the tosylhydrazone

• sodium salt of 4,5-benzotropone (11) and defined carbene–carbene rearrangements of 77–79 before finally it was verified by trapping of unstable intermediates 77–79 (Scheme 14) [77]. In 2002, McMahon reported obtaining the naphthylcarbene rearrangement manifold via the carbonyl groups of the isomeric

An air-stable bisboron complex: a practical bidentate Lewis acid catalyst

• Longcheng Hong,
• Sebastian Ahles,
• Andreas H. Heindl,
• Gastelle Tiétcha,
• Andrey Petrov,
• Zhenpin Lu,
• Christian Logemann and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 618–625, doi:10.3762/bjoc.14.48

• reactions combining the IEDDA step with rearrangements [15] or additional Diels–Alder reactions [16]. However, the methodology requires an air and moisture-sensitive bisboron catalyst. The preparation as well as the handling requires special equipment such as a glovebox, therefore, restricting its

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• with benzaldehyde, p-nitro-, and p-methoxybenzaldehyde as described recently by Ponomarenko and Röschenthaler et al. [34]. Considering our earlier results [31] on TMSOTf-mediated Claisen-type rearrangements of SF5-acetates of allyl alcohols, we favor the initial formation of (Z)-enolates (ketene

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• Eosin Y radical anion. After radical addition of the thiocyanate radical to styrene, the anti-Markovnikov intermediate can form a peroxy radical species with molecular oxygen. Consecutive rearrangements give a β-hydroxythiocyanate, which undergoes fast cyclization to the 5-membered heterocyclic product

From dipivaloylketene to tetraoxaadamantanes

• Gert Kollenz and
• Curt Wentrup

Beilstein J. Org. Chem. 2018, 14, 1–10, doi:10.3762/bjoc.14.1

• tetraoxaadamantanes. Inward-pointing isocyanate, urethane and carbamate groups in bisdioxines. The diisocyanate is obtained by Curtius and Hofmann rearrangements of the diazides and diamides [38][39]. Microwave-assisted tetraoxaadamantane formation. Cyclic bisdioxine ester derivative 34 forming a single mono

Binding abilities of polyaminocyclodextrins: polarimetric investigations and biological assays

• Marco Russo,
• Daniele La Corte,
• Annalisa Pisciotta,
• Serena Riela,
• Rosa Alduina and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2017, 13, 2751–2763, doi:10.3762/bjoc.13.271

• Coulomb repulsion between cationic tail groups. Considering that the polarimetric response of CDs depends on both their intrinsic chirality and on their conformational dynamism, the behaviour observed indicates that our AmCDs experience their most extensive conformational rearrangements as the first