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

Valorisation of plastic waste via metal-catalysed depolymerisation

• Francesca Liguori,
• Carmen Moreno-Marrodán and
• Pierluigi Barbaro

Beilstein J. Org. Chem. 2021, 17, 589–621, doi:10.3762/bjoc.17.53

• temperature (35 °C) but toxic CH2Cl2 solvent (Scheme 1). The reaction using second-generation N-heterocyclic carbene ligands was faster and preferably yielded cyclododecatriene. Larger cyclic butadienes may be used in the production of flame retardants, lubricants and specialty polymers [149][150]. 3.1.3

• electronic effect of the ligand [267]. A reaction mechanism for PLA depolymerisation was proposed, consisting of two consecutive first-order steps, in which Me-La production follows the formation of chain-end groups intermediates [265]. A zinc–N-heterocyclic carbene complex was used as catalysts for the

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

• 100 in good yields and enantioselectivities (21 examples for THCs, up to 98:2 er and 10 examples for THIQs, up to 98:2 er). N-Heterocyclic carbene catalysis N-Heterocyclic carbene (NHC) catalysis was first used in combination with photoredox catalysis by Rovis in 2012. They showed that iminium ions

Metal-free synthesis of phosphinoylchroman-4-ones via a radical phosphinoylation–cyclization cascade mediated by K₂S₂O₈

• Qiang Liu,
• Weibang Lu,
• Guanqun Xie and
• Xiaoxia Wang

Beilstein J. Org. Chem. 2020, 16, 1974–1982, doi:10.3762/bjoc.16.164

• sciences over the last few years [1][4][5]. In general, chroman-4-one derivatives could be obtained via a polarity reversal strategy enabled by the N-heterocyclic carbene (NHC)-catalyzed intramolecular Stetter reaction [6][7][8]. Besides, chroman-4-one derivatives were also constructed via intramolecular

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

NHC-catalyzed enantioselective synthesis of β-trifluoromethyl-β-hydroxyamides

• Alyn T. Davies,
• Mark D. Greenhalgh,
• Alexandra M. Z. Slawin and
• Andrew D. Smith

Beilstein J. Org. Chem. 2020, 16, 1572–1578, doi:10.3762/bjoc.16.129

• Alyn T. Davies Mark D. Greenhalgh Alexandra M. Z. Slawin Andrew D. Smith EaStCHEM, School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom 10.3762/bjoc.16.129 Abstract The N-heterocyclic carbene (NHC)-catalyzed formal [2 + 2] cycloaddition between α

• moderate to good yield as a single diastereoisomer. Keywords: enantioselective catalysis; formal [2 + 2] cycloaddition; N-heterocyclic carbene; ring opening; trifluoromethyl group; Introduction The trifluoromethyl unit holds a prominent and privileged position within organic chemistry [1][2][3][4][5][6

Disposable cartridge concept for the on-demand synthesis of turbo Grignards, Knochel–Hauser amides, and magnesium alkoxides

• Mateo Berton,
• Kevin Sheehan,
• Andrea Adamo and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2020, 16, 1343–1356, doi:10.3762/bjoc.16.115

• combined with a solution-phase reagent, including: (1) copper(I) oxide to produce N-heterocyclic carbene–Cu(I) complexes for use as catalysts [13]; (2) proline to perform proline-based catalytic reactions [14]; (3) zinc powder to produce organozinc halides in tandem with Negishi couplings [15]; (4) zinc

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• undergoing proto-demetallation afforded the final product 46 (Scheme 11B). Initially, the reaction was limited to the generation of racemic products. Ultimately, optimization using McQuade’s six membered N-heterocyclic carbene (NHC) L2 [37] in combination with CuCl led to conditions applicable to different

A systematic review on silica-, carbon-, and magnetic materials-supported copper species as efficient heterogeneous nanocatalysts in “click” reactions

• Pezhman Shiri and
• Jasem Aboonajmi

Beilstein J. Org. Chem. 2020, 16, 551–586, doi:10.3762/bjoc.16.52

• Cu(I)-catalyzed cyclization between CRGO–N3 (93) and 1-propargyl-3-methylimidazolium bromide (94) was used to attach the imidazolium moiety to the surface of the CRGO. Finally, a graphene-containing copper complex of N-heterocyclic carbene, (NHC)-Cu (96), was produced via proton exchange of the

• -heterocyclic carbene) in multiple steps [28]. Initially, imidazole (28) was immobilized on the silica nanomaterial 27 by a nucleophilic attack of 28 on the iodopropylated silica nanomaterial 27 in acetonitrile under reflux for 48 h. The obtained 1-propylimidazole–nanosilica compound ImP–nSiO2 (29) was filtered

• thicker layers of Cu on Au nanoparticles. Other findings in this study were: a) copper leaching decreased using gold nanoparticles, b) increasing the dendron generation increased the diffusion resistance. As shown in Scheme 5, a silica nanomaterial was decorated with a novel copper complex of poly(N

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

• , NHCs (NHC = N-heterocyclic carbene) have become ligands of choice to permit the stabilisation and formation of highly reactive transition metal species [14]. Thus, significant advances have been achieved using this supporting ligand family [15][16][17][18][19]. Recently, our group contributed to this

Formal preparation of regioregular and alternating thiophene–thiophene copolymers bearing different substituents

• Atsunori Mori,
• Keisuke Fujita,
• Chihiro Kubota,
• Toyoko Suzuki,
• Kentaro Okano,
• Takuya Matsumoto,
• Takashi Nishino and
• Masaki Horie

Beilstein J. Org. Chem. 2020, 16, 317–324, doi:10.3762/bjoc.16.31

• by polymerization catalyzed by a nickel complex, leading to the regioregular HT polythiophene (Scheme 1) [8][9]. An additional feature of the deprotonative protocol for polythiophene is the possibility to use chlorothiophene 3, in which the use of a nickel N-heterocyclic carbene (NHC) complex was

Allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions

• Akihiro Yuasa,
• Kazunori Nagao and
• Hirohisa Ohmiya

Beilstein J. Org. Chem. 2020, 16, 185–189, doi:10.3762/bjoc.16.21

• electrophile [8][10][11]. This paper describes in full detail the racemic system using allylic carbonates. The allylic cross-coupling of aromatic aldehydes and allylic carbonates with a silylboronate by the merging of a copper–N-heterocyclic carbene catalyst and a palladium–bisphosphine catalyst produced

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• fluorination of oxindoles with an axially chiral C2-symmetric N-heterocyclic carbene (NHC) palladium complex as a catalyst (Scheme 7a). The corresponding products were obtained in excellent yields but low to moderate enantioselectivities. Meanwhile, Wu and co-workers [42] developed a similar system using a

1,2,3-Triazolium macrocycles in supramolecular chemistry

• Mastaneh Safarnejad Shad,
• Pulikkal Veettil Santhini and
• Wim Dehaen

Beilstein J. Org. Chem. 2019, 15, 2142–2155, doi:10.3762/bjoc.15.211

• mechanically interlocked molecules and molecular machines. We will not concern ourselves in this review with the applications of metal complexes based on N-heterocyclic carbene coordination chemistry, derived of triazoliums or with applications as ionic liquids [26][27][28]. 2. Anion recognition Due to the

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• -hydroxyester 163 was produced from the epoxide 162 employing N-heterocyclic carbene catalysis. Openings of the aziridine ring in 163a with azide or in 163b with in acetic acid provided enantiomerically pure methyl (3S,4S)-4,5-di-N-Boc-amino-3-hydroxypentanoate 164 or 4-N-Boc-amino-3,5-dihydroxypentanoate 165

Hoveyda–Grubbs catalysts with an N→Ru coordinate bond in a six-membered ring. Synthesis of stable, industrially scalable, highly efficient ruthenium metathesis catalysts and 2-vinylbenzylamine ligands as their precursors

• Kirill B. Polyanskii,
• Kseniia A. Alekseeva,
• Pavel V. Raspertov,
• Pavel A. Kumandin,
• Eugeniya V. Nikitina,
• Atash V. Gurbanov and
• Fedor I. Zubkov

Beilstein J. Org. Chem. 2019, 15, 769–779, doi:10.3762/bjoc.15.73

• the ruthenium centre – “the upper” one is the N-heterocyclic carbene (NHC) ligand and “the lower” one is the 2-alkoxybenzylidene ligand. These determine the principal catalytic properties of the ruthenium complexes. Many ligands were tested as the upper part in various publications, which concluded

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

• Łukasz Gułajski,
• Andrzej Tracz,
• Katarzyna Urbaniak,
• Stefan J. Czarnocki,
• Michał Bieniek and
• Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

• -heterocyclic carbene (NHC) ligand were revealed. The presented methodology allows for preparation of a variety of polar and non-polar metathesis products under environmentally friendly conditions. Keywords: catalysis; green chemistry; microwave; N-heterocyclic carbene; olefin metathesis; ruthenium; ultrasound

• ionic tag attached to the benzylidene ligand, with that of catalyst 1a, bearing an ionic tag placed on the N-heterocyclic carbene (NHC) fragment. As model reactions we have selected the ring-closing metathesis (RCM) of the water-soluble substrate 6, the homometathesis of alcohol 8, and more challenging

• Abstract The influence of microwave and ultrasonic irradiation on the performance of ammonium-tagged Ru-based catalysts in olefin metathesis transformations in aqueous media was studied. Differences in the catalytic activity in correlation with the nature of the present counter ion and the size of the N

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• , ruthenium olefin metathesis complexes bearing N-heterocyclic carbene (NHC) ligands, known as second generation catalysts (Figure 1), have shown improved catalytic efficiency over other metathesis catalysts [3][4]. Moreover, their catalytic properties can be finely modulated through variation of the steric

The activity of indenylidene derivatives in olefin metathesis catalysts

• Maria Voccia,
• Steven P. Nolan,
• Luigi Cavallo and
• Albert Poater

Beilstein J. Org. Chem. 2018, 14, 2956–2963, doi:10.3762/bjoc.14.275

• the existing commercial catalysts, playing mainly with the electronic characteristics of the ligands (usually two chlorides and an ylidene ligand) [15][16][17], whereas basically the sterics of the substituents on the N-heterocyclic carbene (NHC) ligand have remained unchanged [18]. Overall, any

The influence of the cationic carbenes on the initiation kinetics of ruthenium-based metathesis catalysts; a DFT study

• Magdalena Jawiczuk,
• Angelika Janaszkiewicz and
• Bartosz Trzaskowski

Beilstein J. Org. Chem. 2018, 14, 2872–2880, doi:10.3762/bjoc.14.266

• investigated cases the partial charge of the carbene carbon atom is similar, resulting in comparable Ccarbene–Ru bond strengths and Ru–P/O dissociation Gibbs free energies. Keywords: catalysts; cationic carbenes; DFT; initiation; metathesis; Introduction The isolation of the first stable N-heterocyclic

• carbene (NHC) by Arduengo [1] was a milestone in organic chemistry which allowed for thorough and systematic studies on all aspects of NHC chemistry in the past 25 years [2][3][4][5][6][7]. It was soon realized that NHCs are a very useful class of ligands for transition metal catalysis as both their

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• modification of the first coordination sphere by adding an N-heterocyclic carbene (NHC) ligand and a chelating styrene to the so-called Grubbs 1st generation catalyst, the relatively air- and moisture-stable Grubbs–Hoveyda type (GH-type) catalysts were obtained [7]. These catalysts do not only show stability

Visible light-mediated difluoroalkylation of electron-deficient alkenes

• Vyacheslav I. Supranovich,
• Vitalij V. Levin,
• Marina I. Struchkova,
• Jinbo Hu and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2018, 14, 1637–1641, doi:10.3762/bjoc.14.139

• energetic UV light (xenon arc lamp) in combination with sodium cyanoborohydride to trigger the reaction of non-fluorinated alkyl iodides [45][46][47]. Subsequently, we showed that silyldifluoromethyl iodide can generate the corresponding gem-difluorinated radical in combination with an N-heterocyclic

• carbene/borane complex and 400 nm light [48]. Results and Discussion Iodide 1a was selected as a model substrate and its reaction with tert-butyl acrylate (2a) was evaluated in the presence of various boron hydrides (Table 1). The reaction was performed in methanol with irradiation by a strip of blue

Cobalt-catalyzed directed C–H alkenylation of pivalophenone N–H imine with alkenyl phosphates

• Wengang Xu and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2018, 14, 709–715, doi:10.3762/bjoc.14.60

• Wengang Xu Naohiko Yoshikai Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore 10.3762/bjoc.14.60 Abstract A cobalt–N-heterocyclic carbene (NHC) catalyst efficiently promotes an ortho C–H

• demonstrated that the combination of a cobalt–N-heterocyclic carbene (NHC) catalyst and a Grignard reagent allows for the arene C–H functionalization with organic halides and pseudohalides under the assistance of nitrogen directing groups [17][22][23][24][25][26][27]. In this connection, Ackermann developed a

Comparative profiling of well-defined copper reagents and precursors for the trifluoromethylation of aryl iodides

• Peter T. Kaplan,
• Jessica A. Lloyd,
• Mason T. Chin and
• David A. Vicic

Beilstein J. Org. Chem. 2017, 13, 2297–2303, doi:10.3762/bjoc.13.225

• facilitate meaningful comparative studies, such as structural and electrochemical ones [2]. N-Heterocyclic carbene (NHC) complexes of copper such as A1 (Scheme 1) were the first well-defined and structurally characterized copper–CF3 complexes that display activity for the trifluoromethylation of aryl halides

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

• Ken Takaki,
• Makoto Hino,
• Akira Ohno,
• Kimihiro Komeyama,
• Hiroto Yoshida and
• Hiroshi Fukuoka

Beilstein J. Org. Chem. 2017, 13, 1816–1822, doi:10.3762/bjoc.13.176

• ; N-heterocyclic carbene; ring enlargement; Stetter reaction; vicinal polyketone; Introduction N-Heterocyclic carbenes (NHCs) have been indispensable catalysts for organic synthesis, particularly for umpolung of various functional groups [1][2][3][4][5][6][7][8][9]. In the Stetter reaction, NHCs