A laterally-fused N-heterocyclic carbene framework from polysubstituted aminoimidazo[5,1-b]oxazol-6-ium salts

• Andrew D. Gillie,
• Matthew G. Wakeling,
• Bethan L. Greene,
• Louise Male and
• Paul W. Davies

Beilstein J. Org. Chem. 2024, 20, 621–627, doi:10.3762/bjoc.20.54

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• , accompanied by the formation of cyano-B(pin) 142. Importantly, in the absence of ZnCl2, intermediate 140 could be detected by HRMS and 11B NMR, highlighting the pivotal role of ZnCl2 in promoting rearomatization. N-Heterocyclic carbene (NHC) catalysis In 2019, Nagao and Ohmiya reported the decarboxylative

• overview of the diverse mechanisms that have been proposed for radical based transformations initiating from NHPI esters. The discussion is organized into four sections: (i) mechanisms under photochemical conditions, (ii) initiation by metal catalysis and stoichiometric reductants, (iii) N-heterocyclic

• carbene (NHC)-catalyzed radical relay, and (iv) mechanisms under electrochemical activation. By discussing selected literature examples, we illustrate how the activation mode of NHPI esters, and the reactivity of the resulting radical species, can vary depending upon the choice of catalytic or

Active-metal template clipping synthesis of novel [2]rotaxanes

• Cătălin C. Anghel,
• Teodor A. Cucuiet,
• Niculina D. Hădade and
• Ion Grosu

Beilstein J. Org. Chem. 2023, 19, 1776–1784, doi:10.3762/bjoc.19.130

• molecule which catalyzes the macrocyclization reaction around the axle (Figure 1b). Results and Discussion In order to access the target [2]rotaxanes we made use of the CuAAC reaction, performed in the presence of a copper(I) N-heterocyclic carbene, a very stable and efficient class of catalysts used in

• active-metal template and clipping methods to yield the target interlocked molecules via [1 + 1] or intramolecular macrocyclizations, realized through CuAAC reactions catalyzed by axle-copper(I) N-heterocyclic carbene complexes. The [2]rotaxane obtained by [1 + 1] clipping (R1) could be only observed by

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• diaminocarbene complex 32 and diamidocarbene (DAC) complex 33. The mononuclear N-heterocyclic carbene (NHC)–copper alkoxide complexes [(6-NHC)CuOt-Bu] (6-NHC = 6-MesDAC (30), 6-Mes (31)) were prepared by the addition of free carbenes to the tetrameric tert-butoxide precursor [Cu(Ot-Bu)]4, or by protonolysis of

Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• with a bulky N-heterocyclic carbene ligand and (2,6-t-Bu2-4-Me-C6H2O)2AlMe (MAD) as the Lewis acid which allowed the direct C-4 alkylation of pyridines 1 (Scheme 12a). With the optimized reaction conditions in hand the group also screened the alkene and pyridine substrate scope which resulted C4

• oxidized by Cu(II) to complete the catalytic cycle. Next, considering the role of N-heterocyclic carbene (NHC) ligands acting as directing group as well as functionalizing unit in arene C–H functionalization reactions with alkynes, Choudhury and group [106] in 2015 developed a protocol for the

• intermolecular C–H annulation of NHC-substituted pyridines with a variety of internal alkynes 187 under rhodium catalysis for the synthesis of annulated and highly decorated pyridines 188 (Scheme 36). The authors used the N-heterocyclic carbene ligand as directing group to prepare imidazo[1,2-a][1,6

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• , which begins with a Cu-catalyzed enantioselective conjugate addition/enolate alkylation tandem reaction sequence utilizing the N-heterocyclic carbene ligand L40 [112]. Ketone 232 was isolated in 61% yield and 81% ee. Hereafter, the authors were able to synthesize the complex tetracyclic structure within

Mechanochemical solid state synthesis of copper(I)/NHC complexes with K₃PO₄

• Ina Remy-Speckmann,
• Birte M. Zimmermann,
• Mahadeb Gorai,
• Martin Lerch and
• Johannes F. Teichert

Beilstein J. Org. Chem. 2023, 19, 440–447, doi:10.3762/bjoc.19.34

• , Germany 10.3762/bjoc.19.34 Abstract A protocol for the mechanochemical synthesis of copper(I)/N-heterocyclic carbene complexes using cheap and readily available K3PO4 as base has been developed. This method employing a ball mill is amenable to typical simple copper(I)/NHC complexes but also to a

• sophisticated copper(I)/N-heterocyclic carbene complex bearing a guanidine moiety. In this way, the present approach circumvents commonly employed silver(I) complexes which are associated with significant and undesired waste formation and the excessive use of solvents. The resulting bifunctional catalyst has

• focus has seldomly been on the preparative methods to access the required catalysts themselves. As case in point, we decided to re-investigate the synthesis of copper(I)/N-heterocyclic carbene (NHC) complexes, which are broadly applicable catalysts for a wide variety of transformations [4][5][6]. While

Group 13 exchange and transborylation in catalysis

• Dominic R. Willcox and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2023, 19, 325–348, doi:10.3762/bjoc.19.28

• /B‒H exchange [114]. Hevia reported a combination of a tris(alkyl)gallium species and bulky N-heterocyclic carbene acted as an FLP for B‒H insertion, and was used subsequently as a catalyst in the hydroboration of ketones, aldehydes, esters, and imines with HBpin [115]. Using an ONO-pincer-supported

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• addition to the electron-rich C=C bond [58] or proton loss followed by β-functionalization [59][60][61]. The iminium cation catalysis is used in the activation of electrophilic properties of enones for the nucleophilic epoxidation by hydroperoxides (Scheme 2B). N-Heterocyclic carbene (NHC) organocatalysis

• -organocatalysts. Organocatalysis classification used in the present perspective. Oxidative processes catalyzed by amines. N-Heterocyclic carbene (NHC) catalysis in oxidative functionalization of aldehydes. Examples of asymmetric oxidative processes catalyzed by chiral Brønsted acids. Asymmetric aerobic α

First example of organocatalysis by cathodic N-heterocyclic carbene generation and accumulation using a divided electrochemical flow cell

• Daniele Rocco,
• Ana A. Folgueiras-Amador,
• Richard C. D. Brown and
• Marta Feroci

Beilstein J. Org. Chem. 2022, 18, 979–990, doi:10.3762/bjoc.18.98

• used as organocatalyst in two classical umpolung reactions of cinnamaldehyde: its cyclodimerization and its oxidative esterification. Keywords: Breslow intermediate; cathodic reduction; flow electrochemistry; N-heterocyclic carbene; oxidative esterification; Introduction Ionic liquids (ILs) are well

• can be modified by the presence of a base or by a single electron cathodic reduction of the C–H between nitrogen atoms of the imidazolium ring (Scheme 1), inducing the formation of a N-heterocyclic carbene (NHC) [7][8]. In recent years, NHCs have achieved great success: they have been frequently used

• reduction of an imidazolium cation to NHC, in an undivided cell under flow conditions, coupled with the anodic generation of Cu(I) from a sacrificial anode to yield the corresponding N-heterocyclic carbene complex [34][35]. In this case, irreversible capture of the NHC by the metallic cation prevented NHC

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