Synthetic approach to 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides based on common β-keto amide precursors

• Yordanka Mollova-Sapundzhieva,
• Plamen Angelov,
• Danail Georgiev and
• Pavel Yanev

Beilstein J. Org. Chem. 2023, 19, 1804–1810, doi:10.3762/bjoc.19.132

• of methods for their synthesis is a very active area of research. Recent contributions to the synthesis of 4-quinolones made use of phosphine-mediated redox cyclization of 1-(2-nitroaryl)prop-2-ynones [39], palladium-catalyzed carbonylative cyclization of 2-bromonitrobenzenes and alkynes [40], TsCl

Lewis acid-promoted direct synthesis of isoxazole derivatives

• Dengxu Qiu,
• Chenhui Jiang,
• Pan Gao and
• Yu Yuan

Beilstein J. Org. Chem. 2023, 19, 1562–1567, doi:10.3762/bjoc.19.113

• nitrogen source (Scheme 1, reaction 2). In 2017, Xu and co-workers [19] developed a copper-mediated annulation reaction to synthesize isoxazoles from two different alkynes. In fact, most methods mostly used highly toxic transition-metal catalysts such as copper metals. In order to develop cheaper and more

• environmentally friendly catalysts, our laboratory recently developed an alternative approach to the synthesis of isooxazoles starting from 2-methylquinoline and alkynes mediated by Brønsted acids in good yields (Scheme 1, reaction 3) [20]. The utilization of main element metal aluminum salts in organic synthesis

• 11). With the optimal reaction conditions in hand, various alkynes were examined as dipolarophiles (Scheme 2). A range of functional groups were tolerated in this reaction, such as alkyl, methoxy, halo, and heterocycles. It was found that electron-deficient groups in the phenyl ring (3g–i) were more

Morpholine-mediated defluorinative cycloaddition of gem-difluoroalkenes and organic azides

• Tzu-Yu Huang,
• Mario Djugovski,
• Sweta Adhikari,
• Destinee L. Manning and
• Sudeshna Roy

Beilstein J. Org. Chem. 2023, 19, 1545–1554, doi:10.3762/bjoc.19.111

• azides without the requirement of alkynes or late-stage modifications. Our initial investigations led us to identify that adding morpholine as a solvent (0.34–0.4 M) in a reaction with 1-(2,2-difluoroethenyl)-4-methylbenzene (1 equiv) and phenyl azide (1.5 equiv) results in the formation of morpholine

• with an organic azide. A relatively wide range of 1,4,5-trisubstituted-1,2,3-triazoles was obtained in 30–70% yields with high regioselectivity and modest functional group tolerability. This work demonstrates that gem-difluoroalkenes can serve as versatile fluorinated building blocks in lieu of alkynes

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• of organic compounds, N-(alkyl/arylthio)phthalimides are also considered good candidates for this purpose. In 2017, Sahoo and co-workers established a method for intramolecular annulation of N-(arylthio)phthalimides 14 and N-(arylthio)succinimides 1 with alkynes 15 in the presence of AlCl3 as an

α-(Aminomethyl)acrylates as acceptors in radical–polar crossover 1,4-additions of dialkylzincs: insights into enolate formation and trapping

• Angel Palillero-Cisneros,
• Paola G. Gordillo-Guerra,
• Fernando García-Alvarez,
• Olivier Jackowski,
• Franck Ferreira,
• Fabrice Chemla,
• Joel L. Terán and
• Alejandro Perez-Luna

Beilstein J. Org. Chem. 2023, 19, 1443–1451, doi:10.3762/bjoc.19.103

• wherein the intermediate enoxyl radical II arising from the addition step evolves via intramolecular addition to tethered alkenes [16][17] or alkynes [18]. We wondered if, in the absence of the pending radical acceptor, the presence of the β-nitrogen atom could nevertheless promote zinc enolate formation

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

• + 2] cycloaddition of azides with alkynes as will be discussed later. Jin Zhang et al. used the same base, namely KOt-Bu in the presence of CuCl to obtain the thiazolylidene–Cu(I) complex 20 (Scheme 10) [23]. In 2012, Zhu and co-workers synthesized NHC–CuCl complexes using alkali carbonates (Na2CO3

• yield by reacting [Cu(CH3CN)4]BF4 with 2 equiv of benzimidazolium salt 38 in the presence of NaOt-Bu (Scheme 14) [28]. The catalytic activity of the complex 39 was studied in the [3 + 2] cycloaddition of azides with alkynes [28]. Coyle et al. reported the synthesis of a series of NHC and ADC (acyclic

• which showed that all complexes adopted a slightly distorted linear geometry. Furthermore, abnormal-NHC and triazolylidene-based Cu(I) complexes exhibited an outstanding catalytic property towards the [3 + 2] cycloaddition of alkynes with azides. Recently, we have reported the synthesis of NHC

One-pot nucleophilic substitution–double click reactions of biazides leading to functionalized bis(1,2,3-triazole) derivatives

• Hans-Ulrich Reissig and
• Fei Yu

Beilstein J. Org. Chem. 2023, 19, 1399–1407, doi:10.3762/bjoc.19.101

• azide was combined with a subsequent copper-catalyzed (3 + 2) cycloaddition with terminal alkynes. This one-pot process was developed with a simple model alkyne, but then applied to more complex alkynes bearing enantiopure 1,2-oxazinyl substituents. Hence, the precursor compounds 1,2-, 1,3- or 1,4-bis

• carbohydrate mimetics, but the reductive cleavage of the 1,2-oxazine rings to aminopyran moieties did not proceed cleanly with these compounds. Keywords: alkynes; azides; copper catalysis; nucleophilic substitution; 1,2-oxazines; Introduction The concept of click reactions [1][2], in particular, the

• ]). Mechanistic aspects of the CuAAC have been studied in detail [16][17]. Whereas the traditional 1,3-dipolar cycloaddition (Huisgen reaction) [18][19][20] of azides and alkynes requires often – but not always – relatively harsh conditions and proceeds with moderate regioselectivity only [21], the copper

Consecutive four-component synthesis of trisubstituted 3-iodoindoles by an alkynylation–cyclization–iodination–alkylation sequence

• Nadia Ledermann,
• Alae-Eddine Moubsit and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2023, 19, 1379–1385, doi:10.3762/bjoc.19.99

• generated by a consecutive four-component reaction starting from ortho-haloanilines, terminal alkynes, N-iodosuccinimide, and alkyl halides in yields of 11–69%. Initiated by a copper-free alkynylation, followed by a base-catalyzed cyclizive indole formation, electrophilic iodination, and finally

• -catalyzed processes for accessing indoles have become attractive alternatives over the past decades [19][20][21][22][23][24]. Besides Larock's indole synthesis employing alkyne anellation [25] and Cacchi's cyclization of ortho-alkynylanilines [20][22] catalytic syntheses of indoles from alkynes have become

• to directly employ these standard conditions to the sequence of ortho-haloanilines 1, terminal alkynes 2, N-iodosuccinimide (3), and alkyl halides 4 to screen the scope of the one-pot synthesis of trisubstituted 3-iodoindoles 5 in a consecutive four-component fashion (Scheme 2). The sequence

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• terminal alkynes at room temperature (Scheme 15a) [67]. The ability to tune the reactivity of the trityl ion rationally improves the approach with excellent regio- and diastereoselectivity for the unsymmetric ethers. In 2018, Ye et al. reported a CDC reaction to form C(sp)–C(sp3) coupling products from

• to afford internal alkynes from substrates with the C(sp3)–H bond mainly located in the α-position to N, O, or S atoms. This method provides a direct and atom-economical alternative for the construction of structurally complex alkyne compounds (Scheme 26) [87]. In addition to iron, various other

•  27) [88]. This route provides an environmentally friendly and practical approach to alkyl-substituted alkynes. Co-catalyzed reactions In recent years, cobalt has exhibited great application potential as a cross-dehydrogenation coupling catalyst due to its low price, environmentally friendliness, and

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• pathways, respectively (Figure 20A). Both protocols were able to successfully engage perfluoroalkyl iodides and bromotrichloromethane in combination with a diverse scope of alkenes and alkynes (Figure 20B). Products of terminal alkenes and alkynes were generally obtained in good to excellent yields while

The unique reactivity of 5,6-unsubstituted 1,4-dihydropyridine in the Huisgen 1,4-diploar cycloaddition and formal [2 + 2] cycloaddition

• Xiu-Yu Chen,
• Hui Zheng,
• Ying Han,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 982–990, doi:10.3762/bjoc.19.73

• ]. The well-known Huisgen 1,4-dipoles have a special kind of zwitterionic intermediates and are usually prepared by a nucleophilic addition of pyridine, quinoline, isoquinoline and other aza-arenes to electron-deficient alkynes [4][5][6][7][8]. The reactive Huisgen 1,4-dipoles have been widely employed

• unprecedented synthetic reactivity of the electron-deficient alkynes, but also provides efficient synthetic methodologies for complex nitrogen-containing heterocycles. The potential application of this reaction in organic synthesis and medicinal chemistry might be significant. Experimental General procedure for

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

• Heck cross-coupling [69][70]. However, researchers have developed various methods for the transition-metal-catalyzed C(sp2)–H olefination using various types of alkenes as coupling partners [71][72][73]. This part of the review covers reports for the alkenylation of pyridine with terminal alkynes

• , acrylates, allenes, and alkynes as coupling partners achieving the functionalized C(sp2)–H-olefinated pyridine frameworks via metal catalysis. ortho-C–H Alkenylation In 2012, Huang and co-workers [74] disclosed a ligand-free oxidative cross-coupling reaction of pyridine with acrylates, acrylamides, and

• . Except lately, in 2020, Chen and group [82] reported a Pd/Cu-catalyzed regio- and stereoselective synthesis of C2-alkenylated pyridines starting from internal alkynes 84 and pyridinium salts in a stereodivergent manner (Scheme 17a). The interesting part of this work was the switching of the alkene

Construction of hexabenzocoronene-based chiral nanographenes

• Ranran Li,
• Di Wang,
• Shengtao Li and
• Peng An

Beilstein J. Org. Chem. 2023, 19, 736–751, doi:10.3762/bjoc.19.54

• -workers reported pyrrole-containing helical NGs 19 and 20. The precursors 17 and 18 were synthesized from pyrrole-containing alkynes and tetracyclone 2 through a typical Diels–Alder reaction. The pair of enantiomers of these aza-[5]helicenes was confirmed by the X-ray crystal structure of racemic

Synthesis, structure, and properties of switchable cross-conjugated 1,4-diaryl-1,3-butadiynes based on 1,8-bis(dimethylamino)naphthalene

• Semyon V. Tsybulin,
• Ekaterina A. Filatova,
• Alexander F. Pozharskii,
• Valery A. Ozeryanskii and
• Anna V. Gulevskaya

Beilstein J. Org. Chem. 2023, 19, 674–686, doi:10.3762/bjoc.19.49

• compounds 7a–e in 42–62% yields, but also gave higher amounts of products 9a–e (10–30%). Thus, the Pd- and phosphine-free Castro–Stephens coupling was a good enough alternative to synthesize alkynes 7. The structure of the double alkynylation product 9e was confirmed by X-ray diffraction data (see

• recrystallization of the crude product from ethanol. Next, the oxidative dimerization of terminal alkynes 6a–e was carried out in an aerobic medium in the CuI/TMEDA/iPr2NH system at room temperature, which proved to be effective in the synthesis of butadiynes 1–4 [15] (Scheme 3). The desired diarylbutadiynes 5a–e

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

• -alkynylketones 129 in good yields. Conjugate additions with organozirconium reagents The hydrozirconation of alkenes and alkynes generates mild organozirconium compounds that can be used in various transformations. Fletcher and co-workers developed the utilization of organozirconium reagents in Cu-catalyzed

• derivatization is possible through the oxidation of the silyl motif to alcohol or the dehydration of the aldol adduct. Other tandem conjugate addition/enolate-trapping reactions In 2016, Nishiyama and co-workers have studied a three-component coupling reaction of alkynes, enones, and aldehydes via direct

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• difunctionalization of norbornene derivatives 15 with alkynes (Scheme 3) [35]. It was noted the reaction is amenable to both electron-donating groups (EDGs) and electron-withdrawing groups (EWGs); however, yields were diminished with increasing electron deficiency. Moreover, the use of the bulkier tert

• product 19c, the latter was obtained in a greatly reduced yield, perhaps due to less ring strain providing a thermodynamic driving force. In 2013, Mannathan et al. discussed a Ni-catalyzed intermolecular three-component difunctionalization of oxabicyclic alkenes 1 with organoboronic acids 20 and alkynes

• exo face of 30b, oxidative cyclization can afford the ruthenacycle 101. Unlike previous works studying Ru-catalyzed cyclizations involving bicyclic alkenes and alkynes [56][57][58][59], the reaction preferentially undergoes β-hydride elimination to generate 102 rather than reductive elimination which

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

• the standard reactions for catalytic hydrogenations with copper(I)/NHC complexes [4]. In this vein, we tested complex 5 from solid and liquid phase synthesis in the catalytic hydrogenation of esters, carbonyl compounds and in the semihydrogenation of alkynes. In the catalytic hydrogenation of ethyl

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• connect a porphyrin with a chromophoric group. Among these, the copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction [1][2] of azides with terminal alkynes is a popular and well established process to link a porphyrin with other moieties via 1,2,3-triazole group [3] (Figure 1). The term “click

• triazoloporphyrins 32a–c and triazole-bridged bisporphyrins 34 in good yields. The “click reaction” of azidoporphyrin 30 with the terminal alkynes 31a–c and 33 in a THF/water (3:1) mixture was investigated by using different catalytic systems. Among these, copper carbene (SIMes)CuBr proved to be a better catalyst

• 55 as sensitizers for dye-sensitized solar cells (DSSCs). These porphyrin conjugates were synthesized through the click reaction between azidoporphyrin 51 and alkynes 52 or 54. Further, porphyrin 57 bearing a CN and a COOH group was prepared by the treatment of porphyrin 55 with 2-cyanoacetic acid

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

• -catalysed hydroboration of alkynes was first reported by Periasamy using N,N-diethylaniline·BH3 as the catalyst and HBcat as the turnover reagent (terminal reductant) [48][49]. This was followed by Hoshi who used dialkylboranes, 9-borabicyclo(3.3.1)nonane (H-B-9-BBN) and dicyclohexylborane (Cy2BH) to

• catalyse the hydroboration of alkynes with HBcat [50]. Hoshi later reported that Cy2BH [51] and in situ generated bis(pentafluorophenyl)borane, Piers’ borane [52], catalysed the hydroboration of alkynes with HBpin, to give alkenyl pinacol boronic esters. Tris(2,4,6-trifluorophenyl)borane [53], tris(3,4,5

• -trifluorophenyl)borane [54], BH3 [55][56][57], and H-B-9-BBN [58] have also been reported as catalysts for the hydroboration of alkynes with HBpin (Scheme 2). Lloyd-Jones et al. investigated the mechanism of this reaction and found transborylation, group 13 exchange between boron atoms, enabled catalytic turnover

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

• favoring reactivity with various types of substrates, ranging from halides to carbonyls and alkenes/alkynes. It is comprehensible that this reagent attracted early interest in natural product synthesis and more precisely on medium-sized ring formation. 4.1 SmI2-mediated Barbier-type ring annulation towards

• ester. Finally, this latter was hydrolyzed or reduced to respectively provide albolic acid (178) and ceroplastol II (179). The scope of the reaction was also extended to various products containing the [X-8-5] tricyclic system (Figure 6). Several functionalized terminal alkynes succeeded in the Pauson

Sequential hydrozirconation/Pd-catalyzed cross coupling of acyl chlorides towards conjugated (2E,4E)-dienones

• Benedikt Kolb,
• Daniela Silva dos Santos,
• Sanja Krause,
• Anna Zens and
• Sabine Laschat

Beilstein J. Org. Chem. 2023, 19, 176–185, doi:10.3762/bjoc.19.17

• ]. Since the early work by Wailes, Schwartz and Buchwald on the Schwartz reagent Cp2Zr(H)Cl and its reactivity towards alkynes, alkenes, and C–X double bonds particularly hydrozirconation has gained much attention [25][26][27][28][29][30]. It has been successfully employed in methodology studies [31][32

• Crombie’s work on dienamides and prepared dienoates 15 by hydrozirconation of terminal alkynes 16 followed by Pd-catalyzed cross coupling with enoates 17 [55][56]. A repetitive approach gave rise to oligoenoates [57]. Hydrozirconations were also combined with carbonylations to install carbonyl groups. For

• example, the sequential hydrozirconation/carbonylation of propargylic ethers 18 reported by Donato [58] yielded α,β-unsaturated lactones 19. Beside the hydrozirconation/acylation sequence of nitriles utilizing acid chlorides published by Majoral/Floreancig [59][60], Cox revealed that terminal alkynes 16

Practical synthesis of isocoumarins via Rh(III)-catalyzed C–H activation/annulation cascade

• Qian-Ci Gao,
• Yi-Fei Li,
• Jun Xuan and
• Xiao-Qiang Hu

Beilstein J. Org. Chem. 2023, 19, 100–106, doi:10.3762/bjoc.19.10

• of 1,2-difunctionalized arenes with alkynes or carbon monoxide (Scheme 1b, III) [13][14][15][16], have been widely applied for the assembly of isocoumarins over the past decades. Recently, the transition-metal-catalyzed ortho C–H activation/annulation of benzoic acids has emerged as an attractive

• approach towards isocoumarins [17][18]. Pioneering examples relying on the Pd, Ru, and Ir-catalyzed C–H cross coupling of benzoic acids with alkenes and alkynes were realized by the groups of Miura [19], Lee [20], Ackermann [21], Zhang [22], Jiang [23], and Jeganmohan [24] et al. Despite these impressive

• easily available, which have been established as versatile synthetic building blocks for the synthesis of cyclic scaffolds [25]. In 2016, Zhu et al. reported the first example of a Rh-catalyzed C–H functionalization of enaminones with alkynes and α-diazo-β-ketoesters to access naphthalenes [26]. Very

Catalytic aza-Nazarov cyclization reactions to access α-methylene-γ-lactam heterocycles

• Bilge Banu Yagci,
• Selin Ezgi Donmez,
• Onur Şahin and
• Yunus Emre Türkmen

Beilstein J. Org. Chem. 2023, 19, 66–77, doi:10.3762/bjoc.19.6

• pyrrole-fused heterocyclic tricycles [33]. The involvement of Nazarov and in particular aza-Nazarov reactions in the cyclization of alkynes that go through metal carbene intermediates has recently been reviewed by Gao and co-workers [34]. In 2019, we reported a highly effective aza-Nazarov cyclization for

Scope of tetrazolo[1,5-a]quinoxalines in CuAAC reactions for the synthesis of triazoloquinoxalines, imidazoloquinoxalines, and rhenium complexes thereof

• Laura Holzhauer,
• Chloé Liagre,
• Olaf Fuhr,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2022, 18, 1088–1099, doi:10.3762/bjoc.18.111

• ) triazoloquinoxaline complexes as well as a new TIQ rhenium complex were synthesized. As a result, a small 1,2,3-triazoloquinoxaline library was obtained and the method could be expanded towards 4-substituted tetrazoloquinoxalines. The compatibility of various aliphatic and aromatic alkynes towards the reaction was

• , a small library of 1,2,3-triazole-substituted quinoxalines was synthesized applying the method of Chattopadhyay et al. [10] with minor adjustments. Altogether, a series of 21 different aliphatic and aromatic terminal alkynes were reacted with tetrazolo[1,5-a]quinoxaline and Cu(I) triflate as a

• the compatibility of the conversion with a diverse set of alkynes. Reduction of the starting material 11a to quinoxalin-2-amine as a side product was observed in some cases (see Supporting Information File 1 for details). The wide range of tolerated alkynes allows the installation of functional groups

Synthesis of N-phenyl- and N-thiazolyl-1H-indazoles by copper-catalyzed intramolecular N-arylation of ortho-chlorinated arylhydrazones

• Yara Cristina Marchioro Barbosa,
• Guilherme Caneppele Paveglio,
• Claudio Martin Pereira de Pereira,
• Sidnei Moura,
• Cristiane Storck Schwalm,
• Gleison Antonio Casagrande and
• Lucas Pizzuti

Beilstein J. Org. Chem. 2022, 18, 1079–1087, doi:10.3762/bjoc.18.110

• cycloaddition reaction of α-diazomethylphosphonates with o-(trimethylsilyl)phenyl triflate in the presence of CsF [13], Cu2+-mediated N−N bond formation from ketimines in the presence of oxygen [14], Pd2+-mediated oxidative benzannulation from pyrazoles and internal alkynes [15], Pd-catalyzed Aza–Nenitzescu