SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

• Julien Borrel and
• Jerome Waser

Beilstein J. Org. Chem. 2024, 20, 701–713, doi:10.3762/bjoc.20.64

• discovery and development of the synthesis of homopropargylic azides by the azido-alkynylation of alkenes. Initially, a strategy involving SOMOphilic alkynes was adopted, but only resulted in a 29% yield of the desired product. By switching to a radical-polar crossover approach and after optimization, a

• terminal azide, despite its implication in the synthesis of complex molecules [3][6]. Therefore, the development of a straightforward reaction to synthesize homopropargylic azides would be of general interest. The azido-alkynylation of alkenes would allow to generate the desired motif in a single step

• the development of the azidobenziodazolone scaffold [17]. This class of derivative showed an improved safety profile while retaining the redox properties of the original reagent. A single example of azido-alkynylation has been reported by Ramasastry and co-workers during a mechanistic study for an

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

• ), alkynylation [88] (Scheme 24C) and C(sp3)–C(sp3) cross-coupling [89] (Scheme 24D). Finally, similar chemistry has been extended to the decarboxylative borylation of RAEs under Ni [90] and Cu [91] catalysis (Scheme 24E). Importantly, the Wang group has independently studied the decarboxylative Negishi coupling

• of RAEs with organozinc reagents under Co-catalysis, effecting diverse arylation, alkenylation, and alkynylation reactions [92]. The second type of reaction is referred to as cross-electrophile coupling and involves the Ni-catalyzed reaction of NHPI esters with aryl- and vinyl halides under reducing

Catalytic multi-step domino and one-pot reactions

• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2024, 20, 254–256, doi:10.3762/bjoc.20.25

• acetaldehyde dimethyl acetal as a masked form of acetaldehyde, which is hydrolyzed in situ, allowing for a higher product yield and fewer byproducts [15]. The group of Müller describes an elegant consecutive four-component reaction involving an alkynylation–cyclization–iodination–alkylation sequence toward

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

• state, in good yield. Keywords: alkynylation; catalysis; cyclization; indoles; iodination; multicomponent reactions; Introduction Indoles and their derived substitution patterns are omnipresent heterocyclic structural motifs in nature [1], many natural products [2][3], drugs [4][5][6][7][8], and dyes

• transition-metal catalysis [31], we disclosed an activating group-free alkynylation–cyclization sequence to (aza)indoles [32][33] that could be readily concatenated with a concluding N-alkylation of the 7-azaindole intermediate in the sense of consecutive three-component coupling–cyclization–alkylation

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

• oligomers 5 can be synthesized by a Glaser oxidative dimerization of monomers 6 (Scheme 1). The obvious route for the synthesis of the latter is the sequential alkynylation of 2,7-diiodonaphthalene 8. In accordance with this strategy, diiodide 8 was cross-coupled with copper(I) arylacetylides (Castro

• –Stephens reaction, method A) and arylacetylenes (Sonogashira reaction, method B). In all cases, even when using a small excess of 8, in addition to the desired monoalkynyl derivative 7, a double alkynylation product 9 was formed (Table 1). The Sonogashira coupling was somewhat more efficient, yielding

• 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

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

• ferrocene ligands. All types of metal enolates generated via these processes were able to react with Michael acceptors and afforded the corresponding products in good yields. The alkynylation of enolates generated by conjugate addition was described by Teodoro and Silva (Scheme 32) [68]. Even though the

• conjugate addition of trialkylaluminum or Grignard reagents was realized only in an achiral manner, this work merits discussion here. Aluminum and magnesium enolates were alkynylated with ethynylbenziodoxolone (EBX). This diastereoselective electrophilic alkynylation afforded the corresponding α

• conjugate alkynylation and consecutive aldol addition (Scheme 49) [91]. The chiral ruthenium complex C2 (Phebox-type)-catalyzed procedure delivered β-hydroxyketone derivatives 192 having α-propargyl groups in good yields, however, only with low diastereoselectivities (up to 3:1). While the syn-diastereomers

Earth-abundant 3d transition metals on the rise in catalysis

• Nikolaos Kaplaneris and
• Lutz Ackermann

Beilstein J. Org. Chem. 2022, 18, 86–88, doi:10.3762/bjoc.18.8

• allow for indirected C–H transformations and herein, homolytic C–H cleavages are described for transformative manganese-catalyzed brominations of tertiary C–H bonds [14]. Finally, electrooxidation enabled the site-selective alkynylation of tetrahydroisoquinolines within a TEMPO/copper regime [15]. As

1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• involving the addition of arylamines to β-NQS 18 followed by N-alkynylation and then Cu(I)-catalyzed heterocyclization with tosyl azide in toluene at room temperature, leading to triazoles 50c–k in moderate to excellent yields (Scheme 14). The research group that most explored the formation of heterocycles

Electrocatalytic C(sp³)–H/C(sp)–H cross-coupling in continuous flow through TEMPO/copper relay catalysis

• Bin Guo and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2021, 17, 2650–2656, doi:10.3762/bjoc.17.178

• electrochemical microreactors can be a viable tool for developing efficient transition-metal electrocatalysis. C(sp3)–H alkynylation of tetrahydroisoquinolines. L* = chiral ligand. TEMPO = 2,2,6,6-tetramethylpiperidine 1-oxyl. DDQ = 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. BPO = benzoyl peroxide. Substrate

Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• photophysical properties (Scheme 16). In 2019, Vlla’s group [76] explored the copper-catalyzed alkynylation of dihydroquinoxalin-2-ones 34 with terminal alkynes under irradiation. 4-Benzyl-3,4-dihydroquinoxalin-2(1H)-one 35 was subjected to an oxidation process with a CuII salt to generate a nitrogen radical

• ). In 2020, Zhang’s group [77] described the photoinduced copper-catalyzed decarboxylative alkynylation of redox-active esters with terminal alkynes. N-Hydroxy-tetrachlorophthalimide (TCNHPI, 36) derived from carboxylic acids was identified as the ideal radical precursor. Under irradiation, the CuI

• the alkyl radical and underwent reductive elimination to deliver the desired product. Liu’s group [78] further applied this protocol to the asymmetric decarboxylative alkynylation of N-hydroxy 2,3-naphthalimide-derived ester 37 with terminal alkynes. Remarkably, the N-hydroxy 2,3-naphthalimide-derived

Recent advances in the tandem annulation of 1,3-enynes to functionalized pyridine and pyrrole derivatives

• Yi Liu,
• Puying Luo,
• Yang Fu,
• Tianxin Hao,
• Xuan Liu,
• Qiuping Ding and
• Yiyuan Peng

Beilstein J. Org. Chem. 2021, 17, 2462–2476, doi:10.3762/bjoc.17.163

• , alkynylation, boronization, phosphorization, etc); ii) discovery of new transformations of 1,3-enynes to other N-heterocycles; and iii) more extensive investigations into the mechanism. Ag/I2-mediated electrophilic annulation of 2-en-4-ynyl azides 1. The proposed mechanism of Ag-catalyzed aza-annulation. The

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• selectivity, which is observed at the more electron-rich and the less sterically hindered position. Manganese-catalyzed late-stage C–H alkynylation Alkynes are invaluable intermediates in organic synthesis and are conventionally prepared via palladium-catalyzed cross-coupling reactions [62]. Moreover, they

• alkynylations of bioactive structural motifs are rare [63]. In 2017, the Ackermann group disclosed a late-stage Mn(I)-catalyzed C–H alkynylation of various complex peptide scaffolds [64]. As shown in Scheme 9, manganese(I) catalysis remarkably resulted in racemization-free alkynylation, representing a step

• alkynylation. Mn-catalyzed late-stage fluorination of sclareolide (1) and complex steroid 3. Late-stage radiofluorination of biologically active complex molecules. Late-stage C–H azidation of bioactive molecules. a1.5 mol % of Mn(TMP)Cl (5) was used. bMethyl acetate was used as a solvent. cThe ratio of α/β

A recent overview on the synthesis of 1,4,5-trisubstituted 1,2,3-triazoles

• Pezhman Shiri,
• Ali Mohammad Amani and
• Thomas Mayer-Gall

Beilstein J. Org. Chem. 2021, 17, 1600–1628, doi:10.3762/bjoc.17.114

• 134 were used as starting material in the Sonogashira and Suzuki reactions. The Sonogashira−Hagihara cross-coupling led to alkynylation at position 5 of the triazole ring in the presence of CuI and Pd(PPh3)4 as catalytic system as well as K3PO4 as base in THF as solvent at 65 °C. However, the Suzuki

Copper-mediated oxidative C−H/N−H activations with alkynes by removable hydrazides

• Feng Xiong,
• Bo Li,
• Chenrui Yang,
• Liang Zou,
• Wenbo Ma,
• Linghui Gu,
• Ruhuai Mei and
• Lutz Ackermann

Beilstein J. Org. Chem. 2021, 17, 1591–1599, doi:10.3762/bjoc.17.113

• Institute for Sustainable Chemistry (WISCh), Georg-August-Universität Göttingen, Tammannstraße 2, 37077 Göttingen, Germany 10.3762/bjoc.17.113 Abstract The efficient copper-mediated oxidative C–H alkynylation of benzhydrazides was accomplished with terminal alkynes. Thus, a heteroaromatic removable N-2

• context, You [25], Huang [26], Liu [27], Li [28], and co-workers elegantly disclosed copper-mediated/catalyzed cascade C−H alkynylation and annulation with terminal alkynes to afford 3-methyleneisoindolinone derivatives, through the assistance of 8-aminoquinoline [29] or 2-aminophenyl-1H-pyrazole [30

• ] auxiliaries (Figure 1a). Besides, the cobalt(II)- [31] or nickel(II)-catalyzed [32][33], pyridine oxide (PyO)-directed tandem alkynylation/annulation was realized by Niu and Song et al., which also provided the 3-methyleneisoindolin-1-one scaffolds (Figure 1b). Notably, a sustainable cupraelectro-catalyzed

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• trifluoromethyl alkynylation product 84 with alkynyl sulfone 83, alkene 81, and Togni reagent 82 as substrates catalyzed by 2,4,6-trimethylpyridine (TMP). The EDA complex formed by electron donor TMP and electron acceptor Togni reagent 82 facilitated electron transfer, yielding trifluoromethyl radical to initiate

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

• alkynylation of cyclopropanes 161 with terminal alkynes that led to the formation of the isomeric fluorinated enynes 164 and 165. Shortly before, a Pd-catalyzed ring-opening sulfonylation of gem-difluorocyclopropanes with the formation of 2-fluoroallylic sulfones 166 has been reported (Scheme 71) [122]. The

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• developed by the authors conferred an excellent methodology to obtain the 9-azabicyclo[3.3.1]nonane ring present in (±)-euphococcinine (2). Kibayashi synthesis – 2002 Kibayashi et al. performed the enantioselective synthesis of (−)-adaline (1). Their approach had as key steps SN2-type alkynylation

• . After the treatment of (−)-46 with the lithium acetylide ethylenediamine complex in THF, a nucleophilic alkynylation occurred, with a reversal of configuration in the reaction center. Then, removal of the 1-(2-hydroxyphenyl)ethyl group via cleavage of the C–N bond, leading to (6S)-ethynylpiperidine

Syntheses of spliceostatins and thailanstatins: a review

• William A. Donaldson

Beilstein J. Org. Chem. 2020, 16, 1991–2006, doi:10.3762/bjoc.16.166

• epoxidation [37] of 5-methyl-2-methylene-4-penten-1-ol gave the epoxyalcohol 92 in 94% ee, which was oxidized to the aldehyde 93. While the addition of the lithium salt of methyl propynoate proceeded in a nondiastereoselective fashion, the use of a zirconium/silver-mediated alkynylation gave the alcohol 94

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• borylations [41][42], heteroarylations [43], and thioesterifications [44]. Additionally, several methods using photoredox chemistry were also published. For instance, the alkylation of isoquinolines under iridium catalysis and alkynylation with eosin Y as the catalyst [45][46]. In this contribution, we

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• , Japan 10.3762/bjoc.16.53 Abstract A series of α- and β-ethynyl-substituted BODIPY derivatives (3a, 4a, 5a, 5b, 6a, 6b) were synthesized by gold(I)-catalyzed direct C–H alkynylation reactions of dipyrromethane and BODIPY, respectively, with ethynylbenziodoxolone (EBX) in a regioselective manner

• -materials. Keywords: alkynylation; BODIPY; direct C–H functionalization; gold(I); Introduction Boron-dipyrromethene (BODIPY, 1) and its derivatives are representative families of fluorophores that have been widely used in applications for bioimaging [1][2][3][4][5][6], photodynamic therapy [7][8][9][10

• Glaser-coupling reactions [37]. Conventionally, an alkynylation of the BODIPY core has been achieved by palladium-catalyzed Sonogashira cross-coupling with halogenated BODIPYs (Figure 1b) [35][37]. However, due to the coexistence of multiple C–H bonds, a regioselective direct C–H alkynylation of the

Controlling alkyne reactivity by means of a copper-catalyzed radical reaction system for the synthesis of functionalized quaternary carbons

• Goki Hirata,
• Yu Yamane,
• Naoya Tsubaki,
• Reina Hara and
• Takashi Nishikata

Beilstein J. Org. Chem. 2020, 16, 502–508, doi:10.3762/bjoc.16.45

• addition (ATRA) [21] (Scheme 1, i–iii). Therefore, we postulated that if we could control the reactivities of the alkynyl–Cu and ATRA adducts, a tandem tertiary alkylation followed by an alkynylation could occur to produce a 1,3-enyne possessing a quaternary carbon center with good regio- and

• stereoselectivity (Scheme 1, this work). Similarly, Zhu’s group has reported that the reaction of an alkyne and an α-bromocarbonyl compound furnishes a highly functionalized 1,3-enyne compound via ATRA followed by an alkynylation reaction [22], but both Pd and Cu are required as catalysts in that case. Our

• methodology can realize a Pd-free catalyst system to prepare complex quaternary carbon atoms. Herein, we report the Cu-catalyzed control of the reactivity of an alkyne (addition and coupling) undergoing tandem tertiary alkylation and alkynylation to produce a 1,3-enyne containing a quaternary carbon center

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• amination of NHP esters. Photocatalytic decarboxylative alkynylation using [Cu(I)(dq)(binap)]BF4. Copper-photocatalyzed alkylation of glycine esters. Copper-photocatalyzed borylation of organic halides. aUnder continuous flow conditions. Copper-photocatalyzed α-functionalization of alcohols with glycine

Emission solvatochromic, solid-state and aggregation-induced emissive α-pyrones and emission-tuneable 1H-pyridines by Michael addition–cyclocondensation sequences

• Natascha Breuer,
• Irina Gruber,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 2684–2703, doi:10.3762/bjoc.15.262

• alkynylation–Michael addition–cyclocondensation (AMAC) multicomponent syntheses of α-pyrones [23]. While most α-pyrones neither fluoresce in solution nor in the solid state specific substitution patterns have been identified for fluorophore design for this heterocyclic family. Tominaga and co-workers

• to α-pyrones through a consecutive alkynylation–Michael addition–cyclocondensation (AMAC) multicomponent synthesis [23]. The reaction can be rationalized by a Sonogashira coupling between an acid chloride and a terminal alkyne furnishing an alkynone, which is transformed without isolation by addition

• –Condon absorption bands. Selected DFT-computed (B3LYP 6-311G**) Kohn–Sham FMOs for 1H-pyridines 6a, 6c, 6e, 6f, and 6g and representing contributions of the longest wavelength Franck-Condon absorption bands. Consecutive three-component alkynylation–Michael addition–cyclocondensation (AMAC) synthesis of α