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

• -pyrones from acid chlorides, terminal alkynes and dialkyl malonates. Consecutive pseudo-four-component alkynylation–Michael addition–cyclocondensation (AMAC) synthesis of 1H-pyridines 5a and an aniline derivative. Consecutive pseudo-four-component alkynylation–Michael addition–cyclocondensation (AMAC

• ) synthesis of 1H-pyridines 5a from acid chlorides 1, terminal alkynes 2 and ethyl cyanoacetate (4). Model system for the optimization of the Michael addition–cyclocondensation reaction step to 1H-pyridine 5a or/and α-pyrone 6a. Formation of α-pyrone 6a and 1H-pyridine 5a at 20 °C. Formation of α-pyrone 6a

Formation of alkyne-bridged ferrocenophanes using ring-closing alkyne metathesis on 1,1’-diacetylenic ferrocenes

• Celine Bittner,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2019, 15, 2534–2543, doi:10.3762/bjoc.15.246

• with high yields whilst giving full conversion of the terminal alkynes. Furthermore, the solvent-dependant reactivity of 2a towards Ag(SbF6) is investigated, leading to oxidation and formation of the ferrocenium hexafluoroantimonate 4 in dichloromethane, whereas the silver(I) coordination polymer 5 was

• isolated from THF solution. Keywords: alkyne metathesis; ferrocene; homogeneous catalysis; molybdenum; terminal alkynes; Introduction Alkyne metathesis, the reversible making and breaking of carbon–carbon triple bonds, is clearly gaining more attention. Not only could a great number of active catalysts

• ]. Only recently, we were able to present a molybdenum complex decorated with hexafluoro-tert-butoxide ligands [MesC≡Mo{OC(CH3)(CF3)2}3] (MoF6; Mes = 2,4,6-trimethylphenyl) which proved to be highly active in the metathesis of internal and even terminal alkynes [42][43][44]. The same accounts for the

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

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• domino reaction of aldehydes 1, 2-aminopyridines (2-APs) 3 and terminal alkynes 2, catalyzed by CuI and co-catalyzed by the NaHSO4·SiO2 system (Scheme 1). The reaction performed with CuI alone gave a moderate yield of the product (only 45%) whereas NaHSO4·SiO2 alone was unable to complete the reaction

• reaction to the product of 4-bromo-substituted nitrostyrylisoxazole 48a (Scheme 18). The attractive feature was successful substitution of the bromo atom with terminal alkynes. Different alkynes applied gave a good yield of up to 81%. This reaction provided a direct and efficient method to produce highly

• coupling reaction for the synthesis of 2-triazolylimidazo[1,2-a]pyridine 74 (Scheme 26) [31]. The reaction involved the use of copper oxide as a catalyst and sodium ascorbate as a reducing agent using triazolyl aldehyde 73, amidine 3 and terminal alkynes 2 as reaction substrates at 70 °C (Scheme 26). Here

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• alkynylpalladium complex 25 in the proposed pathway. Other benzoic acid derivatives such as those bearing a formyl substituent at the ortho position also take part in several multicomponent cyclizations leading to isoindolinones. Thus, 2-formylbenzoate 29, primary amines 2 and terminal alkynes 18 react under

• 106. Oxindoles The simplest protocol for the multicomponent assembly of oxindole heterocycles is the palladium-catalysed reaction involving carbon monoxide, in addition to terminal alkynes, arylboronic acids and alkyl iodides, which has been applied to the preparation of fluorinated 3

Synthesis of 2H-furo[2,3-c]pyrazole ring systems through silver(I) ion-mediated ring-closure reaction

• Vaida Milišiūnaitė,
• Rūta Paulavičiūtė,
• Eglė Arbačiauskienė,
• Vytas Martynaitis,
• Wolfgang Holzer and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2019, 15, 679–684, doi:10.3762/bjoc.15.62

• -furo[2,3-c]pyrazoles starting from commercially available 1-phenylpyrazol-3-ol. Iodination of the latter compound with iodine in DMF smoothly afforded 1-phenyl-4-iodopyrazol-3-ol, which can undergo a Pd-catalyzed coupling with terminal alkynes to give the corresponding 4-alkynyl-3-hydroxy-1-phenyl-1H

Dirhodium(II)-catalyzed [3 + 2] cycloaddition of N-arylaminocyclopropane with alkyne derivatives

• Wentong Liu,
• Yi Kuang,
• Zhifan Wang,
• Jin Zhu and
• Yuanhua Wang

Beilstein J. Org. Chem. 2019, 15, 542–550, doi:10.3762/bjoc.15.48

• optimized reaction conditions. The terminal alkynes with electron-withdrawing groups reacted smoothly to produce the desired products, while alkyl-substituted terminal aldehydes, such as pent-1-yne (2b, Table 3, entry 1), did not produce the cycloaddition product [22][23][24]. tert-Butyldimethylsilyl

• -protected propargyl alcohol 2c had a greatly reduced reactivity (Table 3, entry 2) and the obtained yield was less than 10%. For aromatic terminal alkynes, moderate yields (Table 3, entries 3–6) were obtained regardless of the electron-donating or electron-withdrawing groups, indicating the electronic

Copper(I)-catalyzed tandem reaction: synthesis of 1,4-disubstituted 1,2,3-triazoles from alkyl diacyl peroxides, azidotrimethylsilane, and alkynes

• Muhammad Israr,
• Changqing Ye,
• Munira Taj Muhammad,
• Yajun Li and
• Hongli Bao

Beilstein J. Org. Chem. 2018, 14, 2916–2922, doi:10.3762/bjoc.14.270

• from alkyl diacyl peroxides, azidotrimethylsilane, and terminal alkynes is reported. The alkyl carboxylic acids is for the first time being used as the alkyl azide precursors in the form of alkyl diacyl peroxides. This method avoids the necessity to handle organic azides, as they are generated in situ

• (Table 1, entries 12–14). With the optimized reaction conditions in hand, the scope of the terminal alkynes was screened and the results are depicted in Scheme 2. First, the reactivity of various substituted terminal arylalkynes was examined. Only 1,4-regioisomeric products were formed with good to

• additive-free CuAAC reaction for the synthesis of 1,4-disubstituted 1,2,3-triazoles directly from a variety of readily accessible substrates such as alkyl diacyl peroxides, azidotrimethylsilane, and terminal alkynes. The alkyl carboxylic acids are for the first time being used as the alkyl azide precursors

Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex

• Henrike Ehrhorn,
• Janin Schlösser,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2018, 14, 2425–2434, doi:10.3762/bjoc.14.220

• cleaving the W≡W bond in W2F3 with 1-phenyl-1-propyne. The catalytic alkyne metathesis activity of these metal complexes was determined in the self-metathesis, ring-closing alkyne metathesis and cross-metathesis of internal and terminal alkynes, revealing an almost equally high metathesis activity for the

• bimetallic tungsten complex W2F3 and the alkylidyne complex WPhF3. In contrast, Mo2F6 displayed no significant activity in alkyne metathesis. Keywords: alkylidyne complexes; alkyne metathesis; catalysis; terminal alkynes; tungsten; Introduction While the field of olefin metathesis has seen significant

• the metal tungsten, terminal alkynes at room temperature [54]. Our studies clearly display a strong dependency of the catalytic alkyne metathesis activity on the metal-alkoxide combination. The electrophilicity of the metal sites can be controlled by the number of fluorine atoms of the ancillary

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• . The hydroarylation reaction further extended to pyrroles for selective monoalkenylation using [Cp*Co(CH3CN)3](SbF6)2 as the catalyst [55]. In contrast, branched-selective hydroarylation of terminal alkynes was achieved by Li et al. The addition of arenes 7 to propargyl alcohols, protected propargyl

• limited to terminal alkynes. Additionally, they applied this methodology to design a mitochondria-targeted imaging dye from electron-withdrawing formyl-substituted indoles and alkynes. Later, Maji’s group reported an N-tert-butyl amide-directed mono- and di-alkenylation reactions using a cobalt catalyst

• )-catalyzed hydroarylation of terminal alkynes with arenes. Co(III)-catalyzed hydroarylation of alkynes with amides. Co(III)-catalyzed C–H alkenylation of arenes. Co-catalyzed alkylation of substituted benzamides with alkenes. Co-catalyzed switchable hydroarylation of styrenes with 2-aryl pyridines. Co

Applications of organocatalysed visible-light photoredox reactions for medicinal chemistry

• Michael K. Bogdos,
• Emmanuel Pinard and
• John A. Murphy

Beilstein J. Org. Chem. 2018, 14, 2035–2064, doi:10.3762/bjoc.14.179

•  20) [65]. The scope of the substrates demonstrated is quite broad, with substituted aromatic and aliphatic alkynes being used and a variety of substituents tolerated on the diazonium salt starting material. Terminal alkynes selectively formed 2-substituted benzothiophenes, whereas the

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

• –I motif (Scheme 22) [62]. Hence aryl- and alkyl-substituted terminal alkynes can be coupled via a Sonogashira reaction when PPh3 is used as ligand, while the use of diphenylphosphinoferrocenyl ligand (dppf) allows the Heck-type coupling of acrylates, vinyl ketones and electron-poor styrene

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• irradiation to give only 29% of dimethyl 1,3-diphenylpyrazole-4,5-dicarboxylate while in a wetted-wall photo reactor (Normag) the yield is increased up to 84% (at 17 °C in DCM). Thermal reaction of sydnones with terminal alkynes As early as in his first work [1] dealing with sydnone–alkyne cycloaddition

• with alkyl propiolates (cf. Table 4, entries 6, 7, 23–29, 33, 34, 50–55, 58, 118, 141) and acylalkynes (Table 4, entry 142). Other terminal alkynes, for which the calculated lower HOMO–LUMO energy gaps correspond to the type III mechanism (especially phenylacetylenes, alkylacetylenes

• °C) can contribute to a substantial drop of selectivity. It is also known that some sydnones start to decompose at temperatures exceeding 180 °C [74] which can cause lowering of the pyrazole yield. From a synthetic point of view, the cycloaddition with terminal alkynes represents a very good strategy

Electrochemically modified Corey–Fuchs reaction for the synthesis of arylalkynes. The case of 2-(2,2-dibromovinyl)naphthalene

• Fabiana Pandolfi,
• Isabella Chiarotto and
• Marta Feroci

Beilstein J. Org. Chem. 2018, 14, 891–899, doi:10.3762/bjoc.14.76

• ; Introduction Terminal alkynes, due to the considerable triple-bond strength (839 kJ mol−1), are characterized by a moderate thermodynamic reactivity [1]. Nevertheless, both the C–C triple bond and the terminal C–H bond can be efficiently and selectively activated by metal or metal-free catalysts. Therefore

• , terminal alkynes can be considered as raw material (thus an important resource). The use of terminal alkynes, activated by catalysts, as building blocks or intermediates in the synthesis of a large number of chemicals is extensively summarized in recent reviews [1][2][3]. The recently published papers

• confirm the present interest in the chemistry of terminal alkynes, e.g., in the synthesis of sulfinamides and isothiazoles [4], 1,3-enynes [5], α-monosubstituted propargylamines [6], 2-substituted pyrazolo[5,1-a]isoquinolines [7], etc. Terminal alkynes can be prepared by dehydrohalogenation of vicinal

Progress in copper-catalyzed trifluoromethylation

• Guan-bao Li,
• Chao Zhang,
• Chun Song and
• Yu-dao Ma

Beilstein J. Org. Chem. 2018, 14, 155–181, doi:10.3762/bjoc.14.11

• Trifluoromethylated acetylenes were widely used in medicinal, agrochemical, and material science. In 2010, Qing and coworkers [60] firstly reported a copper-mediated trifluoromethylation of terminal alkynes using TMSCF3 as a trifluoromethyl source. (Scheme 39). At the beginning of the experiment, undesired diyne

• same group [61] developed an improved procedure for the efficient copper-mediated trifluoromethylation of terminal alkynes (Scheme 40). This reaction was conducted at room temperature with a smaller amount of TMSCF3. However, the above-mentioned reaction still required stoichiometric amounts of copper

• TMSCF3 (2 equiv) to the mixture afforded CuCF3. And both terminal alkynes and the rest of TMSCF3 were added to the reaction mixture slowly using a syringe pump. Various arylalkynes bearing electron-donating or -withdrawing groups were converted to the desirable products in good to high yields (Scheme 41

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

• (Scheme 46) [83]. By using Eosin Y as organic dye, aryl sulfinic acids could efficiently be cross-coupled with terminal alkynes. The Markovnikov regioselectivity is rationalized by a radical/radical cross-coupling pathway, instead of radical addition to an unsaturated system. The authors propose that

• Eosin Y as photoredox catalyst generates both, the sulfur-centred radical of the sulfinic acid as well as the α-vinyl carbon-centred radical. Radical/radical cross-coupling leads to the desired vinyl sulfone in Markovnikov orientation. The reaction is applicable to diverse functionalized terminal

• alkynes, bearing electron-donating (methyl, methoxy, amine or hydroxy) and withdrawing substituents (halides, carbonyls or sulfonamides) and also heterocyclic substrates. Various aromatic sulfinic acids could be applied, including methoxy, halogen, trifluoromethyl or acetylamino-substituted benzenes, as

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• . Terminal alkynes could also be submitted to these conditions successfully, albeit in lower yields. 2 Trifluoromethylsulfenylation In 2016, CF3SO2Cl was proposed for the first time as a new electrophilic trifluoromethylsulfenylation reagent by our research group [42]. To achieve that kind of transformation

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• , pyrimidine, thiophene, etc. the Maiti group reported an alternative approach toward α-trifluoromethyl ketones starting from (hetero)arylacetylenes 7 and also aliphatic terminal alkynes 8 (Scheme 5) [24]. The trifluoromethyl radical was generated from CF3SO2Na as indicated earlier, oxygen from air was the

Electrophilic trifluoromethylselenolation of terminal alkynes with Se-(trifluoromethyl) 4-methylbenzenesulfonoselenoate

• Clément Ghiazza,
• Anis Tlili and
• Thierry Billard

Beilstein J. Org. Chem. 2017, 13, 2626–2630, doi:10.3762/bjoc.13.260

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• groups is accessible for the use as precursors of peptidomimetics. Keywords: amino acid analogous side chains; desilylation; Ellman’s chiral sulfinamide; intramolecular Huisgen reaction; peptidomimetics; propargylamines; rearrangement to α,β-unsaturated imines; Introduction Terminal alkynes display an

• rearrangement of 11 were investigated (Figure 9). The ester substituted compounds 11i and 11k were obtained by Sonogashira cross-coupling of the terminal alkynes 7i and 7k with methyl 4- and 3-iodobenzoate, respectively. As the tert-butylsulfinyl group can be cleaved off under mild, acidic conditions [1][25][26

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

• Elisandra Scapin,
• Paulo R. S. Salbego,
• Caroline R. Bender,
• Alexandre R. Meyer,
• Anderson B. Pagliari,
• Tainára Orlando,
• Geórgia C. Zimmer,
• Clarissa P. Frizzo,
• Helio G. Bonacorso,
• Nilo Zanatta and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 2396–2407, doi:10.3762/bjoc.13.237

• reactions were planned between phenylacetylene and compounds 6a–c. The 1,2,3-triazole synthesis from the 1,3-dipolar cycloaddition reaction between 6a–c and terminal alkynes catalyzed by copper salts (CuAAC) [41][42][43] confirms that the reaction passes through an azide intermediate. In addition to mild

Is the tungsten(IV) complex (NEt₄)₂[WO(mnt)₂] a functional analogue of acetylene hydratase?

• Matthias Schreyer and
• Lukas Hintermann

Beilstein J. Org. Chem. 2017, 13, 2332–2339, doi:10.3762/bjoc.13.230

• hydration (Scheme 2a), whereas alkynol cycloisomerization proceeds via rearrangement to a tungsten vinylidene complex and addition of the alcohol hydroxy group to the vinylidene α-carbon [18]. The vinylidene mechanism is related to that of ruthenium-catalyzed anti-Markovnikov hydration of terminal alkynes

• alkynes have not been reported [13] and substrate scope tests for acetylene hydratase have so far failed with higher alkynes [6]. We wished to test the potential activity and regioselectivity of complex 1 for hydration of higher terminal alkynes, as an extension to our studies of ruthenium-catalyzed anti

• allenol 7 and alkenol 8 are impurities already present in distilled starting material. Thus, complex 1 does not show hydration activity against higher terminal alkynes. To further validate those negative results, we wished to demonstrate a positive activity of complex 1, namely the reported hydration of

Mechanochemical synthesis of small organic molecules

• Tapas Kumar Achar,
• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2017, 13, 1907–1931, doi:10.3762/bjoc.13.186

•  11) using 2,3-dichloro-5,6-dicyanoquinone (DDQ) as an efficient oxidant [67]. Su and co-workers have also reported an asymmetric version of the CDC reaction between terminal alkynes and sp3 C–H bonds under high speed ball milling conditions [68]. Several optically active 1-alkynyl

Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

• M. Fernanda N. N. Carvalho,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2017, 13, 1230–1238, doi:10.3762/bjoc.13.122

• cleaved from the bis-alkynyl compounds 4 by reaction with CuCl, but again, there are selectivity issues that prevent a general application [36]. We therefore set out to explore whether some selectivity is observed when lithium salts of terminal alkynes are reacted with the oxoimide 3 in a 1:1 ratio (Table

Transition-metal-free one-pot synthesis of alkynyl selenides from terminal alkynes under aerobic and sustainable conditions

• Adrián A. Heredia and
• Alicia B. Peñéñory

Beilstein J. Org. Chem. 2017, 13, 910–918, doi:10.3762/bjoc.13.92

• halides. Successive reaction with terminal alkynes in the presence of t-BuOK affords the corresponding alkyl alkynyl selenide in moderate to good yields. Finally, this methodology allowed the synthesis of 2-alkylselanyl-substituted benzofuran and indole derivatives starting from convenient 2-substituted

• acetylenes. Keywords: alkynyl selenide; electrophilic cyclization; nucleophilic substitution; potassium selenocyanate; terminal alkynes; Introduction Alkynyl selenides, as many other selenium compounds, have potential anti-oxidant activities, and may play a role in certain diseases such as cancer, heart

• under Cu catalysis [26][27][28][29], from terminal alkynes in the presence of bases and Cu [30][31][32][33], Fe [34][35] or In [36] catalysis, or with t-BuOK without of transition metal [37] have been reported. In general, these methodologies require selenyl halides or diselenides as starting materials