Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• release approach, the Xiao group reported a synthesis of the pyrroles 35.3 in 2014 [153]. They can be accessed via a photocatalytic formal [3 + 2] cycloaddition of the 2H-azirines 35.1 and the alkynes 35.2 (Scheme 35). The use of Mes-Acr-Me+ (OD2) was successful due to its high reduction potential in the

• opening of nitrogen-containing small rings was also exploited by our group in 2019 (Scheme 36) [154]. Starting from the aminocyclopropanes 36.1 and the cyclopropenes 36.2, a [3 + 2] annulation led to the bicyclo[3.1.0]hexanes 36.3. Under visible-light irradiation, the excited-state photocatalyst OD7

• performs an SET oxidation of an cyclopropylaniline 36.1, leading to an N-centred radical cation after ring opening. The latter undergoes a [3 + 2] annulation with cyclopropenes 36.2, affording a bicyclic product 36.3. The key to the broad substrate tolerance relied on using 4DPAIPN (OD7), which is a mild

Synthesis of esters of diaminotruxillic bis-amino acids by Pd-mediated photocycloaddition of analogs of the Kaede protein chromophore

• Esteban P. Urriolabeitia,
• Pablo Sánchez,
• Alexandra Pop,
• Cristian Silvestru,
• Eduardo Laga,
• Ana I. Jiménez and
• Carlos Cativiela

Beilstein J. Org. Chem. 2020, 16, 1111–1123, doi:10.3762/bjoc.16.98

• of the ε-isomer in 4: (1) the initial (Z)-configuration of the oxazolones 2 is retained during the C–H bond activation step to give 3; (2) the relative transoid arrangement in 3 establishes the 1,3-head-to-tail coupling of the exocyclic C=C bonds; (3) the template effect of the Pd2(O2CCF3)2 moiety

• structures obtained for ortho-palladated complexes 3. [2 + 2] Photocycloaddition of cyclopalladated complexes 3 in solution to give the dinuclear cyclobutane ortho-palladated complexes 4. Release of the 1,3-diaminotruxillic bis-amino ester derivatives 5 by methoxycarbonylation of the Pd–C bond in

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• -hydroxytetrachlorophthalimide esters with boronic acids 4-(2-Fluoroethyl)-ʟ-phenylalanine and 3-(2-fluoroethyl)-ʟ-phenylalanine (88a,b), respectively, were synthesized starting from partially protected ʟ- or ᴅ-aspartic acid derivatives 82 which were activated as the N-hydroxytetrachlorophthalimide esters 83. The treatment of

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• (bpy)3)]2+, [Ir(ppy)3], eosin Y, and 4CzTPN [12] (Figure 3). However, some porphyrin and metalloporphyrin derivatives possess adequate potentials to be applied as photoredox catalysts in C–C and C-heteroatom bond formations [10][22]. Furthermore, supramolecular porphyrin-containing molecules, such as

One-pot synthesis of dicyclopenta-fused peropyrene via a fourfold alkyne annulation

• Ji Ma,
• Yubin Fu,
• Junzhi Liu and
• Xinliang Feng

Beilstein J. Org. Chem. 2020, 16, 791–797, doi:10.3762/bjoc.16.72

• twofold [3 + 2] cyclopentannulation and subsequent twofold [4 + 2] benzannulation. The structure of 1 is unambiguously confirmed by X-ray crystallography; 1 adopted a twisted geometry due to the steric hindrance of the phenyl rings and the hydrogen substituents at the bay regions. Notably, compound 1

• peropyrene 1. Furthermore, the observed isotopic distribution was fully consistent with its simulated spectrum (Figure 1). Characterization of the resultant product by single crystal X-ray analysis unambiguously revealed the selective formation of 1 through twofold [3 + 2] pentannulation and sequent twofold

• [4 + 2] benzannulation, instead of the desired tetracyclopenta[cd,fg,jk,mn]pyrene (2). The selective formation of 1 could be rationalized by the steric hindrance of the phenyl rings after the twofold [3 + 2] alkyne pentannulated intermediate (Scheme S2, Supporting Information File 1), and the sequent

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• resulting mixture was extracted with CH2Cl2. The extract was washed with brine, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The mixture was purified by PTLC (ethyl acetate/hexane = 3:2 for 3a, ethyl acetate/hexane = 1:4 for 3b) to afford 3. General experimental procedure

• . The extract was washed with brine, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The mixture was purified by PTLC (CH2Cl2/hexane = 4:1 for 4a, CH2Cl2/hexane = 3:2 for 4b) to afford 4. Preparation of dialkoxides by intramolecular coupling reaction In a similar manner as

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

• , the desired triazole products were generated through the [3 + 2] cycloaddition of the azide and alkyne. The recyclability analysis of these IPSi-supported Cu(I) and Cu(II) catalysts indicated seven consecutive runs with almost equivalent performances. In 2018, silica modified with a benzimidazole

• synthesize benzimidazole–triazole derivatives through a one‐pot sequence of activation of the alkyne, [3 + 2] condensation, cyclization, and aromatization under mild reaction conditions (Scheme 2). Moreover, the BS–Cu(II)@SiO2 (11) catalyst could be recovered and recycled for seven cycles without a notable

• ) (64) (Scheme 10) [32]. An interesting aspect of the heterogeneous catalyst SNIL–Cu(II) (64) is its successful application in the [3 + 2] cyclization synthesis of “click” products under mild reaction conditions. 0.05 mol % of 64 and 2 mol % of sodium ʟ-ascorbate were used to prepare a range of

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

• Qiao Lin,
• Shiling Zhang and
• Bin Li

Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44

• coordination chemistry, and also valuable protecting or directing groups in catalysis [1][2][3]. 2-Oxazolines are a readily stable class of heterocycles resistant to a range of nucleophiles, bases, or radicals [4][5], which can be easily generated from amino alcohols and carboxylic acids, and from alkenes or

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

• area, reporting on the synthesis of the first heteroleptic bis-NHC and mixed NHC/phosphine copper(I) complexes [20][21][22]. Interestingly, these new copper-based complexes have shown excellent activity in the [3 + 2] cycloaddition reaction of azides/sulfonyl azides and alkynes (Scheme 1, right) [22

• diphenylamine, only 20% of the desired product was observed (12c). Interestingly, with benzyl azide, a substrate not containing a sulfonyl moiety, the product obtained is the 1,2,3-triazole derivative [33], resulting from a [3 + 2] cycloaddition of azide and alkyne (Scheme 6). The catalytic system was also

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

• view in comparison with UV-sensitive materials. Synthesis of the bridged heptamethines (IV and V) follows the general route shown in Scheme 3 [2][68][69]. Scheme 4 discloses the use of the chain builders cb and cb0-cb-6 [68][69]. The materials cb-1 and cb-2 were available by reaction of the respective

Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)

• Ryo Takishima,
• Yuji Nishii,
• Tomoaki Hinoue,
• Yoshitane Imai and
• Masahiro Miura

Beilstein J. Org. Chem. 2020, 16, 325–336, doi:10.3762/bjoc.16.32

• 565-0871, Japan Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, Higashi-Osaka, Osaka 577-8502, Japan 10.3762/bjoc.16.32 Abstract A series of optically active bisbenzofuro[2,3-b:3’,2’-e]pyridine (BBZFPy) derivatives was synthesized starting with the readily

• dehydrogenative coupling adopting oxygen atom as the linker [12][13][14][15][16][17]. In particular, bisbenzofuro[2,3-b:3′,2′-e]pyridines (BBZFPys) were found to exhibit intense photoluminescence with relatively high quantum efficiency (Φflu up to 0.70), indicating that the BBFZPy scaffold may serve as a key

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• of various bases, however, the best results were obtained with tetrabutylammonium hydroxide (TBAOH). The suggested mechanism commences with the photoexcitation of photocatalyst 11 to a strongly oxidizing excited state 50 (E1/2 red([Ru(bpy)3]2+*/[Ru(bpy)]3+) = +0.77 V vs SCE). Then, SET from anion 52

Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin: experimental and computational evidence for intramolecular and intermolecular C–F···H–C bonds

• Vuyisa Mzozoyana,
• Fanie R. van Heerden and
• Craig Grimmer

Beilstein J. Org. Chem. 2020, 16, 190–199, doi:10.3762/bjoc.16.22

• over anhydrous MgSO4 and the solvent was removed in vacuo. The resulting light yellow product was purified by silica gel column chromatography with 60% EtOAc in hexane as eluent and 6 was obtained as a yellow crystalline solid (0.78 g, 2.9 mmol, 97%), mp 167–170 ºC, TLC Rf 0.54 (hexanes/EtOAc, 3:2). 1H

The use of isoxazoline and isoxazole scaffolding in the design of novel thiourea and amide liquid-crystalline compounds

• Itamar L. Gonçalves,
• Rafaela R. da Rosa,
• Vera L. Eifler-Lima and
• Aloir A. Merlo

Beilstein J. Org. Chem. 2020, 16, 175–184, doi:10.3762/bjoc.16.20

• , 8, 9, 12 and 13 were then prepared by [3 + 2]-1,3-dipolar cycloaddition of nitrile oxide (ArCNO) formed in situ from oximes and a number of alkenes as dipolarophiles, to yield the precursors of the cycloadducts isoxazolines 2, 7 and 11 regioselectively. The cycloadducts were subjected to SnCl2

Halogen-bonding-induced diverse aggregation of 4,5-diiodo-1,2,3-triazolium salts with different anions

• Xingyu Xu,
• Shiqing Huang,
• Zengyu Zhang,
• Lei Cao and
• Xiaoyu Yan

Beilstein J. Org. Chem. 2020, 16, 78–87, doi:10.3762/bjoc.16.10

• (3)°, 144.12(7)° and 145.6(3)°. The crystal X-ray analyses of 2-BF4 shows that the diiodotriazolium moiety has formed with the tetrafluoroborate anion a triangle in which only two anions and three cations are assembled and one tetrafluoroborate is independent (Figure 3). 2-BF4 crystallizes in the

Starazo triple switches – synthesis of unsymmetrical 1,3,5-tris(arylazo)benzenes

• Andreas H. Heindl and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2020, 16, 22–31, doi:10.3762/bjoc.16.4

• /EtOAc, 2:1, v/v) to yield 16b as red oil (mixture of isomers, 218 mg, 9%). The product was used without further purification. See Supporting Information File 1 for the 1H NMR spectrum. HRESIMS (m/z): [M + H]+ calcd for C27H3279BrN4O6, 587.1500; found, 587.1486. tert-Butyl (E)-2-(3-(2-(tert

• /v, then SiO2, toluene/EtOAc, 5:1 to 3:1, v/v) to yield 17a as red oil (mixture of isomers, 28 mg, 23%). The product was used without further purification. See Supporting Information File 1 for the 1H NMR spectrum. HRESIMS: [M + H]+ calcd for C38H44N7O7, 710.3302; found, 710.3427. tert-Butyl (E)-2-(3

• -(2-(tert-butoxycarbonyl)-2-(4-methoxyphenyl)hydrazinyl)-5-((2,4,6-trimethoxyphenyl)diazenyl)phenyl)-1-phenylhydrazine-1-carboxylate (17b): In a nitrogen-filled glovebox, an oven-dried Schlenk tube was charged with P(t-Bu)3 (9.5 µL, 37 µmol, 15 mol %). All following operations were carried out in a

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• product and purification by flash chromatography (2:1→3:2 petroleum ether/EtOAc) afforded 6a as a red-brown oil (0.0110 g, 16.3 μmol, 55%). 1H NMR (500 MHz, CDCl3) δ 8.85 (br s, 1H), 7.72 (s, 1H), 6.24 (dd, J = 8.0 Hz, 5.4 Hz, 1H), 5.93 (m, 1H), 5.22 (d, J = 6.3 Hz, 1H), 5.15 (d, J = 17.2 Hz, 1H), 5.05 (d

• mmol) and BF3·OEt2 (16 μL, 0.13 mmol). The solution was stirred over 12 h with gradual warming to room temperature. Then, NH4Cl (saturated saturated aq, 5 drops) and NaHCO3 (saturated aq, 5 drops) were added, followed by a conventional extractive workup (CH2Cl2). Purification by preparative TLC (3:2

• conventional extractive workup was performed (CH2Cl2). Preparative TLC (3:2 petroleum ether/EtOAc) afforded, in order of elution, 7a (7.8 mg, 11 μmol, 37% yield, 46% brsm) and recovered 5 (3.7 mg, 5.1 μmol, 18% recovery). 7a: 1H NMR (300 MHz, CDCl3) δ 8.60 (s, 1H), 7.55 (s, 1H), 6.00 (d, J = 5.4 Hz, 1H), 5.94

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

• ) Å, C11–H···N2 127°. Symmetry transformations are i = 1−x, 1−y, 1−z; ii = x, 3/2−y, −1/2+z, iii = 1−x, −1/2+y, −1/2−z. 1H-Pyridine derivatives 5 as solids under daylight (top), under UV light (λexc = 365 nm, c(5) = 10−4 M) in dichloromethane solution (center), and under UV light (λexc = 365 nm) in

AgNTf₂-catalyzed formal [3 + 2] cycloaddition of ynamides with unprotected isoxazol-5-amines: efficient access to functionalized 5-amino-1H-pyrrole-3-carboxamide derivatives

• Ziping Cao,
• Jiekun Zhu,
• Li Liu,
• Yuanling Pang,
• Laijin Tian,
• Xuejun Sun and
• Xin Meng

Beilstein J. Org. Chem. 2019, 15, 2623–2630, doi:10.3762/bjoc.15.255

• Analysis, Qufu 273165, P. R. China 10.3762/bjoc.15.255 Abstract A formal [3 + 2] cycloaddition between ynamides and unprotected isoxazol-5-amines has been developed in the presence of catalytic AgNTf2 in an open flask. By the protocol, a variety of functionalized 5-amino-1H-pyrrole-3-carboxamide

• use of an inexpensive catalyst, simple reaction conditions, simple work-up without column chromatographic purification for most of products and high yields. Keywords: [3 + 2] cycloaddition; isoxazole; pyrrole; silver catalysis; ynamide; Introduction Silver-catalyzed transformations of alkynes have

• employment of isoxazole nucleophiles in gold-catalyzed formal [3 + 2] cycloaddition reaction of ynamides [31][32], and zinc-catalyzed the reaction of ynol ethers [33], giving the respective multi-substituted pyrrole derivatives efficiently (Scheme 2a) [34][35]. The reaction proceeds via an α-imino gold

Chemical synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from Escherichia coli O132 in the form of its 2-aminoethyl glycoside

• Debasish Pal and
• Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2019, 15, 2563–2568, doi:10.3762/bjoc.15.249

• and Galf. In this communication we report on the total synthesis of this pentasaccharide repeating unit of the O-specific polysaccharide in the form of its 2-aminoethyl glycoside (Figure 1) through a [3 + 2] converging strategy. The building blocks were prepared by suitable protecting group

• reducing end of the target pentasaccharide that will allow further conjugation using the terminal amine without affecting the glycosidic stereochemistry. Further retrosynthetic analysis of the target pentasaccharide 1 revealed that a [3 + 2] strategy will be the most suitable one for the total synthesis of

• pentasaccharide repeating unit of the O-specific polysaccharide of Escherichia coli O132 was accomplished through a convergent [3 + 2] strategy. The target pentasaccharide was obtained as its 2-aminoethyl glycoside that offers further possibilities for conjugation with suitable aglycons without hampering the

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

• synthesized via an esterification reaction starting from symmetrical 1,1’-ferrocenoyl dichloride (3) [92] as shown in Scheme 1. To a solution of the corresponding 1-alkynol (13.5 mmol), NEt3 (13.5 mmol), and 4-dimethylaminopyridine (DMAP, 0.5 mmol) in dichloromethane (DCM, 20 mL) at 0 °C the dichloride 3 (2 g

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• complexes 1a–d were evaluated as homogeneous catalysts in two tandem addition/cycloisomerization reactions using alkynes 2 and 3. 2-Alkynylbenzaldehyde 2 [58][59] was chosen as the first model substrate for a cyclization reaction in the presence of methanol as a second nucleophile. This tandem addition

Small anion-assisted electrochemical potential splitting in a new series of bistriarylamine derivatives: organic mixed valency across a urea bridge and zwitterionization

• Keishiro Tahara,
• Tetsufumi Nakakita,
• Alyona A. Starikova,
• Takashi Ikeda,
• Masaaki Abe and
• Jun-ichi Kikuchi

Beilstein J. Org. Chem. 2019, 15, 2277–2286, doi:10.3762/bjoc.15.220

• Keishiro Tahara Tetsufumi Nakakita Alyona A. Starikova Takashi Ikeda Masaaki Abe Jun-ichi Kikuchi Department of Material Science, Graduate School of Material Science, University of Hyogo, 3-2-1, Kouto, Kamigori, Ako, Hyogo 678-1297, Japan Graduate School of Materials Science, Nara Institute of

An overview of the cycloaddition chemistry of fulvenes and emerging applications

• Ellen Swan,
• Kirsten Platts and
• Anton Blencowe

Beilstein J. Org. Chem. 2019, 15, 2113–2132, doi:10.3762/bjoc.15.209

• fulvene to function as a 6π component in reactions with electron-deficient dienes (Scheme 5b) and fulvenes acting as dipolarophiles have been reported for enantioselective [6 + 3] and [3 + 2] cycloadditions [83][84][105]. In general, reactions with electron-rich alkenes will take place preferentially at

Naphthalene diimides with improved solubility for visible light photoredox catalysis

• Barbara Reiß and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 2043–2051, doi:10.3762/bjoc.15.201

• catalysis is mainly [Ru(bpy)3]2+ [21], due to its strong MLCT (metal-to-ligand charge transfer) absorption, the excellent yield of its triplet state and the long lifetime, the versatile redox behavior (Ru3+ vs Ru+) in quenching processes and the chemical and photochemical robustness. Despite their positive