Electron-rich triarylphosphines as nucleophilic catalysts for oxa-Michael reactions

• Susanne M. Fischer,
• Simon Renner,
• A. Daniel Boese and
• Christian Slugovc

Beilstein J. Org. Chem. 2021, 17, 1689–1697, doi:10.3762/bjoc.17.117

• to an activated electrophile, e.g., an electron-deficient olefin, generating a zwitterion (i, Scheme 1). In further course, the zwitterion acts as a nucleophile or as a base [1]. The efficiency of the formation of this β-phosphonium α-carbanionic species depends on the nucleophilicity of the

• activity of differently substituted triarylphosphines in the oxa-Michael addition of alcohols to electron-deficient olefins was investigated. In general, the activity increases with increasing methoxy-substitution in the order TPP < MMTPP < TMTPP. The activity order was rationalized based on DFT

2,4-Bis(arylethynyl)-9-chloro-5,6,7,8-tetrahydroacridines: synthesis and photophysical properties

• Najeh Tka,
• Mohamed Adnene Hadj Ayed,
• Mourad Ben Braiek,
• Mahjoub Jabli,
• Noureddine Chaaben,
• Kamel Alimi,
• Stefan Jopp and
• Peter Langer

Beilstein J. Org. Chem. 2021, 17, 1629–1640, doi:10.3762/bjoc.17.115

• , derivatives 4e and 4f bearing an electron-deficient fluoro or trifluoromethyl group show a hyperchromic shift of their bands located between 340 and 380 nm. In case of the electron-donating methoxy substituent (4g), a bathochromic shift was observed. Besides, a new band appeared at 321 nm which may be

• . Due to their low donating effect, the methyl group in product 4b induce an addition of yellow regions into the external phenyl rings. However, the electron-deficient fluorine atom in derivative 4e results in a decrease of the electron density of the tetrahydroacridine core and the external phenyl

• rings. For product 4f, the high electron-deficient effect of the trifluoromethyl groups induces the appearance of blue surfaces around the tetrahydroacridine core, the ethynyl groups and the external phenyl rings, indicating a significant decrease of their electronic densities. However, a yellow-red

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

• at room temperature. First, several nonactivated arylalkynes containing electron-rich and electron-deficient groups as well as thiophene derivatives afforded the desired 5-arylated triazole derivatives. Then, the diversity of arylboronic acids was explored. The arylboronic acids containing some

• electron-rich, electron-deficient, and halogen moieties were good partners in these reactions as well, affording the 5-arylated triazoles with good to excellent yield (Scheme 33) [58]. A probable mechanism for this transformation is illustrated in Scheme 34. A copper acetylide intermediate 113 is first

Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances

• Thiago S. Silva and
• Fernando Coelho

Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112

• substrates will be reviewed, so electron-deficient olefins like Michael acceptors and even conjugate dienes will not be included in this review. Some examples of hydroallylation reactions have been included since these reactions, like hydroalkylation reactions, also form a new C(sp3)–C(sp3) bond at the

• substituents. Electron-withdrawing groups render the generated radical more susceptible to reaction with electron-rich compounds, whereas substituents that donate electronic density increase the addition reaction rate to electron-deficient ones (Michael acceptors, for example) [55]. Another beneficial aspect

• transferred preferentially to the terminal carbon of an electron-deficient olefin, yielding 41 in 72% yield after 4 days (Scheme 20). The byproducts of isomerization and reduction were also observed under these conditions, and the authors used the Thorpe–Ingold effect to favor the cyclization product by

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• respective hydrazonoyl bromides 8 and smoothly undergo [3 + 2]-cycloadditions with both electron-rich C=C dipolarophiles [27][28][29] and arynes [30], yielding the corresponding pyrazole derivatives. Unexpectedly, they reacted also with electron-deficient polyfluorinated thioamides to give the desired 1,3,4

• fluorine-containing organic molecules combined with the 1,4-quinone moiety can be considered as a challenging problem of current organic synthesis. Thus, the main goal of the present study was to check the course of [3 + 2]-cycloaddition reactions of electron-deficient CF3-substituted nitrile imines 7 with

• products 9i, 9k, and 9l exhibit two overlapping absorption bands in the visible range with maxima at λmax ≈ 400 nm and ≈ 425 nm, respectively. Conclusion The presented study demonstrated that 1,4-quinones undergo efficient [3 + 2]-cycloadditions with in-situ-generated electron-deficient

Cascade intramolecular Prins/Friedel–Crafts cyclization for the synthesis of 4-aryltetralin-2-ols and 5-aryltetrahydro-5H-benzo[7]annulen-7-ols

• Jie Zheng,
• Shuyu Meng and
• Quanrui Wang

Beilstein J. Org. Chem. 2021, 17, 1481–1489, doi:10.3762/bjoc.17.104

• in 38–72% yield. To our gladness, aldehyde 13d, with an electron-deficient nitro group residing on the benzene ring reacted with veratrole under the standard conditions, delivering tetralin 14da in 55% yield. However, using furan as the nucleophile component, the reaction sequence with 13d failed to

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

• Premansh Dudhe,
• Mena Asha Krishnan,
• Kratika Yadav,
• Diptendu Roy,
• Krishnan Venkatasubbaiah,
• Biswarup Pathak and
• Venkatesh Chelvam

Beilstein J. Org. Chem. 2021, 17, 1453–1463, doi:10.3762/bjoc.17.101

• , alkyl N-arylideneglycinates have attracted much attention in recent years. For instance, the metal-catalyzed asymmetric [3 + 2] cycloaddition of ethyl N-benzylideneglycinates with electron-deficient alkenes has been reported to yield substituted pyrrolidines [30]. Recently, we reported the synthesis of

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

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• substituent. In contrast, the reaction with aromatic aldehydes equipped with the electron-deficient substituent produced the desired trisubstituted THP along with recovered starting material. The enantioenriched homoallylic alcohol bearing an electron-deficient substituent, 27 (94% ee), was investigated with

• synthesis of THPs. Developments towards the Prins cyclization. General stereochemical outcome of the Prins cyclization. Regioselectivity in the Prins cyclization. Mechanism of the oxonia-Cope reaction in the Prins cyclization. Cyclization of electron-deficient enantioenriched alcohol 27. Partial

Highly regio- and stereoselective phosphinylphosphination of terminal alkynes with tetraphenyldiphosphine monoxide under radical conditions

• Dat Phuc Tran,
• Yuki Sato,
• Yuki Yamamoto,
• Shin-ichi Kawaguchi,
• Shintaro Kodama,
• Akihiro Nomoto and
• Akiya Ogawa

Beilstein J. Org. Chem. 2021, 17, 866–872, doi:10.3762/bjoc.17.72

• inhibited the desired phosphinylphosphination (see, alkyne 2f), probably because of the decomposition of Ph2P(O)PPh2. Furthermore, an electron-deficient alkyne such as methyl propiolate (2h) failed to provide the desired adduct (3h) [61]. 3-Phenyl-1-propyne (2i) and cyclohexylacetylene (2j) gave 3i and 3j

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

• electrons from the electron-rich tertiary amine nitrogen atom to the electron-deficient benzene ring, achieving intramolecular electron transfer. Selective C–H-functionalization also includes no catalysts, oxidants, additives, acids and bases, which is of great significance in the synthesis and application

• -electron transfer occurs under white-light irradiation, leading to an electron-deficient fluoroalkyl radical. Thereafter, fluoroalkyl radical is captured by 87, affording radical 88 that gives rise to radical intermediate 89 by uptake of iodine. Finally, the dealkylation product 86 is given by removing

• between radicals was carried out, affording thioether derivative 132 (Scheme 46). It has been proved by UV–vis spectroscopy and TDDFT calculations that the EDA complex was formed between an electron-rich mercaptan anion and electron-deficient aryl halides. Most importantly, this approach can be

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• give methanofullerenes Scientists are currently focusing on methods for the functionalization of the fullerene core that provide a high selectivity and yield. The electron-deficient polyene C60 readily undergoes radical addition, nucleophilic addition, and cycloaddition processes. Therein, the decrease

Synthesis of N-perfluoroalkyl-3,4-disubstituted pyrroles by rhodium-catalyzed transannulation of N-fluoroalkyl-1,2,3-triazoles with terminal alkynes

• Olga Bakhanovich,
• Viktor Khutorianskyi,
• Vladimir Motornov and
• Petr Beier

Beilstein J. Org. Chem. 2021, 17, 504–510, doi:10.3762/bjoc.17.44

• catalyst (Table 1, entry 1). Chloroform was found to be the most suitable solvent and varying rhodium catalysts led to the 2a + 2a’ product mixture of various ratios. Rh2(oct)4 and Rh2(esp)2 gave the highest 2a/2a’ ratio, while the electron-deficient Rh2(pfb)4 catalyst gave the lowest 2a/2a’ ratio and an

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• the destabilized ones that have been elegantly reviewed over the past years by Gassman, Tidwell, and Creary [4][5][6]. The so-called electron-deficient carbocations, i.e., carbocations substituted with electron-withdrawing groups, drive original reactions, and the most important one among these

Hydrazides in the reaction with hydroxypyrrolines: less nucleophilicity – more diversity

• Dmitrii A. Shabalin,
• Evgeniya E. Ivanova,
• Igor A. Ushakov,
• Elena Yu. Schmidt and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2021, 17, 319–324, doi:10.3762/bjoc.17.29

• hydrazides appeared to be good recyclization agents as was exemplified by the assembly of 1,4-dihydropyridazines 4ab and 4ag from 4-methylbenzohydrazide (2b) and acetohydrazide (2g) in 69% and 54% isolated yields, respectively. In contrast, the recyclization of hydroxypyrroline 1a with electron-deficient 4

• strongly electron-deficient substituents that finally prevent an acid-catalyzed elimination of hydrazide 2f (vide infra for the mechanism discussion). Finally, the diverse hydroxypyrrolines 1b–e were tested in the studied reaction and the corresponding 1,4-dihydropyridazines 4ba–ea were obtained in 20–51

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

• . The carbene-based methods typically give the highest yields when alkenes with electron-donating substituents are used. There are few examples in which the cyclopropanation by carbene methods of electron-deficient alkenes containing substituents with a large −M effect (for example, CO2R, COR, CN, SO2R

• dibromodifluoromethane is a suitable source of difluorocarbene. However, the same reagent produces low yields in the reactions with electron-deficient alkenes. Dolbier et al. reported the cyclopropanation of α-methylstyrene (7) using dibromodifluoromethane and zinc dust in the presence of iodine (Scheme 3) [18]. The

• fluorosulfonyldifluoroacetate (TFDA) as a difluorocarbene source: Highly efficient methods for the difluorocyclopropanation of both electron-rich and electron-deficient alkenes using FSO2CF2COOSiMe3 (TFDA, 25) as a source of difluorocarbene were described by the Dolbier group in 2000 [13][35]. The difluorocarbene generated by

Selective synthesis of α-organylthio esters and α-organylthio ketones from β-keto esters and sodium S-organyl sulfurothioates under basic conditions

• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Thiago Barcellos,
• Claudio C. Silveira and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2021, 17, 234–244, doi:10.3762/bjoc.17.24

• then attacks the most available sulfur atom of the sodium S-organyl sulfurothioate 2 to produce the keto−enol tautomers B, C, and D. Subsequently, when 4 equiv of NaOH (concentrated solution) are used, the most electron-deficient carbonyl group experiences a quick attack by the HO− anion, generating

Au(III) complexes with tetradentate-cyclam-based ligands

• Ann Christin Reiersølmoen,
• Thomas N. Solvi and
• Anne Fiksdahl

Beilstein J. Org. Chem. 2021, 17, 186–192, doi:10.3762/bjoc.17.18

• -coordinated Au(III) complexes have so far scarcely been reported [37][38][39][40][41][42][43][44]. This is likely a result of the electron deficient character of the amide nitrogens. The coordination was initially tested with the cyclam tetraamide derivatives 2a,b and 4a. Judged from 1H NMR, these ligands

Novel library synthesis of 3,4-disubstituted pyridin-2(1H)-ones via cleavage of pyridine-2-oxy-7-azabenzotriazole ethers under ionic hydrogenation conditions at room temperature

• Romain Pierre,
• Anne Brethon,
• Sylvain A. Jacques,
• Aurélie Blond,
• Sandrine Chambon,
• Sandrine Talano,
• Catherine Raffin,
• Branislav Musicki,
• Claire Bouix-Peter,
• Loic Tomas,
• Gilles Ouvry,
• Rémy Morgentin,
• Laurent F. Hennequin and
• Craig S. Harris

Beilstein J. Org. Chem. 2021, 17, 156–165, doi:10.3762/bjoc.17.16

• compounds 24. In practice, the process was very efficient affording 60 final compounds with a median yield of 47%. Best results were obtained with electron-rich anilines (e.g., compounds 24a–d) and aliphatic amines (e.g., compounds 24k–l). For electron-deficient anilines (e.g., compounds 24e–g), the

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• ]arene. Pillararenes have electron-rich cavities that facilitate the combination with various electron-deficient guest molecules, such as alkylammonium, pyridinium, and imidazolium cations. Compared to other macrocycles, pillararenes exhibit a high degree of symmetry and rigidity, which gives them a

Silver-catalyzed synthesis of β-fluorovinylphosphonates by phosphonofluorination of aromatic alkynes

• Yajing Zhang,
• Qingshan Tian,
• Guozhu Zhang and
• Dayong Zhang

Beilstein J. Org. Chem. 2020, 16, 3086–3092, doi:10.3762/bjoc.16.258

• -rich and electron-deficient moieties at the para- and meta-positions generally reacted smoothly to afford the desired products 2a–o in moderate to good yield. An aromatic alkyne possessing a Cl substituent at the ortho-position also reacted smoothly to provide the corresponding product 2k in 56% yield

All-carbon [3 + 2] cycloaddition in natural product synthesis

• Zhuo Wang and
• Junyang Liu

Beilstein J. Org. Chem. 2020, 16, 3015–3031, doi:10.3762/bjoc.16.251

• Lee [24] independently in 2003. (Scheme 1C and Scheme 1D) In Krische’s synthesis, a stereospecific intramolecular phosphine-catalyzed [3 + 2] cycloaddition of 2-butynoate with electron-deficient alkene 29 afforded cycloadduct 31 in 88% yield as a single diastereomer [25] (Scheme 1C). Later, Lee`s

• (9) was accomplished from 81 in two steps. Phosphine-catalyzed [3 + 2] cycloaddition In 1995, Lu and co-workers reported a phosphine-catalyzed [3 + 2] cycloaddition, employing electron-deficient olefins and either 2,3-butadienoates or 2-butynoates to give a cyclopentene as product [17] (Scheme 5A

• rationalized by the proposed catalytic mechanism (Scheme 7B). The phosphine (i.e., PR3, A) attacks the allene 101 to generate zwitterion intermediate B, which is subjected to a less hindered attack by the isoindigo 100. The oxindole bearing a chlorine atom on isoindigo 100 makes C-3 more electron deficient

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• chemical stimuli yielding different supramolecular products. The porphyrin ligands of the cage [Zn4(8')6]8+ interacted favorably with C70 as a guest, whereas an electron-rich aromatic crown-ether did thread onto the electron-deficient naphthalene diimides of cage [Zn4(7')6]8+ forming mechanically

Ring-closing metathesis of prochiral oxaenediynes to racemic 4-alkenyl-2-alkynyl-3,6-dihydro-2H-pyrans

• Viola Kolaříková,
• Markéta Rybáčková,
• Martin Svoboda and
• Jaroslav Kvíčala

Beilstein J. Org. Chem. 2020, 16, 2757–2768, doi:10.3762/bjoc.16.226

• again the issue. To evaluate how the electron density on the double bond of the oxaenediyne could influence the RCEYM, we also synthesized oxaenediynes bearing an electron-deficient double bond from enediynols 4 and acryloyl chloride or methacryloyl chloride with triethylamine as a base. The formation

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• components (Ni-porphyrin, azo-aryl unit, and tether) have to be carefully designed and tuned regarding their geometry and electronic properties. The Ni-porphyrin should be electron deficient (electron-withdrawing substituents in meso position), the azo-aryl unit should be electron rich (electron-donating

• yields of the Baeyer–Mills reactions, if performed under basic conditions, are higher for electron-deficient amines. 4-Chloropyridines are susceptible to nucleophilic aromatic substitutions [4], which was confirmed by the successful substitution of 3-(3-bromophenylazo)-4-chloropyridine (10) and 3-(3

• -iodophenylazo)-4-chloropyridine (17) with LiSSiMe3 (8) [28], t-BuSH (13) and HSCH2CH2CO2CH3 (15) [29]. Electron-deficient aromatic, silylated thiols exhibit very labile Si–S bonds [30]. Thus, even bulky silyl protection groups are not suitable as protecting groups for the subsequent Suzuki reaction