Chemical approaches to discover the full potential of peptide nucleic acids in biomedical applications

• Nikita Brodyagin,
• Martins Katkevics,
• Venubabu Kotikam,
• Christopher A. Ryan and
• Eriks Rozners

Beilstein J. Org. Chem. 2021, 17, 1641–1688, doi:10.3762/bjoc.17.116

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

• reaction rate-determining step in a radical mechanism in which the alkane participates in both the initiation and propagation steps of the radical chain (Scheme 37C). Photoinduced electron transfer Under photoinduced electron transfer (PET) conditions, olefins generate cation radical species that are

Photoinduced post-modification of graphitic carbon nitride-embedded hydrogels: synthesis of 'hydrophobic hydrogels' and pore substructuring

• Cansu Esen and
• Baris Kumru

Beilstein J. Org. Chem. 2021, 17, 1323–1334, doi:10.3762/bjoc.17.92

• novelty. Here, a metal-free semiconductor graphitic carbon nitride (g-CN)-embedded hydrogel as an initial network was synthesized via redox-couple initiation under dark conditions. Post-photomodification of so-formed hydrogel, thanks to the photoactivity of the embedded g-CN nanosheets, was exemplified in

• similarity to natural tissues, meaning that they are stable networks with high water content [1][2][3]. The simplest synthesis of hydrogels can be conducted in an aqueous solution of a water-soluble monomer and crosslinker (bi- or more functional) in the presence of an initiator (generally radical initiation

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

• . Noteworthy is that the capture of carbon radicals occurred only at the trivalent phosphorus site of Ph2P(O)PPh2. Therefore, the initiation step might also proceed via the attack of the carbon radical generated from V-40 at the trivalent phosphorus site to form Ph2P(O)• selectively. With this information in

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

β-Lactamase inhibition profile of new amidine-substituted diazabicyclooctanes

• Zafar Iqbal,
• Lijuan Zhai,
• Yuanyu Gao,
• Dong Tang,
• Xueqin Ma,
• Jinbo Ji,
• Jian Sun,
• Jingwen Ji,
• Yuanbai Liu,
• Rui Jiang,
• Yangxiu Mu,
• Lili He,
• Haikang Yang and
• Zhixiang Yang

Beilstein J. Org. Chem. 2021, 17, 711–718, doi:10.3762/bjoc.17.60

• mechanisms [1] in microorganisms ultimately leading to the initiation of antibiotic resistance and survival of the microorganisms [2]. In case of Gram-negative pathogenic bacteria, production of β-lactamases [3] is the main arsenal of these microorganisms against antibiotics. The number of β-lactamases is

Molecular basis for protein–protein interactions

• Brandon Charles Seychell and
• Tobias Beck

Beilstein J. Org. Chem. 2021, 17, 1–10, doi:10.3762/bjoc.17.1

• three generalisations [81]. Firstly, errors and kinetic traps are minimised by weak interactions of the assembly units. The weak interactions result in nucleation, the second generalisation, where the initiation of capsid formation is minimised. This in return reduces the kinetic trap. Finally, the

Amine–borane complex-initiated SF₅Cl radical addition on alkenes and alkynes

• Audrey Gilbert,
• Pauline Langowski,
• Marine Delgado,
• Laurent Chabaud,
• Mathieu Pucheault and
• Jean-François Paquin

Beilstein J. Org. Chem. 2020, 16, 3069–3077, doi:10.3762/bjoc.16.256

• three alkyne derivatives were tested in the reaction, with yields ranging from 3% to 85%. Keywords: amine-borane complex; pentafluorosulfanyl chloride; pentafluorosulfanyl substituent; radical addition; radical initiation; Introduction The pentafluorosulfanyl (SF5) substituent has been attracting its

• styrene [48][49][50]. We envisioned that it could be possible to replace the Et3B in Dolbier’s protocol by a stable amine–borane complex that could perform the radical initiation of SF5Cl on its addition on alkenes. This would address the drawbacks associated with the use of Et3B as the radical initiator

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

• the metathesis mechanism: i.e., whether a double (ene-then-yne mechanism) or a triple (yne-then-ene mechanism) bond first enters the initiation step of the precatalyst activation. The group 6 metal-based precatalysts prefer the latter mechanism and yield the endo-products, while Ru precatalysts enable

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• inefficient initiation step (i.e., Φinitiation << 1) (Equation 1). A less common use of quantum yields by organic synthetic chemists is as a measure of how efficiently the reaction uses the light source. Considering photocatalysis is often purported as a green chemistry because it uses light, a more efficient

• 1 with amine catalyst 3 to give enamine intermediate 4. The initiation step is proposed to be a reductive quench of the photocatalyst using 4 as a sacrificial reductant to give [Ru]•−, which can then reduce 2 to give electrophilic radical 2•. Addition of 2• to another molecule of 4 generates α-amino

• likely operates via a radical chain mechanism. Initiation begins with the reductive quenching of the photocatalyst using iPr2NEt as a sacrificial reductant to give [Ru]•−, which then reduces the Lewis acid-coordinated enone 271 to give alkyl radical 271•. In the presence of a second enone 270 and chiral

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• IUPAC as follows: “Change in the rate of a chemical reaction or its initiation under the action of ultraviolet, visible or infrared radiation in the presence of a substance – the photocatalyst – that absorbs light and is involved in the chemical transformation of the reaction partners” [90]. In

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

• enhanced precatalyst preparation, stabilization and initiation, PEPPSI) [23][24]. In addition to pyridine ligands, other compounds with coordinating atoms such as C, N or P have been reported to tune the catalytic activity of the NHC–Pd complexes [25][26][27][28]. Thus, a ligand containing P as the

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• then kept constant or slightly decreased. The possible initiation of the polymerization is presented in Scheme 11, where hydrogen bonding of 36 with water is crucial. In 2013, Wang and co-workers also reported the use of aliphatic ketones and aldehydes as photoinitiators for the photopolymerization of

• -one, as well as formaldehyde (35), efficiently initiated the polymerization of MAA (42), and butanone was the most efficient compound. Since acrylates and methacrylates can be photopolymerized by self-initiation, a blank experiment without the use of any aliphatic ketone 44 or formaldehyde (35) was

• carried out, indicating that the polymerization of MAA (42) was mainly induced by photoinitiation by the aliphatic ketones 44 or formaldehyde (35), rather than by self-initiation of the monomer. Furthermore, oxygen was shown to strongly inhibit the photopolymerization, and an increase in the UV intensity

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

• conjugate acid needed for initiation. Thus, the higher the concentration of PA, the higher the conversion. Figure 3 nicely documents this scenario. In 2019, the first report about NIR-sensitized cationic photopolymerization appeared in combination with a high intensity NIR LED [65]. Such a combination

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

• . Several proposal for the mechanism are found in literature ranging from a closed photoredox catalytic cycle [53][61] to a chain propagation mechanism with photoredox initiation [65]. We evaluated the reference NDI 1 and the cNDI 6 as new photoredox catalysts using this benchmark reaction. The samples were

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

Mechanochemical synthesis of poly(trimethylene carbonate)s: an example of rate acceleration

• Sora Park and
• Jeung Gon Kim

Beilstein J. Org. Chem. 2019, 15, 963–970, doi:10.3762/bjoc.15.93

• polymerization reached over 90% conversion after 2 h (Table 1, entries 10 and 11). While the reaction rate was higher than that of the solution reactions, polydispersity under ball-milling conditions remained low (Mw/Mn = 1.15). To maintain low polydispersity, fast initiation and slow propagation are required

• [28]. In the case of ball-milling polymerization, the time required for the physical mixing of monomer, catalyst, and initiator would result in a delayed initiation of the polymerization. However, the relatively slow propagation rate of DBU-mediated trimethyl carbonate polymerization allowed for well

• -milling polymerization did not allow for controlling the molecular weight distribution, resulting in a broad polydispersity (Mw/Mn) of 2.01 (Table 4, entry 5). As mentioned, fast initiation over chain propagation is one of the requirements in a controlled polymerization. While TBD could chemically enhance

Synthesis of polydicyclopentadiene using the Cp₂TiCl₂/Et₂AlCl catalytic system and thin-layer oxidation of the polymer in air

• Zhargolma B. Bazarova,
• Ludmila S. Soroka,
• Alex A. Lyapkov,
• Мekhman S. Yusubov and
• Francis Verpoort

Beilstein J. Org. Chem. 2019, 15, 733–745, doi:10.3762/bjoc.15.69

• gradually happen during the exposure time of polydicyclopentadiene thin layers in the air as a result of the oxidation of double bonds. A new vibrational band at 1410 cm−1 in the IR spectrum appears which is originating from the primary radicals which are formed alongside the chain initiation. The kinetics

• chain process of PDCPD oxidation follows. Various mechanisms of chain initiation are possible, e.g., the formation of primary free radicals initiating the chain reaction of polymer oxidation (Equation 1). More often, the chain initiation step is described as a bimolecular interaction between oxygen and

• , and can be conveniently described as the reaction given in Scheme 5. Impurities remaining in the polymer after its purification can participate in the initiation of the chain oxidation. These impurities can include initiator or catalyst residues, metal impurities with mixed valences, in particular

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• reactions of 7-oxanorbornene derivatives 13 and 14 were carried out with the so-called “ill-defined” catalysts, namely RuCl3·H2O and Ru(OTs)2(H2O)6 [27][28] (Scheme 3). However, these catalysts had limited usefulness due to a slow initiation rate and detrimental effect of water on the reaction mixture

Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands

• Tegene T. Tole,
• Johan H. L. Jordaan and
• Hermanus C. M. Vosloo

Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19

• for 80 °C, at 420 min. It also showed higher TOF at 60, 90 and 100 °C at 420 min. According to a DFT study by Getty et al. [19] the more positively charged the Ru, the slower the initiation rate of the catalyst. The calculated Mulliken atomic charge of Ru in 7 (0.934) is less positive than in 8 (0.976

• , precatalyst 6 showed a low initiation rate. This is also in agreement with the DFT study of Getty et al. [19], i.e., precatalyst 6 (0.988) has more positive Mulliken’s atomic charge on Ru than both 7 (0.934) and 8 (0.976). Its high activity at 110 °C with 69% selectivity is, however, remarkable for linear

• ruthenacycle. In addition, the relatively low ruthenium metal positive charge on 9 would cause it to have a high initiation rate constant [19]. On the other hand, the 3-Me group in 6 will strengthen the Ru–N chelation via inductive electron-donation and steric repulsion between the methyl group and the two

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

• Łukasz Gułajski,
• Andrzej Tracz,
• Katarzyna Urbaniak,
• Stefan J. Czarnocki,
• Michał Bieniek and
• Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

• initiation step. This unexpected catalytic activity might be due to the fact that catalysts 4b and 1a have different counter ions and therefore we decided to examine if there is an influence of counter ions on the catalytic activity. To achieve this we used analogues of 1a bearing different counter ions (1b

Mechanistic studies of an L-proline-catalyzed pyridazine formation involving a Diels–Alder reaction with inverse electron demand

• Anne Schnell,
• J. Alexander Willms,
• S. Nozinovic and
• Marianne Engeser

Beilstein J. Org. Chem. 2019, 15, 30–43, doi:10.3762/bjoc.15.3

• ) in the reacting solution. In order to enhance the ESI response of putative reactive intermediates, the reaction was performed with the charge-tagged tetrazine 4∙Br (R2, Scheme 5). A continuous-flow setup [4][17][18] was used for fast sampling of the reaction R2 directly after its initiation. A

Ruthenium-based olefin metathesis catalysts with monodentate unsymmetrical NHC ligands

• Veronica Paradiso,
• Chiara Costabile and
• Fabia Grisi

Beilstein J. Org. Chem. 2018, 14, 3122–3149, doi:10.3762/bjoc.14.292

• and 4a clearly outperformed GII-SIMes, with catalyst 4a emerging as the most efficient of all (>97% conversion in 9 min). Complex 5a showed a higher initiation rate with respect to GII-SIMes, but eventually was found to be less efficient due to a decrease in its catalytic activity related to

• comparable to GII-SIMes and HGII-SIMes in the RCM of substrate 7 (Scheme 1), giving full conversion within 30 minutes, whereas the corresponding Hoveyda-type complexes 18b and 19b presented a more pronounced initiation period, giving good conversions in much longer reaction time (2–4 h) [16]. A similar trend

• was observed in the RCM of 9 (Scheme 2), but reaction rates were lower in all cases. As for 20a and 21a, the initiation rates in the RCM of 7 were observed to be faster than GII-SIMes, HGII-SIMes and 19a, while the initiation rates of 20b and 21b were lower than GII-SIMes and HGII-SIMes, but superior

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• = 12). On the basis of these observations, a proposed triplet sensitization mechanism is illustrated in Scheme 4. In this reaction, photocatalyst 8 serves as a catalyst of an initiation step through energy transfer from photoexcited 8* to xanthate 1 to form excited xanthate 1* and regeneration of 8 in

• ). Conclusion We have established a protocol for a photoinduced radical addition of xanthates to olefins using an iridium-based photocatalyst under blue LED irradiation, leading to diverse xanthate adducts. This reaction proceeds through a radical-chain propagation mechanism via an initiation involving a

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• generation of silylium cations is possible. These cations have been described in the literature for initiation of ring-opening polymerization processes [25]. Cations Ph-NVK+ produced in catalytic cycle (Figure 5B) have also been well noted in the literature as highly reactive structures [26][27]. Amines

• photopolymerization initiation as shown in [53] (see Part 3). For this purpose, the Ir complex was more interesting than the Ru one because of the longer excited state lifetime, lower oxidation potential leading to higher interaction rate constants with additives used for ring-opening photopolymerization (e.g

• polymerization reactions Polymerization reactions whose initiation is induced by photoredox catalysts has been detailed in part 1.4. Representative monomer conversions with different photoredox catalysts and upon different irradiation light for free radical polymerization and for cationic polymerization are