α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• ; Introduction When treated with base, acid, heat, or light, many α-hydroxyaldehydes, ketones, or imines 1 undergo a 1,2-shift of one of the α-substituents to the adjacent unsaturated carbon, with a concomitant proton transfer to form compounds of type 2 (Figure 1) [1]. Differing from the related Wagner–Meerwein

Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

• Zara M. Seibel,
• Jeffrey S. Bandar and
• Tristan H. Lambert

Beilstein J. Org. Chem. 2021, 17, 2077–2084, doi:10.3762/bjoc.17.134

• enolate geometry and N–H vs O–H binding). From this transition state, addition of the enolate to the acrylate followed by rapid proton transfer would lead to the glutamate derivative 10 (path a, red dashed line). A competing pathway involving bond formation between the acrylate α-carbon and the imine

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

• have been used as additives in these reactions and are suggested to act as ligands, assist proton transfer and promote the formation of oligovanadates by decreasing the pH value of the solution. The mechanisms of some vanadium-mediated oxidation reactions of alkanes have been studied, most of them

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

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

• that the EDA complex not only undergoes charge transfer but also proton transfer in this approach. The optimization experiment showed that the wavelength of the light source must overlap with the absorption spectrum of the EDA complex. Most importantly, given that the best yield was achieved when the

• that electron transfer is accompanied by proton transfer in the process (Scheme 43). In 2020, Stephenson and colleagues [14] employed 2-methoxynaphthalene (124) and acylated ethyl isonicotinate N-oxide obtained from 125 and trifluoroacetic acid anhydride to form EDA complexes for the preparation of

• -alkyl moiety in 31 or N,N-dimethylaniline (30). This approach utilizes N,N-dimethylaniline (30) as electron donor and N-methylmaleimide (31) as electron acceptor to form an EDA complex, so that single-electron transfer occurs under ultraviolet-light irradiation. Subsequently, intermolecular proton

Synthesis of β-triazolylenones via metal-free desulfonylative alkylation of N-tosyl-1,2,3-triazoles

• Soumyaranjan Pati,
• Renata G. Almeida,
• Eufrânio N. da Silva Júnior and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2021, 17, 762–770, doi:10.3762/bjoc.17.66

• , the enol form of 1,3-dicarbonyl 2 attacks the sulfonyl group in 1 to form intermediate I which later undergoes proton transfer to form intermediate II. Cleavage of the N–S bond in intermediate II generates the β-O-tosylcycloalkenone 4 and triazolyl anion III. Subsequent counter-attack of the triazolyl

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

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

• molecules in aqueous solution. The building blocks pelargonidin chloride (Flavy), 1-naphthol-3,6-disulfonate (1N36S), and poly(allylamine) are depicted in Scheme 2. The aim was to exploit the photoacid's unique capability to undergo photoinduced intermolecular excited state proton transfer reactions, both

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

• -workers proposed that the catalytic mechanism involves a reaction between phosphine catalyst A and allene 82 to give B and/or C (Scheme 5B). Catalytic [3 + 2] cycloaddition of B and/or C and alkene D gives the cyclic intermediates E and F in an equilibrium state through a 1,2-proton transfer. The loss of

• than C-3’, which results in the regioselective formation of intermediate C. Cyclization of intermediate C gives D and subsequent proton transfer produces isomer E. It undergoes elimination to afford the annulation product 103 and the phosphine catalyst A is regenerated. In the same work, Lu and co

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• anticipated sigmoidal shape of a 1:1 bonded complex (see Figure S5a in Supporting Information File 1). The curve shape suggests a more complex chemical equilibrium that involves more than one chemical process generating heat, taking place in the titration experiment. One process is likely a proton transfer

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

• to generate diradical 177 that then adds to the alkene to form diradical 178. A SET between the ketyl radical and the α-carbonyl radical generates enolate intermediate 179, which after proton transfer regenerates the catalyst and releases the desired cyclisation product 180 in a moderate yield and

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• ). Thereafter, a cationic intermediate is afforded by the radical combination between the sulfonyl radical and the 1-naphthyl derivative at the C4 position. Lastly, a proton-transfer process and dissociation result in the formation of the expected coupling product, accompanied by the regeneration of the Cu salt

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• proton transfer to an adjacent oxide atom, forming two bridging-hydroxyls. Subsequently, an adsorbed O2 molecule is reduced by the bridging hydroxyls to form two terminal hydroxides and fill the initial oxygen surface vacancy (Figure 5) [92]. Organic molecules generally weakly associate with the surface

One-pot synthesis of 1,3,5-triazine-2,4-dithione derivatives via three-component reactions

• Gui-Feng Kang and
• Gang Zhang

Beilstein J. Org. Chem. 2020, 16, 1447–1455, doi:10.3762/bjoc.16.120

• nucleophilic addition of another molecule 2 takes place to furnish the tricomponent adduct 4, which undergoes elimination of ammonia to afford the corresponding ring-closed intermediate 7 [37]. The latter undergoes a proton-transfer process to form intermediate 10 [38]. Thereafter, the subsequent step involves

• alkylation process [39]. Finally, proton transfer processes afford the desired product 6 and byproduct 5. Conclusion In summary, we have developed a simple and efficient method for the synthesis of 4-aryl-6-(alkylthio)-3,4-dihydro-1,3,5-triazine-2(1H)-thiones through a catalyst-free multicomponent reaction

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• a thiyl radical (pathway 3) or a thiolate anion (pathway 4) to regenerate the disulfide. Finally, the formed intermediates 67 and 68 furnish the final product 69 by hydrogen (pathway 3) or proton transfer processes (pathway 4), respectively. Disulfide-catalyzed isomerization processes also found

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• 143. A proton transfer generated hydroxyalkanethiolates 144 because the acidity of the thiols is higher than that of alcohols, the newly generated thiolates 144 underwent an intramolecularly nucleophilic displacement to give thietane-3-ols 145 [56] (Scheme 28). In a similar approach

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

• , the authors suggested the reduction of the N-alkoxyphthalimide by the excited copper catalyst, [Cu(I)]*. Then, this radical collapses into an α-oxy carbon-centered radical thanks to an intramolecular proton transfer. This carbon-centered radical then recombines with the α-amino radical that arises

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• OH group, facilitated proton transfer from the γ- to β-carbon atom via a process similar to the elimination/electrophilic addition to alkenes pathway. The computational results discussed above showed that the crucial point for sulfur atom migration was the formation of a tertiary carbocation at the β

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• electrostatic interactions [54]. Moreover, TCs also assist intramolecular atom transfer and rearrangements including hydride or proton transfer and carbon shifts [10]. Eventually, the carbocation is quenched by deprotonation (E1-like) or nucleophilic attack (SN1-like) of water [45]. In contrast to

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• ). As per the proposed mechanism, products 122 were obtained via nucleophilic addition of enamine 124' to electrophilic intermediate 127 (generated from the anodic oxidation of 120) followed by sequential hydrolysis, proton transfer and immediate intramolecular condensation (Scheme 41). Very recently

1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

• Vito A. Fiore,
• Chiara Freisler and
• Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

• vinylphosphonium ion, and a proton transfer finally yields the 1,4-betaine. A kinetic study of the PPh3/DMAD/Meldrum’s acid reaction by spectrophotometric and stopped-flow methods has been published [14]. The initial 1,3-betaine has also been trapped with other electrophiles. The stable 1,4-betaines betaines III

Experimental and computational electrochemistry of quinazolinespirohexadienone molecular switches – differential electrochromic vs photochromic behavior

• Eric W. Webb,
• Jonathan P. Moerdyk,
• Kyndra B. Sluiter,
• Benjamin J. Pollock,
• Amy L. Speelman,
• Eugene J. Lynch,
• William F. Polik and
• Jason G. Gillmore

Beilstein J. Org. Chem. 2019, 15, 2473–2485, doi:10.3762/bjoc.15.240

• similar to what we previously reported for pLW 4a,b [21]. This comparatively slow and purely thermal reversion is consistent with the need for a thermodynamically unfavorable intramolecular (or solvent or adventitious acid/base-mediated) proton transfer to begin the reversion mechanism, as Minkin has

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• , diarylethene derivatives with photoswitchable fluorescent properties were prepared. They are applicable for fluorescence imaging including bio-imaging. On the other hand, a new system called “excited state intramolecular proton transfer (ESIPT)” is reported. In the system, absorption and emission bands are

• largely separated due to the proton transfer, hence it showed strong fluorescence even in the crystalline state. We aimed to construct the photochromic system incorporating the ESIPT mechanism. Results: A diarylethene incorporating a fluorescent moiety that exhibit ESIPT behavior was prepared. The ESIPT

• a large Stokes shift is indispensable for such a system. One of the possible choices to achieve such a large Stokes shift is to introduce the excited-state intramolecular proton transfer (ESIPT). The process of ESIPT is a fast process even comparable to the internal conversion [15][16]. This is

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• exchange was especially developed to describe main-group thermochemistry and noncovalent interactions. It shows very good results in predicting the position of the tautomeric equilibria for compounds with intramolecular hydrogen bonds as well as describing the ground and excited state proton transfer

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