Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

• Vyacheslav I. Supranovich,
• Vitalij V. Levin and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126

• silane is very sensitive to Lewis bases and accordingly it was used as a precursor of difluorocarbene, which can react with enol ethers [19][20] (Scheme 1). We showed that this silane could be involved in the radical chain hydrofluoroalkylation of electron-deficient alkenes, using a boron hydride as a

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

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• high regioselectivity [4]. Based on this reaction, Maruoka reported in 2016 that N-tosylvinylaziridines and alkenes could undergo cyclization reactions to generate pyrrolidines, catalyzed by substituted aryl disulfides under ultraviolet-light irradiation (Scheme 1) [5]. In 1997, Jung and co-workers

• used similar disulfide-catalyzed [3 + 2] cycloaddition reactions for the synthesis of polycyclic frameworks. The irradiation of vinylcyclopropanes with alkenes or alkynes in the presence of dibutyl disulfide afford the desired bi- or tricyclic products with 54–88% yield (Scheme 2) [6]. In 2014, Maruoka

• and co-workers reported an excellent thiyl radical-catalyzed enantioselective cyclization reaction of vinylcyclopropanes with alkenes [7]. For the extension of this concept, in 2018, Miller and co-workers reported a UV-light-promoted disulfide-bridged peptide-catalyzed enantioselective cycloaddition

Recent synthesis of thietanes

• Jiaxi Xu

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

• reactions) of alkenes and thiocarbonyl compounds are another important route for the synthesis of thietanes [15][16], especially, spirothietanes [17][18]. The formal [2 + 2] cycloadditions of hexafluorothioacetone and olefins are also applied in the preparation of bis(trifluoromethyl)-containing thietanes

• derivatives, especially multisubstituted thietanes. 3.1 Synthesis via photochemical [2 + 2] cycloadditions 3.1.1 Synthesis via intermolecular photochemical [2 + 2] cycloadditions: In 1969, the first photo-assisted [2 + 2] cycloadditions of alkenes and thiocarbonyl compounds were applied for the synthesis of

• nm UV light [63]. In 1978, Gotthardt and Nieberl investigated the UV light-induced [2 + 2] cycloaddition reaction of thiones with cyclic alkenes and realized the synthesis of spirothietane derivatives. Under n → π* excitation using Na light, xanthione (196) reacted with acenaphthylene (197), indene

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• two products: the product obtained by pathway A (26a) and a product 26b unique to pathway B. The abstraction–addition process (B) is dominant for three alkenes studied, namely, cyclohexene, cyclooctene, and 3-hexene, with 90–92% of the overall reaction occurring by this mechanism [77]. The reactions

• of the di-tert-butyliminoxyl radical with phenol and its derivatives are faster than with alkenes. The highest reaction rates are observed in the case of electron-donating substituents (Y) in 4-YC6H4OH [35][78]. The hydrogen atom abstraction rate accelerating effect of electron-donating substituents

Synthesis of pyrrolidinedione-fused hexahydropyrrolo[2,1-a]isoquinolines via three-component [3 + 2] cycloaddition followed by one-pot N-allylation and intramolecular Heck reactions

• Xiaoming Ma,
• Suzhi Meng,
• Xiaofeng Zhang,
• Qiang Zhang,
• Shenghu Yan,
• Yue Zhang and
• Wei Zhang

Beilstein J. Org. Chem. 2020, 16, 1225–1233, doi:10.3762/bjoc.16.106

• for making products 12a–d (Scheme 6). Even the allylated intermediates were not terminal alkenes, the Heck reaction gave the Z-products exclusively [52]. A general mechanism for Pd-catalyzed intramolecular Heck reaction of 8a for the synthesis of pyrrolo[2,1-a]isoquinoline 9a is shown in Scheme 7. The

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

• similar strategy for radical generations was applied by Glorius and co-workers. They exploited a combination of organophotoredox and copper catalysis to achieve the conversion of carboxylic acids into alkenes using N,N-diaryldihydrophenazine as an organic photocatalyst [46]. Rose bengal (OD15) was also

• important intermediates to develop new synthetic methods [62]. Their reactivity was first explored in the Meerwein arylation as well as the Gomberg–Bachman and the Sandmeyer reaction [63][64][65]. Similar to C(sp3) radicals, aryl radicals add to unsaturated systems, such as (hetero)arenes, alkenes, or

• -systems: heteroarenes and electron-poor alkenes in particular. Using the tools of organophotocatalysis, this reactive intermediate can be directly obtained from carbonyl derivatives, such as aldehydes, α-keto acids, oxalates, or carbamates through oxidative or reductive decarboxylations, oxidative

Copper-based fluorinated reagents for the synthesis of CF₂R-containing molecules (R ≠ F)

• Louise Ruyet and
• Tatiana Besset

Beilstein J. Org. Chem. 2020, 16, 1051–1065, doi:10.3762/bjoc.16.92

• functional group tolerance and was efficiently applied to the synthesis of CF2PO(OEt)2-containing (hetero)arenes, alkenes and alkynes (Scheme 7, reactions b–d) [50]. Later on, the same group depicted the Pd-catalyzed introduction of the CF2PO(OEt)2 residue on (hetero)aryl iodides [51] by using an in situ

Copper-catalysed alkylation of heterocyclic acceptors with organometallic reagents

• Yafei Guo and
• Syuzanna R. Harutyunyan

Beilstein J. Org. Chem. 2020, 16, 1006–1021, doi:10.3762/bjoc.16.90

• the Šebesta group was the first to report the copper-catalysed addition of organozirconium reagents to N-substituted 2,3-dehydro-4-piperidones (Scheme 4A) [27]. In the latter work, the organozirconium reagents were generated first in situ by the hydrozirconation of alkenes. Subsequently, the L1/Cu

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

• , but accompanied by long reaction times (Scheme 16). In 2014, Yang, Huang, Wang and co-workers reported a photocatalytic sulfonation of alkenes to β-ketosulfones (widely used in the synthesis of compounds with biological activities [44]), using porphyrins supported in CN materials (Scheme 17) [45]. The

• presented a slight decrease after 5 reuse cycles (from 94% to 85% yield). The methodology was applied to a variety of alkenes and the sulfinic acid, and the protocol was compatible with terminal, disubstituted and heteroarene alkenes (Scheme 18). Relevant yields (up to 90%) were obtained for both electron

• (1Δg) the main photoactive species in solution [63][64][65]. Singlet oxygen is a highly reactive electrophile toward electron-rich organic molecules/atoms such as alkenes, dienes, and heteroatoms (N, P, S, Se, etc.) making this molecule very effective in pericyclic reactions and heteroatom oxidations

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

• proceeded efficiently for a wide range of substrates in moderate to excellent yield, including various alkyl halides 93, carbon tetrachloride, 2-norbornene, cyclic alkenes, a terminal disubstituted olefin, and a terminal alkyne. The reaction mechanism was thought to proceed via energy transfer from the

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• decade later, Molander et al. made use of the same disilane as a source of the nucleophile for additions to α,β-unsaturated alkenes and alkynes as Michael acceptors bearing sulfones, nitriles, cyano, amido, and carboxyl ester groups to form β-silylated alkanes and alkenes in good to moderate yields [55

• excellent E:Z ratios within the resulting alkenes. This methodology could be applied to a wide variety of compounds, including those containing heterocycles (176–178). In a later study [67], they found that by changing ligands, a dramatic switch in the selectivity could be induced in silyl additions to

• was obtained, e.g., when simple stilbene was used the reaction led to only traces of product 194 (Scheme 33). With benzoxazole-conjugated alkenes, upon treatment with catalytic Cu complexed by a nonracemic Josiphos ligand (L20), good chemical yields of the desired enantioenriched products 196–199

Cascade trifluoromethylthiolation and cyclization of N-[(3-aryl)propioloyl]indoles

• Ming-Xi Bi,
• Shuai Liu,
• Yangen Huang,
• Xiu-Hua Xu and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2020, 16, 657–662, doi:10.3762/bjoc.16.62

• the direct incorporation of the SCF3 group into organic compounds [9][10][11][12][13][14][15][16], such as alkynes, alkenes, arenes, and alkanes. Despite these impressive advances, there is a continued strong demand for new methods that enable the efficient synthesis of SCF3-containing compounds

• construction of compounds with structural diversity and complexity. In 2014, Wang reported the first radical cascade trifluoromethylthiolation and cyclization of activated alkenes (Scheme 1a) [23]. Afterward, Nevado [24], Hopkinson and Glorius [25], Dagousset and Magnier [26], as well as Fu [27] applied this

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

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

• witnessed. 1.1 ATRA reactions Atom transfer radical addition reactions are linchpin transformations in organic synthesis as they allow an easy difunctionalization of alkenes. Usually, these reactions require the use of a radical initiator or thermal activation to initiate the radical chain. Recently

• ) photocatalyst (Scheme 1) [16]. The [Cu(I)(dap)2]Cl complex had a strong absorption under irradiation at 530 nm using a green LED. Different organic halides and alkenes were reacted, leading to the product by an ATRA reaction pathway with moderate to good yield at room temperature (Scheme 1). The authors

• (Scheme 2). Based on this work, in 2015, Reiser and co-workers reported another ATRA reaction to carry out the trifluoromethylchlorosulfonylation of alkenes (Scheme 3) [18]. They used the same catalyst as above, [Cu(I)(dap)2]Cl, to introduce the CF3 group to different alkenes under green LED irradiation

Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid

• Kaj M. van Vliet,
• Nicole S. van Leeuwen,
• Albert M. Brouwer and
• Bas de Bruin

Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38

• . Single-electron oxidation can produce carbon-centered radicals from substrates such as amines [17], alkenes [18], and carboxylates [19], or by hydrogen-atom transfer to an oxidatively formed thiolate radical [20]. Single-electron reduction produces carbon-centered radicals from, for example, aryl

• , Kokotos and co-workers published a visible light photoredox catalyzed lactone formation from iodoacetic acid and alkenes [29] (Scheme 1). In addition, it has been shown that monochloroacetic acid can be reduced by hydrated electrons [30][31]. The group of Goez developed a strategy for the photoredox

• cyclopropanation. We have screened a series of strongly oxidizing photoredox catalysts and various alkenes, but unfortunately we were thus far unsuccessful in obtaining cyclopropane derivatives (see experimental section). Conclusion We have shown that it is possible to use monochloroacetic acid to form two types

Copper-promoted/copper-catalyzed trifluoromethylselenolation reactions

• Clément Ghiazza and
• Anis Tlili

Beilstein J. Org. Chem. 2020, 16, 305–316, doi:10.3762/bjoc.16.30

• heterocycles with [(bpy)CuSeCF3]2 by the group of Weng. Difunctionalization of terminal alkenes and alkynes with [(bpy)CuSeCF3]2 by the group of Liang. Synthesis of Me4NSeCF3. Oxidative trifluoromethylselenolation of terminal alkynes and boronic acid derivatives with Me4NSeCF3 by the group of Rueping

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• nucleophiles to electron-deficient alkenes (Michael acceptors) represents an efficient and attractive methodology for providing a wide range of relevant chiral molecules. In order to increase the attractiveness of this useful catalytic transformation, some Michael acceptors bearing challenging electron

• accomplished in this stimulating field. Keywords: acylimidazole; N-acyloxazolidinone; N-acylpyrrole; N-acylpyrrolidinone; aldehyde; amide; copper catalysis; electron-deficient alkenes; enantioselective conjugate addition; Michael acceptor; thioester; Introduction Generating high molecular complexity and

• controlling multiple stereogenic centers in a minimum number of steps is nowadays one of the most important challenges in organic chemistry for the synthesis of complex chiral molecules. The transition metal (TM)-catalyzed enantioselective conjugate addition (ECA) of nucleophiles to electron-deficient alkenes

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

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• following three categories: (i) by Wittig or Doebner reaction of indoles bearing a 3-aldehyde group; (ii) by 1,4- or 1,2-addition of α,β-enones or carbonyl compounds, followed by oxidation or elimination, respectively; (iii) by Pd-catalysed oxidative coupling of indoles with activated alkenes. Several

• Pd-catalysed Fujiwara–Moritani or oxidative dehydrogenative Heck reaction via dual C–H activation [21][22][23][24]. One of the early examples of this reaction, reported by Gaunt and co-workers, involved the regioselective, solvent-controlled C3 alkenylation of indoles with alkenes containing electron

• of indoles using Pd(OAc)2 and Pd(II)/polyoxometallate, respectively, as a catalyst and molecular oxygen as the oxidant [26][27]. Verma and co-workers used the reaction between indoles and alkenes in the presence of a Pd(OAc)2 catalyst, a Cu(OAc)2 oxidant, and a 2-(1-benzotriazolyl)pyridine ligand [28

[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

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

• diverse products via formation of C–C bonds. Nucleophiles as diverse as electron-rich arenes or heteroarenes [41][42], alkenes [43], allylmetalloids [44][45][46], enol derivatives [47][48], and organometallics [49] are suitable for the Nicholas reaction. Allenic byproducts are rarely seen, and

Construction of trisubstituted chromone skeletons carrying electron-withdrawing groups via PhIO-mediated dehydrogenation and its application to the synthesis of frutinone A

• Qiao Li,
• Chen Zhuang,
• Donghua Wang,
• Wei Zhang,
• Rongxuan Jia,
• Fengxia Sun,
• Yilin Zhang and
• Yunfei Du

Beilstein J. Org. Chem. 2019, 15, 2958–2965, doi:10.3762/bjoc.15.291

• ][76][77], converting alkynes and alkenes to ketones [78], oxidizing alcohols to aldehydes [79][80], as well as in the direct α-hydroxylation of ketones [81]. Furthermore, it could also be used to realize oxidative C–C [82], C–N [83], and C–O [84] bond formations. However, to the best of our knowledge

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

• the leaving pyrophosphate group and the nucleophilic alkenes in proximity to initiate the C–C-bond forming, carbocation-mediated cascade reactions [10]. The hydrophobic binding pocket stabilizes the reaction intermediates and tames the propagation of carbocations through cation–π and other

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• is essential for the application of SCCs towards chiral recognition and sensing [34][35][36][37]. To the best of our knowledge no self-sorted responsive SCCs have been reported so far. Molecular motors based on overcrowded alkenes are unique photoswitches that are able to undergo unidirectional

• explanation could be that the mixture of stable Z-1 and stable E-1 does not form separate well-defined cage structures, but forms mixed complexes. Conclusion In summary, a new photoresponsive supramolecular coordination complex based on overcrowded alkenes is presented, allowing switching between three

• photoswitching affords a large geometric change of the ligands, only minor changes were observed in binding constants of the different cage structures. These results show that by incorporation of overcrowded alkenes into SCCs the geometry of cage structures can be controlled by light. Different designs might be