Dirhodium(II)-catalyzed [3 + 2] cycloaddition of N-arylaminocyclopropane with alkyne derivatives

• Wentong Liu,
• Yi Kuang,
• Zhifan Wang,
• Jin Zhu and
• Yuanhua Wang

Beilstein J. Org. Chem. 2019, 15, 542–550, doi:10.3762/bjoc.15.48

• radical cation C resulting from cyclopropane ring opening reacts with alkyne substrate 2a generating radical D. The intermediate radical D yielded E through intramolecular radical addition. After hydrogen atom transfer (HAT) from complex A, the desired product is obtained with regeneration of the N

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• to generate intermediate 38 which is oxidized by Cu(II) to provide the CF3-substituted dihydronaphthalenes derivatives 31 along with releasing a proton [65][66]. The trifluoromethylthiolation of MCPs 1 with AgSCF3 was achieved by Shi et al. which proceeds through a sequence of radical addition, ring

• and aldehydes 48 to provide 2-acyl-3,4-dihydronaphthalenes 49 in moderate to excellent yields via a series of radical addition, ring-opening and cyclization in the presence of DTBP (di-tert-butyl peroxide) and Lewis acids (Scheme 12) [73]. Moreover, the experimental results showed MCPs 1 with electron

• radical addition of intermediate 66 to the C–C double bond in MCPs moiety furnishes the more stable benzyl radical intermediate 67, which is ring-opened to give alkyl radical 68. Finally, intermediate 68 goes through SET with the Rh(III) species and intramolecular cyclization with the 2-position of the

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• well as the first pentafluorosulfanylation method starting from sulfur hexafluoride [2]. We are convinced that the value of phenothiazine derivatives in photoredox catalysis is still underestimated. While these compounds found widespread use in ATRA (atom transfer radical addition) polymerization [15

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

• ). 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

Learning from B₁₂ enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

• Keishiro Tahara,
• Ling Pan,
• Toshikazu Ono and
• Yoshio Hisaeda

Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232

• (III) form of 1 has recently been found to catalyze atom transfer radical addition of alkyl halides to olefins (phenyl vinyl sulfone and acrylates) in the presence of NaBH4 [115]. In addition, a new light-driven method for generating acyl radicals from 2-S-pyridyl thioesters was developed through the

Hypervalent iodine compounds for anti-Markovnikov-type iodo-oxyimidation of vinylarenes

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Mikhail A. Syroeshkin,
• Alexander A. Korlyukov,
• Pavel V. Dorovatovskii,
• Yan V. Zubavichus,
• Gennady I. Nikishin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2018, 14, 2146–2155, doi:10.3762/bjoc.14.188

• target products (yields up to 91%). In contrast to previous studies in which oxidants promote the electrophilic addition of iodine to the C=C bond, radical addition predominates in the discovered process. Radical pathway starts from the attack of imide-N-oxyl radicals on the double C=C bond, which allows

Functionalization of graphene: does the organic chemistry matter?

• Artur Kasprzak,
• Agnieszka Zuchowska and
• Magdalena Poplawska

Beilstein J. Org. Chem. 2018, 14, 2018–2026, doi:10.3762/bjoc.14.177

• ) radical addition, (d) formation of phenol, (e) adsorption of phenol onto the graphene sheet. Acknowledgements This work was financially supported by the National Science Centre (Poland) through the grant OPUS No. 2016/21/B/ST5/01774. Artur Kasprzak acknowledges Foundation for Polish Science (FNP) for the

Visible light-mediated difluoroalkylation of electron-deficient alkenes

• Vyacheslav I. Supranovich,
• Vitalij V. Levin,
• Marina I. Struchkova,
• Jinbo Hu and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2018, 14, 1637–1641, doi:10.3762/bjoc.14.139

• with blue light is described. The reaction involves radical addition of 1,1-difluorinated radicals at the double bond followed by hydrogen atom transfer from sodium cyanoborohydride. Keywords: difluoroalkylation; organofluorine compounds; radical addition; visible light; Introduction Applications of

• boron-centered radical anion 5. After the initiation event, the reaction proceeds via a chain mechanism. Thus, radical addition at the double bond gives radical 6, which abstracts a hydrogen atom from cyanoborohydride to generate boryl radical anion 5. The latter species can readily abstract the iodine

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

• Yue Pan,
• Kunfang Jia,
• Yali Chen and
• Yiyun Chen

Beilstein J. Org. Chem. 2018, 14, 1215–1221, doi:10.3762/bjoc.14.103

• NMR spectra of BI-alkynes 3a–f were studied with the focus on the α-carbon, which position directly underwent α-radical addition [19]. The electron density of the α-carbon was decreased in 3a with electron-deficient 3,4-difluoro groups on the benziodoxole, and was increased for 3f with electron

• to optimal 80% yield. Based on mechanistic investigations above, we propose that the electronic effect on benziodoxoles affected both the radical acceptor and oxidative quencher reactivity of BI-alkyne derivatives (Scheme 7). In the alkyl or acyl radical addition step to BI’-alkyne (step 1) and the

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• aromatic [14][15] and heteroaromatic [16][17] SF5 compounds have become readily available and many applications have been described [18][19], the chemistry of aliphatic analogs is still underdeveloped [20]. Generally, the incorporation of SF5 groups into aliphatic positions is based on radical addition of

One-pot preparation of 4-aryl-3-bromocoumarins from 4-aryl-2-propynoic acids with diaryliodonium salts, TBAB, and Na₂S₂O₈

• Teppei Sasaki,
• Katsuhiko Moriyama and
• Hideo Togo

Beilstein J. Org. Chem. 2018, 14, 345–353, doi:10.3762/bjoc.14.22

• acid-catalyzed reaction of phenols and propynoic acids [22] and the (−)-riboflavin-catalyzed photochemical reaction of cinnamic acids [23] were reported recently. Moreover, the use of radical cyclization for the construction of the coumarin skeleton has become widespread. Examples include the radical

• addition–cyclization reactions of aryl 2-alkynoates with RC(=O)CO2H/AgNO3(cat.)/K2S2O8 at 60 °C [24], with Cu(OAc)2/1-trifluoromethyl-3,3-dimethyl-1,2-benziodoxole (Togni reagent) at 60 °C [25], with R2P(=O)H/Ag2CO3(cat.)/Mg(NO3)2 at 100 °C [26], with BrCF2CO2Et/fac-Ir(ppy)3(cat.) under irradiation at rt

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• radical anion then deprotonates the thiyl radical cation. Subsequent addition to the alkene yields the anti-Markovnikov radical intermediate. Radical addition to dioxygen leads finally to the β-ketosulfide, which subsequently is oxidized by the in situ generated hydrogen peroxide radical to the respective

• . Radical addition to the alkyne leads to the anti-Markovnikov adduct via the more stable secondary radical intermediate. As alkyne 2-methyl-3-butyn-2-ol was selected, which is easily prepared from acetylene and acetone on large scale and the respective thiol–yne adducts can be converted into valuable

• as oxidant. Based on radical trapping experiments, the authors suggest that the reaction might proceed via a radical addition pathway. Wang et al. developed a 9-mesityl-10-methylacridinium tetrafluoroborate (Acr+-Mes BF4−) catalyzed radical thiol–ene reaction with broad scope (Scheme 12) [42]. Both

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• moderate to excellent yields. Interestingly, performing the reaction on 1,1-disubstituted alkenes did not impact the yield significantly, while 1,2-disubstituted alkenes provided slightly less satisfying results. Chlorotrifluoromethylation reactions can also be included in cascade radical addition

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• radical from CF3SO2Na with extrusion of SO2. Then, CF3• underwent a radical addition to the alkene to form the radical 29, which was trapped by the aryldiazonium salt to give the radical cation 30. Finally, 30 was reduced by [Ru(bpy)3]2+* to end up with the product 31 (Scheme 13). The

Palladium-catalyzed Heck-type reaction of secondary trifluoromethylated alkyl bromides

• Tao Fan,
• Wei-Dong Meng and
• Xingang Zhang

Beilstein J. Org. Chem. 2017, 13, 2610–2616, doi:10.3762/bjoc.13.258

• , developing efficient methods for the synthesis of such valuable structures has received less attention [10][11][12][13][14][15]. Commonly, fluoroalkylated alkenes can be prepared through fluoroalkyl radical addition of alkynes via an atom transfer pathway [16][17] or cross-coupling of alkenyl halides with

Synthesis of 1,3-cis-disubstituted sterically encumbered imidazolidinone organocatalysts

• Jan Wallbaum and
• Daniel B. Werz

Beilstein J. Org. Chem. 2017, 13, 2577–2583, doi:10.3762/bjoc.13.254

• –Crafts alkylation [23] and in combination with photoredox catalysis (Scheme 1a) [24]. The enantioselective α-alkylation was achieved by merging the common photoredox catalyst Ru(bpy)3Cl2 with imidazolidinone catalyst 3a·TfOH, controlling the stereochemistry of the radical addition via an intermediate

NMR reaction monitoring in flow synthesis

• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31

• . [45], who developed a micro-channelled cell for synthesis and monitoring (MICCS) (Figure 8) and this was integrated into a 500 MHz NMR instrument. The system was used to elucidate the mechanism of the radical addition to an oxime ether with triethylborane (Scheme 1). The use of the NMR micro flow cell

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• (Scheme 2) [15][16][17]. A Mg-(bis)oxazoline complex serves as both a Lewis acid for the activation of α-substituted acrylates 6 towards radical addition and as a chiral template for an enantioselective hydrogen atom transfer from Bu3SnH to the α-ester radical intermediate. The authors found that the

Cascade alkylarylation of substituted N-allylbenzamides for the construction of dihydroisoquinolin-1(2H)-ones and isoquinoline-1,3(2H,4H)-diones

• Ping Qian,
• Bingnan Du,
• Wei Jiao,
• Haibo Mei,
• Jianlin Han and
• Yi Pan

Beilstein J. Org. Chem. 2016, 12, 301–308, doi:10.3762/bjoc.12.32

• cross-dehydrogenative coupling (CDC) reactions of alkanes, which were reported by Li and other groups [11][12][13][14][15]. Recently, several types of reactions with alkanes as substrates have been developed, such as the Minisci reaction with heteroarenes [16][17], radical addition to unsaturated bonds

• [18][19], decarboxylative alkenylation of cycloalkanes with aryl vinylic carboxylic acids [20][21], trifluoromethylthiolation [22], thiolation [23][24], alkenylation [25][26], dehydrogenation−olefination and esterification [27][28], radical addition/1,2-aryl migration [29], cascade alkylation

• final study of this reaction was the investigation of the mechanism. Firstly, a substrate (8a) bearing a hydrogen atom at the nitrogen was tried for the current system. The cyclohexane radical addition product 9aa’, instead of a cyclization product, was observed with 35% yield (Scheme 5a). This result

Synthesis and reactivity of aliphatic sulfur pentafluorides from substituted (pentafluorosulfanyl)benzenes

• Norbert Vida,
• Jiří Václavík and
• Petr Beier

Beilstein J. Org. Chem. 2016, 12, 110–116, doi:10.3762/bjoc.12.12

• for a more widespread use of SF5 compounds are low accessibility of basic building blocks and the lack of understanding of their chemical behavior. Lack of availability of SF5 compounds is particularly evident in aliphatics where radical addition of expensive and toxic SF5Cl to unsaturated compounds

Copper-catalyzed aminooxygenation of styrenes with N-fluorobenzenesulfonimide and N-hydroxyphthalimide derivatives

• Yan Li,
• Xue Zhou,
• Guangfan Zheng and
• Qian Zhang

Beilstein J. Org. Chem. 2015, 11, 2721–2726, doi:10.3762/bjoc.11.293

• addition and a nucleophilic oxygen attack [35]. Very recently, Studer and co-workers presented an aminooxygenation of alkenes with N-fluorobenzenesulfonimide (NFSI) and sodium 2,2,6,6-tetramethylpiperidine-1-olate (TEMPONa) via nitrogen-centred radical addition to the alkene followed by trapping of 2,2,6,6

• , the oxidation of Cu(I) with NFSI provided F–Cu(III)–N complex I, which could transform into a copper(II)-stabilized benzenesulfonimide radical II through a redox isomerization equilibrium. Next, the intermolecular radical addition of II to styrene 1g took place, producing benzylic radical III and Cu

• aminooxygenation reaction of alkenes with phthalimide and (diacetoxyiodo)benzene through cis-aminopalladation and SN2 C–O bond formation [34]. In 2013, Zhu and co-workers described an n-Bu4NI-catalyzed aminooxygenation of inactive alkenes with benzotriazole and water which underwent a nitrogen-centred radical

Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems

• Kirk W. Shimkin and
• Donald A. Watson

Beilstein J. Org. Chem. 2015, 11, 2278–2288, doi:10.3762/bjoc.11.248

• alkenes and alkynes One of the burgeoning areas of copper-catalyzed cross-coupling chemistry is the alkenylation of alkyl halide substrates. This transformation is achieved via formation of a transient radical, addition to a π-system (an alkene or an alkyne), followed by elimination or reincorporation of

• the observed product (Scheme 9). While the reaction conditions are similar to those utilized in atom transfer radical addition and polymerization reactions, the use of excess amine was critical for a robust alkenylation reaction and to avoid atom transfer and polymerization products. Various electron

• the alkyl bromide coupling partner was changed to an α-bromo keto ester, the radical addition is followed by a tautomerization/cyclization event that provides dihydrofurans in excellent yields [38]. The radical formation/addition events proceed largely in the same manner as the aforementioned

Aerobic addition of secondary phosphine oxides to vinyl sulfides: a shortcut to 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl)phosphine oxides

• Svetlana F. Malysheva,
• Alexander V. Artem’ev,
• Nina K. Gusarova,
• Nataliya A. Belogorlova,
• Alexander I. Albanov,
• C. W. Liu and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2015, 11, 1985–1990, doi:10.3762/bjoc.11.214

• the P(O)H species to molecular oxygen has been reported for example for Ph2P(O)H [30]. Then, the radical addition of A to vinyl sulfide, proceeding in an anti-Markovnikov manner, takes place. Subsequently, a 1,2-intramolecular transfer of an H atom within the radical adduct B (from PCH2 group to

Fates of imine intermediates in radical cyclizations of N-sulfonylindoles and ene-sulfonamides

• Hanmo Zhang,
• E. Ben Hay,
• Stephen J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2015, 11, 1649–1655, doi:10.3762/bjoc.11.181

• 6 and 9 that the imine 14 is reduced by radical hydrostannation to give 16 via 15. Finally, protodestannylation of 16 provides isolated product 8. Imine 11 with the ester substituent on C2 is formed by a similar sequence of reactions as 14. However, tin radical addition to 11 produces a captodative

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• probably involved the coupling of the initial aminium radical cation with the radical anion formed by SET to the furanone substrate [46]. An interesting further convolution was observed in the TiO2 and ZnS promoted SCPC reactions of N,N-dimethylaniline (10) with furanone 6. A tandem radical addition