Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• reaction proceeds through concerted hydrogen transfer by an oxidative pathway, reductive elimination, and subsequent isomerization. 1.2 Co(III)-catalyzed hydroarylation of alkynes In 2013, Kanai/Matsunaga and co-workers developed an air-stable Co(III)Cp* catalyst as an economical alternative to Cp*Rh(III

• regioselectivity was driven by a change in mechanism from linear ligand-to-ligand hydrogen transfer to branched base-assisted internal electrophilic-type substitution. In addition to activated and unactivated alkylalkenes, vinylcyclopropanes also underwent hydroarylation reactions with indoles 42 via C–H/C–C

• , a plausible mechanism was proposed. The reaction starts with the generation of the active cobalt(III) species G1 from [Cp*CoI2(CO)], AgSbF6, and arene 53. Subsequently, C–H metallation of G1 by ligand-to-ligand hydrogen transfer provides cobaltacycle G2 and an allene insertion gives intermediate G3

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

• conditions with rate enhancement for the latter setup. It was proposed that the CF3 radical added onto the substrate while the ketyl radical 41 was protonated by HFIP. Then, hydrogen transfer gave the hydrotrifluoromethylated product 40 and the sensitiser was regenerated (Scheme 20). In the same paper, the

Fast and efficient synthesis of microporous polymer nanomembranes via light-induced click reaction

• Qi An,
• Youssef Hassan,
• Xiaotong Yan,
• Peter Krolla-Sidenstein,
• Tawheed Mohammed,
• Mathias Lang,
• Stefan Bräse and
• Manuel Tsotsalas

Beilstein J. Org. Chem. 2017, 13, 558–563, doi:10.3762/bjoc.13.54

• radicals. Additional thiol moieties can undergo hydrogen transfer to the vinyl radical leading to thiyl radicals and vinyl sulfides. The vinyl sulfides can then undergo a thiol–ene coupling (TEC) reaction, leading to bis-sulfide species. TYC has been used for surface modification [21][22

New approaches to organocatalysis based on C–H and C–X bonding for electrophilic substrate activation

• Pavel Nagorny and
• Zhankui Sun

Beilstein J. Org. Chem. 2016, 12, 2834–2848, doi:10.3762/bjoc.12.283

• that halogen bonding was the key interaction for catalyst action. In 2014, the Tan group revisited the original study by Bolm and co-workers and re-investigated halogen bond induced hydrogen transfer to C=N bonds (Scheme 20) [91]. Various charged and uncharged electron-deficient iodoarenes were tested

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

Solving the puzzling competition of the thermal C²–C⁶ vs Myers–Saito cyclization of enyne-carbodiimides

• Anup Rana,
• Mehmet Emin Cinar,
• Debabrata Samanta and
• Michael Schmittel

Beilstein J. Org. Chem. 2016, 12, 43–49, doi:10.3762/bjoc.12.6

• pathway if the trapping reaction by hydrogen transfer is no more rate determining. Keywords: DFT computation; diradical; enyne-carbodiimides; hydrogen transfer; thermal cyclization; Introduction The thermal cyclizations of enediynes [1][2][3][4][5][6], enediallenes [7][8][9][10], bisallenes [11], enyne

• state [26][45], we decided to implement the N,N-dimethylaminomethyl group at the alkyne terminus. Two factors should be favorable for effective hydrogen transfer: (i) the nitrogen atom [51] stabilizes the incipient radical center and (ii) six equivalent hydrogens are available for transfer. Radical

• side equilibrium with the starting enyne-carbodiimide. The diradical can be trapped in good yield by hydrogen transfer and possibly also other reactions (e.g., addition to unsaturated bonds), if this process has a sufficiently low barrier [23]. Conclusion Experimental and computational techniques have

Synthesis and structures of ruthenium–NHC complexes and their catalysis in hydrogen transfer reaction

• Chao Chen,
• Chunxin Lu,
• Qing Zheng,
• Shengliang Ni,
• Min Zhang and
• Wanzhi Chen

Beilstein J. Org. Chem. 2015, 11, 1786–1795, doi:10.3762/bjoc.11.194

The enantioselective synthesis of (S)-(+)-mianserin and (S)-(+)-epinastine

• Piotr Roszkowski,
• Jan. K. Maurin and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2015, 11, 1509–1513, doi:10.3762/bjoc.11.164

• more active form [9]. In a key step in the enantioselective synthesis of mianserin and epinastine we applied the asymmetric reduction of the prochiral imine by asymmetric hydrogen transfer reaction (ATH) [10][11][12][13][14]. The proposed strategy could be used for the preparation of the title

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• the hydrogen transfer catalyzed by transition metal complexes. In these reactions, compounds with a double bond or a C–Hal bond act as oxidants (hydrogen acceptors). Examples of these reactions with aldehydes or primary alcohols as C–H reagents are given in Table 2. Crotononitrile, acetone, and benzyl

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• the hydrogen transfer conditions using the Pd black–formic acid system. Only one of the two pure isomers 40 was found to bind to chitin synthase. Plant et al. reported another approach to uracil polyoxins via the Ugi reaction [82]. In this work, the desired products 44 were assembled from 2′,3

Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• titanium species, photolysis at 254 and 300 nm, respectively, led only to trace amounts of the hydroxymethylation product 4 via a (triplet carbonyl) excited-state hydrogen-transfer process, obviously a sluggish process under these conditions (Table 1). In the presence of titanium complexes TiCln(OiPr)4−n

• conditions for route I are fulfilled for TiCl2(OR)2, a species that is capable of oxidizing methanol in the excited state and simultaneously acting as a ground-state Lewis acid that complexes the carbonyl compound. A much weaker Lewis acid such as Ti(OR)4 is capable of methanol oxidation but prefers hydrogen

• transfer at the first or second oxidation event. The pinacolization route II is favoured for heterogeneous and dye-catalyzed conditions. Interestingly, the combination of TiO2 P25 with an organic dye prefers largely the hydrogenation route III [45]. On the surface of the relatively large semiconductor

Visible-light-induced, Ir-catalyzed reactions of N-methyl-N-((trimethylsilyl)methyl)aniline with cyclic α,β-unsaturated carbonyl compounds

• Dominik Lenhart and
• Thorsten Bach

Beilstein J. Org. Chem. 2014, 10, 890–896, doi:10.3762/bjoc.10.86

• could occur by hydrogen transfer to the starting material, i.e., the α,β-unsaturated carbonyl compound [39], which would explain why the yields never exceeded 50%. Upon hydrogen transfer the α,β-unsaturated carbonyl compound would give a cyclic α-acyl radical, which would be capable to re-oxidize the

Aerobic radical multifunctionalization of alkenes using tert-butyl nitrite and water

• Daisuke Hirose and
• Tsuyoshi Taniguchi

Beilstein J. Org. Chem. 2013, 9, 1713–1717, doi:10.3762/bjoc.9.196

• intramolecular radical hydrogen transfer reactions. An 1,5-hydrogen shift is the most favourable process [17], and useful methods such as the Barton reaction and the Hofmann–Löffler–Freytag reaction have been reported [18][19][20]. Recently, we reported a novel radical multifunctionalization reaction of

Diastereoselective radical addition to γ-alkyl-α-methylene-γ-butyrolactams and the synthesis of a chiral pyroglutamic acid derivative

• Tomoko Yajima,
• Eriko Yoshida and
• Masako Hamano

Beilstein J. Org. Chem. 2013, 9, 1432–1436, doi:10.3762/bjoc.9.161

• hydrogen transfer from the H-donor (n-Bu3SnH or TTMSS) to the intermediate radical determined the stereochemistry of the product. In the case of the reaction of unprotected lactam by using a bulky H-donor (Table 1), hydrogen transferred from the opposite side of the γ-alkyl group and the cis-product was

• -protecting group (pivaloyl or acetyl) bidentately coordinate to the Lewis acid to form a six-membered chelate. The Lewis acid coordinates from the opposite side of the γ-alkyl group, and hydrogen transfer occurred from the same face as the γ-alkyl substituent to give trans-selectivity. However, strong trans

Simple and rapid hydrogenation of p-nitrophenol with aqueous formic acid in catalytic flow reactors

• Rahat Javaid,
• Shin-ichiro Kawasaki,
• Akira Suzuki and
• Toshishige M. Suzuki

Beilstein J. Org. Chem. 2013, 9, 1156–1163, doi:10.3762/bjoc.9.129

• was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic acid. Keywords: catalytic tubular reactor; flow chemistry; formic acid; hydrogenation; p-aminophenol; p-nitrophenol; Introduction The flow reaction process enables

Intramolecular carbonickelation of alkenes

• Rudy Lhermet,
• Muriel Durandetti and
• Jacques Maddaluno

Beilstein J. Org. Chem. 2013, 9, 710–716, doi:10.3762/bjoc.9.81

• competitive protonation of the fragile intermediate alkylnickel 2-Ni. While the Pd-catalyzed reductive Heck reaction promoted by a hydride generated in situ is well known [23][24], the nickel-catalyzed process is likely to occur through a radical hydrogen transfer from the DMF [20][25]. The N-allylaniline 1c

Electron and hydrogen self-exchange of free radicals of sterically hindered tertiary aliphatic amines investigated by photo-CIDNP

• Martin Goez,
• Isabell Frisch and
• Ingo Sartorius

Beilstein J. Org. Chem. 2013, 9, 437–446, doi:10.3762/bjoc.9.46

• agreement between experimental and calculated values of ∆G‡298. Keywords: amines; CIDNP; electron transfer; free radicals; hydrogen transfer; ketones; kinetics; photochemistry; self-exchange; Introduction Sensitized hydrogen abstractions from tertiary aliphatic amines present a mechanistic spectrum with a

• for different free radicals with XA as opposed to AQ. It is natural to assign hydrogen transfer to the slower of the two exchanges and electron transfer to the faster one. This is corroborated by the absolute strengths of the CIDNP effects with these two sensitizers. There is an approximate

• radicals can escape either from the radical-ion pairs or from the pairs of neutral radicals. Each type of radical can undergo self-exchange with ground-state molecules DH (by electron transfer, with rate constant kET; by hydrogen transfer, with rate constant kHT), which does not affect the chemical

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

• Nicole Zimmermann,
• Robert Hilgraf,
• Lutz Lehmann,
• Daniel Ibarra and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1246–1255, doi:10.3762/bjoc.8.140

• chain at C5 would provide the desired stereochemical outcome of the hydrogenation reaction (Scheme 4). We expected the free hydroxy group of 16 to coordinate to an appropriate homogenous hydrogenation catalyst, controlling the stereochemical course of the hydrogen transfer from the same side as the side

Sonogashira–Hagihara reactions of halogenated glycals

• Dennis C. Koester and
• Daniel B. Werz

Beilstein J. Org. Chem. 2012, 8, 675–682, doi:10.3762/bjoc.8.75

• used as a neutral epoxidation reagent leading to a facial-selective epoxide formation [34][35][36]. The so-obtained highly reactive acetal epoxide was either attacked by a superhydride, such as LiBHEt3 [31], or by a Lewis acidic hydrogen transfer agent, such as DIBAL-H [32][33]. In the former case, an

Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups

• Branislav Husár,
• Norbert Moszner and
• Ivan Lukáč

Beilstein J. Org. Chem. 2012, 8, 337–343, doi:10.3762/bjoc.8.37

• subsequent reactions leading to photoproducts [21]. The rate-determining step in photoinitiation by CQ/amine is hydrogen transfer by the excited n→π* triplet state of the carbonyl group of CQ from the alkylamino group [8][9]. The photochemistry of the low molecular CQ in the polystyrene (PS) film was the

Multicomponent reaction access to complex quinolines via oxidation of the Povarov adducts

• Esther Vicente-García,
• Rosario Ramón,
• Sara Preciado and
• Rodolfo Lavilla

Beilstein J. Org. Chem. 2011, 7, 980–987, doi:10.3762/bjoc.7.110

• - and N-substituents [22][23][24][25] (for related isoquinoline oxidations, see [26][27]). Related oxidative processes involve, for instance, a cascade Povarov–hydrogen transfer reaction using Tf2NH as a catalyst and the imine as an oxidant, as recently described [28]. In addition, Povarov adducts

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan

• Axel G. Griesbeck,
• Jörg Neudörfl and
• Alan de Kiff

Beilstein J. Org. Chem. 2011, 7, 518–524, doi:10.3762/bjoc.7.60

• ., produced by an intermolecular PET), the corresponding decarboxylation proceeds to give N-phthaloyl tryptamine (14) (Scheme 3). The histidine derivative 9 is expected to undergo PET with oxidation of the aryl group with the lowest efficiency and thus a Norrish II process (γ-hydrogen transfer with subsequent

• temperature and in ethanol at low temperatures are known: Triplet acetone, acetophenone and xanthone in acetonitrile are quenched by 1 via energy transfer; the rate constant is almost diffusion-controlled and somewhat smaller for benzophenone. The sole product from the photolysis of 1 is the double hydrogen

• transfer product 2. On the other hand, phthaloyl derivatives of C-unprotected α-amino acids (e.g., derivatives of Gly, Ala, Val, Ile, Phe) undergo efficient photodecarboxylation to yield the corresponding amines, β-amino acids are converted to benzazepines, and γ-amino acids to benzopyrrolizidines (Scheme

A stable enol from a 6-substituted benzanthrone and its unexpected behaviour under acidic conditions

• Marc Debeaux,
• Kai Brandhorst,
• Peter G. Jones,
• Henning Hopf,
• Jörg Grunenberg,
• Wolfgang Kowalsky and
• Hans-Hermann Johannes

Beilstein J. Org. Chem. 2009, 5, No. 31, doi:10.3762/bjoc.5.31

• material 4. In the absence of a catalytically active layer that promotes a hydrogen-transfer reduction [9][10], we propose an acid-catalysed hydride transfer of the type reported by Carlson and Hill [11]. Thereby, a carbenium ion such as 14, 16 or 17 (only the case of 16 is discussed in the following) can

Chemoselective reduction of aldehydes by ruthenium trichloride and resin- bound formates

• Basudeb Basu,
• Bablee Mandal,
• Sajal Das,
• Pralay Das and
• Ashis K. Nanda

Beilstein J. Org. Chem. 2008, 4, No. 53, doi:10.3762/bjoc.4.53

• ® resins; chemoselectivity; hydrogen transfer; reduction of carbonyl group; ruthenium chloride; Introduction Reduction of carbonyl functionality by transition metal-catalyzed transfer hydrogenation (CTH) with the aid of a suitable hydrogen donor is a valuable synthetic tool and has proved to be a viable

• . The reaction conditions appear to be mild and base-free, and give high yields of the corresponding alcohols and free of any by-product. Of interest is that, although the use of base co-catalysts for metal complex catalyzed hydrogen transfer is common [27][28][29][30], the present reaction conditions