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

• efficient. Tubes with thin internal coatings of TiO2 have also been employed with some success (see below); research to improve their reusability is underway. Review Generation of ROS and organic oxidations When TiO2 is irradiated in the presence of moisture and atmospheric oxygen, the water acts as the

• application undergoing extensive trials is of self-cleaning garments [19] that may prove effective particularly for army wear in desert conditions. ROS generated from semiconductor photoredox catalysis (SCPC) have also been put to use in a good number of preparative oxidations so taking the place of toxic

• metals (such as chromium and manganese) [20][21][22]. Many SCPC oxidations of aromatics have been reported, but of these it is perhaps the oxidation of benzene to phenol that is the most industrially significant [23][24]. Unfortunately, product selectivity is poor because the phenol itself undergoes

Tetrathiafulvalene-based azine ligands for anion and metal cation coordination

• Awatef Ayadi,
• Aziz El Alamy,
• Olivier Alévêque,
• Magali Allain,
• Nabil Zouari,
• Mohammed Bouachrine and
• Abdelkrim El-Ghayoury

Beilstein J. Org. Chem. 2015, 11, 1379–1391, doi:10.3762/bjoc.11.149

• precursors 1 and 2 as well as of ligands L1 and L2 was investigated by cyclic voltammetry (Figure 6 and Table 3). The measurements in the case of precursors 1 and 2 show two reversible oxidations at E1ox = +0.26 V, E2ox = +0.75 V and E1ox = +0.32 V, E2ox = +0.77 V vs Ag/Ag+, respectively, that are anodically

• two reversible oxidations at E1ox = +0.20 V, E2ox = +0.70 V and E1ox = +0.25 V, E2ox = +0.70 V vs Ag/Ag+, respectively) that are cathodically shifted when compared to the ones of 1 and 2 indicating that the pyridine-hydrazone group is less electron deficient than the corresponding

New tris- and pentakis-fused donors containing extended tetrathiafulvalenes: New positive electrode materials for rechargeable batteries

• Shintaro Iwamoto,
• Yuu Inatomi,
• Daisuke Ogi,
• Satoshi Shibayama,
• Yukiko Murakami,
• Minami Kato,
• Kazuyuki Takahashi,
• Kazuyoshi Tanaka,
• Nobuhiko Hojo and
• Yohji Misaki

Beilstein J. Org. Chem. 2015, 11, 1136–1147, doi:10.3762/bjoc.11.128

• oxidation relates to the orbital energy, the first oxidations of 5–9 might occur at lower potentials than TTPY. The energy differences between the HOMO and HOMO–1 of all the donors (0.041–0.113 eV) were smaller than that of TTPY (0.186 eV). In particular, the orbital energies of the HOMO and HOMO–1 of 8a

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

• Luke J. O’Driscoll,
• Sissel S. Andersen,
• Marta V. Solano,
• Dan Bendixen,
• Morten Jensen,
• Troels Duedal,
• Jess Lycoops,
• Cornelia van der Pol,
• Rebecca E. Sørensen,
• Karina R. Larsen,
• Kenneth Myntman,
• Christian Henriksen,
• Stinne W. Hansen and
• Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

• aromaticity occurs: 2 contains a single aromatic, 6 π-electron 1,3-dithiolium system, and 3 possesses two such systems (Figure 1). These oxidations occur at low potential (E11/2 = 0.34 V and E21/2 = 0.73 V vs Ag/AgCl in MeCN [4]) and can be performed sequentially and reversibly. Additionally, both 2 and 3 are

A hybrid electron donor comprising cyclopentadithiophene and dithiafulvenyl for dye-sensitized solar cells

• Gleb Sorohhov,
• Chenyi Yi,
• Michael Grätzel,
• Silvio Decurtins and
• Shi-Xia Liu

Beilstein J. Org. Chem. 2015, 11, 1052–1059, doi:10.3762/bjoc.11.118

• synthesized and characterized. Both of them undergo two reversible oxidations and strongly absorb in the visible spectral region due to a photo-induced intramolecular charge-transfer (ICT) transition. To a great extent, the electronic interaction between the D and A units is affected by the presence of a

• of the reference compound 6 was carried out as well. The latter undergoes two reversible oxidations at 0.44 V and 0.75 V vs Fc+/Fc, hence at values which are lower than the oxidation potentials of the individual components DTF [24] and CPDT [25]. This observation indicates the formation of an

• electron donor and a cyanoacrylic acid either directly linked or linked through a phenyl spacer. Both of them show two reversible oxidations and strongly absorb in the visible spectral region. As evidenced by electrochemical and optical data, the electronic interaction between the D and A units is greatly

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• -conjugated tetraethynylethene (TEE) spacer as in compound 1a (Figure 1), then the two TTFs behave as independent redox centres that are oxidized at the same potentials in cyclic voltammetry (two two-electron oxidations) [8][9][10]. However, by bridging the two TTFs with an additional TEE in a cyclic

• structure, as in the radiaannulene 2a, communication between the two TTFs is observed in the cyclic voltammetry experiment, and the first two-electron event showed the waves diverging from each other (two stepwise oxidations) [10]. In addition, the intermediate radical cation showed an IVCT absorption at

• slightly more difficult to oxidize owing to the presence of the electron-withdrawing alkyne system. The acyclic compounds 1a and 5–7 all undergo two reversible two-electron oxidations; that is, the two TTFs are oxidized at the same potentials when separated by butadiyne, gem- or trans-TEE, or bis

A simple and efficient method for the preparation of 5-hydroxy-3-acyltetramic acids

• Johanna Trenner and
• Evgeny V. Prusov

Beilstein J. Org. Chem. 2015, 11, 323–327, doi:10.3762/bjoc.11.37

• briefly tested, but were found to produce rather mediocre yields of hydroxylated compounds. Attempted oxidations with Oxone or air gave no product at all. Our efforts to improve the yield of the desired product by variation of reaction conditions were rather fruitless, and therefore, our attention was

Photovoltaic-driven organic electrosynthesis and efforts toward more sustainable oxidation reactions

• Bichlien H. Nguyen,
• Robert J. Perkins,
• Jake A. Smith and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2015, 11, 280–287, doi:10.3762/bjoc.11.32

• relative oxidation potential of the various groups in solution. The group with the lowest oxidation potential is the group that will be oxidized. Chemical oxidations, however, do not have this limitation. They can be selective for one substrate based on steric effects, chirality, or other factors. For this

• less than those obtained when the overall system was more carefully controlled. Conclusion A broad range of electrochemical oxidations can be performed in a fashion that consumes only visible light and generates hydrogen gas as the only byproduct. The reactions include both direct and indirect

• , commercially available, photovoltaic cell. Electrochemical recycling of a chemical oxidant. Examples of solar-driven direct electrochemical oxidations. Overoxidation of dithioketal. Examples of solar-driven, indirect electrochemical oxidations. Solar-driven synthesis of C-glycosides. Solar-driven oxidative

The Shono-type electroorganic oxidation of unfunctionalised amides. Carbon–carbon bond formation via electrogenerated N-acyliminium ions

• Alan M. Jones and
• Craig E. Banks

Beilstein J. Org. Chem. 2014, 10, 3056–3072, doi:10.3762/bjoc.10.323

• to the C–H activation of low reactivity intermediates. In this article, containing over 100 references, we highlight the development of the Shono-type oxidations from the original direct electrolysis methods, to the use of electroauxiliaries before arriving at indirect electrolysis methodologies. We

Recent advances in the electrochemical construction of heterocycles

• Robert Francke

Beilstein J. Org. Chem. 2014, 10, 2858–2873, doi:10.3762/bjoc.10.303

• using electron transfer mediators (Scheme 1) play an important role. With regard to selectivity, the direct method is often complementary to typical chemical oxidations and reductions, since electrochemical oxidation or reduction proceeds via discrete electron transfer steps rather than atom transfer

Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids

• Roman Matthessen,
• Jan Fransaer,
• Koen Binnemans and
• Dirk E. De Vos

Beilstein J. Org. Chem. 2014, 10, 2484–2500, doi:10.3762/bjoc.10.260

• electrocarboxylation of 1,3-butadiene (Table 1) are illustrated in Scheme 8. They are divided into three categories, with (a) the sacrificial anode dissolution, (b) the proton forming reactions and (c) the oxidations evolving other free cations. In case a stable platinum anode is used, a C5:C6:C10 product mixture is

Aryl substitution of pentacenes

• Andreas R. Waterloo,
• Anna-Chiara Sale,
• Dan Lehnherr,
• Frank Hampel and
• Rik R. Tykwinski

Beilstein J. Org. Chem. 2014, 10, 1692–1705, doi:10.3762/bjoc.10.178

• , unfortunately, no clear trend observed for the oxidation potentials based on the substitution pattern of the aryl moieties, although both oxidations appear somewhat easier for pentacene 3f as a result of the two electron-donating methoxy groups attached to the pendent phenyl ring. Aryl-substituted pentacenes 3a

Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol

• Marina Caporaso,
• Giancarlo Cravotto,
• Spyros Georgakopoulos,
• George Heropoulos,
• Katia Martina and
• Silvia Tagliapietra

Beilstein J. Org. Chem. 2014, 10, 1454–1461, doi:10.3762/bjoc.10.149

• Selective oxidations of alcohols are some of the most important transformations in organic synthesis. Therefore, reactions that employ reusable heterogeneous catalysts and molecular oxygen are highly desirable from atom economy and environmental impact point of view [1][2][3]. A number of methods have been

The Ugi four-component reaction as a concise modular synthetic tool for photo-induced electron transfer donor-anthraquinone dyads

• Sarah Bay,
• Gamall Makhloufi,
• Christoph Janiak and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 1006–1016, doi:10.3762/bjoc.10.100

• potentials were plotted against for extrapolating the half-wave potentials E1/2 for a scan rate v = 0 mV·s−1 assuming an ideal Nernstian behavior. In the cyclic voltammograms of the phenothiazine–anthraquinone dyads 8a–d, typical for phenothiazine derivatives [41][42][78], first reversible oxidations E1/20

• -withdrawing anthraquinone moiety does not affect the first and second reversible oxidations of the phenothiazinyl moiety in the Do–Acc dyad 8c. The system 8d containing two conjugated phenothiazinyl moieties is particular since the second oxidation wave originates from the electronic coupling within the

Rapid pseudo five-component synthesis of intensively blue luminescent 2,5-di(hetero)arylfurans via a Sonogashira–Glaser cyclization sequence

• Fabian Klukas,
• Alexander Grunwald,
• Franziska Menschel and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2014, 10, 672–679, doi:10.3762/bjoc.10.60

• (Table 3). Most cyclovoltammograms display reversible Nernstian one-electron oxidations in the anodic region between 1.06 and 1.25 V (vs Ag/AgCl) (Table 3). Expectedly, with increasing electron density the oxidative potential diminishes. The compounds 2f, 2g, 2l, and 2n could not be measured by cyclic

Integration of enabling methods for the automated flow preparation of piperazine-2-carboxamide

• Richard J. Ingham,
• Claudio Battilocchio,
• Joel M. Hawkins and
• Steven V. Ley

Beilstein J. Org. Chem. 2014, 10, 641–652, doi:10.3762/bjoc.10.56

• –Ponndorf–Verley reductions [22] and Oppenauer oxidations [23] where zirconia activation is required). In fact, it seems that the extent of hydration of pyrazine-2-carbonitrile is proportional to the initial water content of the zirconium catalyst. To confirm this hypothesis, we ran a control experiment in

The Flögel-three-component reaction with dicarboxylic acids – an approach to bis(β-alkoxy-β-ketoenamides) for the synthesis of complex pyridine and pyrimidine derivatives

• Mrinal K. Bera,
• Moisés Domínguez,
• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 394–404, doi:10.3762/bjoc.10.37

• obtained heterocycles by palladium-catalyzed couplings or by oxidations are reported. We also describe the simple synthesis of a structurally interesting macrocyclic bispyrimidine derivative incorporating a 17-membered ring, whose configuration was elucidated by DFT calculations and by subsequent reactions

• addition we exemplarily investigated subsequent transformations of these compounds either by palladium-catalyzed cross-couplings or by oxidations of the 4-methyl groups of the pyrimidine subunits. Although the yields for the crucial initial multicomponent reactions leading to the bis(β-methoxy-β

A unified approach to the important protein kinase inhibitor balanol and a proposed analogue

• Tapan Saha,
• Ratnava Maitra and
• Shital K. Chattopadhyay

Beilstein J. Org. Chem. 2013, 9, 2910–2915, doi:10.3762/bjoc.9.327

• oxidations involving the aldehyde 16 as the intermediate. Taken as a hole the described synthesis of 7 from 8 and 9 proceeded in eight linear steps in an overall yield of 22%. The synthesis of the azepine unit [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] was achieved following our

Novel supramolecular affinity materials based on (−)-isosteviol as molecular templates

• Christina Lohoelter,
• Malte Brutschy,
• Daniel Lubczyk and
• Siegfried R. Waldvogel

Beilstein J. Org. Chem. 2013, 9, 2821–2833, doi:10.3762/bjoc.9.317

• ester substituent, the detour via protecting groups in the synthesis of alkylated triptycene 17 was subsequently avoided. Therefore, alkylated diketone 18 was synthesized, starting from (−)-isosteviol (Scheme 8). Since alkenes are known to participate in Riley oxidations as well, rendering allylic

A protecting group-free synthesis of the Colorado potato beetle pheromone

• Zhongtao Wu,
• Manuel Jäger,
• Jeffrey Buter and
• Adriaan J. Minnaard

Beilstein J. Org. Chem. 2013, 9, 2374–2377, doi:10.3762/bjoc.9.273

• synthesis of the Colorado potato beetle pheromone (Scheme 2). An additional challenge was the presence of an alkene in the substrate, as the orthogonality of 2-catalyzed alcohol oxidations with alkenes had not been studied. In our approach, Sharpless asymmetric epoxidation of readily available geraniol or

Elucidation of the regio- and chemoselectivity of enzymatic allylic oxidations with Pleurotus sapidus – conversion of selected spirocyclic terpenoids and computational analysis

• Verena Weidmann,
• Mathias Schaffrath,
• Holger Zorn,
• Julia Rehbein and
• Wolfgang Maison

Beilstein J. Org. Chem. 2013, 9, 2233–2241, doi:10.3762/bjoc.9.262

• Chemistry and Food Biotechnology, Heinrich-Buff-Ring 58, 35392 Gießen Department of Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany 10.3762/bjoc.9.262 Abstract Allylic oxidations of olefins to enones allow the efficient synthesis of value-added products from simple

• olefinic precursors like terpenes or terpenoids. Biocatalytic variants have a large potential for industrial applications, particularly in the pharmaceutical and food industry. Herein we report efficient biocatalytic allylic oxidations of spirocyclic terpenoids by a lyophilisate of the edible fungus

• developed. The oxidations follow a radical mechanism and the regioselectivity of the reaction is mainly determined by bond-dissociation energies of the available allylic CH-bonds and steric accessibility of the oxidation site. Keywords: allylic oxidation; CH-activation; chiral separation; enones; flavors

Synthesis of enantiomerically pure N-(2,3-dihydroxypropyl)arylamides via oxidative esterification

• Akula Raghunadh,
• Satish S More,
• T. Krishna Chaitanya,
• Yadla Sateesh Kumar,
• Suresh Babu Meruva,
• L. Vaikunta Rao and
• U. K. Syam Kumar

Beilstein J. Org. Chem. 2013, 9, 2129–2136, doi:10.3762/bjoc.9.250

• ][6] or (ii) catalytic oxidations with peroxides and chiral transition metal complexes [7][8][9]. The oxidative esterification of aldehydes involving oxidation followed by a C–O or C–N bond formation has received significant synthetic interest of late. Various transition metal complexes are employed

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• . Sequential oxidations of 141, similar to the biosynthesis of the aristolactams (Scheme 14), yields yagonine (146), which could be converted to aristoyagonine (136) via a benzilic acid-type rearrangement [121]. The first syntheses of aristoyagonine (136) were reported by Castedo and Suau (Scheme 19) [121][122

Gold-catalyzed regioselective oxidation of propargylic carboxylates: a reliable access to α-carboxy-α,β-unsaturated ketones/aldehydes

• Kegong Ji,
• Jonathan Nelson and
• Liming Zhang

Beilstein J. Org. Chem. 2013, 9, 1925–1930, doi:10.3762/bjoc.9.227

• the tertiary counterpart underwent gold-catalyzed 3,3-rearrangement preferentially [21] and hence was not a viable substrate. Except entry 7, the gold-catalyzed oxidations proceeded with excellent regioselectivities (>25:1), and the desired α-acyloxy α,β-unsaturated ketones/aldehyde were isolated with

• the ones with low selectivities, L1AuNTf2 offered again dramatic improvements (entries 5, 8 and 9) although at the expense of the geometric selectivities of the major product. The excellent regioselectivities of gold-catalyzed oxidations of propargylic carboxylates, albeit unexpected, could be readily

Mechanistic studies on the CAN-mediated intramolecular cyclization of δ-aryl-β-dicarbonyl compounds

• Brian M. Casey,
• Dhandapani V. Sadasivam and
• Robert A. Flowers II

Beilstein J. Org. Chem. 2013, 9, 1472–1479, doi:10.3762/bjoc.9.167

• -electron oxidations employing δ-aryl-β-dicarbonyl compounds have been carried out on arenes containing pendant β-ketoesters [10][11]. When Mn(III)-based oxidants are employed, secondary oxidations of the 2-tetralone products can occur [10][11]. Cerium(IV) ammonium nitrate (CAN) is a versatile, inexpensive

• addition, when 2.2 equivalents of CAN were employed, no products of secondary oxidations were obtained. Based on this observation, the single-electron oxidations of a variety of δ-aryl-β-dicarbonyl substrates with CAN in MeOH were performed to determine the scope of the reaction. DFT calculations were used