Exploring endoperoxides as a new entry for the synthesis of branched azasugars

• Svenja Domeyer,
• Mark Bjerregaard,
• Henrik Johansson and
• Daniel Sejer Pedersen

Beilstein J. Org. Chem. 2017, 13, 644–647, doi:10.3762/bjoc.13.63

• the reaction was performed with the sensitizer rose bengal the diene was observed to quickly disappear from the system and only a low yield of endoperoxide 17 was obtained. Due to the many problems encountered with the Boc-protection strategy it was abandoned at this stage and we turned our attention

• exchanging the sensitizer with tetraphenylporphyrin (TPP) to give a good yield of the desired endoperoxide 19. Likewise, diene 15 was converted to the corresponding endoperoxide 18 in good yield using TPP, whereas no product was obtained using rose bengal. With endoperoxides 18 and 19 in hand the stage was

A flow reactor setup for photochemistry of biphasic gas/liquid reactions

• Josef Schachtner,
• Patrick Bayer and
• Axel Jacobi von Wangelin

Beilstein J. Org. Chem. 2016, 12, 1798–1811, doi:10.3762/bjoc.12.170

• , O3, H2, Cl2, acetylene, NOx, CO, CO2, etc.) but obviously bear several challenges with regard to a reproducible and precise control of the addition and mixing of the three phases: the liquid phase, containing organic substrates, the photo-active component (catalyst or sensitizer), the solvent, and

• to oxidation chemistry of utmost sustainability. Under irradiation in the presence of a sensitizer, singlet oxygen can easily be generated from the triplet ground state. Several applications of such photooxidations to chemical synthesis have been reported [71][72][73], in recent years most

• . Following an optimized Schenck ene reaction procedure, N-methyl-1,2,3,6-tetrahydrophthalimide (1a) was reacted with molecular oxygen in the presence of methylene blue as sensitizer (Scheme 6). The resultant hydroperoxide motif (2a) constitutes a valuable carbocyclic building block. For reasons of

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

Biradical vs singlet oxygen photogeneration in suprofen–cholesterol systems

• Fabrizio Palumbo,
• Francisco Bosca,
• Isabel M. Morera,
• Inmaculada Andreu and
• Miguel A. Miranda

Beilstein J. Org. Chem. 2016, 12, 1196–1202, doi:10.3762/bjoc.12.115

• photolysis of dyads 1 and 2. Photoreaction pathways generating biradical and singlet oxygen species of a sensitizer (S), like SP, KP or TPA, covalently linked to Ch. The obtained percentages under anaerobic conditions are given in parenthesis. Photophysical parameters of dyads in CH2Cl2. Supporting

From steroids to aqueous supramolecular chemistry: an autobiographical career review

• Bruce C. Gibb

Beilstein J. Org. Chem. 2016, 12, 684–701, doi:10.3762/bjoc.12.69

• photochemical conversions [38][39][40][41]. One particularly enjoyable example of a reaction in the capsule formed by octa-acid came through collaboration between our group, Ramamurthy’s, and the group of the late Nicholas Turro (Figure 9) [42][43]. If a solution of a capsular complex of the sensitizer

• dimethylbenzil is irradiated, the encapsulated sensitizer is excited and can transfer its energy to an oxygen molecule adventitiously entering the capsule. (Although guest exchange is slow on the NMR timescale, there is a much faster dynamic breathing of the capsule that allows small molecule entry and egress

The chemical behavior of terminally tert-butylated polyolefins

• Dagmar Klein,
• Henning Hopf,
• Peter G. Jones,
• Ina Dix and
• Ralf Hänel

Beilstein J. Org. Chem. 2015, 11, 1246–1258, doi:10.3762/bjoc.11.139

• has been investigated by many authors [18][19][20]. In most cases this photooxidation involves singlet oxygen that is generated from triplet oxygen by irradiation in the presence of a sensitizer such as chlorophyll. Since the above experiment was carried out in the absence of a sensitizer, the

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

• characterized by NMR and HRMS analyses. Electronic properties To estimate the energy values of the frontier orbitals (HOMO and LUMO) of dyes 1 and 2 that are essential for the evaluation of two critical processes in DSSC devices, namely the electron injection from the photo-excited sensitizer to the TiO2

• extinction coefficients on the order of 6 × 104 M−1 cm−1 (Table 1). The lowest-energy absorption band is attributed to ICT transitions originating from electronic excitations from MOs spread over the hybrid donor to the MO localized on the cyanoacrylic acid. Compared to 2, sensitizer 1 shows for the lowest

Synthesis of carbohydrate-scaffolded thymine glycoconjugates to organize multivalency

• Anna K. Ciuk and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2015, 11, 668–674, doi:10.3762/bjoc.11.75

• is required as triplett sensitizer in this process [5]. Irradiation with light of ≥ 290 nm was performed during a period of 3 and 6 hours, respectively. After irradiation, the solvents were removed and the product investigated without any purification or further separation. 1H NMR-spectroscopic

An integrated photocatalytic/enzymatic system for the reduction of CO₂ to methanol in bioglycerol–water

• Michele Aresta,
• Angela Dibenedetto,
• Tomasz Baran,
• Antonella Angelini,
• Przemysław Łabuz and
• Wojciech Macyk

Beilstein J. Org. Chem. 2014, 10, 2556–2565, doi:10.3762/bjoc.10.267

• generated by the photocatalyst upon visible light irradiation suggest the electron transfer from the excited sensitizer (chromium(III) complex) to the conduction band of TiO2. The reduction of the rhodium complex was confirmed by spectroscopic studies made in the presence of irradiated TiO2 and upon

Oxidative phenylamination of 5-substituted 1-hydroxynaphthalenes to N-phenyl-1,4-naphthoquinone monoimines by air and light “on water”

• Julio Benites,
• Juan Meléndez,
• Cynthia Estela,
• David Ríos,
• Luis Espinoza,
• Iván Brito and
• Jaime A. Valderrama

Beilstein J. Org. Chem. 2014, 10, 2448–2452, doi:10.3762/bjoc.10.255

• by on-water oxidative phenylamination of 1,5-dihydroxynaphthalene (1) and 5-acetylamino-1-hydroxynaphthalene (5) with oxygen-substituted phenylamines under aerobic conditions and either solar or green LED radiation, in the presence of rose bengal as singlet oxygen sensitizer. As compared to the

• green route for the preparation of N-phenyl-1,4-naphthoquinone monoimines by on-water oxidative coupling reaction of 1-hydroxynaphthalene derivatives with oxygen-substituted phenylamines under solar light or green LEDs radiation, rose bengal as singlet oxygen sensitizer and aerobic conditions. Results

• then in the same flask, the arylamination of 2 to the respective aminoquinones was accomplished [14]. The on-water photooxygenation of 1,5-DHN (1) was carried out for 5 h in round-bottom flasks, under the presence of 1.6 mmol % of rose bengal (RB) as singlet oxygen sensitizer, by using sunlight

Photorelease of phosphates: Mild methods for protecting phosphate derivatives

• Sanjeewa N. Senadheera,
• Abraham L. Yousef and
• Richard S. Givens

Beilstein J. Org. Chem. 2014, 10, 2038–2054, doi:10.3762/bjoc.10.212

• triplet sensitized photolysis in the presence of benzophenone (BP), a well-established triplet sensitizer, at 254 nm under O2-free conditions was Φdis = 0.022. These combined results demonstrate that the reactive excited state is a triplet that is partially quenched by O2 under ambient conditions

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

• particle surfaces, CB, VB = conduction and valence band. Homogeneous sensitizer variation for the acetophenone model reaction. Substrate variation under optimized conditions. Photohydroxymethylation of keto esters: 1,2-diol and lactone formation. Heterogeneous sensitizer variation for model reaction in

Metal and metal-free photocatalysts: mechanistic approach and application as photoinitiators of photopolymerization

• Jacques Lalevée,
• Sofia Telitel,
• Pu Xiao,
• Marc Lepeltier,
• Frédéric Dumur,
• Fabrice Morlet-Savary,
• Didier Gigmes and
• Jean-Pierre Fouassier

Beilstein J. Org. Chem. 2014, 10, 863–876, doi:10.3762/bjoc.10.83

• different photopolymerization reactions: FRP, CP and FRPCP. The associated systems are characterized by an outstanding photosensitivity; the catalytic pathways ensure a regeneration of the PIC and avoid any lost of reactivity upon irradiation. A bleaching of the sensitizer can be observed in excess of

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• (DCA) as the sensitizer [242]. After irradiation of diazene 34 in an argon matrix at 10 K, biradical 35 was detected by IR spectroscopy and the reaction of the latter with oxygen at 10 K proceeded regioselectively to give dioxolane 36 (Scheme 12) [243]. Bicyclic peroxide 2-heptyl-3,4-dioxabicyclo[3.3.0

• % yields. 2,4,6-Triphenylpyrylium tetrafluoroborate was used as the sensitizer for singlet oxygen generation (Scheme 54) [301]. It was found that tris(bipyrazyl)ruthenium(II) [(Ru(bpz)3(PF6)2] is an excellent photocatalyst for the synthesis of 1,2-dioxanes by aerobic photooxygenation of α,ω-dienes [302

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• achieved using UV light with a sensitizer. This approach and subsequent chemistries are also outside the scope of this review. Interested readers are referred to these reviews [7][19][20][21]. Review Iminium ions Intercepted by carbon nucleophiles One of the major modes of reactivity for amine radical

Continuous flow photocyclization of stilbenes – scalable synthesis of functionalized phenanthrenes and helicenes

• Quentin Lefebvre,
• Marc Jentsch and
• Magnus Rueping

Beilstein J. Org. Chem. 2013, 9, 1883–1890, doi:10.3762/bjoc.9.221

• visible light in the presence of a sensitizer [22], but, to the best of our knowledge, no reports on broadly applicable light-induced oxidative photocyclizations in flow are known. Herein, we report the first photocyclization of polysubstituted olefins using a continuous flow process and discuss

Electron self-exchange activation parameters of diethyl sulfide and tetrahydrothiophene

• Martin Goez and
• Martin Vogtherr

Beilstein J. Org. Chem. 2013, 9, 1448–1454, doi:10.3762/bjoc.9.164

• , diethyl sulfide DES and tetrahydrothiophene THTP, for which we have barred the direct deprotonation at Cα by the choice of a suitable sensitizer; for these substrates, a relayed deprotonation is also impossible because they are not sufficiently basic; however, D•+ can stabilize by dimer formation with

• +85 kJ/mol for triethylamine, the quencher used in our earlier work [21][22][23], so for any sensitizer the radical pair containing lies about 75 kJ/mol higher above the reactants in the case of the amine. From the oxidation potentials in the literature (DES, 1.65 V [27]; triethylamine, 0.96 V [21

• S, not N, cast some doubt on whether these reported potentials are the true equilibrium potentials for these irreversible redox systems. In any case, a sensitizer that is a potent electron acceptor but has no hydrogen-abstracting power is mandatory to shift the energetics so as to stop the

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• those that react with it (path c'). Thus, tertiary amines are known to undergo deprotonation from the α-position to produce a radical that is in turn easily oxidized to the iminium cation. In the present examples, such radicals are oxidized by the ground-state sensitizer (E = −1.12 V versus SCE for the

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

• -derived radicals (radical cations DH•+ or α-amino alkyl radicals D•) with the parent amine DH; the acid–base equilibrium between DH•+ and D• also plays no role. Although the sensitizer does not at all participate in the observed processes, it has a pronounced influence on the CIDNP kinetics because the

• duration and, thus, fall within the relevant kinetic range. In a series of previous CIDNP studies on triethylamine with different aromatic carbonyl compounds as sensitizers [5][6][7], we have used the dependence of the polarization pattern on the sensitizer and the solvent to show that these reactions are

• always two-step hydrogen abstractions according to Scheme 1. The source of the polarizations can be either the initially formed radical-ion pair where A•− and DH•+ are the radical anion of the sensitizer A and the radical cation of the amine DH, or a secondary pair of neutral radicals , where AH• and D

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

• ]. In the second experiment, the parent hydrocarbon 2 was irradiated in the presence of vinylacetylene (199) and a triplet sensitizer (benzophenone). Besides the photodimers of 199, the [2 + 2] photoadduct 200 was isolated in low yield [137]. 1.4.2 Ionic reactions Regardless of what types of reactions

Cyclodextrin nanosponge-sensitized enantiodifferentiating photoisomerization of cyclooctene and 1,3-cyclooctadiene

• Wenting Liang,
• Cheng Yang,
• Masaki Nishijima,
• Gaku Fukuhara,
• Tadashi Mori,
• Andrea Mele,
• Franca Castiglione,
• Fabrizio Caldera,
• Francesco Trotta and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2012, 8, 1305–1311, doi:10.3762/bjoc.8.149

• from that reported for the conventional sensitizer-appended monomeric cyclodextrins, affording chiral (E)-cyclooctene and (E,Z)-cyclooctadiene in enantiomeric excesses critically dependent on the solution pH and solvent composition employed, revealing the active roles of chiral void spaces of CDNS in

• , inducing stronger ICD at the 1La band (Figure 1c). Assuming the 1:1 stoichiometry, we calculated the apparent binding constant, averaged over the CD units of CDNS, as 4000 M−1 in water at 25 °C. This value is smaller than those obtained with the sensitizer-modified CDs reported previously [36], for which

• of CDNSs, it is likely that some of the carboxyl groups in PDA are not incorporated in the polymer chain, and hence, the solution pH may change the ionic state of the remaining carboxyl groups, affecting the sensitizer conformation and also the product selectivity. The conformational change of the PM

Triple-channel microreactor for biphasic gas–liquid reactions: Photosensitized oxygenations

• Ram Awatar Maurya,
• Chan Pil Park and
• Dong-Pyo Kim

Beilstein J. Org. Chem. 2011, 7, 1158–1163, doi:10.3762/bjoc.7.134

• -terpinene. Photosensitized oxygenation of (−)-citronellol The photosensitized oxygenation of citronellol is an industrially important synthetic transformation [47] as it is used for bulk production of a fragrance, rose oxide (Scheme 1). The reaction was performed with methylene blue as a sensitizer in

• sensitizer. The results from the triple-channel microreactor and the batch reaction presented in Table 3 clearly indicate the efficiency of the former. Photosensitized oxygenation of α-terpinene The photosensitized oxygenation of α-terpinene is a Diels–Alder type [4 + 2] cycloaddition reaction. The product

• of the reaction is ascaridole, which is widely used as an anthelmintic drug, in tonic drinks and in food flavoring [49]. The reaction was successfully carried out in the triple-channel microreactor with methylene blue as a sensitizer, as above. Significant reduction in the reaction time was again

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• is multiplicity-dependent: The direct irradiation of 1a leads to the dibenzocyclooctatetraene 3a in a singlet reaction that occurs via an initial [2 + 2] cycloaddition followed by a [4 + 2] retro-Diels–Alder reaction [27][28][29][30]. In the presence of a triplet sensitizer, e.g., acetone or

• (trifluoromethyl)phenyl substituents. Notably, not even the commonly employed sensitizer acetone is capable of inducing the DPM rearrangement of 1i. Considering the different photophysical and photochemical properties of the carbonyl and thiocarbonyl chromophores [49], it may be that a similar difference exists

Photoinduced homolytic C–H activation in N-(4-homoadamantyl)phthalimide

• Nikola Cindro,
• Margareta Horvat,
• Kata Mlinarić-Majerski,
• Axel G. Griesbeck and
• Nikola Basarić

Beilstein J. Org. Chem. 2011, 7, 270–277, doi:10.3762/bjoc.7.36

• unreacted 5 was recovered. This finding is in accordance with acetone acting as a triplet sensitizer and the anticipated triplet state reactivity of the phthalimide in the H-abstraction reactions. Furthermore, the addition of H2O as a protic solvent also increased the reactivity of the phthalimide, based on

Synthesis of cationic dibenzosemibullvalene-based phase-transfer catalysts by di-π-methane rearrangements of pyrrolinium-annelated dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 119–126, doi:10.3762/bjoc.7.17

• presence of an appropriate sensitizer, such as acetone or benzophenone, dibenzobarrelene (DBB) rearranges to dibenzosemibullvalene (DBS), whereas the direct excitation leads to dibenzocyclooctene (DBC) through the singlet excited-state (Scheme 1) [4][5][7]. The DPM photorearrangement of dibenzobarrelene

• -sensitizing functionality attached, namely the benzophenone unit. Although in acetone the dibenzobarrelene 2g underwent a DPM rearrangement with full conversion (Scheme 4), the irradiation of 2g in water or acetonitrile solution in the absence of an external sensitizer only induced a relatively low conversion

• separated. Since the covalent attachment of a sensitizer unit to the dibenzobarrelene chromophore did not induce the desired triplet sensitization, the ionic auxiliary strategy [19] was applied to achieve triplet-sensitization in the solid-state, i.e., the sensitizer was introduced as counter anion. For