Topochemical control of the photodimerization of aromatic compounds by γ-cyclodextrin thioethers in aqueous solution

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2013, 9, 1858–1866, doi:10.3762/bjoc.9.217

• complexes with polycyclic aromatics, such as naphthalene, anthracene (ANT), and acenaphthylene (ACE) [25]. In the following we report on the photochemistry of ANT, ACE and coumarin (COU), templated by complexation in several hydrophilic γ-CD thioethers 1–7 (Figure 1 and Figure 2). Special attention will be

• paid to both the quantum yields Φ and stereoselectivities of the photodimerizations. Results and Discussion Photodimerization of anthracene Due to the fact that the inclusion compounds of ANT in native β-CD or γ-CD are completely insoluble in water, only the aqueous photochemistry of hydrophilic ANT

• also favors the formation of the anti dimer. (c) The anti dimer appears to better fit into the γ-CD cavity than the syn isomer, as depicted in Figure 4. Stereoselective photodimerization of coumarin The photochemistry of COU and its derivatives is rather complex because the quantum yield and

[3 + 2]-Cycloadditions of nitrile ylides after photoactivation of vinyl azides under flow conditions

• Stephan Cludius-Brandt,
• Lukas Kupracz and
• Andreas Kirschning

Beilstein J. Org. Chem. 2013, 9, 1745–1750, doi:10.3762/bjoc.9.201

• from the corresponding vinyl azide. Keywords: azirines; cycloaddition; flow chemistry; flow reactors; inductive heating; nitrile ylides; photochemistry; vinyl azides; Introduction Recently, photochemistry has seen a renaissance despite the fact that under batch conditions specialized reaction vessels

• are required, in which the light source is placed in the centre of the reaction mixture: Technically this setup is difficult to control for large scale industrial applications because the issue of transferring a substantial amount of heat has to be addressed. On the other hand, photochemistry allows

• -chemistry laboratories, photochemistry has found a wider interest in the chemical community [17][18]. Particularly large-scale photochemical syntheses can simply be achieved by numbering-up miniaturized flow reactors in a parallel set-up. Uniform irradiation can be guaranteed when the penetration depth of

Thermochemistry and photochemistry of spiroketals derived from indan-2-one: Stepwise processes versus coarctate fragmentations

• Götz Bucher,
• Gernot Heitmann and
• Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1668–1676, doi:10.3762/bjoc.9.191

• ) should be thermochemically activated (Scheme 2) [22]. To test the above hypothesis, we now investigate the thermochemistry and the photochemistry of the ketals 1 and 3, derived from indan-2-one and ethylene glycol, and cis-2-butene-1,4-diol (Scheme 3). The ketal 2, derived from 1,3-propanediol, was

• :1. It is noted, however, that the formation of CO may well be due to photolysis of CO2 due to hard UV radiation (λ = 185 nm) also emitted by the Hg low-pressure lamp used [24]. In contrast to the very clean photochemistry of 1, flash vacuum pyrolysis FVP (T = 870 °C) of 1, followed by trapping of

• . Relative to [CO2] = 1.0, the concentrations of the other pyrolysis products are as follows: [CO] = 27.2, [IN] = 3.8, [ET] = 15.9, [BC] = 11.4, [XY] = 1.3, [AA] = 3.9 [25]. Formaldehyde is formed as a minor product only. The photochemistry of ketals 2 and 3 was investigated as well by matrix isolation

Organotellurium-mediated living radical polymerization under photoirradiation by a low-intensity light-emitting diode

• Yasuyuki Nakamura and
• Shigeru Yamago

Beilstein J. Org. Chem. 2013, 9, 1607–1612, doi:10.3762/bjoc.9.183

• been widely employed in conventional radical polymerization for various applications such as coatings, adhesives, gels and microelectronics [4][5][6][7]. The major motivation for the utilization of photochemistry in LRP is that it enables the dormant species to be activated under mild thermal

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

• solvent reorganization. Keywords: CIDNP; electron transfer; free radicals; kinetics; photochemistry; pyrylium salts; self-exchange; sulfides; Introduction Single-electron transfer is probably the simplest chemical process of an organic molecule, because usually no full bonds are broken or formed. For

New core-pyrene π structure organophotocatalysts usable as highly efficient photoinitiators

• Sofia Telitel,
• Frédéric Dumur,
• Thomas Faury,
• Bernadette Graff,
• Mohamad-Ali Tehfe,
• Didier Gigmes,
• Jean-Pierre Fouassier and
• Jacques Lalevée

Beilstein J. Org. Chem. 2013, 9, 877–890, doi:10.3762/bjoc.9.101

• ; photocatalysts; photoinitiators; radical photopolymerization; Introduction Free radical sources are encountered in various areas such as organic chemistry, biochemistry and polymer chemistry. In the field of polymer photochemistry applied to photopolymerization reactions, they are referred to as photoinitiators

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

• hand, the very structure of electronically excited states makes them both easily oxidized (by donating the electron promoted to an empty orbital) and reduced (an electron is transferred to the low-lying semi-occupied orbital). As a result, redox reactions are quite common in photochemistry and occur

• aromatic compounds known to participate in photosubstitution or photocatalytic alkylation reactions. It was proposed to ascertain whether these may accumulate, as often observed in electrochemistry [33][34] and by pulse radiolysis [35], but rarely in photochemistry. Results The acceptors chosen for this

4-Pyridylnitrene and 2-pyrazinylcarbene

• Curt Wentrup,
• Ales Reisinger and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 754–760, doi:10.3762/bjoc.9.85

• -diazacyclohepta-1,2,4,6-tetraene (20). Further photolysis causes ring opening to the ketenimine 27. Keywords: carbene–nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction The carbene–nitrene interconversion exemplified with

3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

• Curt Wentrup,
• Nguyen Mong Lan,
• Adelheid Lukosch,
• Pawel Bednarek and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 743–753, doi:10.3762/bjoc.9.84

• either the nitrenes or the diazacycloheptatetraenes to nitrile ylides. Keywords: carbene-nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction A multitude of rearrangements of heterocyclic nitrenes have been described

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

A chemist and biologist talk to each other about caged neurotransmitters

• Graham C.R. Ellis-Davies

Beilstein J. Org. Chem. 2013, 9, 64–73, doi:10.3762/bjoc.9.8

• glutamate itself onto neurons [35]. Since these original reports, many other groups have reproduced these results, so they are probably reliable. A recently developed caged glutamate that uses different photochemistry ("RuBi-Glu") is also reported to be inert towards AMPA receptors [33]. This study also

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• Jonathan P. Knowles Luke D. Elliott Kevin I. Booker-Milburn School of Chemistry, University of Bristol, Cantock’s Close, Bristol, BS8 1TS, UK. 10.3762/bjoc.8.229 Abstract Synthetic photochemistry carried out in classic batch reactors has, for over half a century, proved to be a powerful but under

• -utilised technique in general organic synthesis. Recent developments in flow photochemistry have the potential to allow this technique to be applied in a more mainstream setting. This review highlights the use of flow reactors in organic photochemistry, allowing a comparison of the various reactor types to

• be made. Keywords: cycloaddition; flow chemistry; photocatalysis; photochemistry; photooxygenation; Introduction The use of ultraviolet light to carry out bond-forming reactions in synthetic organic chemistry has a long history dating back to the mid-19th century. The observation by Trommsdorff [1

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

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

• the photochirogenic reaction. Keywords: cyclodextrins; 1,3-cyclooctadiene; cyclooctene; nanosponge; photochirogenesis; photoisomerization; Introduction The precise control of chiral photoreactions, or photochirogenesis, is one of the most challenging topics in current photochemistry [1][2][3]. Weak

• intermolecular interactions, short lifetime and high reactivity of the excited-state substrate are the major causes that prevent efficient asymmetric induction in chiral photochemistry. A supramolecular approach to photochirogenesis provides a convenient and also promising tool to facilitate the excited-state

• the product by adding alcohol. The latter result in particular revealed the active roles of chiral voids in CDNS as novel photochirogenic reaction media, encouraging the further application of CDNS to chiral photochemistry. (a) Circular dichroism spectra of 3 (67 μg/mL) (black), 4 (67 μg/mL) (red) and

Photochemistry with laser radiation in condensed phase using miniaturized photoreactors

• Elke Bremus-Köbberling,
• Arnold Gillner,
• Frank Avemaria,
• Céline Réthoré and
• Stefan Bräse

Beilstein J. Org. Chem. 2012, 8, 1213–1218, doi:10.3762/bjoc.8.135

• Toxicology and Genetics, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany 10.3762/bjoc.8.135 Abstract Miniaturized microreactors enable photochemistry with laser irradiation in flow mode to convert azidobiphenyl into carbazole with high efficiency

• alternative method enabled by the maturing microreaction technology and the use of flow chemistry [4][5][6] is the integration of synthesis and screening in one integrated lab-on-a-chip approach [7]. Using this methodology we have integrated photochemistry in a miniaturized reaction setup to enable

• combinatorial flow chemistry in lab-on-a-chip applications. Photochemical processes are in this case particularly interesting because of their enhanced molecular activation [8]. Photochemistry in microreactors is an emerging research area [9], and especially photocatalytic reactions have been investigated in

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

• Rick C. White,
• Benny E. Arney Jr. and
• Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

• Rick C. White Benny E. Arney Jr. Heiko Ihmels Department of Chemistry, Sam Houston State University, Huntsville, TX 77341, USA Department of Chemistry, Universität Siegen, Adolf-Reichwein-Str. 2, 57068 Siegen, Germany 10.3762/bjoc.8.134 Abstract The photochemistry of a phenyl and 1,2-diphenyl

• considered. Keywords: diradicals; mechanisms; photochemistry; Introduction Photoinduced ring-opening or ring-fragmentation processes constitute an important type of reaction in organic photochemistry and have been examined both from a mechanistic and a synthetic point of view [1][2][3][4][5]. Mechanistic

• in the photochemistry of vicinal diaryloxiranes based on the photochemical formation of methyl ethers in methanol solution [8]. Mechanistically, stereoselective oxygen scrambling was found in the photoextrusion of carbon dioxide from benzyl benzoate esters [9]. Furthermore, photodecarboxylation

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• fluorescent dye close to the photoswitch giving rise to a fluorescence change upon isomerization. The introduction of azobenzene-modified biomolecules in zebrafish proved that the photochemistry of azobenzenes was similar in vivo and in vitro, and that appropriate azobenzenes could be stable in vivo for days

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• devices. Many different organic photochromic molecules are known in photochemistry, such as azobenzenes, stilbenes, spiropyranes, fulgides, diarylethenes and chromenes among many others (Figure 1) [16]. The photochromic processes that take place when such compounds are illuminated can be divided in three

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

• Raphael Reuter and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2012, 8, 877–883, doi:10.3762/bjoc.8.99

• , however, only one azobenzene unit is incorporated. One of the reasons is the synthetic challenge associated with the preparation of such oligomers. Solubility and, especially, selectivity issues have to be addressed. Another reason is the higher complexity of the photochemistry of these multi-photochromic

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

• (CQ) in the presence of H-atom donors such as ethers (H abstraction), or more efficiently tertiary amines (electron/proton transfer), is known to be an effective photoinitiator for curing methacrylate-based dental restorative resins [1][2][3][4][5][6][7][8][9]. CQ photochemistry in solution in the

• 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

• literature [31]. The goal of this work was to prepare a more easily accessible racemic MCQ and to compare the photochemistry of MCQ/S with that of low molecular CQ in PS films in the presence of oxygen. Results and Discussion Synthesis of MCQ Racemic MCQ was synthesized in seven steps from (±)-10

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• reaction conditions using the flow reactor allowed minimization of secondary photochemical reactions. Keywords: azepinones; azides; continuous flow; nitrenes; photochemistry; Findings Although photochemical rearrangements are an important class of reactions for heterocycle synthesis [1][2], their use is

Microphotochemistry: 4,4'-Dimethoxybenzophenone mediated photodecarboxylation reactions involving phthalimides

• Oksana Shvydkiv,
• Kieran Nolan and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2011, 7, 1055–1063, doi:10.3762/bjoc.7.121

• superior results thus proving the superiority of microphotochemistry over conventional technologies. Keywords: microflow; microreactor; photochemistry; photodecarboxylation; phthalimide; Introduction Organic photochemistry is a highly successful synthesis method that allows the construction of complex

• molecules with a “flick of a switch” [1][2][3][4]. Light is furthermore considered a clean “reagent” and consequently, photochemistry has contributed extensively to the growing field of Green Chemistry [5][6][7]. It is therefore surprising that synthetic organic photochemistry has been widely neglected by

• the chemical industry. In fact, most photochemical production processes in industry were developed and realized decades ago [8][9][10][11]. A major drawback of photochemistry as a modern research and development (R&D) tool has been the usage of specialized reactors and lamps, which are often

Chemistry in flow systems II

• Andreas Kirschning

Beilstein J. Org. Chem. 2011, 7, 1046–1047, doi:10.3762/bjoc.7.119

• highlight three areas. First of all, we have the application to photochemistry, which has the chance of experiencing a renaissance particularly in an industrial environment. Second, flow chemistry lends itself naturally to the synthesis and direct application of reactive intermediates or reactive reagents

Fine-tuning alkyne cycloadditions: Insights into photochemistry responsible for the double-strand DNA cleavage via structural perturbations in diaryl alkyne conjugates

• Wang-Yong Yang,
• Samantha A. Marrone,
• Nalisha Minors,
• Diego A. R. Zorio and
• Igor V. Alabugin

Beilstein J. Org. Chem. 2011, 7, 813–823, doi:10.3762/bjoc.7.93

• photochemistry open an additional dimension for the control of chemical reactivity by enabling many, otherwise impossible, synthetic transformations, but this mode of activation also provides useful spatial and temporal control of chemical processes that are required to occur in the right place and at the right

• photochemistry is vital for unraveling the mechanistic scenarios that account for DNA cleavage by these compounds (Figure 3) [25]. As illustrated in Figure 3, multiple reaction pathways are potentially unlocked by the photoactivation of alkyne conjugates. In the past, we observed dramatic differences in

• potentially lead to a stronger pH-dependency on the photochemistry of the respective lysine conjugate, which is controlled by the protonation-gated intramolecular electron transfer from the α-amino group [25]. Interestingly, the meta-isomer has a noticeably longer singlet lifetime than the other two isomers

Intraannular photoreactions in pseudo-geminally substituted [2.2]paracyclophanes

• Henning Hopf,
• Vitaly Raev and
• Peter G. Jones

Beilstein J. Org. Chem. 2011, 7, 658–667, doi:10.3762/bjoc.7.78

• crystal lattice locks the relative orientation of the substrate molecules or their photoreactive groups. If the orientation is favorable for reaction, reactivity increases. Unlike photochemistry in homogeneous solution, this often leads to highly selective formation of the photoproducts. Schmidt coined

• experimental elucidation of solid-state photochemistry. This showed that the supramolecular arrangement of molecules in the crystal plays a more important role for reaction control than the simple alignment of double bonds. Long-range molecular movements within crystals upon photochemical reaction and even

• topotactic single-crystal to single-crystal reactions were found, although the latter are rare. The subject has been comprehensively covered by recent reviews [6][7][8]. Reactions of inclusion complexes are a variation of the solid-state photochemistry topic [9]. Here, co-crystals of a host compound and the