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

• active pharmaceutical compounds [33][34][35]. The photolysis of 2-azidobiphenyl (1) with the help of a conventional UV-lamp has been used for the synthesis of carbazole (2) since 1960 (Scheme 1) [36][37][38][39]. However, there are only a few examples of substituted products obtained by this reaction

• -capillaries, bottom: ¼ in. screw connections. Photolysis results in batch setup (flask) with a xenon lamp (400 W, λ > 345 nm). Carbazole synthesis in miniaturized photoreactors Type II (PEEK and Teflon), flow control, P = 0.92 W. Carbazole synthesis in miniaturized photoreactors Type II (PEEK and Teflon

• ), power control, flow 26 mL/h. Test setup with continuously operating, miniaturized photoreactor. The miniaturized photoreactor (PEEK) during photolysis. Synthesis of carbazole (2) by photolysis. Synthesis of arylazides 2 by solid-phase synthesis. Supporting Information Supporting Information File 370

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

• because of its rapid secondary reaction. However, oxiranes have been observed as persistent intermediates under essentially identical conditions during photolysis of cyclic carbonates 1a and 1b, thus it is unlikely that they are formed to a significant extent in the photoreaction of 8. Similarly, we

• products with the methyl groups of the standard. Mass spectrometric data were recorded on photolysates immediately after reactions. Photolysis of cyclic carbonate esters 1a and 1b in acetonitrile. Photoreactivity of styrene glycol sulfite (8). Photochemical pathway for photoextrusion of SO2 from cyclic

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

• )azobenzene (10) revealed very different behaviours. While the azoderivative 4 exhibits a very slow thermal isomerisation, which can be nicely followed by conventional time-resolved absorption spectroscopy, the thermal back reaction of azophenol 10 must be determined by the laser flash-photolysis technique

On the bromination of the dihydroazulene/vinylheptafulvene photo-/thermoswitch

• Virginia Mazzanti,
• Martina Cacciarini,
• Søren L. Broman,
• Christian R. Parker,
• Magnus Schau-Magnussen,
• Andrew D. Bond and
• Mogens B. Nielsen

Beilstein J. Org. Chem. 2012, 8, 958–966, doi:10.3762/bjoc.8.108

• dark. All melting points are uncorrected. All spectroscopic measurements (including photolysis of DHA to VHF and kinetics studies on the thermal conversion of VHF to DHA) were performed in a cuvette of 1 cm path length. Photoswitching experiments were performed by using a 150 W xenon arc lamp equipped

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• was the first to observe norcaradiene (2) directly, by employing low-temperature photolysis, and an activation barrier of 11 ± 2 kcal·mol−1 was determined for the formation of 2 from 1, with the product being 4 kcal·mol−1 less stable [25]. Strong electron-withdrawing groups at the methylene bridge

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• ] or photochemically [8][9][10][11][12][13][14][15][16][17], giving different pyrazole and/or pyrazoline derivatives, depending on the applied dipolarophile (Scheme 1). Namely, sydnones are masked 1,3-dipoles that by photolysis give nitrile imine intermediates, or in thermal reactions react as cyclic

• remaining in the structure [18]. We have been studying photochemical reactions of conjugated heterostilbene derivatives in which the sydnone moiety is part of a heterostilbene [17] (1, Figure 3) or is directly attached at the ortho position to the stilbene 2 [21][22][23]. Upon photolysis of compound 1

• result of competitive photolysis of the sydnone moiety was confirmed on irradiation of 1 in the presence of acrolein and isolation of the pyrazoline derivative (F, Figure 3) [17]. In the case of stilbenylsydnones 2, where the sydnone moiety is directly connected to the ortho position of the stilbene, the

Multistep flow synthesis of vinyl azides and their use in the copper-catalyzed Huisgen-type cycloaddition under inductive-heating conditions

• Lukas Kupracz,
• Jan Hartwig,
• Jens Wegner,
• Sascha Ceylan and
• Andreas Kirschning

Beilstein J. Org. Chem. 2011, 7, 1441–1448, doi:10.3762/bjoc.7.168

• , vinyl azides can be converted into the corresponding 2H-azirines by thermolysis or alternatively by photolysis [5]. The highly reactive azirines can further react as dipolarophiles, dienophiles, electrophiles or nucleophiles [6] thereby accessing oxazoles and isoxazoles [7]. In addition, 2H-azirines

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

• Berlin, Germany 10.3762/bjoc.7.129 Abstract Photolysis of aryl azides to give nitrenes, and their subsequent rearrangement in the presence of water to give 3H-azepinones, is performed in continuous flow in a photoreactor constructed of fluorinated ethylene polymer (FEP) tubing. Fine tuning of the

• simple to achieve by running the reactor over an extended period. Additionally, the precise control of the reaction conditions and the continuous removal of products inherent in flow systems can offer improved yields and selectivities [8][15]. Nitrenes generated by aryl azide photolysis are important

• tools, both for preparative heterocycle synthesis [16][17] and for photoaffinity labeling of proteins [18][19][20]. The photolysis of aryl azide 1 [21], a well-studied and widely used reaction [22][23][24][25][26][27][28][29][30], generates the singlet aryl nitrene intermediate 12 (Scheme 1). Ring

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

• . Photolysis of tetraene 11. Photolysis of trans,trans-dienal 10. Cis–trans-isomerizations of the double bonds of the pseudo-geminal cyclophanes 11 and 19. Preparation of the vinylcyclopropanes 22–24. Crystallographic data for compounds 13, 15, (Z,Z)-22, 23 and 24.

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• proposed that the benzoxepine structure is achieved via a pseudo-Paternò–Büchi pathway (Scheme 39), while the dihydrobenzofurans arise from a Norrish-type II reaction and cyclization. Griesbeck supports his proposed mechanism by flash laser photolysis, where a long lived (some seconds) intermediate with an

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

• photophysical and photochemical properties of N-phthaloylvaline methyl ester (1) have been studied by nanosecond laser flash photolysis (λexc = 248 or 308 nm) [5]. The quantum yield of fluorescence is low (ФF = 10−2), whereas that of phosphorescence at −196 °C is large (0.5). The triplet properties of 1 at room

• 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

• from tyrosine and histidine 8 and 9, respectively, were photochemically active and gave decarboxylation and cleavage products. In contrast to photolysis in pure acetone [10], irradiation of the tyrosine substrate 8 in basic water/acetone resulted solely in the decarboxylation product 11. Under

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

• (804.7): C, 53.73; H, 3.01; N, 6.96; S, 7.97. Found: C, 53.58; H, 2.79; N, 6.84; S, 7.97. General procedure for the synthetic photolysis in solution (GP2): Solutions of the substrate (10−3–10−2 mol/l) were placed in a Duran flask (acetone) or quartz test tube (other solvents), and argon gas was bubbled

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

• % yield. Products 7 decomposed on prolonged irradiation. The photochemical reaction was more efficient in solvent system containing acetone rather than CH3CN. After 18 h irradiation in acetone–H2O, complete conversion of 5 was achieved, whereas under the same photolysis conditions in CH3CN–H2O, 72% of

• the conversion of the starting material under the same irradiation conditions. Thus, after 1 h photolysis of 5 in acetone, only 5% of 5 was converted to products, whereas after photolysis in acetone–H2O, a 60% conversion was achieved. This suggests that phthalimide in the triplet excited state, in a

• procedure for semi-preparative photolysis of N-(4-homoadamantyl)phthalimide (5) Phthalimide 5 (10 mg, 0.034 mmol) was dissolved in 20 mL of the appropriate solvent, CH3CN, CH3CN–H2O (3:1), acetone or acetone–H2O (3:1) in a quartz cuvette. The solutions were purged with N2 for 20 min and irradiated in a

Reciprocal polyhedra and the Euler relationship: cage hydrocarbons, C_nH_n and closo-boranes [B_xH_x]²⁻

• Michael J. McGlinchey and
• Henning Hopf

Beilstein J. Org. Chem. 2011, 7, 222–233, doi:10.3762/bjoc.7.30

• derivative of this simplest of the Platonic bodies by photolysis of tetra-tert-butylcyclopentadienone, (17). As depicted in Scheme 1, the initial "criss-cross" product, 18, eventually loses CO to yield 19, as a stable crystalline material [9]. Presumably, in addition to the unfavorable electronic factors

• substituents (e.g., t-Bu, CF3, Ph; 20) have been available for more than three decades via photolysis of sterically encumbered benzenes [10]. The marked deviation from planarity in these systems favors the formation of Dewar benzenes, 21, which undergo [2 + 2] cycloadditions to produce the prismane skeleton

• , 22, (Scheme 2). However, the parent prismane, 9, proved much more elusive and was finally obtained in 2% yield by treatment of benzvalene, (23), with N-phenyltriazolindione, (24), to give cycloadduct 25; conversion to the azo compound 26 and photolysis to extrude nitrogen finally led to 9 [11

Photocycloaddition of aromatic and aliphatic aldehydes to isoxazoles: Cycloaddition reactivity and stability studies

• Axel G. Griesbeck,
• Marco Franke,
• Jörg Neudörfl and
• Hidehiro Kotaka

Beilstein J. Org. Chem. 2011, 7, 127–134, doi:10.3762/bjoc.7.18

• ]. Surprisingly, in the absence of aldehydes as the potential reaction partners, the conversions of 7f–h were significantly lower, suggesting the possibility of an energy transfer from the excited singlet or triplet aldehyde to the isoxazole. Since the photolysis of 7d and 7e in presence of benzaldehyde showed

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

• resin. The photolysis of the cationic dibenzobarrelene derivatives 2a–d, which bear two identical N-alkyl substituents, was carried out in acetone solutions (λ > 310 nm), and the conversion of the dibenzobarrelene was monitored by 1H NMR spectroscopy. The dibenzosemibullvalene derivatives 3a–d were

• -reaction during the direct photolysis of compounds 2a–d, leading to the formation of complex reaction mixtures. The triplet-sensitized photoreaction of the dibenzobarrelene derivatives 2e,f, which carry two different alkyl substituents at the quaternary pyrrolidinium, gave two isomeric

• ). Synthesis of dibenzosemibullvalene derivatives General procedure for the photolysis in solution (GP-2): Solutions of the substrates (10−2 to 10−3 mol/l) were placed in a 200 ml Duran flask (acetone) or a quartz test tube (other solvents), and argon gas was bubbled through the solution for at least 20 min

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

• Feng-Feng Kong,
• Jian-Bo Wang and
• Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

• . Photoproducts 2 and 3 have no significant absorption for light at above 290 nm. Hence, a secondary photolysis of the oxetane products (2 or 3) should not occur unless there is prolonged irradiation. Compositions in photoreaction mixture were quantified by 1H NMR spectroscopy (300 MHz) directly on the crude

Olefin metathesis in nano-sized systems

• Didier Astruc,
• Abdou K. Diallo,
• Sylvain Gatard,
• Liyuan Liang,
• Cátia Ornelas,
• Victor Martinez,
• Denise Méry and
• Jaime Ruiz

Beilstein J. Org. Chem. 2011, 7, 94–103, doi:10.3762/bjoc.7.13

• produced after decomplexation by visible-light photolysis which removes the temporary activating CpFe+ group [36][37][38]. These compounds are then ideal substrates for RCM and CM. New structures were obtained using this strategy with durene, p-xylene, mesitylene, and pentamethylcobalticinium [39][40][41

Light-induced olefin metathesis

• Yuval Vidavsky and
• N. Gabriel Lemcoff

Beilstein J. Org. Chem. 2010, 6, 1106–1119, doi:10.3762/bjoc.6.127

• conclusions were: a: W(CO)5 and CO are created by photolysis of W(CO)6. The reactivity of W(CO)5 was found to be solvent dependent. b: The intensity of irradiation, and the concentrations of both olefin and catalyst had a significant effect on reaction yields. c: The RCH=CCl2 produced in the reaction was a

The efficient synthesis of dibenzo[d,d′]benzo[1,2-b:4,3-b′]dithiophene and cyclopenta[1,2-b:4,3-b′]bis(benzo[d]thiophen)-6-one

• Zhihua Wang,
• Sheng Zhu,
• Jianwu Shi and
• Hua Wang

Beilstein J. Org. Chem. 2009, 5, No. 55, doi:10.3762/bjoc.5.55

• photolysis of RCH(SPh)2 (R = benzo[b]thiophene). However, a non-photochemical method for preparing 1 has, to the best of our knowledge, not been reported. In our work, with 3,3′-bis[benzo[b]thiophenyl] (3) [18] as starting material, 1 (see Figure 1) was synthesized efficiently via formylation and McMurry

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• -scale from −1 ps to 1 ps and the logarithmic scale thereafter. a) Two-dimensional overview plot of the transient absorbance changes in false colour coding. a.u. = arbitrary units. b) Temporal behaviour of the absorbance changes at a detection wavelength of 470 nm. c) Results from laser-flash photolysis

Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl)paracyclophane – an inverse photochromic system. (Photoactive cyclophanes 5)

• Henning Hopf,
• Christian Beck,
• Jean-Pierre Desvergne,
• Henri Bouas-Laurent,
• Peter G. Jones and
• Ludger Ernst

Beilstein J. Org. Chem. 2009, 5, No. 20, doi:10.3762/bjoc.5.20

• for MCH solution in Figure 9. One observes a drop of 50% absorbance after 8 cycles for MCH and 5 cycles for CH3CN (not shown). The photolysis at 306 nm must involve one or several photoreactions leading to products transparent at 392 nm. Thermal dissociation (a retro Diels-Alder reaction, see below

Diastereoselective and enantioselective reduction of tetralin- 1,4-dione

• E. Peter Kündig and
• Alvaro Enriquez-Garcia

Beilstein J. Org. Chem. 2008, 4, No. 37, doi:10.3762/bjoc.4.37

• % conversion) [6], and by photolysis of the Dewar benzene 5 at low temperature in a solid matrix [7] (Scheme 2). While dione 2 is readily synthesized, it remains a chemically unexplored curiosity. This simple molecule, and its π-metal complexes, drew our attention and interest for their potential in synthesis

Synthesis of spiropyrans: H-abstractions in 3-cycloalkenyloxybenzopyrans

• Satish C. Gupta,
• Mandeep Thakur,
• Somesh Sharma,
• Urmila Berar,
• Surinder Berar and
• Ramesh C. Kamboj

Beilstein J. Org. Chem. 2007, 3, No. 14, doi:10.1186/1860-5397-3-14

• cleavage. Synthesis of 3-Cycloalkenyloxybenzopyrans. Photolysis of 6-chloro-3-(1"-cyclohept-2"-enyloxy)-2-(2'-furyl)-4-oxo-4H-1-benzopyran. Photolysis of 6-chloro-3-(1"-cycloalk-2"-enyloxy)-2-[2'-(5-methylfuryl)]-4-oxo-4H-1-benzopyrans. Mechanism of product formation from 3-Cycloalkenyloxybenzopyrans by

• photolysis. Supporting Information Supporting Information File 14: Experimental Data. The data provided represents the yield, melting point, IR, 1H NMR and elemental analysis of the compounds. Acknowledgements We thank UGC, New Delhi for generous financial support for this work.