High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

• Sergei V. Chapyshev,
• Denis V. Korchagin,
• Patrik Neuhaus and
• Wolfram Sander

Beilstein J. Org. Chem. 2013, 9, 733–742, doi:10.3762/bjoc.9.83

• of the pyridine ring to give triplet mononitrenes 12 and 13 as the primary photoproducts. On further irradiation, quintet dinitrenes 15 and 16 and septet trinitrene 18 are formed. The maximum yield of the latter is about just 2%. Preferential photodissociation of the azido groups located in ortho

• triplet nitrenes 12–14 at the PBE/DZ level of theory. UB3LYP/6-311+G* orbital density in the LUMO of triazide 11 and CIS/6-311+G* orbital density in the highest singly occupied orbital of excited state 11a-S1*. Examples of selective photolysis of the azido groups. Possible photoproducts of triazide 11

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

• fact we could only find two references describing photoreactions involving bisallenes. Thus, irradiation of the epoxide 197 in benzene-d6 (NMR experiment) yielded a plethora of photoproducts, among them two photodimers to which structure 198 was assigned by spectroscopic measurements (Scheme 47) [136

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

• of cyclic carbonate esters such as 1b, as evidenced by the interception with appropriate trapping reagents; whereas the formation of persistent primary photoproducts has not been observed [13]. In contrast, we have found that under significantly milder photochemical conditions (3 h versus 15 h), the

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

• transformation, an analogous study with low molecular CQ doped in a PS matrix was first performed. Elucidation of the structures of low molecular photoproducts was conveniently followed by spectral methods [22] and by isolation from the polymer matrix followed by spectral identification [21]. The results of the

•  3 according to the low molecular study [21] were formed to a much lesser extent. Since the phototransformation of CQ to 11 is not quantitative, n + m = 99.7; the remaining 0.3 consists of cyclopentenoic acids 14 and other unknown photoproducts. The increase of the molecular weight of MCQ/S during

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

• ). The structure of the photoproducts was determined by spectroscopic methods. The molecular ions of 11 and 12, m/z 248 in the mass spectra, indicate that the structures have lost CO2 relative to the starting compound. In the 1H and 13C NMR spectra, the signals are found in an area which is

• spectra. Nevertheless, the proton H-5 of the fused benzene ring in structure 12 is in the multiplet together with other aromatic protons, which is in accordance with the proposed structure. The structure of the photoproducts was confirmed by an additional experiment on the crude reaction mixture with DDQ

• mixture of 11 and 12 along with decomposition and high-molecular-weight products. On shorter irradiation time (10 min, in benzene or acetonitrile) 3a (trans isomer) afforded, according to 1H NMR, the photomixture of predominantly 3b (cis isomer) with only traces of starting 3a and tricyclic photoproducts

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

• addition of 11 to 2. Technical details of the two reactor types. Energy efficiencies of the two reactor types. Supporting Information Supporting Information contains full experimental procedures and NMR data of all photoproducts. Supporting Information File 232: Full experimental details and NMR data

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

• any detectable photoproducts. The success in preparing cyclobutane derivative 4 (n = 1) from the corresponding cinnamophane diester 3 (n = 1, quantitative yield) led us to attempt to prepare the corresponding cyclobutane dialdehyde derivative 16 (Scheme 6). Unfortunately, although this was the only

• paracyclophanes not be observed, this would not necessarily constitute a proof against diradical(oid) intermediates in these reactions. However, if derivatives such as 21 were among the photoproducts the involvement of radicals in the photoisomerizations would be indicated. We therefore reacted the bis-aldehyde 9

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

• , enantiomerically pure amine by salt formation. An optically active salt is obtained, which consequently crystallizes in a chiral space group. The irradiation of these salts in the solid-state leads to enantiomerically enriched photoproducts. This approach has been successfully applied to the carboxy-substituted

• of the reaction mixture. Instead, 1H NMR spectroscopic analysis revealed slow decomposition of the dibenzobarrelene derivative 1i upon irradiation with no formation of distinct photoproducts. In contrast, the irradiation of compound 1i in the presence of 2 molar equiv of either tetrabutylammonium

• with chiral mandelate, camphorsulfonate and binaphthyl phosphonate in a variety of solvents including acetone, acetonitrile, ethyl acetate, dichloromethane, and benzene. Although the DPM rearrangement of the dibenzobarrelene 1i took place readily upon irradiation and the semibullvalene photoproducts

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

• activity [53][54][55]. Thus, photoproducts derived from 5 may also exhibit antiviral activity, although that is yet to be substantiated. Results and Discussion The synthesis of homoadamantylphthalimide 5 started from homoadamantanone 3 which is easily prepared by the ring enlargement of adamantanone with

• major product. For example, when the irradiation was performed in acetone–H2O for 4 h (see the Experimental), the ratio of the isolated starting phthalimide 5 and the photoproducts 6 and 7 was 10:8:6. However, prolonged irradiation in acetone–H2O (18 h) gave only alcohol 6 which was isolated in 53

• phthalimide [54][62][63]. The structures of photoproducts was determined by spectroscopic methods. In the 1H NMR spectrum of 6, in the aromatic region, 4 well-resolved signals are present, indicating the loss of symmetry of the aromatic part of the molecule (compared to the symmetry in 5). Similarly, in the

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

• Junya Arimura,
• Tsutomu Mizuta,
• Yoshikazu Hiraga and
• Manabu Abe

Beilstein J. Org. Chem. 2011, 7, 265–269, doi:10.3762/bjoc.7.35

• 1a was increased; however, no concentration effect was observed (entry 2). Under the reaction conditions, the formation of polymeric products increased as evidenced by 1H NMR analysis of the photolysate. Even with low concentrations of 1a (entry 3), the intramolecular photoproducts A and B were not

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

• -controlled formation of the corresponding triplet 1,4-biradical and high stereocontrol due to SOC-controlled crossing from the triplet to the singlet surface [4][5]. Reaction behavior of the photoproducts 9a–c All bicyclic oxetanes obtained in the analytical photochemical experiments as well as in

• preparative studies (i.e., 9a–c) were acid labile and decomposed already in the presence of catalytic amounts of acid to give solely the starting materials. The photoproducts are also thermally labile and decompose at temperatures above approximately 100 °C, again to give solely the starting materials. Thus

• 6.09. Colorless needles, unit cell parameters: a = 13.3045(8), b = 6.9356(6), c = 17.5348(10), β = 129.284(3), space group P21/c. Structures of the photoproducts 9a–9c in the crystal. Synthetic routes to isoxazoles 7a–7e. Synthetic routes to isoxazoles 7f–7h. Benzaldehyde photocycloaddition to 7a–7e

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

• isolated by crystallization directly from the photolysate in 67–85% yield. The photoproducts were identified and characterized by 1H NMR and 13C NMR spectroscopy, mass spectrometry, and elemental analyses. The dibenzosemibullvalene structure of the photoproducts 3a–d was confirmed by 1H NMR spectroscopy

• : 4.17, 4.91; 3fI: 4.31, 5.05 ppm; 3fII: 4.20, 5.02, in CDCl3). After column chromatography and subsequent recrystallization, the major photoproducts 3eI and 3fI were isolated in low yields (15% and 18%). The relative configuration of the ammonium functionality was deduced from NOE experiments

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

• significantly. According to our understanding of these oxetanes [10], this low efficiency was considered to be due to poor stability of the photoproducts, in particular oxetanes 3. To verify this speculation, the yield and the regioselectivity were tracked over an irradiation time of 15 min for the DMT-1e (5 mM

• experimental error of 5%. According to our understanding of the stability of oxetanes, 3 are less stable than 2. The constant ratio of 2/3 implies that no significant decomposition of the photoproduct oxetanes occurs in the photochemical reaction. In other words, the stability of photoproducts in the systems

• . 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

Anthracene functionalized terpyridines – synthesis and properties

• Falk Wehmeier and
• Jochen Mattay

Beilstein J. Org. Chem. 2010, 6, No. 54, doi:10.3762/bjoc.6.54

• establishing the identity of the photoproducts from 5a and 5b after UV irradiation. 1H NMR-spectra of the irradiation products (after evaporation of solvent) indicate that there is more than one reaction pathway, the number and overlapping of peaks (especially in the aromatic region) made assignments

• . Conclusion Whilst the synthesis of the target molecules 5a and 5b and their iron(II)-complexes (6a–b) was successful, investigations regarding their photochemistry were unsatisfactory: Apparently, the anthryl moieties do not undergo the desired [4 + 4]-cycloaddition reaction and the photoproducts could not

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

• of conjugated systems [10][11][12][13][14][15][16][17] and may be interesting for information storage materials because the photoproducts can be operated in visible light. Inverse photochromism was recently observed for some vinylogs of cinnamophanes [18][19], such as compound 1 (Figure 2). Several

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

• produced two products 5c and 6c along with some 3. 3. Discussion The structures of the photoproducts 5c and 6c were consistent with their spectral parameters [see Supporting Information File 1]; both the spiropyrans exhibited the presence of ions at m/z 155 and m/z 202 values in their mass spectra; these

• yielded 7a, 7b, 7c only and no photoproducts similar to 5 (R = CH3) could be isolated although the 1H NMR of the crude photolysate of 2b did show the presence of 5b (R = CH3) in small proportions. These photoconversions of the cycloalkenyloxy chromones (1a, 1b, 1c, 1d, 2a, 2b and 2c) to pyronospiropyrans

• ), followed by 1,5-H migration in 8a. [21] The spiropyrans 6 (R = H) bearing cyclopropanes are the secondary photoproducts formed as a result of the further reorganization of 5 (R = H), through a ring contraction-ring expansion mechanism. [22][23] The formation of acetylcyclopropane compound 7 (R = CH3) from

Photosonochemical catalytic ring opening of α-epoxyketones

• Hamid R. Memarian and
• Ali Saffar-Teluri

Beilstein J. Org. Chem. 2007, 3, No. 2, doi:10.1186/1860-5397-3-2

• of photocatalytic ring opening of α-epoxyketones 1b, 1d and 1f, the same substituents on the phenyl ring of the benzoyl group (1c and 1e) have a smaller effect. In the cases of 1b and 1d, the ratios of the diastereomeric photoproducts are inversed. We have proposed the involvement of three different

• photoproducts 3a-f and 4a-f (hydrogen located on C-2) shows exactly the ratios of diastereomeric products and is provided [see Supporting Information File 1]. Concerning the effect of ultrasound on the rate of ring opening of α-epoxyketones, we propose that increasing the rate of reaction is caused by efficient

• -f, the ratios of diastereomeric photoproducts have not been changed too much using ultrasound irradiation. In order to explain the results obtained, we have compared the results of the semi-empirical PM3 calculations on the complexes of 1a-f + 2 in the ground state with those of α-epoxyketones 1a-f