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

• , 13C, HSQC and NOEDIFF) and mass spectrometry analysis, including high-resolution measurements. Because of the rigidity of the steroidal skeleton, NOE experiments were necessary to assign the stereochemistry of the new chiral centers generated upon photocyclization. In both photoproducts, the most

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

• lamp in deuteriochloroform. The only process that we could observe was a “polymerization” reaction, which slowly destroyed the substrate. Likewise, no photocyclization to the divinylcyclobutene derivate 51 was noted. [2 + 2] Photodimerizations of olefins have often been described, whether in solution

Design and synthesis of novel bis-annulated caged polycycles via ring-closing metathesis: pushpakenediol

• Sambasivarao Kotha and
• Mirtunjay Kumar Dipak

Beilstein J. Org. Chem. 2014, 10, 2664–2670, doi:10.3762/bjoc.10.280

• be correct, when we found that the DA adduct undergoes a smooth [2 + 2] photocyclization [31] upon exposure to UV light to generate caged dione 20 in good yield (80%). The structure of the photoadduct was assigned as 1,9-diallyl PCUD 20 on the basis of the spectral data (Scheme 2). Having prepared

Selenium halide-induced bridge formation in [2.2]paracyclophanes

• Laura G. Sarbu,
• Henning Hopf,
• Peter G. Jones and
• Lucian M. Birsa

Beilstein J. Org. Chem. 2014, 10, 2550–2555, doi:10.3762/bjoc.10.266

• intramolecular photocyclization, yielding the corresponding ladderane isomers [9][10][11]. The ethynyl group is well known for its ability to undergo coupling reactions, making the pseudo-geminal bis(acetylene) 1 and its derivatives good candidates for building molecular scaffolding [12][13]. The reaction

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

• Dae Won Cho,
• Patrick S. Mariano and
• Ung Chan Yoon

Beilstein J. Org. Chem. 2014, 10, 514–527, doi:10.3762/bjoc.10.47

• combined observations made in these investigations demonstrate the unique features of SET-promoted photocyclization reactions that make them well-suited for the use in the synthesis of functionalized crown ethers. In addition, while some limitations exist for the general use of SET-photochemical reactions

• in large-scale organic synthesis, important characteristics of the photoinduced macrocyclization reactions make them applicable to unique situations in which high temporal and spatial control is required. Keywords: lariat-type crown ethers; SET-promoted photocyclization; α-silylether-terminated

• efficient fashion. Previous studies [31][32][33][34][62][63][64][65][66][67] in our laboratories resulted in the development, mechanistic elucidation, and synthetic application of various kinds of SET-promoted photocyclization reactions of α-trialkylsilyl donor-linked imide acceptor systems and led to an

Total synthesis of (+)-grandiamide D, dasyclamide and gigantamide A from a Baylis–Hillman adduct: A unified biomimetic approach

• Andivelu Ilangovan and
• Shanmugasundar Saravanakumar

Beilstein J. Org. Chem. 2014, 10, 127–133, doi:10.3762/bjoc.10.9

• photocyclization [22], intramolecular cyclization of the aldehyde 27 was considered for the preparation of gigantamide A (7). The aldehyde 27 in turn could be prepared from dasyclamide (6). Conditions and results for the oxidation of dasyclamide (6) to give gigantamide A (7) are outlined in Table 1. The results

A combined continuous microflow photochemistry and asymmetric organocatalysis approach for the enantioselective synthesis of tetrahydroquinolines

• Erli Sugiono and
• Magnus Rueping

Beilstein J. Org. Chem. 2013, 9, 2457–2462, doi:10.3762/bjoc.9.284

• Erli Sugiono Magnus Rueping Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany 10.3762/bjoc.9.284 Abstract A continuous-flow asymmetric organocatalytic photocyclization–transfer hydrogenation cascade reaction has been developed. The new protocol allows

• optically active tetrahydroquinolines. Readily available substituted 2-aminochalcones were envisioned to undergo photocyclization to the corresponding quinolines which in the presence of a chiral BINOL-derived phosphoric acid diester and Hantzsch dihydropyridine as hydride donor [32][33][34][35][36][37

• programmable syringe pump. The product solution was collected in a flask wrapped with aluminium foil to prevent further irradiation. Our initial investigation of reaction conditions involved the photocyclization–reduction cascade of 2-aminochalcone 1a in the presence of Hantzsch dihydropyridine 4 as hydrogen

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

• Quentin Lefebvre Marc Jentsch Magnus Rueping Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany 10.3762/bjoc.9.221 Abstract A continuous flow oxidative photocyclization of stilbene derivatives has been developed which allows the scalable synthesis of

• backbone functionalized phenanthrenes and helicenes of various sizes in good yields. Keywords: continuous-flow reactor; flow chemistry; helicenes; light-driven cyclization reaction; photocyclization; stilbenes; Introduction Phenanthrenes are versatile intermediates toward polycyclic aromatic hydrocarbons

• of scalable and flexible syntheses [1][2][3][4][5]. Following the pioneering examples of Scholz [6] and Martin [7] in 1967, the photocyclization of stilbene derivatives under UV-light irradiation is now a classical method for the synthesis of phenanthrenes and helicene-like molecules [8]. However

Cyclization of substitued 2-(2-fluorophenylazo)azines to azino[1,2-c]benzo[d][1,2,4]triazinium derivatives

• Aleksandra Jankowiak,
• Emilia Obijalska and
• Piotr Kaszynski

Beilstein J. Org. Chem. 2013, 9, 1873–1880, doi:10.3762/bjoc.9.219

• experimental results are augmented with DFT computational results. Results and Discussion Cyclization and cation formation Salts 1 were prepared by photocyclization of the corresponding azo derivatives 4 in the presence of Ca2+ ions in aqueous MeCN (Scheme 1). Diazenes 4 show weak absorption bands in the

• ]. Interestingly, the trifluoro derivative 4d had exceptionally limited thermal stability: After heating at 60 °C in CDCl3 it was converted to another species also containing the picoline fragment, according to the 1H NMR analysis. The new compound did not undergo photocyclization and was not analyzed further

• MHz (1H) and 100 MHz (13C) in CD3CN, DMSO-d6 or CDCl3 and chemical shifts are refered to the solvent peaks (1.96, 2.54 and 7.26 ppm, respectively). Photocyclization and preparation of salts 1. General Porcedure Method A [7]: Azo compound 4 (1.0 mmol) and calcium p-toluenesulfonate (190 mg 0.5 mmol) or

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

• possible to cycle many times between these two intermediates (Figure 2 and Figure 3), but eventually signal intensity was lost, probably because another reaction, the cyclization to the isocarbazole 49, took place. This reaction is analogous to the photocyclization of o-biphenylylnitrene to isocarbazole

The effect of the formyl group position upon asymmetric isomeric diarylethenes bearing a naphthalene moiety

• Renjie Wang,
• Shouzhi Pu,
• Gang Liu and
• Shiqiang Cui

Beilstein J. Org. Chem. 2012, 8, 1018–1026, doi:10.3762/bjoc.8.114

• photocyclization reaction yielded the nonfluorescent closed-ring isomers 1c–3c, resulting in a decrease in emission intensity as compared to the open-ring isomers 1o–3o. The back irradiation by visible light of appropriate wavelength (λ > 500 nm) regenerated the open-ring isomers 1o–3o, and recovered their

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• prepare anilinopyridines, with final indole ring closure occurring by either a second cross-coupling [45] or a photocyclization [46]. The former, sequential cross-coupling strategy closely follows the previous work by Queguiner [47]. A Fischer indole synthesis route through the 2-pyridylhydrazone of

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

• upon the addition of a drop of water suggest that benzoxazines are also the intermediate products in our case but are rapidly hydrolyzed during work-up and purification. Although one can suggest the intermediacy of the triplet diradical in the photocyclization of o-amido acetylene 6, this

• (Figure 8c). Only glycerol at pH 6 and glycerol and DMSO at pH 8 showed ~10% of protection. Little effect was observed for NaN3, suggesting that the formation of singlet oxygen via triplet energy transfer is inefficient, possibly because of a short triplet lifetime and fast intramolecular photocyclization

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

• prepare the biscyclopropane analog of 11, the bisvinylcyclopropane 19 (or one of its cis-isomers) and subject this presumably strained hydrocarbon to our photocyclization conditions. Of course, this system also has various options to react, among them the photoisomerization to a mono- or all-cis

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

• resulting in regio- or stereoselective product formation. Indeed, this approach has been employed to carry out stereoselective photoreactions, for example [2 + 2] cycloaddition [4], [4 + 4] photocycloaddition [5], Norrish–Yang cyclization [6], and [6π] photocyclization [7]. Asymmetric photoreactions have

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

• been proposed that an intermediate in the synthesis of [5]peristylane may be a viable precursor to the still unknown D3h [43.56]nonahedrane, (13). As shown in Scheme 12, the diene-dione 63 can be readily converted to the double enone 64 which undergoes [2 + 2] photocyclization to yield the pentacyclic

A perfluorocyclopentene based diarylethene bearing two terpyridine moieties – synthesis, photochemical properties and influence of transition metal ions

• Falk Wehmeier and
• Jochen Mattay

Beilstein J. Org. Chem. 2010, 6, No. 53, doi:10.3762/bjoc.6.53

• expected signals (see Experimental Section and Supporting Information File 1). Photochromism of the free ligand The obtained terpyridine substituted diarylethene 10a shows the anticipated photochromic behavior, undergoing photocyclization under irradiation with UV-light (Scheme 4). Figure 1 shows the

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

• (1), an interesting [5]heterohelicene, has not received much attention during the last decade because of a lack of efficient synthesis, which limits its application in material science. Photocyclization is normally employed for preparing heterohelicenes with 1,2-diaryl ethenes as precursors. Wynberg

• et al. [15] reported the synthesis of 1 in 57% yield by the photocyclization of 1,2-di(2-benzo[b]thienyl)ethene in benzene. Kudo et al. [16] improved the preparative yield of 1 up to 85% with the same precursor in the same way. Sugimoto et al. [17] reported the preparation of 1 in 19% yield via the