A Novel dioxano-annellated benzofuroxan

Oxidation of 6-amino-7-nitro-1,4-benzodioxane using alkaline hypochlorite affords 1,4-benzo-dioxano[6,7-c]furoxan in a very good yield. Pyrolysis of 6-azido-7-nitro-1,4-benzodioxane failed to give the same product. The structure of the new furoxan is confirmed by the spectra.     

Photoelectron spectral study of the thermolysis of benzofuroxan

Photoelectron spectroscopy data have shown that thermolysis of benzofuroxan vaporin vacuo results in thermal abstraction of the exocyclic oxygen to afford a nonvolatile product, which decomposes to give nitrogen monoxide, carbon monoxide, and carbon dioxide.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2238–2240, December, 1994.     

Photoreaction of nitrobenzenes with hydrobromic acid

Nitrobenzene and three of its derivatives (3-CO₂H, 3-OH, and 4-OH) react efficiently when irradiated (λ >340 nm) in concentrated hydrobromic acid typically to give high yields of 2,4,6-tribromoanilines. The quantum yield (Φ = 0.16 for nitrobenzene) is not changed appreciably by the electron withdrawing carboxy substituent, but is lowered by the electron donating hydroxy substituent. The reactivity suggests that electron transfer from bromide ion to the n,π* triplet is the primary process.     

13C NMR spectra of benzofuroxan and related compounds

The ¹³C n.m.r. spectrum of benzofuroxan at ?15°C is assigned on the basis of selective decoupling experiments and by comparison with the ¹³C chemical shifts of model compounds. The ¹³C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the ¹³C spectrum of benzofuroxan in CDCl₃, a barrier of 14·0 ± 0·2 kcal mol^?1 is obtained for the degenerate tautomerism in this compound.     

An Unusual Photoreaction of 3,4-Di-O-benzyl-hypericin

 Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct led to an activated oxygen species which then attacked the proton sponge.     

An Unusual Photoreaction of 3,4-Di-O-benzyl-hypericin

Summary.  Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct led to an activated oxygen species which then attacked the proton sponge. Received July 17, 2000. Accepted July 20, 2000     

Synthesis and Photoreaction of 5-Aikenyloxypsoralen Derivatives

Abstract— In order to investigate the intramolecular "quenching" of the photoexcitation of some 5-alkenyloxypsoralen derivatives, we have prepared model compounds in which a psoralen moiety was linked at position 5 to a terminal double bond via a polymethylenic chain of various length (n = 2-9). The isolation and characterization of photocycloadducts obtained for each compound after irradiation at 365 nm in a polar solvent was performed. The results on the photoreactivity of this series of compounds show that the 3,4-pyrone double bond of 5-alkoxypsoralens is the most reactive. Four kinds of intramolecular photocycloadducts between the 3,4-pyrone double bond and the chain unsaturation were obtained according to the length of the linking chain: cis-syn, trans-syn, cis-anti and trans-anti. Their structures were established by a combination of ¹H and ¹³C NMR and fully assigned by ^lH NOE (nuclear Overhauser effect) and ¹H-¹³C HMQC (heteronuclear multiquantum correlation) spectroscopies. No traces of 4',5' adducts were detected.     

Photoreaction of pyrido[2,3-c]furoxan

When pyrido[2,3-c]furoxan 4 was irradiated in acetonitrile containing a little water with a low pressure mercury lamp, 3-nitro-2-pyridone 5 was obtained. When compound 4 was irradiated in the presence of morpholine with a low pressure mercury lamp in an argon atmosphere, 6-morpholinopyridine 2,3-dioxime 6 , 6-morpholinopyrido[2,3-c]furazan 7 , 3-amino-6-morpholino-2-nitropyridine 8 , and 3-amino-4,6-dimorpholino-2-nitropyridine 9 was produced. The results of photoreaction study indicated the only photo-product to be compound 6 . The main difference between these two reactions may be considered due to the behavior of nitrogen in the pyridine ring.     

L-缬氨酸旋光异构的两种光反应可能途径

利用密度泛函理论(DFT)和从头算分子轨道理论对L-缬氨酸的旋光异构光反应机理进行了研究. 分别用B3LYP和MP2方法在6-311++G(d, p)基组级别上全优化得到了S₀和T₁态反应路径上的反应物、产物、中间体以及过渡态结构的几何构型, 给出了反应能垒, 利用含时密度泛函理论(TD-DFT)中的B3LYP/6-311++G(d, p)方法优化得到了S₁态反应路径上的平衡态几何构型. 通过分析反应途径上各个驻点的几何构型特征, 确定了L-缬氨酸在激发态可能通过手性碳上的氢原子以羰基氧或氨基氮为中转媒介发生质子迁移来完成旋光异构反应. 进一步用自洽反应场理论中的极化连续模型(PCM)方法探讨了溶剂化效应对旋光异构反应机理的影响.     

Photoreaction between benzoylthiophenes and N-BOC-tryptophan methyl ester

Drug-induced photoallergy requires as the first step formation of covalent drug-protein photoadducts. One of the key amino acids involved in this process is tryptophan (Trp). In this context, several diaryl ketones, including 2-benzoylthiophene (BT), [2-(5-benzoyl-5-thienyl)]-2-methylpropanoic methyl ester (TPA methyl ester) and 4-(2-thienylcarbonyl)phenyl]-2-methylpropanoic methyl ester (SUP methyl ester) have been irradiated in the presence of N-BOC-(L)-tryptophan methyl ester. Laser flash photolysis has allowed to detect three neutral radicals (ketyl, indolyl and skatolyl radicals) resulting from formal hydrogen-atom abstraction. This correlates well with the isolation of homodimers, as well as with cross-coupling products, in the preparative irradiation. The main cross-coupling products were in all cases lactones arising from the reaction of the Trp-derived skatolyl radicals with the corresponding ketyl radicals. These lactones were obtained as the (4R) stereoisomers with remarkable diasteroselectivity. No coupling products through the phenyl p-position of BT or TPA methyl ester were found. By contrast, ketone homodimers and cross-coupling products arising from reaction through the thienyl 5-position were obtained when using BT and SUP methyl ester; this is very interesting, because stable LAT-derived products are difficult to isolate.     

Photoreaction of 2-dicyanomethylene-1,2,3,4-tetrahydro-1,4-methanonaphthalene

Upon irradiation, 2-dicyanomethylenebenzonorbornene f$\text{3}$ was converted into 1-dicyanomethylenebenzobicyclo[3.1.1]heptene $\text{4}$. The reaction pathway is discussed with reference to the photoreaction of parent hydrocarbon.     

Photoreaction between 2-benzoylthiophene and phenol or indole

Laser flash photolysis, density functional theory (DFT) calculations, and product studies have been performed to understand the mechanism of photoreduction of 2-benzoylthiophene (BT) in the presence of phenol or indole. Time-resolved experiments showed that BT ketyl (BTH) and phenoxy (PhO) or indolyl (In) radicals are generated with high rate constants and quantum yields close to 1. However, low conversions (specially in the case of indole) of the starting reagents are obtained upon prolonged lamp irradiation, indicating that recombination within the radical pairs must occur to a large extent, regenerating the starting materials. The solvent-dependence of the quenching rate constants, together with DFT theoretical studies, indicate fundamental differences between the mechanisms of the reaction of BT triplet with phenol and indole. Thus, data for phenol agree with the involvement of a hydrogen-bonded exciplex BT(.)HOPh, where concerted electron and proton transfer leads to the BTH(.)OPh radical pair. However, in the case of indole, electron transfer at the BT(.)HIn stage precedes proton transfer. Finally, C-C cross-coupling products have been isolated and characterized in the preparative irradiation of BT in the presence of phenol and indole. The structures of the products have been confirmed by alternative synthesis.     

微流光反应技术制备树脂状维生素D_3

合成维生素D_3的关键步骤是7-去氢胆固醇光照开环合成预维生素D_3,目前合成是在釜式光反应器中进行,原料转化率低,产物提纯难度大,产品生产周期长。本文利用微流光反应技术开展预维生素D_3的制备研究,与传统釜式光反应器相比,原料转化率从低于30%提高到95%,光照产物无需纯化,可直接通过热异构化反应制备树脂状维生素D_3,生产周期大为缩短。     

A Regiospecific Photoreaction for Synthesis of 3-Phenylpyridines

The regiospecific photocoupling of 3-(4-chloro-phenyl)-1,1-rdimethylurea with pyridine to afford 3-(4-dimethyl-ureidophenyl)pyridine was used to develop a synthetic scheme for the preparation of 3-phenylpyridine.     

Photoreaction of FMN-tricine and its participation in photophosphorylation

Abstract— In the presence of light, Tricine efficiently reduced flavin. Under aerobic conditions, oxygen uptake was observed. Inhibition studies with superoxide dismutase, with cytochrome c as electron acceptor, suggested that about 50% of the reduced oxygen was superoxide anion. Oxygen uptake by this system was markedly inhibited by 2.5 mM phenol or salicyl aldehyde. A rapid and convenient assay for superoxide dismutase was developed based on the light-induced reduction of cytochrome c by flavin mononucleotide (FMN) and Tricine. Reduction of cytochrome c in chloroplasts without addition of ferredoxin appears to be mediated by superoxide anions, as indicated by inhibition of this reaction by superoxide dismutase. Loss of photophosphorylation by sonication of chloroplasts could be partially prevented by the presence of Tricine and FMN during sonication. Phosphorylation under these conditions was dependent on white light, but no evidence for the participation of superoxide anion could be obtained with internal or external superoxide dismutase.