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     

Unusual Photoreaction of Triquinacene within Self‐Assembled Hosts

Triquinacene is a concave tricyclic hydrocarbon with diverse photoreactivity. In the cavity of an electron‐accepting molecular host, triquinacene was specifically photooxidized at the peripheral allylic position into an alcohol, 1‐hydroxytriquinacene, via guest‐to‐host electron transfer. The unusual reactivity stems from the extremely electron‐deficient triazine panel ligand of the host cage, which allows the cage to function as a good electron acceptor. Thus, self‐assembled coordination cages can serve not only as molecular‐sized reaction vessels but also function electronically as redox media. Dissolved molecular oxygen is indispensable for the photoreaction and immediately traps a photogenerated radical.     

Synthesis of An Unusual Tetrahydrofuro[3,4-D] Oxazole Ring System

ABSTRACT

Treatment of methyl 3-amino-3-deoxy-5,6-O-isopropylidene-β-D-allofuranoside, prepared in four steps from diacetone-D-glucose, with N,N-dimethylformamide dimethyl acetal resulted in the formation of a novel bicyclic tetrahydrofuro[3,4-d]oxazole ring system.     

Photoreaction of benzofuroxan

Benzofuroxan 5 , upon irradiation using a high pressure mercury lamp with a Pyrex filter in acetonitrile containing a little water, afforded 1H-azepine-2,7-dione 6 . The initial stage of this reaction would be formation of a highly reactive intermediate possessing two nitrile oxide functions. On the other hand, when compound 5 was irradiated using a low pressure mercury lamp in acetonitrile containing a little water, it afforded 6H-furazano[4,5-c]carbazole 3-oxide 11 and compound 6 . The structure of compound 11 was determined by an X-ray structural analysis. In the presence of an aromatic hydrocarbon, the formation of compound 11 was decreased and that of compound 6 was increased. Mechanistic studies on the photoreaction suggest that the photosensitized formation of compound 6 with the aromatic hydrocarbon may be carried out by the reabsorption of the fluorescence of it near 365 nm and the presence of it may quench the formation of compound 11 .     

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.     

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.     

Benzocyclobutadienes: An Unusual Mode of Access Reveals Unusual Modes of Reactivity

The reaction of an aryne with an alkyne to generate a benzocyclobutadiene (BCB) intermediate is rare. We report here examples of this reaction, revealed by Diels–Alder trapping of the BCB by either pendant or external electron‐deficient alkynes. Mechanistic delineation of the reaction course is supported by DFT calculations. A three‐component process joining the benzyne first with an electron‐rich and then with an electron‐poor alkyne was uncovered. Reactions in which the BCB functions in a rarely observed role as a 4π diene component in Diels–Alder reactions are reported. The results also shed new light on aspects of the hexadehydro‐Diels–Alder reaction used to generate the benzynes.     

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.     

Unusual Reaction of Sodium 1,6-Dioxo-2,4-alkadiene-3,4-diolates under Acid Hydrolysis Conditions

The reaction of sodium 1,6-dioxo-2,4-alkadiene-3,4-diolates with HCl solution afforded unexpected hydrolysis products, namely (2Z)-2-hydroxy-4-oxobut-2-enoic (2,4-dioxobutanoic) acid esters. The structural features of the synthesized compounds were discussed on the basis of IR, ¹H NMR spectroscopy, mass spectrometry and X-ray diffraction analysis data.     

不平“钒”的金属元素*

钒是地壳中含量第21丰富元素,是人体必需的微量元素。介绍钒元素的发现、自然分布以及在人体内的循环。重点从化学结构分析钒酸盐磷酸盐的拮抗作用机制,从生化机理阐述钒化合物对激酶与磷酸酶的调节、对RNA和DNA功能的影响、对活性氧作用的影响,从人体健康视角探讨钒对治疗糖尿病和癌症及保护心血管等的潜在药理学作用。     

傅克反应的异常产物

苯和草酰氯单乙酯在三氯化铝作用下发生傅克反应,在低温(0 ℃)条件下生成苯乙酮酸乙酯,而在高温(70 ℃)条件下首次得到了9,10-二甲基蒽,其结构经1H NMR,13C NMR和单晶X-衍射仪表征.     

An Improved Synthesis of S-3,4-Dehydroproline

S-3,4-dehydroproline (5, S-Δ^3,4-Pro) has been shown¹ to be a potent inhibitor of collagen synthesis in mammalian cells due, at least in part, to its action as a prolyl hydroxylase inhibitor. The replacement in peptides of proline with S-Δ^3,4-Pro has given analogues with modified biological activities.^2,3 In addition, reductive deuteration or tritiation of these S-Δ^3,4-Pro containing peptides gives 3,4-²H₂-Pro or 3,4-³H₂-Pro analogues of high specific enrichment.⁴ S-Δ^3,4-Pro was initially obtained⁵ by chemical resolution or selective enzymatic hydrolysis of R,S-3,4-dehydroprolinamide. A better process⁴ involves resolution of R,S-N-t-butyloxycarbonyl-3,4-dehydroproline with R-α-methyl-p-nitrobenzylamine. In this paper, we report improvements in the synthesis of R,S-Δ^3,4-Pro (3) and the direct resolution of this material with natural (+)-tartaric acid. An important feature     

Unusual samples: An everyday occurrence

Which analyst hasn't been confronted with that 'problem sample'? Happily, for most, unusual and difficult samples are the exception rather than the rule, but for the forensic scientist they are an everyday occurrence. Eva Blacklock has taken a lighthearted look at some of the more bizarre samples she has encountered in the course of her career.