Cyclic compounds photolysis

The photolysis of 4-substituted 2,3-dimethyl-3-isoxazolin-5-ones has been studied. Irradiation in methanol or ethanol with a 100 W high-pressure mercury lamp through a Pyrex filter of a 4-phenylthio compound produced a semithioacetal (Scheme 5). In contrast, an H, Cl or OPh moiety gave no reaction. The use of alkylthio substitution gave similar products. Cyclic compounds yielded cyclic products (Scheme 5), and the photolysis of (29) in benzene... 

Various fluorinated cyclic compounds containing -N=N- bonding can be decomposed by the elimination of nitrogen The photolysis of phenylfluorodiazi-rine results in the formation of the intermediate phenylfluorocarbene, which can react instantaneously with olefins [7<5] (equation 45)... 

Scheme 6.18 Reaction mechanism for the photolysis of cyclic compounds 85 and 86...

Laser flash photolysis experiments showed that the (Reaction 8.17) reacts with cyclic oligosilanes 42, 43 and 44 in benzonitrile by an electron transfer mechanism [43]. The rate constant ( et) for the three-membered cyclic compound 42 is found to be 7.0 x 10 M s, whereas for the other two compounds it was more than two orders of magnitute lower, i.e., (1-2) X 10 M- s-. ... 

The photolysis of various cyclic compounds containing silicon atoms in the ring have been found to lead to the formation of transient intermediates containing multiple bonds to silicon. For example, Boudjouk and coworkers observed that photolysis of the trisi-latriselenacyclohexane 330 gave rise to the silaselenone 331, captured as the insertion product into the ring of D3, yielding the product 332168 (equation 30). 

In cycloaddition reactions of carbon cumulenes with suitable substrates, [2+1], [2+2], [3+2] and [4+2] cycloaddition reactions giving rise to the formation of cyclic compounds are observed. In general, [2+1] cycloaddition reactions afford three-membered ring compounds with an attached double bond, and sometimes the initially formed cycloadducts rearrange to form an isomeric three-membered ring cycloadduct. An example is the addition of diphenylcarbene to dialkylthioketenes where the initially formed cycloadduct 15 on photolysis produces the isomer 16, with bulky substituents on the three-membered ring. ... 

The course of the photolysis of a number of cyclic sulfoxides, however, has been shown not to involve simple photoextrusion processes. In fact, the work of Schultz and Schlessinger19,20 and Still and coworkers21 has shown the existence of a novel desulfurization pathway leading to cyclic ethers or to carbonyl compounds by formal loss of the sulfur atom only, by certain cyclic sulfoxides. 

The photolysis reactions of some other cyclic azo compounds are shown below(1B-18) ... 

Many reports concerning the direct and sensitized photolysis of cyclic azo compounds have appeared/11 Photolysis of meso and d,l forms of azo compound (2) results in varying mixtures of products (3), (4), and (5) ... 

The conditions for reliable cyclic voltametry determination of trace Sn concentrations in sea water were investigated. All organotin compounds should be converted to Sn(II) by UV-photolysis adsorption on mercury drop in the presence of 40 pM of tropolone (1) cyclic voltametry stripping shows two cathodic peaks, corresponding to the two-step process Sn(IV) — Sn(II) -> Sn(0)29. A complex of Sn ions with catechol can be accumulated in a glassy carbon mercury film electrode, followed by stripping voltametry measurement in the cathodic direction, at pH 4.2-4.7. Interference occurs when Cu, Cd and Cr are present LOD 0.5 pg/L for 300 s accumulation30. 

In the case of compound 4 photolysis with a medium pressure mercury lamp results in exclusive cleavage of the C—Sn bond fi to the carbonyl group, while the terminal C—Sn bond remains intact. The cyclic ketone 5 and the a, /Lunsaturated ketone 6 are produced in equal if low yields (18%)19. The reduced reactivity of remote C—Sn bonds in such compounds appears to be a general feature of their chemistry, and is also observed in acyclic systems. Thus the photochemistry of organotin compounds with carbonyl groups in the /3-position can be classified as follows ... 

Heterocyclic derivatives such as 59 provide a convenient route to the synthesis of many cyclic germanium compounds87. For instance, photolysis of 59 in the presence of alkynes 60 or 61, or allenes 62, produces the unsaturated heterocyclic compounds 63 or 64, respectively. 

The mechanism has been ascertained by laser flash photolysis. Besides aromatic substitution, it is possible to obtain cyclic products by using meta-substituted compounds 279 due to the para-directing effect of the nitro group [222, 223]. 

Insertion of the carbenes, via a low-lying singlet state close to the ground-state triplet, generated by photolysis of the diazo compounds (128), into the CO bond of cyclic ether solvents (THF, THP, dioxane) gave rise to polyether-bridged azulenes such as (129). ... 

Photochemical behaviour of compounds 83-86 [33] in the gas phase has been reported, in order to distinguish between silyl radical and silylene formation. Photolysis of the noncyclic precursors 83 and 84 gave products derived from silyl radicals, which come from a direct Si—Si bond homolysis, with a little evidence of silylene formation. In contrast, dimethylsilylene (Mc2Si ) was observed as a direct photoproduct from the cyclic precursors 85 and 86. The reaction sequence including a Sni step shown in Scheme 6.18 for the formation of dimethylsilylene was proposed to explain the different observations for cyclic and noncyclic systems. 

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