Oxygenation with Singlet Oxygen

Oxidation t,/2 = 10 h for photosensitized oxygenation with singlet oxygen at near-surface natural water, 40°N, midday, midsummer (Zepp Schlotzhauer 1979)... 

Surface water computed t,/2 = 0.13 h at near-surface of a water body, for direct photochemical transformation, and t,/2 = 0.79 d for direct photolysis in a 5-m deep inland water body with no sediment-water partitioning, t,/2 = 1.2 d with sediment-water partitioning to top cm bottom sediment and t,/2 = 10 h for photosensitized oxygenation with singlet oxygen at near-surface natural water, 40°N, midday, midsummer (Zepp Schlotzhauer 1979) ... 

The synthesis of the non-natural ( )-7,14-epz-l(15),8-dolastadien-7,14-ol (rac-7yl4-epi-l09) was published by Paquette in 1986 and is highlighted by a photochemical rearrangement of the 6,6,6-tricyclic a,yS-epoxy ketone 148 into the 5,7,6-tricyclic dolastane skeleton (149) (Scheme 23) [84]. The succeeding hydroxylation of carbon atom by photo oxygenation with singlet oxygen as well as a DIBAH reduction of a keto function proceeded with an undesired substrate-induced diastereoselectivity to provide the racemic 7,14-epimer of the natural dolastane 109. 

Reaction between oxygen and butadiene in the Hquid phase produces polymeric peroxides that can be explosive and shock-sensitive when concentrated. Ir(I) and Rh(I) complexes have been shown to cataly2e this polymerisation at 55°C (92). These peroxides, which are formed via 1,2- and 1,4-addition, can be hydrogenated to produce the corresponding 1,2- or 1,4-butanediol [110-63-4] (93). Butadiene can also react with singlet oxygen in a Diels-Alder type reaction to produce a cycHc peroxide that can be hydrogenated to 1,4-butanediol. 

Oxidation and reduction can initiate changes leading to heterocycle-heterocycle conversions. The reaction of tetraphenylfuran with singlet oxygen (Scheme 34) (B-73MI50303) and that of isoxazoles with LAH (Scheme 35) are examples. 

Dithiolylium-4-olate, 2,5-diphenyl-reactions with singlet oxygen, 6, 831... 

When the valence tautomeric mixture of oxepin and benzene oxide is treated with singlet oxygen, the primary product is the 1,4-endoperoxide 3 which has proven to be too labile for isolation.219 Its formation can be rationalized by a 1,4-addition across the diene system of the benzene oxide structure 3 then rearranges to ba s-3,6,9-trioxatetracyclo[6.1.0.02 4.05 ]nonane (transbenzene trioxide, 4). 

The pyrazine I reacts with singlet oxygen to yield the endoperoxide 2, which is converted into the 1,3,6-oxadiazepine 4 on treatment with triphenylphosphanc. It is thought that the reaction involves deoxygenation to the bicyclic oxirane 3 as the key intermediate.320... 

The formation of bacteriochlorins from chlorophyll derivatives has also been studied.8 The reduction product 16 of methyl 3 -oxorhodochlorin-l 5-acetate (see Section 1.2.2.) undergoes photooxygenation with singlet oxygen to yield finally a bacteriochlorin 17. 

Dihydro-2f/-pyran-2-one has been prepared by reductive cycliza-tion of 5-hydroxy-2-pentynoic acid [2-Pentynoic acid, 5-hydroxy-], which is obtained in two steps from acetylene [Ethyne] and ethylene oxide [Oxirane] 3 and by the reaction of dihydropyran [277-Pyran, 3,4-dihydro-] with singlet oxygen [Oxygen, singlet].4,5 2ff-Pyran-2-one has been prepared by pyrolysis of heavy metal salts of coumalic acid [2//-Pyran-5-carboxylic acid, 2-oxo-],8 by pyrolysis of a-pyrone-6-carboxylic acid [211 - Pyran-6-carboxyl ic acid, 2-oxo-] over copper,7 and by pyrolysis of coumalic acid over copper (66-70% yield).8... 

Carbonyl oxides (formed by the reaction of diazo compounds with singlet oxygen) may also be used to oxidize sulphoxides74. The corresponding sulphone is formed in reasonable yields and the reaction may be carried out in the presence of the sulphide functionality. The reaction proceeds as shown in equation (21) and involves initial nucleophilic attack by the carbonyl oxide on the sulphoxide sulphur atom followed by the facile departure of the carbonyl compound yielding the required sulphone. 

Autoxidation reaction of alkenes with singlet oxygen... 

Cycloaddition reactions can occur with retention of configuration in the pseudoexcitation band (Sect 1.1) whereas [2jt H-2jtJ reactions are symmetry-forbidden in the delocalization band. Experimental evidence is available for the stereospecific [2-1-2] cycloaddition reactions between A and olefins with retention of configuration (Scheme 14) [82]. A perepoxide intermediate was reported to be trapped in the epoxide form [83] in the reaction of adamantylideneadamantane with singlet oxygen affording dioxetane derivatives [84]. 

In 1987, more than a decade before our proposal of the geminal bond participation [94], ene reactions of allylsilanes with singlet oxygen was reported to afford the Z-isomers more than the -isomers of ally lie hydroperoxides (Scheme 40) [106],... 

The dioxygen molecule exists in two forms a triplet or ground state in which it is a stable biradical and a singlet or excited state in which it is not a radical. Reactions of carotenoids with singlet oxygen have already been presented in this chapter and we now focus on the reactions of carotenoids and oxygen in the ground or triplet state. 

Analogs of conduritols from toluene cA-dihydrodiol by reaction with singlet oxygen followed by scission with thiourea (Figure 8.7d) (Carless et al. 1989). 

Certain compounds react with singlet oxygen in a different manner, giving dioxe-tanes as products.178... 

Numerous reactions, involving either transformation or conservation of the phosphazene unit, have been reported. The oxidation of the indanone phosphazene, 12, with singlet oxygen yields the corresponding ketone and triphenylphosphine oxide presumably via... 

CT-induced damage, consistent with theoretical predictions that the HOMO of guanine doublets is localized on the 5 -G [90]. Conversely, non-specific oxidation of both guanines is indicative of an alternative chemistry, for instance reaction with singlet oxygen. 

Reaction of /rart.v-[lr(CO)X(PPh3)2], X = halogen, is 10s—109 times faster with singlet oxygen than with triplet oxygen and yields the same product species (384) in both cases.620... 

Of the substrates that have worked well, let us first illustrate the 7-alkylidene-2,3-dioxabicyclo[2.2.1]heptane system 10. It was known that fulvenes react with singlet oxygen at low temperatures to afford the corresponding endoperoxides however, attempts to isolate these labile compounds led to decomposition, although NMR identification was possible at —70 °C 19>. When reduction of the singlet oxygenates with diimide was performed at —50 °C, the bicyclic peroxides 10 were obtained in high yield (Eq. 7) 20). 

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