Oxygen, singlet examples

Depending on the 7-substituent, the norcaradiene endoperoxide can be the major cycloadduct with singlet oxygen. For example, whereas the parent system (R = H) affords only about 4% of the norcaradiene endoperoxide 30a), the 7-cyano derivative... 

This explanation was shown to be incorrect by investigation 95) of reactions of a number of a-diketones (benzil, biacetyl, 1-phenyl-1,2-propanedione) in the presence of olefins in oxygen saturated solutions. Slow consumption of diketone was observed with relatively rapid consumption of olefin and concomitant formation of epoxides, often in high yield. Many of the olefins which underwent this reaction do not form epoxides at all with singlet oxygen. For example, tetraphenylporphin-sensitized photooxygenation of tetramethylethylene afforded hydroperoxide 111 quantitatively while a biacetyl-sensitized reaction yielded the epoxide 112. Further, it was shown that the... 

The peroxide radical can go to a product by abstraction and generate for example an acid and another radical. Commonly, acetic acid and also formic acid are formed in considerable amount during oxidative pyrolysis. The previous mechanism can probably explain the formation of these small molecules. The oxygen (singlet oxygen) may also react with the double bond forming a dioxetane intermediate ... 

Murray et al. [440—443] have shown that the reactions of ozone with a wide variety of compounds yield adducts which decompose to singlet oxygen for example, reactions (199) and (200), p. 490. 

Characteristic reactions of singlet oxygen lead to 1,2-dioxetane (addition to olefins), hydroperoxides (reaction with aHyhc hydrogen atom), and endoperoxides (Diels-Alder "4 -H 2" cycloaddition). Many specific examples of these spectrally sensitized reactions are found iu reviews (45—48), earlier texts (15), and elsewhere iu the Engchpedia. 

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. 

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