Oxidation with singlet oxygen

The main interest originated from the easy reversibility of the reaction using it as a singlet oxygen source. 

Methyl-substituted naphthalenes react with singlet oxygen,818 820 825 826 but the reactivity depends on the position of the substituents. Whereas 2-methylnaphthalene is 

Anthracene and its 9,10-disubstituted derivatives add singlet oxygen to form the 9,10-endoperoxide,825-827 but strong directing effect is displayed by substituents in the 1,4 positions 827 

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Experimental evidence of the formation of intermediate peroxide moieties in photo-oxidation of nitrones has been provided (463). Oxidation with singlet oxygen was observed in the photoirradiation of DMPO (464). 

Danishefsky dienes [98] cycloadd to Cjq in refluxing toluene or benzene [5, 38, 99-101]. The diene 103 adds in 60% yield to Cjq to give the desilylated ketone 104 [5,101]. Acid-catalyzed methanol elimination then furnishes the enone 105 in 82% yield (Scheme 4.17). As already described, this enone can be reduced by DIBAL-H to the corresponding alcohol for further functionalization. The same a,(3-un-saturated alcohol can also be obtained in better yield by Diels-Alder reaction of Cg0 with butadiene, followed by oxidation with singlet oxygen to the allylic hydroperoxide and PPhj reduction to the desired alcohol [101]. This sequence yields the allylic alcohol in 53%, starting from Cjq without the need of isolating intermediates. 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

In fact, the oxidation with singlet oxygen of alkenes not possessing allylic hydrogens is known to involve a 1,2-dioxetane intermediate15 16 (see Section 9.2.2). 

When l,6-imino-10-annulene (68) is oxidized with singlet oxygen and the product is thermolyzed, the homobenzene derivative 69 is formed. This, on treatment with nitrosyl chloride in the presence of triethylamine gives 25 in 5% yield.38 Also, annulene 70 on treatment with bromine gives the dibromoarene... 

Figure 7 Oxidation of cholesterol regiochemistry of the oxidation with singlet oxygen and of autoxidation (50).

The total synthesis proceeds in >10 steps on solid phase and includes various transformations, including an asymmetric Diels-Alder reaction, oxidation with singlet oxygen, and olefin metathesis. This synthesis sequence is among the most advanced and demanding solid-phase syntheses developed so far for chemical genomics experiments. It demonstrates that the total synthesis of complex natural products in multi-step sequences on solid phase is feasible. 

Polydienes also can undergo oxidation with singlet oxygen. The present consensus is that the oxidation of polydienes with singlet oxygen occurs via a so-called ene-mechanism ... 

Oxidation with singlet oxygen is subject to sterk effects but can show poor regioselectivity. For example, (+)-3-carene (52) is oxidized to produce a mixture of all three possible regioisomeric hydroperoxides with oxygenation occurring at the face of the allyl systm 0 qx>site the gem-dimethylcyclo-propane unit in each case (equation 22). - ... 

This procedure represents an efficient method for the preparation of rearranged allylic alcohols from allies similar to allylic oxidations with singlet oxygen but complementary to those obtained from selenium dioxide. The reagent must be prepared in situf ... 

During the conversion of alkenes into epoxy alcohols by allylic oxidation with singlet oxygen, an oxygen atom is usually removed from the allylic hydroperoxide by reduction, only to be subsequently reintroduced in the resulting epoxy alcohol by epoxidation with an external oxygen donor. 

Other oxidations with singlet oxygen are conversions of alkenes into epoxides [43, of secondary alcohols into ketones via alcohol hydroperoxides [44, 45] (equation 9) and the oxidative degradation of tertiary amines to secondary amines [46] (equation 10). 

Generally, oxidation with singlet oxygen and peroxy radicals are the two important oxidative processes for environmental pollutants in water. The rate constants for reactions of PAHs with singlet oxygen and peroxy radicals (Mabey et al. 1981) and the typical concentrations of the two oxidants in environmental waters (Mill and Mabey 1985) suggest that these reactions may not be important in controlling the overall fate of PAHs in water. 

Hydroperoxides 1 and cyclic peroxides 2 are formed in diene based rubbers by oxidation with singlet oxygen 02 [14]. 

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