Deoxygenative nucleophilic transformations

This feature of the reactions of azine W-oxides is of a general character. Indeed, the so-called deoxygenative nucleophilic transformations of azine W-oxides and their cationic forms into products have been established to involve the aMfo-aromatization step, in which the W-oxide, W-alkoxy, or W-acyloxy functions are auxiliary groups, facilitating elimination of hydrogen from the intermediate o -adducts (Scheme 19) [11, 45, 90-93] (for more details [215]). 

Furoxans and benzofuroxans undergo thermal and photochemical ring cleavage, reactions with nucleophiles, Boulton-Katritzky rearrangement, reduction and deoxygenation, ring transformation, etc. (see also Section 5.05.6.2). 

Some routes of chemical transformations of nitrile oxides connected with the problem of their stability were briefly discussed in Section 1.2. Here only two types of such reactions, proceeding in the absence of other reagents, viz., dimerization to furoxans and isomerization to isocyanates, will be considered. All other reactions of nitrile oxides demand a second reagent (in some cases the component is present in the same molecule, and the reaction takes place intramolecularly) namely, deoxygenation, addition of nucleophiles, and 1,3-dipolar cycloaddition reactions. Also, some other reactions are presented, which differ from those mentioned above. 

Besides reduction, other transformations were performed, for example, reductive amination, nucleophilic 1,2-addtion, deoxygenation or olefination/reduction and thionation (Enders and Grondal 2006 Grondal 2006). 

Nucleophilic reagents will also effect deoxygenation. Di- or trisubstituted oxiranes have been transformed to olefins stereospecifically with inversion via a phosphobetaine (Eq. 102). ... 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

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