Hydrogen peroxide: A versatile reagent in organic synthesis

Abstract

(A) Hydrogen peroxide is a versatile reagent for the oxidation of sulfides to sulfoxides. Racemic and chiral sulfoxides can be obtained. Zhu and co-workers have reported the asymmetric oxidation of sulfides as well as the kinetic resolution of sulfoxides with hydrogen peroxide in air by a salan-vanadium catalyst; this method provides an efficient procedure for the preparation of chiral sulfoxides in good chemical yields and excellent enantiomeric purities.2 (B) Hydrogen peroxide has been extensively used for the transformation of alkenes into alcohols. The hydroboration-oxidation sequence constitutes a powerful method for the regio- and stereoselective synthesis of alcohols; usually the OH group binds to the less-substituted carbon atom (anti-Markovnikoff product).3 Besides, Knochel and co-workers used diphosphines as ligands in the rhodium-catalyzed asymmetric hydroboration of styrene derivatives. The Markovnikoff product was obtained in good yield and good enantiomeric excess.3c (C) Syn-dihydroxylation of alkenes is carried out with hydrogen peroxide in the presence of catalytic osmium tetroxide.4 A clean and safe method under organic-solvent and metal-free conditions was also reported.5 Another way to afford 1,2-diols is a rhodium-catalyzed syrc-addition of bis(catecholato)diboron and subsequent oxidation with hydrogen peroxide.6 (D) Hydrogen peroxide can be used as oxidizing agent in Baeyer-Villiger oxidation to transform ketones into esters or cyclic ketones into lactones. The asymmetric version of this reaction has also been reported using platinum(II) complexes7 or a novel planar-chiral bisflavin8 as catalysts. An unexpected rearrangement of the initially formed ring-expanded lactone was observed and used in the total synthesis of farnesiferol.9 (E) Hydrogen peroxide provides an efficient conversion of alkenes into the respective epoxides. This epoxidation gives the product in good to excellent yields. A range of substrates such as α,β-unsaturated carbonyl compounds or functionalized olefins has been used. Metallic10 or organic11 catalysts can be used; it is also possible to carry out the epoxidation in an enantioselective manner. (F) The oxidative work-up with hydrogen peroxide after ozonolysis gives carboxylic acids or ketones. Hodgson et al. have successfully used this reaction to complete the stereoselective synthesis of cis-nemorensic acid and 4-hydroxy-cis-nemorensic acid.12 (G) Gopinath and Patel13 reported a new catalytic oxidative esterification of aldehydes. This method has advantages over previous methods with respect to the use of environmentally benign catalyst and reagent, cost-effectiveness, high efficiency, mild reaction conditions, shorter reaction times, and facile isolation of the desired products. (H) Direct ketohydroxylation can be achieved when olefins are treated with hydrogen peroxide in chloroform containing a catalytic amount of 12-tungstophosphoric acid (WPA, 10%) combined with cetylpyridiniumchloride (CPC, 30%) as phase-transfer catalyst at 60°C. Various α-hydroxyketones can be obtained in good yields and high regioselectivities.14. © Georg Thieme Verlag Stuttgart.