Alkyl hydroperoxides synthesis

Alkyl hydroperoxysilanes, preparation, 783 Alkyl hydrotrioxides, structural chemistry, 132 Alkyl iodides, dioxirane oxidation, 1158 Alkyl methyl sulfonates, alkyl hydroperoxide synthesis, 673... 

Synthesis. Dialkyl peroxides are prepared by the reaction of various substrates with hydrogen peroxide, hydroperoxides, or oxygen (69). They also have been obtained from reactions with other organic peroxides. For example, dialkyl peroxides have been prepared by the reaction of hydrogen peroxide and alkyl hydroperoxides with alMating agents, eg, RX and olefins (33,66,97) (eqs. 24—27). 

Finally, it is appropriate to close this chapter with an example from the roots of fine chemicals the dyestuff, indigo. Manufacture of indigo involves chemistry (see Fig. 2.15) which has hardly changed from the time of the first commercial synthesis more than a hundred years ago (see earlier). Mitsui Toatsu has developed a two-step process in which indole is produced by vapour-phase reaction of ethylene glycol with aniline over a supported silver catalyst (Inoue et al., 1994). Subsequent liquid-phase oxidation of the indole, with an alkyl hydroperoxide in the presence of a soluble molybdenum catalyst, affords indigo. 

Results of a chemical activation induced by ultrasound have been reported by Nakamura et al. in the initiation of radical chain reactions with tin radicals [59]. When an aerated solution of R3SnH and an olefin is sonicated at low temperatures (0 to 10 °C), hydroxystannation of the double bond occurs and not the conventional hydrostannation achieved under silent conditions (Scheme 3.10). This point evidences the differences between radical sonochemistry and the classical free radical chemistry. The result was interpreted on the basis of the generation of tin and peroxy radicals in the region of hot cavities, which then undergo synthetic reactions in the bulk liquid phase. These findings also enable the sonochemical synthesis of alkyl hydroperoxides by aerobic reductive oxygenation of alkyl halides [60], and the aerobic catalytic conversion of alkyl halides into alcohols by trialkyltin halides [61]. 

In this review, we focus mainly on the preparative utility of organic peroxides, and only few mechanistic investigations are discussed. This review covers synthetic methodologies for the preparation of alkyl hydroperoxides and dialkyl peroxides (Section II) and the synthetic use of these peroxides in organic chemistry (Section III). In Section II, general methods for the synthesis of organic hydroperoxides and dialkyl peroxides are discussed, as well as the preparation of enantiomerically pure chiral hydroperoxides. The latter have attracted considerable interest for asymmetric oxidation reactions during the last years. 

SCHEME 12. Synthesis of hydroperoxides from silyl enol ethers TABLE 3. Preparation of alkyl hydroperoxides via singlet oxygen oxygenation... 

An alternative method for dialkyl peroxide synthesis is the nucleophilic addition of an alkyl hydroperoxide to an alkene under acid catalysis reported by Davies and coworkers (Scheme 31, path B) ". A similar reaction is the nucleophilic addition of alkylhy-droperoxides to vinyl ethers under acid catalysis, producing perketals. Perketals can be deprotected under mild conditions (THF/water/acetic acid) and this hydroperoxide protection-deprotection sequence has been used by Dussault and Porter as a means for the resolution of racemic hydroperoxides (see also Section II.A.2) . In this respect more detailed studies were carried out with the perketals 75, which were prepared via reaction of alkyl hydroperoxides with vinyl ethers (Scheme 33). Weissermel and Lederer reported that in the presence of teri-butyl hypochlorite, a-chlorodialkyl peroxides can be formed in yields between 12% and 45% (Scheme 31, path C)". a-Alkoxydialkyl peroxides and diperoxyacetals were prepared by Rieche and coworkers via acid catalyzed reaction of one or two equivalents of alkyl hydroperoxides with acetals, ketals or aldehydes (Scheme 31, path D)" or by methylation of the corresponding a-alkoxy hydroperoxides with diazomethane (yields 11%, 27%)" . The diperoxyacetals 76 were isolated in yields ranging from 39 to 77%. 

TABLE 8. Results of the synthesis of dialkyl peroxides through reaction of alkyl hydroperoxides with epoxides... 

Alkyl halides, hydroperoxide synthesis, 327-8 Alkyl hydroperoxides anion ligands, 114-19 covalent radii, 114, 118-19 dihedral angles, 119 geometric parameters, 115-8 tetrahedral distortion, 119 artemisinin formation, 133-4 chlorotriorganosilane reactions, 779-83 crystal structure, 105-14 anomeric effect, 110-11 geometric parameters, 106-9 hydrogen bonding, 103-5, 111-14 tetrahedral distortion, 110 determination, 674... 

The search for a new epoxidation method that would be appropriate for organic synthesis should also, preferably, opt for a catalytic process. Industry has shown the way. It resorts to catalysis for epoxidations of olefins into key intermediates, such as ethylene oxide and propylene oxide. The former is prepared from ethylene and dioxygen with silver oxide supported on alumina as the catalyst, at 270°C (15-16). The latter is prepared from propylene and an alkyl hydroperoxide, with homogeneous catalysis by molybdenum comp e ts( 17) or better (with respect both to conversion and to selectivity) with an heterogeneous Ti(IV) catalyst (18), Mixtures of ethylene and propylene can be epoxidized too (19) by ten-butylhydroperoxide (20) (hereafter referred to as TBHP). 

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