Alkenes alkyl hydroperoxide catalysts

Sulfides are generally oxidized much faster than alkenes, and in the presence of excess oxidant further oxidation to the sulfone occurs. In the cases where the reaction is conducted in an asymmetric way, the chiral catalytic system may react faster with one enantiomeric sulfoxide to form the sulfone than with the other, so that kinetic resolution of the primarily formed sulfoxide may occur. In general, the reaction is carried out with alkyl hydroperoxides like TBHP in the presence of a metal catalyst like Mo, W, Ti or V complexes. In some cases the sulfoxidation with hydroperoxides can take place without the need of a metal catalyst. Both examples will be discussed in the following. 

As already mentioned above, sulfides are oxidized to the corresponding sulfoxides with alkyl hydroperoxides in the presence of various metal catalysts like Mo, W, Ti and V. In the presence of excess hydroperoxide further oxidation to the sulfone occurs. Sulfides are generally oxidized much faster than alkenes, which is reflected in the selective oxidation of unsaturated sulfides exclusively at the sulfur atom. During the last years many asymmetric versions of this reaction have been developed and can be mainly divided... 

The use of alkyl hydroperoxides in the metal-catalyzed epoxidation of alkenes is their most important synthetic application. High-valence d° metals such as Mo(VI), W(VI), V(V), and Ti(IV) are the most effective catalysts 24 245,278,279,285,286 Used as soluble complexes or as heterogenized supported catalysts, they can give epoxides in near-quantitative yields. 

There are also several situations where the metal can act as both a homolytic and heterolytic catalyst. For example, vanadium complexes catalyze the epoxidation of allylic alcohols by alkyl hydroperoxides stereoselectively,57 and they involve vanadium(V) alkyl peroxides as reactive intermediates. However, vanadium(V)-alkyl peroxide complexes such as (dipic)VO(OOR)L, having no available coordination site for the complexation of alkenes to occur, react homolyti-cally.46 On the other hand, Group VIII dioxygen complexes generally oxidize alkenes homolytically under forced conditions, while some rhodium-dioxygen complexes oxidize terminal alkenes to methyl ketones at room temperature. 

Since the metal-alkene association preceding the peroxymetalation reaction in mechanism (B) is a pure Lewis acid/Lewis base interaction, it would be expected that compounds having alkylperoxy groups bonded to a Lewis acid center should be active for the epoxidation of alkenes. This is indeed found for boron compounds, which are active as catalysts for the epoxidation of alkenes by alkyl hydroperoxides.246,247 Isolated boron tris(alkyl peroxides), B(OOR)3, have been shown to epoxidize alkenes stoichiometrically, presumably through alkylperoxyboration of the double bond (equation 76).248... 

Early work on the electrophilic addition of hydrogen peroxide to alkenes was performed in the presence of an acid catalyst, usually sulfuric acid364 or p-toluenesulfonic acid.363 The reaction proceeds via Markovnikov-directed protonation of the double bond (Scheme 3). Subsequent nucleophilic attack of hydrogen peroxide on the carbocation, followed by loss of a proton, furnishes the alkyl hydroperoxide.366... 

A material prepared by anchoring titanium(IV) on to the walls of a high-area, crystalline mesoporous silica (MCM41) has been used as an alkene epoxidation catalyst with alkyl hydroperoxides.204 The effect of replacing one of the three O—Si= groups to which the Ti(IV) is bound by an O—Ge= group is reported to lead to an increase in catalytic activity of up to 18% in die epoxidation of cyclohexene, although no explanation is provided and it is notable diat the selectivity towards the formation of cyclohexene oxide (versus cyclohexenol and cyclohexane-1,2-diol) was inferior to that with the non-modified system.205... 

Oxidations by oxygen and catalysts are used for the conversion of alkanes into alcohols, ketones, or acids [54]-, for the epoxidation of alkenes [43, for the formation of alkenyl hydroperoxides [22] for the conversion of terminal alkenes into methyl ketones [60, 65] for the coupling of terminal acetylenes [2, 59, 66] for the oxidation of aromatic compounds to quinones [3] or carboxylic acids [65] for the dehydrogenation of alcohols to aldehydes [4, 55, 56] or ketones [56, 57, 62, 70] for the conversion of alcohols [56, 69], aldehydes [5, 6, 63], and ketones [52, 67] into carboxylic acids and for the oxidation of primary amines to nitriles [64], of thiols to disulfides [9] or sulfonic acids [53], of sulfoxides to sulfones [70], and of alkyl dichloroboranes to alkyl hydroperoxides [57]. 

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