Selenium compounds alkene epoxidation

Vinyl selenides have been lithiated at the a-position by LDA983,984 at —78 °C in THF to give a-(arylselanyl)vinyllithiums 680, a-(methylselanyl)vinyllithiums 681 being obtained by selenium-lithium transmetallation from l,l-bis(methylselanyl)alkenes with n-BuLi in THF or t-BuLi in ether at —78 °C985 986. These intermediates reacted with alkyl halides, epoxides, carbonyl compounds and DMF985, the final deprotection being performed by mercury(II) salts986. 

Several acidic oxides such as M0O3, WO3 and compounds of selenium, arsenic and boron are effective catalysts for the epoxidation of alkenes by H2O2 through generation of inorganic peroxo acids, such as peroxoselenic and peroxoarsonic acids. ... 

It is noteworthy that selenium, arsenic and boron compounds are also effective catalysts for the selective epoxidation of alkenes by H2O2 (equations 34-36). It is generally thought that peroxyselenic and peroxyarsonic acids act as reactive intermediates in a way similar to that of peroxycarboxylic acids. Metaboric acid, HBO2, acts as both an epoxidation catalyst and a dehydrating agent. The resulting orthoboric acid can be dehydrated back to metaboric acid. ... 

Selenoxides are even more reactive than amine oxides. In fact, many types decompose spontaneously on generation at room temperature. Synthetic procedures based on selenoxide eliminations usually involve synthesis of the corresponding selenide followed by oxidation and elimination. We have already discussed examples of these procedures in Chapter 4 where the synthesis of a,/ -unsaturated carbonyl compounds (Section 4.7) was considered. In addition to the electrophilic addition of selenenyl halides and related compounds to alkenes and enolate selenenation, which was discussed in Section 4.5, selenides can be readily formed by nucleophilic displacement on halides, tosylates, or epoxides.Selenium is also capable of stabilizing an adjacent carbanion so that a-selenenylcarbanions are accessible carbon nucleophiles. One versatile procedure involves conversion of ketone to fe/5-selenoketals which are then cleaved by butyllithium. These carbanions... 

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