Arsenic compounds alkene epoxidation

Among the heavy main group elements arsenic has received the most attention. Arsonium ylides react with carbonyl compounds to yield either the alkenes or epoxides, depending upon the structure of the ylide and the reaction conditions. )espite their toxicity, arsenic compounds can be handled safely. 

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. ... 

The first report of such effects was in a study of the reactions of a series of tris(p-substituted phenyl)arsonium ylides with benzaldehyde all these ylides gave epoxides in high yield save for the tris(p-dimethylamino) compound, which gave instead the trans-alkene L In further experiments replacement of a triphenylarsonium group by a tris(p-methoxyphenyl)arsonium group was found to have little effect on the ratio of products and inclusion of the arsenic atom in a strained ring also had no effect. ... 

Arsonium ylides were discovered near the turn of the century, but their reactions with carbonyl compounds did not become elucidated until the 1960s. In a broad sense, arsonium ylides are midway in chemical behavior between ylides of phosphorus and those of sulfur. Stabilized arsonium ylides react with carbonyl compounds to afford alkenes, whereas the unstabilized analogs give rise to epoxides. More subtly, the nature of the substituents on either the ylide arsenic or carbon atom can alter the course of the reaction the choice of solvent can exert a similar effect. ... 

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. ... 

With HMPA, Wittig reactions that give ( )-alkenes were also observed (eq 18), as was the directed selectivity of a semista-bilized arsonium ylide towards carbonyl compounds. The arsenic ylide was generated from LDA in THF or THF/HMPA solution to give exclusively epoxide (eq 19) or diene (eq 20), respectively. ... 

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