Boron compounds alkene epoxidation

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... 

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. ... 

The anti-cancer compound coriolin 23 has three fused five-membered rings and two epoxides. Notice that the 3/5 and both 5/5 ring fusions are cis. There have been many syntheses of coriolin, most using stereochemistry from folded precursors.7 We shall feature a couple of examples. Matsomoto s synthesis involves the hydroboration of alkene 24. The addition of borane is cis 25 and the boron is replaced by OH with retention of configuration to give 26. The hydroboration occurred on the outside of the molecule, on the same face as the ring junction hydrogens.8... 

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. ... 

Reviews.—Recent reviews involving olefin chemistry include olefin reactions catalysed by transition-metal compounds, transition-metal complexes of olefins and acetylenes, transition-metal-catalysed homogeneous olefin disproportionation, rhodium(i)-catalysed isomerization of linear butenes, catalytic olefin disproportionation, the syn and anti steric course in bi-molecular olefin-forming eliminations, isotope-elfect studies of elimination reactions, chloro-olefinannelation, Friedel-Crafts acylation of alkenes, diene synthesis by boronate fragmentation, reaction of electron-rich olefins with proton-active compounds, stereoselectivity of carbene intermediates in cycloaddition to olefins, hydrocarbon separations using silver(i) systems, oxidation of olefins with mercuric salts, olefin oxidation and related reactions with Group VIII noble-metal compounds, epoxidation of olefins... 

The g.l.c. separation of cis- and /m/w-epoxy-esters forms the basis of a new procedure for determining the proportion of cis- and tra/w-isomers in a mixture. The report that w-chloroperbenzoic acid can be used at 90 without decomposition in the presence of suitable radical inhibitors may be of value when epoxidizing alkenes of reduced reactivity. Several fluorostearic acids have been prepared by interaction of mesyloxy-acids with tetrabutyl-ammonium fluoride in acetonitrile. A procedure for methylation (by diazomethane in the presence of boron trifluoride) and demethylation (by reaction with sodium borohydride and iodine, followed by methanol), with retention of optical activity, could prove useful in the synthesis of compounds of known configuration. ... 

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