Vanadyl 2, epoxidation using

Very interesting results were obtained during studies on the epoxidation of /f-hydroxy enones 8. Attempts at selective epoxidation under typical basic conditions failed and 2 3 mixtures of syn- and anf/-epoxides 9 were obtained. Surprisingly, epoxidation using Sharpless conditions, titanium tetraisopropoxide/tm-butyl hydroperoxide or vanadyl acetylacetonate/rm-butyl hydroperoxide, which are normally unreactive towards simple enones, proceeded smoothly, yielding exclusively syn-epoxy alcohols syn-9. No epoxidation took place for the corresponding nitrile or when the hydroxy function was blocked as a silyl ether32. 

Group 5 metal-promoted oxidations epoxidations using vanadyl acetylacetonate... 

The vanadium(IV) complex of salen in zeolite was found to be an effective catalyst for the room temperature epoxidation of cyclohexene using t-butyl hydroperoxide as oxidant.88 Well-characterized vanadyl bis-bipyridine complexes encapsulated in Y zeolite were used as oxidation catalysts.101 Ligation of manganese ions in zeolites with 1,4,7-triazacyclononanes gives rise to a binu-clear complex stabilized by the zeolites but allows oxidation with excellent selectivity (Scheme 7.4). 

The readily available catalyst vanadyl bisacelylacetonate when used with r-bulyl hydroperoxide in benzene will oxidize secondary alcohols (Scheme 20) much mote rapidly than primary ones (rate ratio > 100 1), but the other oxidizing prqieities of this system, in particular the epoxidation of allylic alcohols and the cleavage of 1,2-diols might well limit its uses somewhat. ... 

Vanadyl salen complexes epoxidized cyclohexene presumably through intermediate hydroperoxides formed by radical chain autoxidation <1997105927, 1998TL5923>. Reactions using vanadium complexes have been carried out in liquid carbon dioxide <19990M4916>. 

Hydrogen peroxide or t-butyl hydroperoxide may be used in the presence of a catalyst such as sodium tungstate(VI) or vanadyl acetylaceto-nate [ MeC0CH=C(0 )Me 2V0] for the epoxidation of allylic alcohols. The stereochemistry of the hydroxyl group has a profound effect on the stereochemistry of epoxidation. A system which has been applied to allylic alcohols, to make optically active epoxides, utilizes titanium(rV) isopropoxide, t-butyl hydroperoxide and either of the enantiomeric forms of diethyl tartrate. This system forms chiral epoxides of predictable stereochemistry. When the reactivity of epoxides is combined with the... 

The most direct way to prepare VO(acac)2 is by the reaction of vanadyl sulfate with a source of the ligand. Vanadium(V), such as V205, can be reduced to vanadium(IV) by ethanol solvent in the presence of sulfuric acid. Reaction with acetylacetone in sodium carbonate yields the desired product. The synthesis we will use produces the complex in high yield directly in a system that can visually shed light on the active catalyst species in the epoxidation of olefins, Figure 9.4. 

Allylic alcohols, for example geraniol, 2-methylallyl alcohol, 3,3-dimethylallyl alcohol, 3-buten-2-ol, l-octen-3-ol, and l-hexen-3-ol, are epoxidized with tert-butyl hydroperoxide in the presence of a vanadyl salen oxo-transfer catalyst in supercritical CO2. The metal catalyst was prepared in a simple two-step, Schiff base-type reaction to form the salen ligand, followed by complexation to the vanadyl group. The use of non-toxic supercritical CO2 in the presence of the new epoxidation vanadium catalyst led to yields and diastereoselectivities that were comparable to those resulting from the use of environmentally hazardous solvents such as CH2CI2 [59]. 

The synthesis of the ( )-l 1-HETE (92), ( )-12-HETE (25) began by treating epoxide 89b with acetic acid and saturated aqueous KBr in THE to afford a mixture of bromohy-drin 93 and its regioisomer (14-bromo, 15-hydroxy) in 95% yield in a 2 1 ratio, respectively (Scheme 3.25). Oxidation using tert-butyl hydroperoxide in the presence of vanadyl... 

Catalyst in Oxidation Reactions. DBTO has been used as a catalyst in Fe -mediated oxidation of thiols to disulfides, even though Tri-n-butyl(methoxy)stannane seems to be better suited for this purpose. Epoxidation of terminal alkenes in a two-phase system (chloroform-water) containing H202/ammonium molyb-date/DBTO has also been reported. A combination of DBTO and t-Butyl Hydroperoxide oxidizes allylic alcohols with moderate regio- and stereoselectivity. Tri- and tetrasubstituted double bonds are most easily oxidized and the selectivities are comparable to those of the corresponding Vanadyl Bis(acetylacetonate) mediated reactions. 

The widely used asymmetrical epoxidation of allylic alcohols developed by Katsuki and Sharpless employs tert-batyl hydroperoxide (TBHP), enantiomerically pure tartaric acid esters, and isopropyl titanium(TV) (6). Similar results were obtained using TBHP and vanadyl acetyl acetonate VO(acac>2 and hexacarbonyl molybdenum [7,8]. The drawback of these reactions are their restriction to allylic alcohols, which is required as anchor group for the formation of the intermediate complex. 

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