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Introduction
The sharpless epoxidation forms an epoxy alcohol from an alkene; the vanadium catalyst, vanadyl acetylacetonate, VO(acac)2 is used to form an epoxy alcohol from an allylic alcohol. The structure of the catalyst is shown in Figure 1. An allylic alcohol is an alkene with a methyl hydroxide functional group and any other functional group at the other position on the carbons of the double bond. When forming the epoxy alcohol the double bond is transformed into a three-membered ring with an oxygen heteroatom. The advantage of the vanadium catalyst, as opposed to traditional peroxy acid epoxidations, is that it will chemoselectively react with allylic alcohols and not alkenes.

Advances in vanadium catalyzed epoxidation reactions
Chemoselectivity refers to the process in which a reaction modifies a specific functional group in the presence of other functional groups in the substrate. For asymmetric epoxidations, the reactions are highly chemoselective and the reaction can be carried out in the presence of many other functional groups. An example of chemoselective scheme is shown in Figure 2. The re/si face attack to form the product reflects the cis/trans configuration of the starting olefin. However, when moving to an asymmetric cyclic epoxidation, the chemoselectivity is almost lost. This is due to the fixed nature of the cyclic substrate. The presence of enantioselectivity in this reaction is obvious due to the preference of the face attack to form a single chiral molecule (as opposed to a racemate) from an achiral allylic alcohol. The stereoselectivity depends on the size of the ring. For medium ring allylic alcohols using vanadium catalysts, the products preferred the cis conformation, whereas other peroxy acid epoxidations preferred the trans conformation. It is difficult to achieve high degrees of enantioselectivity required for the production of biologically active molecules. Vanadium catalysts increase the selectivity of the epoxidation reaction. This increased efficiency applies to pharmaceuticals, food additives, and pesticides.