| Abstract |
Epoxidation of olefins is normally earned out by per-acid, hydrogen peroxide, oxone, sodium hypochlorite etc. in presence of a suitable organic or metal catalyst. The drawbacks of these methods are unsafe handling, toxicity problem, requirement in stoichiometric amount w.r.t. substrate, high cost etc. Chiral epoxidation of olefins with environment friendly catalytic system that can be recycled is highly desirable in the context of Green Chemistry for preparation of many industrially important compounds. Having conceived such an idea, a system was explored and developed a recyclable method to prepare chirally pure epoxides directly from olefins using a novel chiral acid 2,3:4,6-di-0-isopropylidene-2-keto-L-gulonic acid monohydrate as chiral inducer and aqueous hydrogen peroxide or anhydrous hydrogen peroxide in the form of urea hydrogen peroxide adduct (UHP) as oxidant and lipase enzyme as catalyst. Under the influence of lipase, the chiral acid 2,3:4,6-di-6>-isopropylidene-2-keto-L-gulonic acid monohydrate is converted to per-acid in situ by the oxidant urea hydrogen peroxide which in turn transfers oxygen to olefin inducing chirality to the product epoxide. Using this technique, important epoxide building blocks of different industrially important compounds can be prepared with good yield and moderate enantioselectivity. |