Styrene epoxide, asymmetric synthesis

Substituted alkenes as well as terminal olefins and styrene derivatives are epoxidized in high yield and enantiomeric excess under homogeneous reaction conditions. Very recently, the first chiral salen complexes which are selectively soluble in perfluorinated solvents have been synthesized and their application in asymmetric synthesis has been investigated [39,40]. 

The importance to use optically pure isomers as pharmaceuticals, food additives, agrochemicals, (etc) is becoming more and more evident. The classical resolution still accounts for a large part of chiral production, however the asymmetric synthesis and the use of chiral separation system one becoming increasingly popular. The enantioseletive hydrolytic resolution of racemic epoxides was performed in the ZSM-5/MCM-41 membrane system containing chiral salen complexes. The chiral salen complexes immobilized on the membrane showed a very high enantioselectivity in the hydrolysis of epichlorohydrine, epoxybutane, styrene oxide and 1,2-epoxyhexane. 

Styrene epoxide is a valuable building block and is used in the production of the antihelmintic drug Levamisole. The styrene epoxide for the synthesis of drugs must be enantiopure. There are some chemical asymmetric synthetic routes but the yields are only in the range 45-50%. 

In addition, the salicylaldehyde derivative 5 has been reacted with 1,2-diaminoethane to divinylsalenes which were afterwards copolymerized with styrene to cross-linked polymers in which Co(II) was introduced [21]. Also divinyl-substituted Mn(II salen complexes have been successfully copolymerized [22,23]. The aim of this interesting research is the synthesis of heterogeneous catalysts for the asymmetric epoxidation of olefins using chiral Mn(III)-salen complexes [24]. 

Laibinis used a three steps synthesis for the polystyrene-supported salen 307 (Scheme 126) [189-190], Asymmetric epoxidation was carried out in biphasic conditions with NaOCl as the oxidant in presence of 307mii as catalyst. The enantiomeric excesses and the yields of AE with styrene (9% ee, 7% yield), cA-P-methylstyrene (79% ee, 2% yield) or dihydronaphtalene (42% ee, 46% yield) were low to modest. 

Synthesis of (S)-styrene oxide via asymmetric epoxidation of styrene with a recombinant whole-cell catalyst containing a styrene monooxygenase. 

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