Abstract
The asymmetric ring-opening of epoxides is an important reaction in organic synthesis, since it allows for the enantioselective installation of two vicinal functional groups with specific stereochemistry within one step from a highly available starting material. An effective class of catalysts for the asymmetric ring-opening of epoxides is metal–salen complexes. This review summarizes the development of metal–salen catalyzed enantioselective desymmetrization of meso-epoxides and kinetic resolution of epoxides with various nucleophiles, including the design and application of both homogeneous- and heterogeneous epoxide-opening catalysts as well as multi-metallic covalent and supramolecular catalytic systems.
Highlights
The availability of enantiomerically pure or enriched compounds is crucial for several different fiel1d.sInotfrcohdeumctisotnry including pharmaceutical, biological, agricultural, and materials chemistry [1,2]
We present an overview of the development and application of metal–salen complexes as catalysts for the ARO of epoxides
Drawing on knowledge gained in their previous work on the asymmetric epoxidation of alkenes [24,25,26], they found that by using the same salen ligand and exchanging the manganese(III) for chromium(III), the ARO of cyclic meso-epoxides with TMSN3 as nucleophile could be catalyzed in high yields and with high enantioselectivities
Summary
The availability of enantiomerically pure or enriched compounds is crucial for several different fiel1d.sInotfrcohdeumctisotnry including pharmaceutical, biological, agricultural, and materials chemistry [1,2]. IInn tthhee llaatttteerr ccaassee,, tthhee ccaattaallyysstt hhaass ttoo bbee aabbllee ttoo ddiiffffeerreennttiiaattee bbeettwweeeenn tthhee ttwwoo eennaannttiioommeerrss aanndd pprreeffeerreennttiiaallllyy ttrraannssffoorrmm oonnee ooff tthheemm iinnttoo tthhee rriinngg--ooppeenneedd pprroodduucctt wwiitthh high regioselectivity and enantioselectivity. This process is a kinetic resolution (KR). Using the catalyst in the ARO of cyclohexene oxide with TMSN3 yielded products with up to 80% ee, compared to 26% ee obtained with complex 1 under the same reaction conditions. Yang and coworkers [53] used Cr–salen complex 1 (Scheme 4) to catalyze the ARO of mesoepoxides with TMSN3 as an example reaction to investigate the efficiency of their liquid-solid hybrid catalysts.
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