draft lab ###3 - Asymmetric SynthesisUse of a Chiral...

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Asymmetric Synthesis- Use of a Chiral Manganese Catalyst for the Enantioselective Epoxidation of Alkenes Ju-Hyun Bae Third experiment report, University of Wisconsin, Madison Wisconsin 53703 [email protected] Abstract R 4 R 1 R 3 R 2 R 4 R 1 R 3 R 4 R 1 R 2 R 3 O O R 2 or [o] Jacobsen's Catalyst N N O O Mn Cl C(CH 3 ) 3 (H 3 C) 3 C (H 3 C) 3 C C(CH 3 ) 3 Jacobsen’s catalyst is an extremely useful for making epoxide rings because it can be synthesized from readily available, easy, and cheap starting materials. Despite of this aspect, it helps to epoxide alkene to change a useful oxygen-baring ring compound. By comparing percentages of enantioselective epoxidation of styrene and 1, 2- Dihydronaphthalene through GC and SFC analysis, selectivities were reasonably investigated. In this experiment , why selectivity matters in expoxidation and how this affect on the reaction discussed. Moreover, some certain questions relate to structures of alkene and catalyst’s explained. Introduction Carbon carbon double bond has been considered a compound that has many possibilities of transformation. Oxygen-bearing, epoxide from oxidation reaction is one of these transformations. This epoxide transformation has been developed by peroxide. However, the Illinois chemist (now at Harvard Univ.) Eric N. Jacobsen reported the enantioselctive epoxidation(ee) of ‘unfunctionalized’ olefins can be catalyzed by chiral manganese complexes. The catalyst for the asymmetric epoxidation, styrene and 1,2- Dihydronaphthalene has a great aspect because it can synthesize easily from common and cheap starting mateials such as (R, R)-1,2-diaminocclohexane and cis/trans isomers of the diamine. Jacobsen’s catalyst can synthesize in three steps including Schiff base. Finally, [(R, R)-N, N’-Bis (3,5-di-tert-butylsalicylidene)-1,2-cyclo-hexanediaminato-(2-)] manganese (III) chloride is made. Two Alkenes listed above catalyzed from this compound to epoxides. However, becoming an epoxide is based on their selectivity, which relates to enantiomers. Herein we describe selectivities of these epoxide products, investing the details of selectivity. Moreover, analyzing enantioselective epoxidation percentage also gives details of selectivity. Through these details, some questions such as ‘highest ee’s should be related to cis-olefins bearing one big and one small substitutent’, ‘Why (R,R)-catalyst give different enatiomer to (S,S)-catalyst’, and ‘spatial orientation of epoxidation mechanism’ will be focused on in this report.
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All materials were purchased form sigma Aldrich and used without purification. Instruments those used for H-NMR Varian Mercury Plus 300 and for IR Spectrum were Vector 22, Tensor 27 with 4000 - 400 wave length ( μ m). The instrument and method data for the SFC is: Manufacturer: Berger; Column: AD-Dex; Eluent: CO2, modifier: isopropanol (3%), flow: 2 ml/min. Experimental Procedures
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draft lab ###3 - Asymmetric SynthesisUse of a Chiral...

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