Asymm_Ox_HO

Asymm_Ox_HO - Reisman, 242a Sharpless Asymmetric...

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( R , R )-(+)-DET ( S,S )-(–)-DET Sharpless Asymmetric Epoxidation: OH H R 1 R 2 – example of ligand accelerated catalysis – sometimes diisopropyltartrate (DIPT) gives improved ee – no reaction in the absence of an allylic alcohol Z alkenes are least reactive and least selective – homoallylic alcohols are significantly less selective – see also: Schreiber, JACS , 1987 , 2525 R 1 R 2 OH O ( S,S )-(–)-DET, Ti( i -OPr) 4 , TBHP 4Å MS, CH 2 Cl 2 , –20 °C ( R,R )-(+)-DET, Ti( i -OPr) 4 , TBHP 4Å MS, CH 2 Cl 2 , –20 °C R 1 R 2 OH O ( S,S )-[Mn-salen]Cl catalyst: R 3 R 1 R 2 O ( R , R )-[Mn-salen]Cl (5 mol%) NaOCl ( S , S )-[Mn-salen]Cl (5 mol%) NaOCl R 1 R 2 H R 3 H R 3 R 1 R 2 O H (S) (S) N N O O Mn Cl t -Bu t -Bu t -Bu t -Bu Mn O Cl N O N O NaOCl key references: JACS 1991 , 113 , 7063 JOC 1992 , 57 , 4320 ACIE 1997 , 36 , 1720 (mechanism) JACS 1998 , 120 , 948 Jacobsen Asymmetric Epoxidation: ( R , R )-[Mn-salen]Cl – active catalyst is Mn(V)-oxo species – cis olefins give epoxides with highest ee's – no directing group required – terminal olefins react with poor selectivities – catalyst prep: Org. Syn .
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This note was uploaded on 01/03/2012 for the course CH 242a taught by Professor List during the Fall '10 term at Caltech.

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Asymm_Ox_HO - Reisman, 242a Sharpless Asymmetric...

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