Oxidations - OXIDATIONS Oxidations Carey & Sundberg:...

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OXIDATIONS 5 Oxidations Carey & Sundberg: Chapter 12 problems: 1a,c,e,g,n,o,q; 2a,b,c,f,g,j,k; 5; 9 a,c,d,e,f,l,m,n; 13 Smith: Chapter 3 March: Chapter 19 I. Metal Based Reagents 1. Chromium Reagents 2. Manganese Rgts. 3. Silver 4. Ruthenium 5. other metals II Non-Metal Based Reagents 1. Activated DMSO 2. Peroxides and Peracids 3. Oxygen/ ozone 4. others III. Epoxidations Metal Based Reagents Chromium Reagents - Cr(VI) based - exact stucture depends on solvent and pH - Mechanism: formation of chromate ester intermediate Westheimer et al. Chem Rev. 1949 , 45 , 419 JACS 1951 , 73 , 65. C R R H O Cr HO O - O - O R R + HCrO 3 - + H + + H 2 O H + HCrO 4 - R 2 CH-OH Jones Reagent (H 2 CrO 4 , H 2 Cr 2 O 7 , K 2 Cr 2 O 7 ) J. Chem. Soc. 1946 39 Org. Syn. Col. Vol. V , 1973 , 310. - CrO 3 + H 2 O H 2 CrO 4 (aqueous solution) K 2 Cr 2 O 7 + K 2 SO 4 - Cr(VI) Cr(III) (black) (green) - 2°- alcohols are oxidized to ketones O R R acetone Jones reagent R 2 CH-OH - saturated 1° alcohols are oxidized to carboxylic acids. R H O R H HO OH R OH O acetone Jones reagent hydration RCH 2 -OH Jones reagent acetone - Acidic media!! Not a good method for H + sensitive groups and compounds
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OXIDATIONS 6 Me 3 Si OH SePh CO 2 CH 3 Me 3 Si SePh O O H 17 C 8 OH O O O H 17 C 8 O O 2) CH 2 N 2 acetone 1) Jones, acetone JACS 1982 , 104 , 5558 Jones JACS 1975 , 97 , 2870 Collins Oxidation (CrO 3 •2pyridine) TL 1969 , 3363 - CrO 3 (anhydrous) + pyridine (anhydrous) CrO 3 •2pyridine - 1° and 2° alcohols are oxidized to aldehydes and ketones in non-aqueous solution (CH 2 Cl 2 ) without over-oxidation - Collins reagent can be prepared and isolated or generated in situ. Isolation of the reagent often leads to improved yields. - Useful for the oxidation of H + sensitive cmpds. - not particularly basic or acidic - must use a large excess of the rgt. OH O O ArO CrO 3 •(C 5 H 5 N) 2 CH 2 Cl 2 JACS 1969 , 91 , 44318. O O O ArO H CrO 3 catalyzed (1-2 mol % oxidation with NaIO 6 (2.5 equiv) as the reozidant in wet aceteonitrile. oxidized primary alcohols to carboxylic acids. Tetrahedron Lett. 1998 , 39 , 5323. Pyridinium Chlorochromate (PCC, Corey-Suggs Oxidation) TL 1975 2647 Synthesis 1982 , 245 (review) CrO3 + 6M HCl + pyridine pyH + CrO 3 Cl - - Reagent can be used in close to stoichiometric amounts w/ substrate - PCC is slighly acidic but can be buffered w/ NaOAc HO OHC OH O O CHO O O TL , 1975 , 2647 PCC, CH 2 Cl 2 JACS 1977 , 99 , 3864. PCC, CH 2 Cl 2
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OXIDATIONS 7 - Oxidative Rearrangements Me Me OH O JOC 1977 , 42 , 682 PCC, CH 2 Cl 2 OH Me O Me JOC 1976 , 41 , 380 PCC, CH 2 Cl 2 - Oxidation of Active Methylene Groups O O O O O O PCC, CH 2 Cl 2 JOC 1984 , 49 , 1647 PCC, CH 2 Cl 2 - PCC/Pyrazole PCC/ 3,5-Dimethylpyrazole JOC 1984 , 49 , 550. N
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Oxidations - OXIDATIONS Oxidations Carey & Sundberg:...

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