Dolbier HW Solutions 388

Dolbier HW Solutions 388 - Catalytic hydrogenation would...

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Reaction at the other a position gives an intermediate that cannot dehydrate. ( h ) b -Diketones readily undergo alkylation by primary halides at the most acidic position, on the carbon between the carbonyls. 18.24 ( a ) Conversion of 3-pentanone to 2-bromo-3-pentanone is best accomplished by acid-catalyzed bromination via the enol. Bromine in acetic acid is the customary reagent for this transformation. ( b ) Once 2-bromo-3-pentanone has been prepared, its dehydrohalogenation by base converts it to the desired a , b -unsaturated ketone 1-penten-3-one. Potassium tert -butoxide is a good base for bringing about elimination reactions of secondary alkyl halides; suitable solvents include tert -butyl alcohol and dimethyl sulfoxide. ( c ) Reduction of the carbonyl group of 1-penten-3-one converts it to the desired alcohol.
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Unformatted text preview: Catalytic hydrogenation would not be suitable for this reaction because reduction of the dou-ble bond would accompany carbonyl reduction. 1-Penten-3-one H 2 C CHCCH 2 CH 3 O 1-Penten-3-ol H 2 C CHCHCH 2 CH 3 OH 1. LiAlH 4 , diethyl ether 2. H 2 O KOC(CH 3 ) 3 CH 3 CHCCH 2 CH 3 O Br 2-Bromo-3-pentanone CHCCH 2 CH 3 H 2 C O 1-Penten-3-one Br 2 acetic acid CH 3 CH 2 CCH 2 CH 3 O 3-Pentanone CH 3 CHCCH 2 CH 3 O Br 2-Bromo-3-pentanone 1 KOH O O 1,3-Cyclo-hexanedione H 2 C CHCH 2 Br Allyl bromide CH 2 CH 2 CH O O 2-Allyl-1,3-cyclohexanedione (75%) O O C 6 H 5 CH OH (Cannot dehydrate; reverts to starting materials) HO 2 , C 6 H 5 CHO 482 ENOLS AND ENOLATES...
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