Dolbier HW Solutions 499

Dolbier HW Solutions 499 - 2 COOCH 2 CH 3 COOCH 2 CH 3...

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( l ) Acid hydrolysis converts the diester in part ( k ) to a malonic acid derivative, which then undergoes decarboxylation. ( m ) Lithium diisopropylamide (LDA) is used to convert esters quantitatively to their enolate ions. In this reaction the enolate of tert -butyl acetate adds to benzaldehyde. 21.23 ( a ) Both ester functions in this molecule are b to a ketone carbonyl. Hydrolysis is followed by decarboxylation. ( b ) Examine each carbon that is a to an ester function to see if it can lead to a f ve-, six-, or seven- membered cyclic b -keto ester by a Dieckmann cyclization. 2 COOCH 2 CH 3 COOCH 2 CH 3 COOCH 2 CH 3 Cyclization gives a five-membered ring; b -keto ester deprotonated under reaction conditions; this is the observed product (C 12 H 18 O 5 ). O H 3 C COOCH 2 CH 3 COOCH 2 CH 3 2 COOCH 2 CH 3 COOCH 2 CH 3 COOCH 2 CH 3 Cyclization not likely; resulting ring is four-membered and highly strained.
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Unformatted text preview: 2 COOCH 2 CH 3 COOCH 2 CH 3 COOCH 2 CH 3 O H 3 C COOCH 2 CH 3 CH 3 CH 2 OOC Cyclization to a five-membered ring possible, but b-keto ester cannot be deprotonated to give a stable anion. H 2 O, H 2 SO 4 heat O CH 3 CH 2 COOCH 2 CH 3 COOCH 2 CH 3 O CH 3 CH 2 Diethyl 3-ethylcyclopentanone-2,5-dicarboxylate 3-Ethylcyclopentanone (C 7 H 12 O) CH 3 COC(CH 3 ) 3 C 6 H 5 CHCH 2 COC(CH 3 ) 3 OH O O LDA 1. C 6 H 5 CH 2. H 1 OC(CH 3 ) 3 OLi H 2 C C O tert-Butyl acetate Lithium enolate of tert-butyl acetate tert-Butyl 3-hydroxy-3-phenylpropanoate O H 3 C CH 2 COOH (4-Methyl-3-oxocyclohexyl)acetic acid (isolated yield, 80%) O H 3 C CH(COOCH 2 CH 3 ) 2 Diethyl 2-(4-methyl-3-oxocyclohexyl)malonate H 2 O, HCl heat ESTER ENOLATES 593...
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