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Unformatted text preview: 19.1 (a) Write a mechanism for all steps of the Claisen condensation that take place when ethyl propanoate reacts with ethoxide ion. (b) What products form when the reaction mixture is acidified? Answer: (a) H 3 CHC COC 2 H 5 H O + OC 2 H 5 H 3 CHC COC 2 H 5 O + C 2 H 5 OH H 3 CHC COC 2 H 5 O H 3 CH 2 C C O C 2 H 5 O H 3 CHC COC 2 H 5 O + H 3 CH 2 CC H C COC 2 H 5 CH 3 C 2 H 5 O O O H 3 CH 2 CC H C COC 2 H 5 CH 3 O O + H 3 CH 2 CC C H CH 3 COC 2 H 5 O O + OC 2 H 5 OC 2 H 5 H 3 CH 2 CC C CH 3 COC 2 H 5 O O + C 2 H 5 OH H 3 CH 2 CC C CH 3 COC 2 H 5 O O H 3 CH 2 CC C CH 3 COC 2 H 5 O O H 3 CH 2 CC C CH 3 COC 2 H 5 O O H 3 O + (rapid) H 3 CH 2 CC H C CH 3 COC 2 H 5 O O H 3 CH 2 CC C CH 3 COC 2 H 5 OH O (b) H 3 CH 2 CC H C CH 3 COC 2 H 5 O O and H 3 CH 2 CC C CH 3 COC 2 H 5 OH O 19.2 What product would you expect from a Dieckmann condensation of diethyl heptanedioate (diethyl pimelate)? (b) Can you account for the fact that diethyl pentanedioate (diethyl glutarate) does not undergo a Dieckmann condensation? Answer: (a) Ethyl-2-oxocyclohexanecarboxylate O COC 2 H 5 O (b) Because the four members ring is not stable. 19.3 Write mechanisms that account for the products that are formed in the two crossed Claisen condensations just illustrated. (1) OC 2 H 5 C O (1)NaOC 2 H 5 (2)H 3 O + OC 2 H 5 H 3 C C O + C O H 2 C C O OC 2 H 5 Mechanism: OC 2 H 5 H 2 C C O H OC 2 H 5 OC 2 H 5 H 2 C C O OC 2 H 5 H 2 C C O Ph OC 2 H 5 C O C O H 2 C C O OC 2 H 5 OC 2 H 5 C O H C C O OC 2 H 5 C O H C C O OC 2 H 5 H OC 2 H 5 C O H 2 C C O OC 2 H 5 H 3 O + (2) H 2 C C O OC 2 H 5 + C 2 H 5 O OC 2 H 5 C O (1)NaOC 2 H 5 (2)H 3 O + CH OC 2 H 5 OC 2 H 5 C O C O Mechanism: Ph CH C O OC 2 H 5 H OC 2 H 5 Ph H C OC 2 H 5 C O C 2 H 5 O OC 2 H 5 C O Ph CH C OC 2 H 5 OC 2 H 5 O C O OC 2 H 5 Ph C OC 2 H 5 C O OC 2 H 5 C O H OC 2 H 5 Ph C OC 2 H 5 OC 2 H 5 C O C O O H H H CH OC 2 H 5 OC 2 H 5 C O C O 19.4 What products would you expect to obtain from each of the following crossed Claisen condensations? (a) Ethyl propanoate + diethyl oxalate (1)NaOCH 2 CH 3 (2)H 3 O + (b) Ethyl acetate + ethyl formate (1)NaOCH 2 CH 3 (2)H 3 O + Answer: (a) H 3 C C H OC 2 H 5 C O C O OC 2 H 5 C O (b) H H 2 C C O OC 2 H 5 C O 19.5 Show how you might synthesize each of the following compounds using, as your starting materials, esters, ketones, acyl halides, and so on. (a) O O H O O H HCCH 2 CH 2 CH 2 CH 2 CH 2 COC 2 H 5 O O NaOEt H 3 O (b) O O NaOEt H 3 O O O CH 3 CCH 2 CH 2 CH 2 COEt O O NaOEt CH 3 Br T.M O O CO 2 C 2 H 5 CO 2 C 2 H 5 (c) O O OEt EtO + EtOOCCH 2 CCH 2 COOEt CH 3 CH 3 NaOEt H 3 O T.M 19.6 Keto esters are capable of undergoing cyclization reactions similar to the Dieckmann condensation. Write a mechanism that accounts for the product formed in the following reaction: CH 3 C(CH 2 ) 4 COC 2 H 5 O O (1)NaOEt (2)H 3 O O O 2-Acetyleyclopentanone Mechanism: CH 3 C(CH 2 ) 4 COC 2 H 5 O O (1)NaOEt (2)H 3 O O O CH 3 CCHCH 2 CH 2 CH 2 COC 2 H 5 H O O CH 3 CCHCH 2 CH 2 CH 2 COC 2 H 5 O O OC 2 H 5 T.M OEt 19.7 Occasional side products of alkylations of sodioacetoacetic esters are compounds with the 19....
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