584 ESTER EN。 LATES 21.15 To undergo a Claisen condensation, an ester must have at least two protons on the a carbon 2RCH, COCH, CH3 NaOCH, CH3 RCH,CCCOCH2 CH3 Na 2CH CH2OH The equilibrium constant for condensation is unfavorable unless the B-keto ester can be deproton- ated to form a stable anion (a) Among the esters given, ethyl pentanoate and ethyl 3-methylbutanoate undergo the Claisen L Natch. ch CHaCH,,CH,COCH, CH CHa,CH,CH, CCHCOCH,CH Ethyl 3-ox0-2-propylheptanoate 1. NaOCH,CH, (CH3)2CHCH2 COCH CH3 2Ht (CH,) CHCH, CCHCOCH, CH3 CH(CH3h2 Ethyl 3-methylbutanoate Ethyl 2-isopropyl-5-methyl- 3-oxohexanoate (b) The Claisen condensation product of ethyl 2-methylbutanoate cannot be deprotonated; the uilibrium constant for its formation is less than 1 CHCH..CH CH CH, CHCCCOOCH,CH3 CH3 CH,CH Ethyl 2-methylbutanoate No protons on a-carbon atom form stabilized enolate by depr (c) Ethyl 2, 2-dimethylpropanoate has no protons on its a carbon; it cannot form the ester enolate required in the first step of the Claisen condensation H, C CH CCOCH,CH3 OCH,CH no reaction H3 Ethyl 2, 2- dimethylpropanoate 21.16(a) The Claisen condensation of ethyl phenylacetate is given by the equation 00 NaOCH.CH C6H CH,COCH, CH CBHSCH, CCHCOCH,CH Ethyl phenylacetate Ethyl 3-oXo-2, 4-diphenylbutanoat Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website21.15 To undergo a Claisen condensation, an ester must have at least two protons on the carbon: The equilibrium constant for condensation is unfavorable unless the -keto ester can be deproton￾ated to form a stable anion. (a) Among the esters given, ethyl pentanoate and ethyl 3-methylbutanoate undergo the Claisen condensation (b) The Claisen condensation product of ethyl 2-methylbutanoate cannot be deprotonated; the equilibrium constant for its formation is less than 1. (c) Ethyl 2,2-dimethylpropanoate has no protons on its carbon; it cannot form the ester enolate required in the first step of the Claisen condensation. 21.16 (a) The Claisen condensation of ethyl phenylacetate is given by the equation 1. NaOCH2CH3 2. H C6H5CH2COCH2CH3 O Ethyl phenylacetate C6H5CH2CCHCOCH2CH3 O O C6H5 Ethyl 3-oxo-2,4-diphenylbutanoate OCH2CH3 H3C CH3CCOCH2CH3 O CH3 C no reaction Ethyl 2,2- dimethylpropanoate Ethyl 2-methylbutanoate CH3CH2CHCOCH2CH3 O CH3 No protons on -carbon atom; cannot form stabilized enolate by deprotonation CH3CH2CHCCCOOCH2CH3 O CH3 CH2CH3 CH3 NaOCH2CH3 K  1 1. NaOCH2CH3 2. H (CH3)2CHCH2COCH2CH3 O Ethyl 3-methylbutanoate (CH3)2CHCH2CCHCOCH2CH3 O O CH(CH3)2 Ethyl 2-isopropyl-5-methyl- 3-oxohexanoate 1. NaOCH2CH3 2. H CH3CH2CH2CH2CCHCOCH2CH3 O CH2CH2CH3 O Ethyl 3-oxo-2-propylheptanoate CH3CH2CH2CH2COCH2CH3 O Ethyl pentanoate 2RCH2COCH2CH3 NaOCH2CH3 O Na 2CH3CH2OH RCH2CCCOCH2CH3 R O O 584 ESTER ENOLATES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website