Chem.62.Chapt19

Chem.62.Chapt19 - Chapter 19-1 Chemistry of Enolates Ester...

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Chapter 19-1 Chem 62 Ester Enolates Chemistry of Enolates The carbonyl group is probably the most important functional group in organic synthesis. Two fundamental reactions: nucleophilic addition (C=O is the electrophile) alkylation (carbonyl group, that is, the enolate, is the nucleophile) C O O Nu enolate formation and alkylation C O C O C O H C O E "enolate ion" Acidities in DMSO compound pK CH 3 C CH 2 O Ph H Ph C CH 2 O Ph H C CH O CH 3 H C CH O OCH 3 H Ph C CH O Ph H Ph C CH O SPh H N CH 2 C H EtO C CH 2 O H EtO C CH O Ph H Me 2 NC CH 2 O H EtO C CH O SPh H CH 3 S CH 2 O H CH 3 C CH O H Cl H CH(CO 2 Et) 2 H CH(CN) 2 CH 3 C CH O H CO 2 Et H CH 2 NO 2 H CH(COCH 3 ) 2 H CH(NO 2 ) 2 E + _ Nu: 13 11 11 10 9 4 35.1 34 21.4 22.7 30 31.3 17.1 17.7 22.9 24.1 24.6 26.5 5 17 Bases pK 41 35.1 29.8 32.2 31.4 29.0 36 NH 2 CH 3 SOCH 2 CH 3 CH 2 O (CH 3 ) 3 CO HO CH 3 O Et 2 N N H CH 3 CH 3 CH 3 CH 3 N Li CH 3 CH 3 CH 3 CH 3 lithium diisopropyl amide LDA BuLi THF, -78°C (CH 3 ) 3 Si N (CH 3 ) 3 Si Li N CH 3 CH 3 CH 3 CH 3 Li less basic than LDA more hindered than LDA LHMDS LTMP NaH, KH, CH 3 O Na +, (CH 3 ) 3 CO K + B: CH 3 CO 2 —H
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Chapter 19-2 Chem 62 Claisen Condensation n- Bu OEt O O Bu Bu OEt O Bu OEt O + EtO then H 3 O + R OEt O H H H + EtOH R OEt O H R OEt O R OEt O O R EtO R OEt O O R H H EtO + R OEt O O R R OEt O O R R OEt O O R H H O + H H R OEt O EtO H H ethyl pentanoate Use of the same alkoxide as the ester prevents transesterification during the Claisen condensation O CO 2 R O CO 2 R O CO 2 R O CO 2 R O CO 2 R EtO OEt O O EtO OEt O O EtO OEt O O O CO 2 Et EtO O CO 2 Et O CO 2 Et Dieckmann Condensation Reviews: Schaefer, Bloomfield Organic Reactions 1967 , 15 , 1.
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Chem.62.Chapt19 - Chapter 19-1 Chemistry of Enolates Ester...

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