Hydrogens between carbonyl groups in β diketones pk

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hydrogens between carbonyl groups in β -diketones, (pK a 9), alpha-hydrogens between carbonyl groups in β -ketoester, (pK a 11), and alpha-hydrogens between carbonyl groups in β -diester, (pK a 13). 2. Beta-diketone Synthesis with ketones and esters .
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CH 3 COEt CH 2 O R R CH 2 pK a ~20 + O ~25 pK a Na + - OEt/HOEt or NaH 2) H 3 O , H 2 O ketone ester 1) O CH 3 CCHCCH 2 R R O beta-diketone C CCH 2 R CH 3 C O ONa Na via pK a ~9 R a. Intramolecular Beta-diketone Synthesis : get 5 or 6 membered rings. CH 3 CCH 2 CH 2 CH 2 CH 2 COEt O O ! ! ! would give 7-membered ring so doesn't happen would give 5-membered ring ketone ! hydrogens more acidic than ester ! hydorgens 1) , H 2 O Na + - OEt/HOEt 2) H 3 O O CCH 3 O beta-diketone II. REACTIONS OF BETA-DICARBONYL COMPOUNDS: Beta-dicarbonyl compounds as Synthetic Intermediates A. Enolate Alkylations : A method of joining carbons, so it is synthetically very useful. An S n 2 reaction, step 2, follows the enolization step. 1. RCCH 2 COR' O O + Na + - OR'/HOR' 1) 2) R"X (use full equiv. of base) O O RC-CH-COR' R" + R'OH pK a ~11 R"- can be: methyl, or primary (reacts slowly with secondary) alkyl group; acyl RC O - ,
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or O - ROCCH 2 , as in an α -bromoester, or O RCCH 2 - , as in an α -bromoketone. (Also R" can be CH 2 , as in benzylic halides or CH 2 CHCH R , as in allylic halides.) X can be: Br, I, OTs, etc. R"X can be: O , oxacyclopropane. The -OR' group on the original ester can just be an -R' group, so that the original compound is a beta-diketone. 2. The second α -hydrogen can also be replaced as shown in C below.
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B. Beta-Ketoacid Decarboxylation (3-Ketoacid Decarboxylation) : Removing CO 2 ; applies to any Beta-Ketoester 1.
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  • Spring '08
  • Nasiri
  • Reaction, Claisen condensation, mixed claisen condensation

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