23 - CHAPTER 23 -Dicarbonyl Compounds Protons flanked by...

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CHAPTER 23 β -Dicarbonyl Compounds Protons flanked by two carbonyl groups are acidic. The acidity of hydrogens flanked by two carbonyl groups is enhanced by resonance stabilization of the resulting anion.
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When only a single α -hydrogen is present, the Claisen condensation fails because the addition product lacks the additional acidic proton necessary to drive the equilibrium: (CR 2 instead of CH 2 )
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Base treatment of a β -ketoester that lacks protons in α position leads to retro-Claisen condensation Mixed Claisen condensations start with two different esters, are typically unselective and furnish product mixtures unless one of the esters has no α - hydrogens.
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The Dieckmann condensation is an intramolecular version of the Claisen condensation. Products are cyclic 3-keto ( β -keto) esters. The method works best for the formation of 5 and 6 The method works best for the formation of 5- and 6- membered rings. Ketones undergo mixed Claisen reactions. Ketones are more acidic than esters. They are deprotonated and react before the ester has a chance to undergo sel condensation a chance to undergo self-condensation.
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Synthetic utility of the Claisen condensation.
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This note was uploaded on 12/26/2008 for the course CHEM CHEM 140C taught by Professor Finn during the Spring '08 term at UCSD.

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23 - CHAPTER 23 -Dicarbonyl Compounds Protons flanked by...

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