CH.23_DICARBONYL_COMPDS

CH.23_DICARBONYL_COMPDS - Chemistry 118C Workshop chapter...

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Chemistry 118C Workshop Jim Hollister chapter 23 LSC/UC Davis NOTE: This outline does not include the details of reactions before mixed Claisen Condensation Reactions. I. PREPARATION OF BETA-DICARBONYL COMPOUNDS A. Claisen Condensation : an ester which must have at least two acidic alpha-hydrogens can condense with another molecule of the same ester to yield a beta-ketoester. Requires a stoichiometric amount of an alkoxide and its corresponding alcohol. B. Retro-Claisen : occurs if the carbon between two beta-dicarbonyl carbons in a ketoester has one or no acidic alpha-hydrogens on it. An alkoxide and corresponding alcohol are the reagents. C. Mixed Claisen Condensation with two different esters: One of the esters should have no alpha hydrogens so that only one product is produced. D. Dieckmann Condensation : An intramolecular Claisen Condensation which works best with 1, 6 and 1, 7 diesters to form 5-membered and 6-membered rings, respectively. E. Double Claisen Condensation : With diesters and dicarbonyls [as CH 3 O(C=O)(C=O)OCH 3 ] to give cyclic compounds. It starts with an inter molecular Claisen Condensation followed by a intra molecular Claisen Condensation. (May not have been covered in lecture and is not it text.) F. Mixed Claisen Condensation between Ketones and Esters : Can get beta-diketones (also get beta-ketoesters with carbonates and ketones, and get beta-ketoaldehydes with formates and ketones). O HCOR O ROCOR Carbonates, ; formates, 1. Learn : Alpha-hydrogens on ketones are more acidic (pK a 20) than alpha- hydrogens on esters (pK a 25), so mixed products can be avoided. (Also learn: alpha- 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).
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This note was uploaded on 01/31/2011 for the course CHE 118c taught by Professor Nasiri during the Spring '08 term at UC Davis.

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CH.23_DICARBONYL_COMPDS - Chemistry 118C Workshop chapter...

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