Ch_322b_19.08

Ch_322b_19.08 - The end result is the same with formation...

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Michael Additions of 1,3-Dicarbonyls The addition of 1,3-dicarbonyls to ! , " -unsaturated carbonyl compounds under base-catalyzed conditions are referred to as Michael additions . These additions are understandable in terms of concepts already discussed that describe the formation and reactivity of enolate anions derived from 1,3-dicarbonyl compounds, and the mode of addition to conjugated enone systems. CH 3 C=CHCOEt CH 3 ethyl 3-methyl- 2-propenoate O = EtOOC EtOOC CH 2 + diethyl malonate cat amt NaOEt EtOH, 25 o C CH 3 C-CH 2 COEt O CH 3 CH(CO 2 Et) 2
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A Mechanism formation of enolate anion NaOEt + CH 2 (COOEt) 2 catalytic amount Na + - CH(COOEt) 2 + EtOH small amount of enolate anion Alternatively, the proton source in the above step can be diethyl malonate (pK a = 10.7) , which is more acidic than ethanol (pK a = 16) . However, since ethanol is the solvent, its concentration is much greater than the diethyl malonate.
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Unformatted text preview: The end result is the same with formation of more enolate anion of the diethyl malonate to drive along the conjugate addition reaction. conjugate addition of enolate anion + :CH(COOEt) 2 CH 3 C=CH-COEt CH 3 O =-CH 3 C-CH CH 3 CH(COOEt) 2 COEt O-enolate anion of ester proton transfer and trapping of enolate anion CH 3 C-CH CH 3 CH(COOEt) 2 COEt O-+ EtOH CH 3 C-CH 2-COEt CH 3 CH(COOEt) 2-O + EtO base is reformed. Further Synthetic Modifications Alkaline hydrolysis and heating to induce decarboxylation of the malonic acid subunit yields 3,3-dimethylglutaric acid . CH 3 C-CH 2-COEt CH 3 CH(COOEt) 2 O = (i) dil NaOH, heat (ii) H 3 O + CHCCH 2 COOH CH 3 CH 3 HOOC HOOC CH CCH 2 COOH CH 3 CH 3 HOOC HOOC heat >100 o C (-CO 2 ) HOOCCH 2 CCH 2 COOH CH 3 CH 3 3,3-dimethylglutaric acid...
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Ch_322b_19.08 - The end result is the same with formation...

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