Rc ch 2 cor o o 1 1 equiv oh 2 h h 2 o or acid

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RC-CH 2 -COR' O O 1) 1 equiv - OH 2) H + , H 2 O OR acid hydrolysis H + , H 2 O 3-ketoester O O RC-CH 2 -COH (also called saponification) base hydrolysis 3-ketoacid + HOR' catalytic amt.) ( mild heat (decarboxylates) RCCH 3 + CO 2 O The heat step can be combined with the acid step. methyl ketone 2. Mechanism of Decarboxylation CH 2 C O O H C R O heat ( ) as 100 o C CH 2 O H R + O C O C ketoacid enol tautomerizes R C O CH 3 methy ketone a. If you see a ketone, ask yourself if it could have come from β -dicarbonyl chemistry. A ketone is very difficult to make with aldol condensation. Also you can't normally do β -dicarbonyl chemistry to get an aldehyde because it does aldol condensation. b. If the R group above is -OH, as after malonic ester hydrolysis ( see D below), a carboxylic acid results. carboxylic acid CH 3 C O tautomerizes endiol diacid C O C O + C CH 2 O H as 100 o ) ( heat O C HO CH 2 C O O H HO HO c. Realize that one or both α -hydrogens in the original dicarbonyl compound can be substituted by enolate alkylation. C. Acetoacetic Ester Synthesis : Leads to methyl ketones which can be substituted once or twice. The actual starting 3-ketoester need not be an acetoacetic ester as ethyl 3-oxobutanoate (ethyl acetoacetate), which can be bought or made from a Claisen Condensation of ethyl ethanoate.
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O CH 3 COEt 2 1)NaOEt 2) H + , H 2 O O O CH 3 CCH 2 COCH 2 CH 3 aceto ethyl part part part acetate A generic acetoacetic ester synthesis follows. RC-CH O 2) R"X NaOR'/HOR' + O O RCCH 2 COR' 1) (enolate) R" R 1 3) NaOR'/ HOR' (enolate) (alkylate) 4) R 1 X (alkylate) R 1 O O RC-C-COR' R" 5) OH, (base hydrolysis to carboxylate) 6) H + , H 2 O, heat (decarboxylation & tautomerization) get ~11 pK a R 1 or R" = alkyl, acyl, ROCCH 2 - O - RCCH 2 O , O R 1 X X R" , or = D. Malonic Ester Synthesis : Leads to carboxylic acids which can be substituted once or twice.
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