Decarboxylation of glycidic acids

The classical solution to this problem is the decarboxylation of glycidic acids37-1 66, used by Woodward38 in his Lysergic acid synthesis. The Wittig reaction was... 

Apart from the reaction of cyclohexanecarboxylic acid with methyllithium, cyclohexyl methyl ketone has been prepared by the reaction of cyclohexylmagnesium halides with acetyl chloride or acetic anhydride and by the reaction of methylmagnesium iodide with cyclohexanecarboxylic acid chloride. Other preparative methods include the aluminum chloride-catalyzed acetylation of cyclohexene in the presence of cyclohexane, the oxidation of cyclohexylmethylcarbinol, " the decarboxylation and rearrangement of the glycidic ester derived from cyclohexanone and M)utyl a-chloroj)ropionate, and the catalytic hydrogenation of 1-acetylcycIohexene. "... 

Aromatic and aliphatic aldehydes have been prepared in good yields by the decarboxylation and isomerization of the corresponding glycidic acids. Esters of the latter are obtained by treating a ketone with ethyl chloro-acetate in the presence of sodium amide (method 127). The glycidic esters are first converted to the sodium salts with sodium ethoxide and then treated with aqueous hydrochloric acid under gentle reflux. By this procedure, a-phenylpropionaldehyde has been prepared from acetophenone in an over-all yield of 38%. Other details have been discussed. ... 

The initial product of the decarboxylation tautomerises to give the carbonyl compound. This is called the glycidic acid rearrangement. 

Darzens condensation. Formation of a- and (i-epoxy esters (glycidic esters) by the condensation of aldehydes or ketones with esters of a-haloacids the corresponding thermally unstable glycidic acids yield aldehydes or ketones on decarboxylation. 

The lipase from Serratia marcescens has a high enantioselectivity (E = 135) for the (2R,3S)-(4-methoxyphenyl) glycidic acid methyl ester, which acts as a competitive inhibitor. The formed acid (hydrolyzed (+)-methoxyphenylglycidate) is unstable and decarboxylates to give 4-methoxyphenylacetaldehyde this aldehyde strongly inhibits and deactivates the enzyme. It is removed by transfer to the aqueous phase by formation of a water-soluble adduct with sodium hydrogen sulfite added to the aqueous phase. The bisulfite acts also as a buffer to maintain constant pH during synthesis. 

The decaiboxylation of the glycidic acids obtained in this study was studied under various pyrolytic and catalytic conditions although moderate to good yields of product could be obtained, the ovei l synthetic potential of the homologation sequence shown in Scheme 17 remains limited due to the lack of a general method for mild and rapid decarboxylation. 

Since glycidic esters can usually be prepared from carbonyl compounds and chloroacetic esters, hydrolysis of the ester group and decarboxylation of the resulting glycidic acid gives as end-product the aldehyde containing one carbon atom more than those in the aldehyde or ketone ... 

The mechanism of gas-phase decomposition of ethyl and ethyl 3-phenyl glycidate has been studied by DFT and MP2 methods. The results indicated that the ethyl group is eliminated as ethylene through a concerted six-membered cyclic TS, and the unstable intermediate glycidic acid decarboxylates rapidly to give the corresponding aldehyde via a five-membered cyclic TS. 

Submitting a glycidic ester, to an alkaline hydrolysis at a temperature comprised between about 10° C. and about 40° C. for a period of time comprised between 6 and about 24 hours, to obtain an alkaline salt of the epoxyacid. Decarboxylating the compound in acidic ambient, at a temperature comprised between aobut 10° C. and about 40° C., for a period of time comprised between about 1 and about 8 hours, to obtain the ketone. Source Cannata 1991... 

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