Decarboxylation malonate

A p-keto ester can be hydrolyzed to a p-keto acid, and heating leads to decarboxylation. Malonic acid derivatives, as well as P-ketone acids decarboxylate upon heating. 

A p-keto ester can be hydrolyzed to a P-keto acid, and heating leads to decarboxylation. Malonic acid derivatives, as well as P-ketone acids decarboxylate upon heating 63,109, 111, 135. Enolate anions react with alkyl halides by an S]v2 reaction to give alkylated carbonyl compounds 65, 67, 70, 84, 108, 116, 127,... 

The starting materials are acetyl CoA and malonyl CoA. Successive molecules of malonyl CoA are added to a primer molecule of acetyl CoA with accompanying decarboxylation. Malonate consists of three C atoms. After decarboxylation a 2 C body remains. Thus, in effect, the biosynthesis of the fatty acids consists in arranging 2 C units in series, as we had already deduced from the constitution of the fatty acids. In discussing the biosynthesis in detail the following constituent processes have to be recognized ... 

Decarboxylation of malonic acid derivatives is a well studied process in the biosynthesis of biomolecules such as long-chain fatty acids and polyketides. A decarboxylase that exhibits enantioselectivity for substituted malonates would be useful for producing ophcally active carboxylic acids, hi fact, malonyl-CoA decarboxylase does catalyze an enantioselective decarboxylation (Figure 3.2) [5], but malonyl-CoA is an unsuitable precursor for optically active substances. Instead, we focused on the prochiral-activated compoimd arylmalonate, an intermediate of malonic ester synthesis, to develop a method for enantioselective decarboxylation. Malonates are stable at room temperature but readily decompose to arylacetate and CO2 at high temperatures. This suggests that the decarboxylation of arylmalonate may occur naturally if arylmalonate acts as a substrate for a decarboxylase. 

The role of the base is apparently primarily that of a proton remover from the reactive methylene group thus if B represents the base, reaction (i) gives the carbanion, which then combines with the positive carbon of the carbonyl group (reaction ii) the product regains a proton from the piperidinium ion, and then by loss of water followed by mono-decarboxylation of the malonic acid residue gives the final acid. 

By hydrolysis of substituted malonic esters with 50 per cent, potassium hydroxide, followed by decarboxylation of the resulting malonic add by heating above the m.p. or, better, by rendering the aqueous solution of the potassium salt of the dibasic acid strongly acid and refluxing the mixture, for example ... 

The addition of active methylene compounds (ethyl malonate, ethyl aoeto-acetate, ethyl plienylacetate, nltromethane, acrylonitrile, etc.) to the aP-double bond of a conjugated unsaturated ketone, ester or nitrile In the presence of a basic catalyst (sodium ethoxide, piperidine, diethylamiiie, etc.) is known as the Michael reaction or Michael addition. The reaction may be illustrated by the addition of ethyl malonate to ethyl fumarate in the presence of sodium ethoxide hydrolysis and decarboxylation of the addendum (ethyl propane-1 1 2 3-tetracarboxylate) yields trlcarballylic acid ... 

The last-named reaction provides an excellent method for the preparation of a-substituted glutaric acids the intermediate alkyl (aryl) -2-cyanoethyl-malonate is both hydrolysed and decarboxylated re ily by boiling with an excess of 48 per cent, hydrobromic acid solution. 

Synthesis No control is needed in the first step there is only one enolisable H atom on eitlier aldehyde. If we use malonic acid for the second step, cychsation and decarboxylation will be spontaneous (Monatshefte, 1904, 2 13). 

The phenylacetic acid derivative 469 is produced by the carbonylation of the aromatic aldehyde 468 having electron-donating groups[jl26]. The reaction proceeds at 110 C under 50-100 atm of CO with the catalytic system Pd-Ph3P-HCl. The reaction is explained by the successive dicarbonylation of the benzylic chlorides 470 and 471 formed in situ by the addition of HCl to aldehyde to form the malonate 472, followed by decarboxylation. As supporting evidence, mandelic acid is converted into phenylacetic acid under the same reaction conditions[327]. 

Geranyl acetoacetate (685) is converted into geranylacetone (686). On the other hand, a mixture of E- and Z-isomers of 688 is obtained from neryl acetoacetate (687). The decarboxylation and allylation of the allyl malonate or cyanoacetate 689 affords the o-allylated acetate or nitriie[447]. The trifluoromethyl ketone 691 is prepared from cinnamyl 4.4,4-trifluoroacetoace-tate (690)[448],... 

The allyl cyanoacetate 731 can be converted into an a, /3-unsaturated nitrile by the decarboxylation-elimination reaction[460], but allyl malonates cannot be converted into unsaturated esters, the protonation and allylation products being formed instead. 

The decarboxylation of allyl /3-keto carboxylates generates 7r-allylpalladium enolates. Aldol condensation and Michael addition are typical reactions for metal enolates. Actually Pd enolates undergo intramolecular aldol condensation and Michael addition. When an aldehyde group is present in the allyl fi-keto ester 738, intramolecular aldol condensation takes place yielding the cyclic aldol 739 as a main product[463]. At the same time, the diketone 740 is formed as a minor product by /3-eIimination. This is Pd-catalyzed aldol condensation under neutral conditions. The reaction proceeds even in the presence of water, showing that the Pd enolate is not decomposed with water. The spiro-aldol 742 is obtained from 741. Allyl acetates with other EWGs such as allyl malonate, cyanoacetate 743, and sulfonylacetate undergo similar aldol-type cycliza-tions[464]. 

Hydrogenolysis of the diallyl alkylmalonate 757 with formic acid in boiling dioxane affords the monocarboxylic acid 758. Allyl ethyl malonates are converted into ethyl carboxylates[471]. The malonic allyl ester TV-allylimide 759 undergoes smooth deallylation in refluxing dioxane to give the simple imide 760(472]. The allyl cyanoacetate 761 undergoes smooth decarboxylation to give... 

One effective method for synthesis of tryptophan derivatives involves alkylation of formamido- or acetamido- malonate diesters by gramine[l,2]. Conversion to tryptophans is completed by hydrolysis and decarboxylation. These reactions were discussed in Chapter 12. An enolate of an a-nitro ester is an alternative nucleophile. The products can be converted to tryptophans by rcduction[3,4],... 

The three isomers of thiazoleacetic acid can be decarboxylated, the order of facility being 2>5>4, though the relative stability depends on each particular compound and the reaction conditions (72-75). This reaction may be used to obtain certain alkylthiazoles (73). Malonic derivatives can also be decarboxylated to give aliphatic thiazole acids (49, 51)... 

Compounds that readily undergo thermal decarboxylation include those related to malonic acid On being heated above its melting point malonic acid is converted to acetic acid and carbon dioxide... 

Transition state in thermal decarboxylation of malonic acid... 

The thermal decarboxylation of malonic acid derivatives is the last step m a multistep synthesis of carboxylic acids known as the malonic ester synthesis This synthetic method will be described m Section 21 7... 

Section 19 17 11 Dicarboxylic acids (malonic acids) and p keto acids undergo thermal decarboxylation by a mechanism m which a p carbonyl group assists the departure of carbon dioxide... 

Converting the C 2 alkylated derivative to the corresponding malonic acid deriva tive by ester hydrolysis gives a compound susceptible to thermal decarboxylation Tern peratures of approximately 180°C are normally required... 

Section 21 7 The malonic ester synthesis is related to the acetoacetic ester synthesis Alkyl halides (RX) are converted to carboxylic acids of the type RCH2COOH by reaction with the enolate ion derived from diethyl mal onate followed by saponification and decarboxylation... 

The physical properties of cyanoacetic acid [372-09-8] and two of its ester derivatives are Hsted ia Table 11 (82). The parent acid is a strong organic acid with a dissociation constant at 25°C of 3.36 x 10. It is prepared by the reaction of chloroacetic acid with sodium cyanide. It is hygroscopic and highly soluble ia alcohols and diethyl ether but iasoluble ia both aromatic and aUphatic hydrocarbons. It undergoes typical nitrile and acid reactions but the presence of the nitrile and the carboxyUc acid on the same carbon cause the hydrogens on C-2 to be readily replaced. The resulting malonic acid derivative decarboxylates to a substituted acrylonitrile ... 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

Uses. Malonic acid is used instead of the less expensive malonates for the introduction of a CH—COOH group under mild conditions by Knoevenagel condensation and subsequent decarboxylation. The synthesis of 3,4,5-trimethoxycinnaniic acid, the key intermediate for the coronary vasohdator Cinepa2et maleate [50679-07-7] (5) involves such a pathway (13). 

The first ester function of the malonates is hydrolyzed much more easily than the second. This property can be used for synthesizing a large number of carboxyUc acids by alkylation or acylation of a malonate followed by hydrolysis and decarboxylation of one ester group. This is the case for ethyl... 

Reactions. The chemical properties of cyanoacetates ate quite similar to those of the malonates. The carbonyl activity of the ester function is increased by the cyano group s tendency to withdraw electrons. Therefore, amidation with ammonia [7664-41-7] to cyanoacetamide [107-91-5] (55) or with urea to cyanoacetylurea [448-98-2] (56) proceeds very easily. An interesting reaction of cyanoacetic acid is the Knoevenagel condensation with aldehydes followed by decarboxylation which leads to substituted acrylonitriles (57) such as (29), or with ketones followed by decarboxylation with a shift of the double bond to give P,y-unsaturated nitriles (58) such as (30) when cyclohexanone [108-94-1] is used. 

With active methylene compounds, the carbanion substitutes for the hydroxyl group of aHyl alcohol (17,20). Reaction of aHyl alcohol with acetylacetone at 85°C for 3 h yields 70% monoaHyl compound and 26% diaHyl compound. Malonic acid ester in which the hydrogen atom of its active methylene is substituted by A/-acetyl, undergoes the same substitution reaction with aHyl alcohol and subsequendy yields a-amino acid by decarboxylation (21). 

Fig. 2. Synthesis of uma2enil (18). The isonitrosoacetanihde is synthesized from 4-f1iioroani1ine. Cyclization using sulfuric acid is followed by oxidization using peracetic acid to the isatoic anhydride. Reaction of sarcosine in DMF and acetic acid leads to the benzodiazepine-2,5-dione. Deprotonation, phosphorylation, and subsequent reaction with diethyl malonate leads to the diester. After selective hydrolysis and decarboxylation the resulting monoester is nitrosated and catalyticaHy hydrogenated to the aminoester. Introduction of the final carbon atom is accompHshed by reaction of triethyl orthoformate to...

Order of thermal stabiUty as determined by differential thermal analysis is sebacic (330°C) > a2elaic = pimelic (320°C) > suberic = adipic = glutaric (290°C) > succinic (255°C) > oxahc (200°C) > malonic (185°C) (19). This order is somewhat different than that in Table 2, and is the result of differences in test conditions. The energy of activation for decarboxylation has been estimated to be 251 kj/mol (60 kcal/mol) for higher members of the series and 126 kJ/mol (30 kcal/mol) for malonic acid (1). 

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