Esters conversion

Conversely, ester condensation reactions join acyl groups from CoA derivatives to Schiff bases derived from glycine or serine. Succinyl-CoA is the acyl donor... 

In organic chemistry the term is used to describe the conversion of an ester to an acid and an alcohol (saponification), the addition of the elements of water to a molecule, e.g. the conversion of a nitrile to an amide... 

This method is to be recommended when only a small quantity of the acid is availa ble, since both the conversion of the acid into its silver salt (p. 445) and of the latter to the ester give almost quantitative yields. 

The conversion of the compounds under investigation into coloured derivatives (e.g., the separation of carbonyl compounds by conversion into their 2 4-dinitrophenylhydrazones, etc. of hydrocarbons through their picrates of alcohols through their 3 5-dinitrobenzoates of glucose, fructose and other simple sugars through their p-phenylazobenzoyl esters). 

Ethyl a-bromopropionate. This preparation illustrates the facile bromination of an acid chloride (propionyl chloride) in the presence of red phosphorus, and the subsequent conversion of the bromoacid chloride into the ethyl ester by direct interaction with ethanol. 

By the Fries reaction. This is a variant of the Friedel-Craft reaction it consists in the conversion of an ester of a phenol to the corresponding o- and p-hydroxyketone, or a mixture of both, by treatment with anhydrous aluminium chloride ... 

Acyl hahdes may be identified by —hydrolysis to the corresponding acids (the latter may be further characterised as in Section IV,175) conversion into amides (Section IV,191), anihdes or p-toluidides (Section IV,100) and conversion into sohd esters (Section IV,183). 

To prepare the free sulphinic acid, dissolve some of the sodium salt in cold water and cautiously acidify with hydrochloric acid avoid an excess of mineral acid since it dissolves the sulphinic acid to a certain extent. The resulting p-tolueneaulphinic acid is difflcult to dry without partial conversion into the sulphonic acid and thiolsulphonic ester... 

Acid derivatives are made directly from acids or by conversion from other acid derivatives depending on their stabihty. The most important are esters (RCOiEt), amides (RCO2NR2), anhydrides (RCOO COR) and add clilorides (RCOCI). Arrange these in an order of stabilily, the most reactive at the top of the list, the most stable at the bottom. 

The conversion of carboxylic acid derivatives (halides, esters and lactones, tertiary amides and lactams, nitriles) into aldehydes can be achieved with bulky aluminum hydrides (e.g. DIBAL = diisobutylaluminum hydride, lithium trialkoxyalanates). Simple addition of three equivalents of an alcohol to LiAlH, in THF solution produces those deactivated and selective reagents, e.g. lithium triisopropoxyalanate, LiAlH(OPr )j (J. Malek, 1972). 

Usually esters cannot be reduced directly to the corresponding ethers. Eflicient conversion with the NaBH4 —BF3 reagent is only possible, if the alcohol component is tertiary (G.R. Pettit, 1962 B). 

There are, however, two useful alkylating-redudng methods. One is the methylenation of the ester carbonyl group with Tebbe s reagent, the other is the conversion of thionolactones to cyclic thioketals and subsequent reduction. 

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

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],... 

Hydroxythiazoles give 2-chIorothiazole derivatives almost quantitatively upon treatment with phosphorus oxychloride (221, 229, 428). This constitutes a convenient synthesis method for these compounds when the conversion of 2-aminothiazoles to 2-chlorothiazole derivatives fails. Esters of thiocarbamic acid or thiourethanes also react with a-halocarbonyl compounds to give the corresponding 2-alkoxythiazoles (50, 68, 209, 272). 

These methods were not applicable to all acids, and various alternative routes were investigated. The conversion of an acid to its methri ester by diazomethane is a method of choice when other methods are unsatisfactory (6, 30, 61, 65). With appropriate alcohols thiazoleanhydrkies give the esters or diesters in good yield (64), dimethyl 2-phoiyl-4,5-thiazoledicarboxylate (13) has been prepared in this way (Scheme 8) (17). 

The conversion of esters to hydrazides and of hydrazides to the sulfonyl derivatives occurs in good yield in the McFadyen-Stevens synthesis, but the decomposition of sulfonyl derivatives gives low yields of the desired products, for example, thiazole hydrazide (28) with 10% excess of PhSOjCl in pyridine gave a 75% yield of l-phenylsulfonyl-2-(4-methyl-5-thiazo ecarbonyl)hydrazine (29) (66). The Newman-Caflish modification of the McFadyen-Stevens synthesis gave 37% 4-methyl-5-thiazole-carboxaldehyde (30) (Scheme 27). 

The following conversion has been reported in the chemical literature It was earned out in two steps the first of which involved formation of a p toluenesulfonate ester Indicate the reagents for this step and show how you could convert the p toluenesulfonate to the desired product... 

Overall the reaction leads to addition of two hydroxyl groups to the double bond and IS referred to as hydroxylation Both oxygens of the diol come from osmium tetraox ide via the cyclic osmate ester The reaction of OSO4 with the alkene is a syn addition and the conversion of the cyclic osmate to the diol involves cleavage of the bonds between oxygen and osmium Thus both hydroxyl groups of the diol become attached to the same face of the double bond syn hydroxylation of the alkene is observed... 

Conversion to p toluenesulfonate es ters (Section 8 14) Alcohols react with p toluenesulfonyl chloride to give p toluenesulfonate esters Sulfo nate esters are reactive substrates for nucleophilic substitution and elimma tion reactions The p toluenesulfo nate group is often abbreviated —OTs... 

Section 19 13 Among the reactions of carboxylic acids their conversions to acyl chlo rides primary alcohols and esters were introduced m earlier chapters and were reviewed m Table 19 5... 

Conversions of acid anhydrides to other carboxylic acid derivatives are illustrated m Table 20 2 Because a more highly stabilized carbonyl group must result m order for nucleophilic acyl substitution to be effective acid anhydrides are readily converted to carboxylic acids esters and amides but not to acyl chlorides... 

Conversion of Esters to Other Carboxylic Acid Derivatives... 

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

The preference for O acylation of phenols arises because these reactions are kmetically controlled O acylation is faster than C acylation The C acyl isomers are more stable how ever and it is known that aluminum chloride is a very effective catalyst for the conversion of aryl esters to aryl ketones This isomerization is called the Fries rearrangement... 

In keeping with its biogenetic origin m three molecules of acetic acid mevalonic acid has six carbon atoms The conversion of mevalonate to isopentenyl pyrophosphate involves loss of the extra carbon as carbon dioxide First the alcohol hydroxyl groups of mevalonate are converted to phosphate ester functions—they are enzymatically phosphorylated with introduction of a simple phosphate at the tertiary site and a pyrophosphate at the primary site Decarboxylation m concert with loss of the terti ary phosphate introduces a carbon-carbon double bond and gives isopentenyl pyrophos phate the fundamental building block for formation of isoprenoid natural products... 

There are ill-defined limits on EI/CI usage, based mostly on these issues of volatility and thermal stability. Sometimes these limits can be extended by preparation of a suitable chemical derivative. For example, polar carboxylic acids generally give either no or only a poor yield of molecular ions, but their conversion into methyl esters affords less polar, more volatile materials that can be examined easily by EL In the absence of an alternative method of ionization, EI/CI can still be used with clever manipulation of chemical derivatization techniques. 

Acylated Corticoids. The corticoid side-chain of (30) was converted iato the cycHc ortho ester (96) by reaction with a lower alkyl ortho ester RC(OR )2 iu benzene solution ia the presence of i ra-toluenesulfonic acid (88). Acid hydrolysis of the product at room temperature led to the formation of the 17-monoesters (97) ia nearly quantitative yield. The 17-monoesters (97) underwent acyl migration to the 21-monoesters (98) on careful heating with. In this way, prednisolone 17a,21-methylorthovalerate was converted quantitatively iato prednisolone 17-valerate, which is a very active antiinflammatory agent (89). The iatermediate ortho esters also are active. Thus, 17a,21-(l -methoxy)-pentyhdenedioxy-l,4-pregnadiene-liP-ol-3,20-dione [(96), R = CH3, R = C Hg] is at least 70 times more potent than prednisolone (89). The above conversions... 

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