Propanoates, methyl 2- substituted

Many polyketides have one or more methyl substituents on their carbon chain. In some cases -adenosylmethionine is the source of a methyl group in others methylmalonyl CoA (from propanoic acid) substitutes for acetate during chain assembly. 

Electrochemical fluorination of a-cyclohexenyl-substituted carboxylic (acetic, propanoic, butanoic, and pentanoic) acid esters (methyl, ethyl, and propyl) results in a series of both perfluoro-9-alkyl-7-oxabicyclo[4 3 OJnonanes and per-fluoro-8-alkoxy-9-alkyl-7-oxabicyclo[4.3.0]nonanes [<8S] (equation 19)... 

Methyl trifluoropyruvate alkylates a series of substituted indoles catalysed by the chiral non-racemic 2,2/-bipyridylcopper(II) triflate complex (32) to form methyl 3,3,3- trifluoro-2-hydroxy-2-indole-3-yl propanoates [e.g. (33)] in high enantiomeric excess and good yield.37... 

Table 4.5 Examples of the different electronic substitution constants used in QSAR studies. Inductive substituent constants (crO are the contribution the inductive effect makes to Hammett constants and can be used for aliphatic compounds. Taft substitution constants (cr ) refer to aliphatic substituents but use propanoic acid (the 2-methyl derivative of ethanoic acid) as the reference point. The Swain-Lupton constants represent the contributions due to the inductive (.F) and mesomeric or resonance (R) components of Hammett constants. Adapted from An Introduction to the Principles of Drug Design and Action by Smith and Williams 3rd Ed. (1998) Ed. H.J.Smith. Reproduced by permission of Harwood Academic Publishers.

A few comments on the values of r and (r+ - - r ) (cf. Table VIII) are necessary. Increasing hydrocarbon content decreases the hydrophilic property of the anion (cf. formic, acitic, propanoic, butanoic, 3-methyl-butanoic, and benzoic acids) resulting in the decrease of hydration the trend eventually levels off. Hydrophilic substitution increases hydration (cf. acetic, chloroacetic, cyanoacetic, glycolic acids cf. glutaric, succinic, and malonic acids cf. benzoic and salicyclic acids). Also note that r is smallest for benzoic acid and largest for malonic acid. These trends cannot be fortuitous. 

A reaction which is applicable to the synthesis of imidazoles substituted at C-4 by sulfur substituents is the interaction of a-chloro-a-phenyl thioketones (prepared from the corresponding diazoketones) with ammonia and carboxylic acids. Although the detailed reaction course is yet uncertain, it bears a close resemblance to the reactions of a-chloro ketones with amides. The method has been used to prepare 2-ethyl-4-methyl-5-phenylthioimidazole (145) using ammonia, propanoic acid and 1-chloro-l-phenylthiopropanone (Scheme 82). 

The structure of the western corn rootworm sex pheromone is 8-methyl-2-decanol propanoate (] 6) and four stereoisomers are possible (Figure 7). In our synthesis (3), we coupled a chiral 5-carbon unit to a 6-carbon fragment that had the requisite substitution to allow resolution at the oxygenated carbon. As mentioned earlier, (S)-2-methylbutyric acid was available to us from the alcohol. D-Isoleucine served as a source for the (R)-acid. Nitrosation, followed by decarboxylative oxidation of the intermediate hydroxyacid led to the (R)-2-methylbutyric acid in 96% ee. The process of fractional crystallization was... 

Monosaccharide oxiranes undergo the homo-Horner reaction with phosphoryl-substituted carbanions to give monosaccharides fused with a cyclopropane ring. " a-D-Mannopyrano-side 9, a precursor in an enantiospecific route to (4-)- and ( —)-chrysanthemumdicarboxylic acids, was synthesized in 50% yield by the reaction of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside (8) with ethyl 2-(diethoxyphosphoryl)propanoate. " ... 

Porphyrins. Collective name derived from Greek porphyra=purple, purple snail, for the widely distributed purple (red) natural pigments formally prepared from the parent skeleton of porphine by substitution of the macrocylic tetrapyrrole framework with methyl, vinyl, acetic acid, propanoic acid units, or other substituents. 

Just as an ester enolate anion reacts with an aldehyde or ketone via acyl addition, it is also reasonable that the enolate anion of an aldehyde or a ketone may react with an ester via acyl substitution. In the former reaction, the ester enolate is the nucleophile in the latter reaction, a ketone or aldehyde enolate is the nucleophile. When cyclohexanone (80) is treated with LDA (THF, -78°C) and then with methyl propanoate, the initial product is 81. Loss of OMe completes the acyl substitution sequence to give diketone 82. There is nothing special or unusual about these two variations. Virtually any ketone or aldehyde enolate reacts with an ester to form 1,3-diketones such as 82. 

Esters (4.48) have one carbon substituent at the carbonyl and one -OR group. They are formed from acids and alcohols (Figure 4.11), and the name of the ester is a combination of the acid and alcohol names. The name of the alcohol used the form of a substituent, methyl, ethyl, phenyl, etc., and the acid part now takes the suffix -oate, to indicate the ester functionality. Thus 4.49 is methyl propanoate. The most common error that students make in naming esters is that they don t recognize the functional group and try to name them as substituted ketones. If you are finding the nomenclature of these difficult, it s often helpful to separate the ester into the acid and alcohol from which it was made. 4.50 was made from ethanoic (acetic) acid and 1-penta-nol hence, the name is 1-pentyl ethanoate or 1-pentyl acetate. In text, esters may be written as... 

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