1.4- Dicarbonyl compounds from carboxylic acids

The procedure has been extended to tlie synthesis of 2-fluoro-l,3-dicarbonyl compounds from 2-fluoro-2-phosphonyl-1,3-dicarbonyl compounds readily obtained by reaction of diethyl 1-fluoro-l-(ethoxycarbonyl)methylphosphonate with aromatic carboxylic acid chlorides or alkyl chloroformates. The reaction proceeds smoothly by the MgCl2-induced P-C bond cleavage at room temperature of 1-acyl or 1-(alkoxycarbonyl)- -fluoro-l-fethoxycarbonyDmethylphosphonates. ... 

The key feature in the decarboxylation of malonic acid derivatives is that they are 1,3-dicarbonyl compounds with the acidic proton of the acid in close proximity to a carbonyl oxygen that is two carbon atoms away from the carboxyl unit. The proximity of these units is essential, which is why decarboxylation occurs with 1,3-dicarbonyl compormds and 7 o with 1,4-dicarbonyl compounds. This is a form of an elimination reaction (see Chapter 12). Going back to the expected product, 97 from 96, it is clear that this is a 1,3-dicarbonyl compound capable of decarboxylation upon heating. That is precisely what occurs, so the product is 98 rather than 97. Decarboxylation of malonic acid derivatives gives functionalized carboxylic acids. 

Nucleophilic substitution, e.g. the preparation of thiocyanates from lipophilic alcohols, can be facilitated by substrate hydrophilation via ammonioethanesulfonic acid esters (betylates)i . Mercaptans can be easily prepared from alcohols with inversion of configuration via thiolic esters prepared with thioacetic acid in the presence of 2-fluoro-pyridinium salts . C-Sulfenylation of / -dicarbonyl compounds with mercaptans by air oxidation in the presence of tetraethylammonium fluoride has been reported . Activated thiolic and selenolic esters can be prepared at room temperature from carboxylic acids and aryl thiocyanates or selenocyanates in the presence of tri-n-butylphosphine i. Phenylselenolactones have been obtained under very mild conditions from unsaturated acids and benzeneselenyl chloride. ... 

Vitamin C, also known as L-ascorbic acid, clearly appears to be of carbohydrate nature. Its most obvious functional group is the lactone ring system, and, although termed ascorbic acid, it is certainly not a carboxylic acid. Nevertheless, it shows acidic properties, since it is an enol, in fact an enediol. It is easy to predict which enol hydroxyl group is going to ionize more readily. It must be the one P to the carbonyl, ionization of which produces a conjugate base that is nicely resonance stabilized (see Section 4.3.5). Indeed, note that these resonance forms correspond to those of an enolate anion derived from a 1,3-dicarbonyl compound (see Section 10.1). Ionization of the a-hydroxyl provides less favourable resonance, and the remaining hydroxyls are typical non-acidic alcohols (see Section 4.3.3). Thus, the of vitamin C is 4.0, and is comparable to that of a carboxylic acid. 

On the basis of the above experimental facts, enaminones 42 are considered to be usable as the dinucleophilic reagents for the RTF reaction leading to 4-aminopyridine-3-carboxylic acid derivatives 41 (Table 11) [60]. Enaminones 42 are readily prepared by only mixing 1,3-dicarbonyl compounds 19 and amines without solvent. When enaminone 42i derived from ethyl ace-toacetate 19a and propylamine is used, the RTF reaction proceeds to afford ethyl AT-propyl-4-aminopyridine-3-carboxylate 41i in 88% yield. The amino group of 41 is easily modified by changing amine, and pyridine-3-carboxylic... 

Attempts to react enol(ate)s of esters with aliphatic aldehydes are doomed as the aldehyde will simply condense with itself. If the ester is replaced by a malonate 60, there is so much enol(ate) from the (5-dicarbonyl compound that the reaction is good. This style of aldol reaction is often called a Knoevenagel reaction10 and needs only a buffered mixture of amine and carboxylic acid. The enol reacts with the aldehyde 61 in the usual way and enolisation of the product 62 usually means that dehydration occurs under the conditions of the reaction. 

Regarding ozonation processes, the treatment with ozone leads to halogen-free oxygenated compounds (except when bromide is present), mostly aldehydes, carboxylic acids, ketoacids, ketones, etc. [189]. The evolution of analytical techniques and their combined use have allowed some researchers to identify new ozone by-products. This is the case of the work of Richardson et al. [189,190] who combined mass spectrometry and infrared spectroscopy together with derivatization methods. These authors found numerous aldehydes, ketones, dicarbonyl compounds, carboxylic acids, aldo and keto acids, and nitriles from the ozonation of Mississippi River water with 2.7-3 mg L 1 of TOC and pH about 7.5. They also identified by-products from ozonated-chlorinated (with chlorine and chloramine) water. In these cases, they found haloalkanes, haloalkenes, halo aldehydes, haloketones, haloacids, brominated compounds due to the presence of bromide ion, etc. They observed a lower formation of halocompounds formed after ozone-chlorine or chloramine oxidations than after single chlorination or chlorami-nation, showing the beneficial effect of preozonation. 

Imidazole-4-carboxylates have been made from amidines derived from or-ainino acids (see Section 2.2.1 and Table 2.2.1), by Claisen rearrangement of the adduct formed when an arylamidoxime reacts with a propiolate ester (see Section 2.2.1 and Scheme 2.2.6), from a-aminocarbonyls with cyanates or thiocyanates (see Section 4.1 and Table 4.1.1), from a-oximino- 6-dicarbonyl compounds heated with an aUcylamine (see Section 4.1 and Scheme 4.1.7), and by anionic cycloaddition of an alkyl isocyanoacetate to diethoxyacetonitrile (see Section 4.2 and Scheme 4.2.11 see also Scheme 4.2.12). A further useful approach is to use an appropriate tricarbonyl compound with an aldehyde and a source of ammonia (see Chapter and Scheme 5.1.1). Irradiation of 1-alkenyltetrazoles bearing an ester substituent may have applications (see Section 6.1.2.3). 

The applications of ruthenium tetroxide range from the common types of oxidations, such as those of alkenes, alcohols, and aldehydes to carboxylic acids [701, 774, 939, 940] of secondary alcohols to ketones [701, 940, 941] of aldehydes to acids (in poor yields) [940] of aromatic hydrocarbons to quinones [942, 943] or acids [701, 774, 941] and of sulfides to sulfoxides and sulfones [942], to specific ones like the oxidation of acetylenes to vicinal dicarbonyl compounds [9JS], of ethers to esters [940], of cyclic imines to lactams [944], and of lactams to imides [940]. 

Rubottom oxidation reactions have been conducted on enolsilanes derived from a number of different carbonyl derivatives including carboxylic acids and esters.15 For example, the Rubottom oxidation of bis(trimethylsilyl)ketene acetal 30 provided a-hydroxy carboxylic acid 31 in 81% yield. Use of alkyl trimethylsilyl ketene acetal substrates generates a-hydroxy esters, as seen in the conversion of 32 to 33.16 The synthesis of 3-hydroxy-a-ketoesters (e.g., 36) has been accomplished via Rubottom oxidation of enolsilanes such as 35 that are prepared via Homer-Wadsworth-Emmons reactions of aldehydes and ketones with 2-silyloxy phosphonoacetate reagent 34.17 The a-hydroxylation of enolsilanes derived from P-dicarbonyl compounds has also been described, although in some cases direct oxidation of the P-dicarbonyl compound is feasible without enolsilane formation.18... 

Hydroxy radical initiated oxidation of alkynes is important from the point of view of both atmospheric and combustion chemistry. Hatakeyama and coworkers have measured rate constants for the reaction of HO with acetylene, propyne and 2-butyne under atmospheric conditions. It has been suggested, based on product studies, that the jS-hydroxyvinyl radicals further react with molecular oxygen to form the corresponding peroxyl radicals and their subsequent reactions give carboxylic acid, a-dicarbonyl compounds and acyl radicals. 

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