Enol ethers from carboxylic acids

Sulfuric acid Carboxylic acid esters from carboxylic acids and enol ethers... 

Aldehydes of different types can be conveniently prepared from the next lower halides through carbinols which are split by dia-zotized sulfanilic acid Aliphatic aldehydes in particular can be easily obtained from carboxylic acids through N-acylethylenimi-es Aldehydes, in turn, can be converted directly into nitriles with hydroxylamine hydrochloride Ketones can be efficiently prepared from ethylene derivatives via boranes and, in high purity, from labile alcohols by oxidation in an aq.-ethereal two-phase medium Heating aliphatic acids with reduced iron powder proved to be an excellent method for the prepn. of sym. straight-chain ketones /5-Aminoketones unobtainable by Mannich reaction may be prepared via halogenomagnesium enolates... 

Monoalkyl ethers of (R,R) 1,2-bis[3,5-bis(trifluoromethyl)phenyl]ethanediol, 24, have been examined for the enantioselective protonation of silyl enol ethers and ketene disilyl acetals in the presence of SnCU (Scheme 12.21) [25]. The corresponding ketones and carboxylic acids have been isolated in quantitative yield. High enantioselectivities have been observed for the protonation of trimethylsilyl enol ethers derived from aromatic ketones and ketene bis(trimethylsilyl)acetals derived from 2-arylalkanoic acids. 

Interposing an additional carbon atom between the indazole nucleus and the acetic acid side chain provides another compound that shows anti-inflammatory activity in model systems. Reduction of the carboxylic acid in the indazole (38-1) by means of hthium aluminum hydride leads to the carbinol (38-2). Alkylation of the enolate from the alcohol with methyl 2-bromo-2-methylpropionate leads to the corresponding ether. Saponification gives the free acid and thus bindarit (38-3) [40]. 

Considerable work has been devoted to the search for agents devoid of the sedative effect that accompanied some of the earlier antihistamines. One stratagem for achieving that comprises adding a function that will diminish the likelihood that the dmg will cross the blood-brain barrier. The antistamine emedastine (41-3), for example, incorporates a terminal ether that can be potentially metabolized to a carboxylic acid. Alkylation of the imidazole (41-1), available from imidazol-2-one by reaction with phosphoms oxychloride, with the chloroether (41-2) leads to a reaction on nitrogen to afford (41-3). Displacement of the enol chloride in that intermediate with A-methyl-l-4-diazepine (41-4) leads to emedastine (41- 5) [43]. 

NOC1 and an alcohol 9-9 From ozonides 9-10 Oxidative cleavage of enol ethers 9-13 Reaction between carboxylic acids and lead tetraacetate 9-18 Oxidation of ethers 9-22 Oxidation of primary alcohols or aldehydes... 

Another site-selective reaction of 35 with a,/3-unsaturated carboxylic acid derivatives in the presence of a Lewis acid has been reported (Scheme 25) [35]. The intermediate 37 possesses two nucleophilic sites the zirconium alkyl and the enol ether moieties. Starting from 37, two competing pathways lead accordingly to cyclopropane (38, path a) and/or cyclobutane (39, path b) derivatives. The... 

The procedure described here involves the metallation of dihydrofuran and subsequent alkylation with an alkyl iodide (bromides are much less reactive).5 The resulting substituted dihydrofuran, the intermediate postulated in the Larson procedure, is then treated with chromic acid to hydrolyze the enol ether and oxidize the resulting primary alcohol to the corresponding carboxylic acid as in the Larson procedure. The isolated oxidation product is of suitable purity for subsequent reactions, but if necessary, recrystallization from hexanes is readily accomplished. ... 

The synthesis, starting from a bifunctional initiator followed by quenching the double-headed living ends, gives homotelechelic polymers (method B). Carboxylate-capped telechelic poly(isobutyl vinyl ether) has been obtained in this way [82], where the adduct of a bifunctional vinyl ether with trifluoroacetic acid is the initiator, and the quencher is the malonate anion. For method C, a bifunctional trimethylsilyl enol ether, CH2=C[OSi(CH3)3]C6H4OCH2CH20C6H4[(CH3)3SiO]C=CH2, is a useful terminator (chain coupler) for vinyl ethers [142,147] and a-methyl-styrene [159] (see also Section VI.B.4). 

The direct fluorination with elemental fluorine at — 78 "C of trimethylsilyl enol ethers derived from diketones results in the formation of the corresponding monofluoro diketones 11 in moderate yield. The trimethylsilyl ethers from cyclic diketones undergo smooth fluorination to give the enol forms, c.g. 12, and not the keto forms.Higher yields are generally observed for the analogous reactions of silyl derivatives of esters, carboxylic acids, malonates, dimethyl amides and lactones (Table 4). ... 

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