Isoxazolecarboxylic Acids

The synthesis of isoxazolecarboxylic acids has been well investigated. They can be prepared either from compounds which already contain an isoxazole nucleus or by isoxazole ring-closure methods using appropriate starting materials containing carboxy or alkoxycar-bonyl groups. 

4-Substitutedisoxazole-3,5-dicarboxylic acids have been prepared from ethyl nitroacetate and an aldehyde (63BCJii50). A related reaction leads to diethyl 4-hydroxyisoxazole-3,5-dicarboxylate (334) and involves the reaction of acetonedicarboxylic acid ester (333) with nitrosyl chloride (78JHC1519). 

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The isoxazolecarboxylic acids are the most intensively investigated of the isoxazole derivatives, and a detailed compilation of their physiochemical properties has been made 62HC(17)l,p. 177). Similar studies have also been carried out with the 5-isoxazolones (62HC(17)l,p. 124), and pK values of 1,2-benzisoxazole derivatives are listed in Table 4. 

Properly substituted isoxazolecarboxylic acids can be converted into esters, acid halides, amides and hydrazides, and reduced by lithium aluminum hydride to alcohols. For example, 3-methoxyisoxazole-5-carboxylic acid (212) reacted with thionyl chloride in DMF to give the acid chloride (213) (74ACS(B)636). Ethyl 3-ethyl-5-methylisoxazole-4-carboxylate (214) was reduced with LAH to give 3-ethyl-4-hydroxymethyl-5-methylisoxazole (215) (7308(53)70). 

IsoxazoIe-5-carboxyIic acid anilide, 3,4-diphenyI-synthesis, 6, 86 Isoxazolecarboxylic acids applications, 6, 128 IR spectra, 6, 5 potentiometry, 6, 11 reactions, 6, 52 synthesis, 6,27, 85-86 thermochemistry, 6, 10 IsoxazoIe-3,4-dicarboxyIic acid esters... 

The isoxazoles 89 and 90 have been studied in detail by IR and H NMR spectroscopy. The structure of isoxazoles 89 was also confirmed by their oxidation with potassium permanganate in acetone to 3-alkyl(aryl)-5-isoxazolecarboxylic acids. 

A mixture of unsaturated ethers 119 and 120 obtained from methoxybu-tenyne and diethylcarbonate, when reacted with hydroxylamine in an acidic medium, quantitatively forms the ethyl esters of isoxazolecarboxylic acids 129 (81H146). 

Chemical Name 5-Methvl-3-isoxazolecarboxylic acid 2-benzylhydrazide Common Name —... 

An efficient one-pot synthesis of isoxazolines, using soluble polymer-supported acrylate has been described (174). Thus, the addition of 1,4-benzenedicarbonitrile N,N -dioxide (generated from N, N -dihydroxy-1,4-benzenedicarboximidoy 1 dichloride) to polyethylene glycol-supported 2-propenoic acid 2-hydroxyethyl ester 32 (P = polyethylene glycol support) followed by cleavage of the bond with the support gave 3,3/-(l,4-phenylene)bis[4,5-dihydro-5-isoxazolecarboxylic acid] di-Me ester (33) in 97% yield. 

No further refs found under Isoxazole derivs or Isoxazolecarboxylic acid in CA 1947-1971... 

Chemical Name 5-Methyl-3-isoxazolecarboxylic acid 2-benzyIhydrazide Common Name -Structural Formula ... 

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