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Hydrogenation isoxazoles

In general, the solubility of heterocyclic compounds in water (Table 33) is enhanced by the possibility of hydrogen bonding. Pyridine-like nitrogen atoms facilitate this (compare benzene and pyridine). In the same way, oxazole is miscible with water, and isoxazole is very soluble, more so than furan. [Pg.31]

Acid-catalyzed hydrogen exchange is used as a measure of the comparative reactivity of different aromatic rings (see Table 5). These reactions take place on the neutral molecules or, at high acidities, on the cations. At the preferred positions the neutral isoxazole, isothiazole and pyrazole rings are all considerably more reactive than benzene. Although the 4-position of isothiazole is somewhat less reactive than the 4-position in thiophene, a similar situation does not exist with isoxazole-furan ring systems. [Pg.57]

Isoxazoles are also rather stable to nucleophilic attack by OH at carbon. For reactions with base at a ring hydrogen atom, leading, for example, to ring opening of isoxazoles, see Section 4.02.1.7.1. [Pg.62]

Isoxazoles are presently known to undergo hydrogen exchange, nitration, sulfonation, halogenation, chloroalkylation, hydroxymethylation, Vilsmeier-Haack formylation, and mercuration. The Friedel-Crafts reaction on the isoxazole nucleus has not yet been reported. [Pg.12]

Nucleophilic replacement of hydrogen on an isoxazole is unknown and replacement of substituents is discussed in Section 4.16.3.3. In this series it is difficult to identify reactions involving addition to the ring as, in many instances, they are rapidly followed by elimination or ring cleavage sequences. [Pg.28]

The treatment of 3-acylisoxazoles (438) with hydroxylamine hydrochloride gives furazan ketones (439). On the other hand, furazan ketones (439) rearrange to 3-acylisoxazoles (438) with a loss of hydroxylamine under the influence of a mineral acid. Thus, by refluxing phenacylphenylfurazan with concentrated alcoholic hydrogen chloride, 3-benzoyl-5-phenyl-isoxazole is formed similarly, phenyl(phenacylphenyl)furazan gives 3-benzoyl-3,5-diphenyl-isoxazole (62HC(17)1, p. 35). [Pg.82]

Phenyldiazonium salts react with malonaldioxime to produce a 2-isoxazoline (7 IGEPl 920245), and the diazo ketone (484) when photolyzed gave a mixture of 2-isoxazoline and an isoxazole by a 1,5 carbon-hydrogen insertion. A phenyl migration was apparently not involved (Scheme 124) (66CC689). [Pg.97]

Isoxazole compounds can be converted into the corresponding isothiazoles by successive catalytic hydrogenation, sulfuration with phosphorus pentasulfide and oxidation with chloranil (72AHC(14)l, 75SST(3)541). 2,1-Benzisoxazoles give the 2,1-benzisothiazoles directly, by the action of phosphorus pentasulfide in either pyridine or molten imidazole (73SST(2)556, 77SST(4)339). (See also Chapter 4.16 for further discussion of these topics.)... [Pg.170]

Isoxazole, 3-methoxymethyl-5-methyl-oxidation, 6, 27 Isoxazole, methyl-bromination, S, 88 homolytic halogenation, 6, 51-52 potentiometry, 6, 10 Isoxazole, 3-methyl-basicity, 6, 20 halogenation, 6, 24 hydrogen exchange, 6, 21 sulfonation, 6, 24 synthesis, 6, 83 Isoxazole, 4-methyl-synthesis, 6, 83 Isoxazole, 5-methyl-basicity, 6, 20... [Pg.687]

A particular case of the synthesis of isoxazoles via -diketone derivatives is the preparation of 3-halogenoisoxazoles (11) from -nitroketones (9) treated with hydrogen halides. This inter-... [Pg.368]

The synthetic possibilities for isoxazoles and their hydrogenated derivatives by the formation of the 1—5 and 1—3 bonds are hardly exhausted it is to be expected that the scope of these interesting reactions will be considerably enlarged. [Pg.378]

Further, isoxazole derivatives were subjected to two related reactions. 3,5-Dimethylisoxazole was found to react in the presence of dry hydrogen chloride with aromatic aldehydes (chlorobenzylation, 72- 71),and with formaldehyde in the presence of sulfuric acid it undergoes hydroxymethylation (72- 73). ... [Pg.388]

No direct nucleophilic substitution of the hydrogen atoms in the isoxazole nucleus a or y to the nitrogen is as yet known. Thus, the Chichibabin reaction fails in the isoxazole series because of the cleavage of the heterocyclic nucleus under these conditions. It is the lability of the isoxazole ring toward nucleophilic reagents that makes the chemical behavior of isoxazole fundamentally different from that of pyridine. [Pg.390]

C. Reductive Cleavage of Isoxazoles and of Their Hydrogenated Derivatives... [Pg.412]

Another group of reactions with the predominant cleavage of the ring comprises catalytic hydrogenation of isoxazole derivatives and has been investigated only recently. The most commonly used catalyst has been Raney nickel,but use has sometimes been made of platinum catalysts. Hydrogenolysis of the 0—N bond (172—>173) occurs in isoxazole, its homologs,and their functional derivatives, for example, isoxazole carboxylic acids- and 5-aminoisoxazoles. ... [Pg.415]

The monoimines of the substituted -diketones formed can usually be isolated but sometimes they undergo further reactions. Thus, 5-substituted 3-chloroisoxazoles yield / -ketonitriles, and hydrogenation of 5-acylaminoisoxazoles (174) is a general method of synthesizing 4-hydroxypyrimidines (175). 2 3,214 One should note the increased stability of the isoxazole ring in styrylisoxazoles toward reduction. No hydrogenolysis of the 0—N... [Pg.415]

Under the conditions used for the reductive cleavage of the O—N bond in isoxazoles, a similar reaction readily occurs with isoxa-zolines, e.g. on treatment with organomagnesium compounds and on catalytic hydrogenation.- Hydrogenolysis of the O—N bond (180 181 182 183) was used to elucidate the structure of isoxa-zolones from -ketoesters. -... [Pg.417]

Shaw concluded that hydrogenation of 3-alkyl-4-aminomethylene isoxazol-5-ones (184) in the presence of palladium catalyst resulted in the saturation of either the endocyclic double carbon-nitrogen bond or the exocyclic double C—C bond with the retention of the heterocyclic nitrogen-oxygen bond. Recent data reported by Kochetkov et al. on the properties, and in particular on hydrogenation, of isoxazolid-5-ones - indicate, however, that Shaw had probably ob-... [Pg.417]

Acetoxy-4-androsteno[2,3-d] isoxazole Maleic anhydride Hydrogen peroxide Sodium methoxide... [Pg.1543]

A solid-phase synthesis of 3-substituted isoxazoles 31 in good yields and purities was achieved by 1,3-DC of polymer-supported vinyl selenide with in situ generated nitrile oxides treatment of intermediate isoxazolines 30 with an excess of hydrogen peroxide resulted in the release of isoxazoles 31 while the use of Mel/Nal led to 3-substituted 5-iodoisoxazolines... [Pg.291]

A23-22-Oxo steroids 424 have been synthesized via 1,3-dipolar cycloaddition of steroidal nitrile oxides to low-molecular dipolarophiles. Cycloaddition of 2-propynyl bromide to 20-carbonitrile oxide, followed by hydrogenation of the isoxazole derivative, gives 22-enamino-24-keto steroid. The latter has then been converted into the target enones in several steps (465). [Pg.92]


See other pages where Hydrogenation isoxazoles is mentioned: [Pg.3339]    [Pg.3339]    [Pg.122]    [Pg.143]    [Pg.36]    [Pg.60]    [Pg.69]    [Pg.5]    [Pg.11]    [Pg.26]    [Pg.88]    [Pg.145]    [Pg.552]    [Pg.687]    [Pg.794]    [Pg.9]    [Pg.365]    [Pg.407]    [Pg.20]    [Pg.1543]    [Pg.616]    [Pg.151]    [Pg.286]    [Pg.294]    [Pg.294]    [Pg.304]    [Pg.288]   
See also in sourсe #XX -- [ Pg.83 ]




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