A-Hydroxyacetophenone

Phenyl-3,6-dihydro-l,3,4-oxadiazin-2-one (50) is a high temperature blowing agent used primarily for polycarbonates (qv). It is prepared by the reaction of a-hydroxyacetophenone and methyl carbazate (52), made from hydrazine and dimethyl carbonate (175) ... 

The AFO reaction has seen very few variations since it was first reported in 1934. However, the most significant modification was reported in 1958 by Ozawa and further elaborated by Smith and others. Prior to this modification the intermediate chalcones were purified and then subjected to hydrogen peroxide in a basic medium. With the modification, the chalcone was generated in situ, from an aldehyde and a hydroxyacetophenone, and then allowed to react with aqueous hydrogen peroxide in the presence of sodium hydroxide to deliver the flavonol. Smith and coworkers conducted a limited study to examine the scope and limitations of this modification.Flavonols were delivered in 51-67% however, no flavonols were isolated with highly reactive aldehydes such as p-nitrobenzaldehyde and when 2-hydroxy-4-methoxyacetophenone was used. 

Several studies have been made of oxidations of ketols by Cu(II). Simple cupric salts deposit cuprous oxide, but this has been overcome by using a citrate complex of Cu(II) or a 1 1 (mole) pyridine-water mixture. A recent detailed account is that of Wiberg and Nigh ° , who found the stoichiometry and rate law for the oxidation of a-hydroxyacetophenone by Cu(II) acetate to be, respectively,... 

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways <06JOC5616>. A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported <06SC2461>. 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals <06S1943>. Oxidation of N-... 

Ketones having at least one hydrogen next to the carbonyl group can be hydroxylated to form a-hydroxy ketones (acyloins). Acetophenone is oxidized to a-hydroxyacetophenone by o-iodosobenzoic add. In the presence of potassium hydroxide and methanol, dimethyl acetal is obtained, which on subsequent hydrolysis gives the hydroxy ketone in 83% yield (equation 400) [790],... 

Combretoxazolones like 21 were obtained in 60-70% yields by reaction of appropriate a-hydroxyacetophenones with arylisocyanates and subsequent cyclization by refluxing in acetic acid. 

Optically active P-hydroxysulfoximines which catalyze the asymmetric borane reduction of ketones [110], also catalyze the same reaction with sodium borohydride/trimethylsilyl chloride system as reducing agent [126]. Reduction of a protected a-hydroxyacetophenone afforded the alcohol with 90% ee. 

Subramanian [18] has used gas chromatography-mass spectrometry to study the photodecomposition products such as benzaldehyde, a-hydroxyacetophenone, phenyl glycol, a-methoxyacetophenone, and a-henzyloxyacetophenone produced upon UV irradiation of polystyrene peroxide. Diaz and co-workers [19] carried out similar studies on polybenzyl methacrylates and polybenzyl acrylates. 

Hydroxylated aromatic ketones represent valuable intermediate compounds in the synthesis of important fragrances and pharmaceuticals. For example, the resorcinol acylation products are employed for the production of valuable fine chemicals such as 4-0-octyl-2-hydroxybenzophenone (UV light absorbent for polymers) and ipriflavone (antiosteopenic drug). a-Hydroxyacetophenone (o-HAP) and p-hydroxyacetophenone (p-HAP) are widely used for the synthesis of aspirin and paracetamol (4-acetaminophenol), respectively [103]. a-HAP represents also a key intermediate for the production of 4-hydroxycoumarin and warfarin, which are both used as anticoagulant drugs in the therapy of thrombotic disease [104], and it is also employed for the synthesis of flavo-nones [105,106]. 

In recent apphcations of this methodology, a-hydroxyacetophenones or benzoins, and phenylhydrazine [501] as well as a-amino acetophenones and phenyl- or methyUiydrazine [502], both in the presence of CUCI2, were utihzed for the synthesis of 2-substituted 1,2,3-triazoles, for example ... 

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