6-Hydroxyacetylenic acids

Hydroxyacetylenic acids. The dianion of propiolic acid (1) can be generated at -45° with LDA in 1 1 THF—HMPT solution. The dianion reacts with epoxides to form 5-hydroxyacetylenic acids (2) in moderate yields. The products can be converted into substituted 5,6-dihydro-2H-pyrane-2-ones, a ring... 

Derivatives of Y-hydroxyacetylenic acids, which are useful intermediates in the synthesis of butenolides, are prepared from propiolic acid and ester anions. Alk-2-ynoic and 2-allenic esters are prepared by the oxidation of 3,4-disubstituted 2-pyrazolin-5-ones with lead(iv) tetra-acetate in the absence and presence of BF3 respectively. Py-Unsaturated esters are produced in high yield by the palladium-catalysed decarboxylation-carbonylation of allylic carbonates. Magnesium enolates of esters react with nitriles to give (Z)-3-amino-alk-2-enoates. Enol lactones react with diethyl methoxycarbonylmethylphosphonate to give cyclic unsaturated keto-esters (Scheme 66). ... 

Hydroperoxy-2-nitropropane, 256 p-Hydroquinone, 331,393,418 p-Hydroquinone dimethyl ethers, 432 Hydroquinones, 72 Hydrosilylation, 562 Hydroxamic acids, 204 2-Hydroximino-l-phenylpropane, 124 ai-Hydroxyacetophenone, 342 (3-Hydroxyacetylenes, 144-145 a-Hydroxy acids, 492 (5-Hydroxy acids, 301 1-Hydroxyadamantane, 126 a-Hydroxyaldehydes, 342 3o-Hydroxy-5a-androstene-17-one, 227-228... 

Several intermediates are either known or postulated to exist in the uncase reaction (Fig. 10-4), whose final product is allantoin. Studies with labeled uric acid have shown that C-6 is eliminated in this reaction as COj. Because a label ( N) at N-1 is found equally in the ureide and hydantoin portions of allantoin, the existence of a symmetrical intermediate such as hydroxyacetylene-diureine-carboxylic acid has been assumed. 

Fig. 3-55. Degradation of the semicarbazone of glyoxylic acid with Hydroxyacetylene diureide acid permanganate carboxylic acid...

If the enzyme uricase is present, as it is in many animals, uric acid may be converted to allantoin. It has been postulated by Schuler and Reindel that hydroxyacetylene-diureine-carboxylic acid may be an intermediate in the reaction. Klemperer believes that uroxanic acid, hy-droxyacetylene-diureine-carboxylic acid, and allantoin are all formed by the hydrolysis of an unknown compound which is directly formed by the action of uricase on uric acid. ... 

Propargyltrimethylsilane (162) reacts with saturated aldehydes and ketones in the presence of a catalytic quantity of tetra-n-butylammonium fluoride to produce a-hydroxyallenes U63). ° a,/3-Unsaturated or aromatic aldehydes give products contaminated with /3-hydroxyacetylenes. Analogous reactions with l-trimethylsilylbut-2-yne are preferably performed at low temperatures (-60 °C) with titanium tetrachloride as catalyst. Propargyltrimethylsilane also reacts with acid chlorides at low temperatures and in the presence of aluminium chloride to give moderate yields of a-allenic ketones (164). ... 

High yields of a, -unsaturated methyl ketones are obtained from acid-catalysed hydrolysis of readily available -hydroxyacetylenes [equation (22)]. ... 

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