Oxamates synthesis

Works on the oxidation of uric acid has unequivocally established the triazine structure > ° (9) of oxonic acid. This is further confirmed by the straightforward synthesis described by Piskala and Gut. ° The reaction of biuret (11) with potassium ethyloxalate yielded a potassium salt (24), that with ethyl oxamate, the amide of oxonic acid (25). Both these compounds were converted to 5-azauracil. An analogous reaction with diethyloxalate which should produce an ester of oxonic acid resulted in a mixture of urethane and parabanic acid, however. 

The direct conversion of alcohols and amines into carbamate esters by oxidative carbonylation is also an attractive process from an industrial point of view, since carbamates are useful intermediates for the production of polyurethanes. Many efforts have, therefore, been devoted to the development of efficient catalysts able to operate under relatively mild conditions. The reaction, when applied to amino alcohols, allows a convenient synthesis of cyclic urethanes. Several transition metal complexes, based on Pd [218— 239], Cu [240-242], Au [243,244], Os [245], Rh [237,238,246,247], Co [248], Mn [249], Ru [224,250-252], Pt [238] are able to promote the process. The formation of ureas, oxamates, or oxamides as byproducts can in some cases lower the selectivity towards carbamates. 

The reaction protocol was further extended to the concise synthesis of poly-oxamic acid, the unique polyhydroxyamino acid side-chain moiety of the antifungal polyoxin antibiotics (63). Treatment of the template 205 under standard thermal cycloaddition conditions with (5)-glyceraldehyde acetonide led to the formation of a single diastereoisomer 208 in 53% yield. Subsequent template removal released polyoxamic acid 209 in essentially quantitative yield. This represents a matched system, with the mismatched system leading to more complex reaction mixtures (Scheme 3.70). 

In 2006, Enders and Vrettou [32] reported a concise total synthesis of (-l-)-poly-oxamic acid (82) through an organocatalytic Mannich reaction (Scheme 17.12). Asymmetric Mannich reaction of ketone 79 and Boc-protected imine 80 using L-proline 24 afforded the adduct 81 in 85% yield as a mixture of diastereomers with 92% ee (>98 2 dr). A stereoselective reduction of 81 using L-selectride, followed by ozonolysis and subsequent acid deprotection completed the total synthesis of (-l-)-polyoxamic acid (82). 

Oxaloacetate decarboxylase, 23 Oxalic acid, 20, 21, 23 Oxamic acid, 20 Oxazolones, 200 6-Oxoestradiol, 89, 479 3-Oxo-5,10-secosteroids, 461-468 synthesis of acetylenic and allenic, 462, 463... 

Binuclear complexes of Ni and Pd containing oxamidinate (OXAM) ligands have been successfully employed in the synthesis of tetramethyl and tetraphenyl metallate complexes (Scheme The methyl derivative 10 has a... 

Oxalic ester synthesis 16, 812 Oxalyl chloride, reaction with amines 16, 502 Oxamic acid derivatives... 

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