Parabanic acid 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. 

Lithiation at the C2 position of the imidazole ring by means of n-BuLi was followed by a treatment with tosyl azide which furnished the corresponding 2-azido imidazole in a yield of 89%. This azido group was reduced to an amino group with palladium on carbon under hydrogen atmosphere (in a yield of 95%). Finally, the 2-aminoimidazole was treated with a TMS-activated derivative of parabanic acid, a reaction that afforded the target molecule naa-midine G in a yield of 78%. This eight-step synthesis provided naamidine G in a total yield of (95 x 97 x 85 x 98 x 81 x 89 x 95 x 78) 41%. 

A soln. of 3-(3,4-dichlorophenyl)-l-isopropyl-l-(2-propynyl)urea and oxalyl chloride in benzene refluxed 8 hrs. 3-(3,4-dichlorophenyl)-l-(2-propynyl)-parabanic acid. Y 81.5%.—This is a convenient synthesis of 1,3-subst. parabanic acids from readily available 1,1,3-trisubst. ureas. F. e., also from thioureas, s. P. J. Stoffel, J. Org. Ghem. 29, 2794 (1964) f. ring closures with oxalyl chloride s. J. Org. Ghem. 29, 2796 parabanic acids from ureas and 2-iminothiazolidine-4 -diones from thioureas s. H. Ulrich and A. A. R. Sayigh, J. Org. Ghem. 30, 2781 (1965). 

Raghavan and coworkers have reported on the preparation of 4-hydroxybenzoic add esters (parabans) possessing antimicrobial activity by esterification of 4-hydroxybenzoic acid (Scheme 6.153) [299]. Optimum results were obtained using the alcohol (1-butanol) as solvent in the presence of catalytic amounts of zinc(II) chloride or p-toluenesulfonic acid (pTsOH) under atmospheric conditions. After 5 min of microwave irradiation at 120 °C, ca. 40% conversion to the ester was observed. Related studies on the synthesis of long-chain aliphatic esters have been described by Mariani and coworkers [300]. 

The first successful synthesis of l,l-diamino-2,2-dinitroethene was reported in 1998 [2] by the group from FOI. It was initially isolated in low yield after hydrolysis of the product mixture obtained from the mixed acid (nitric and sulphuric acid) nitration of 2-methylimidazole (9). The choice of reaction conditions is rather critical Nitration with nitric acid in 101-105% sulphuric acid gave a mixture of parabanic add (10) and 2-methyl-4-... 

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