Oxazoles cyanamides

N—C—O + C—C. The construction of the oxazole ring by the condensation of a-halogeno ketones with primary amides (equation 122) is the Bliimlein-Lewy synthesis (1884/1888). The method succeeds best when the resulting oxazole contains one or more aryl substituents. The use of formamide leads to oxazoles with a free 2-position and in this case it is possible that the reaction proceeds as in equation (113). 2-Aminooxazoles are produced by the action of a-halogeno ketones on urea and its derivatives (equation 123) or on cyanamide (80ZOR2185). The mercury(II) sulfate-catalyzed condensation of alkynic alcohols or their esters with primary amides leads to trisubstituted oxazoles (equation 124). 

C—C—O+N—C. a-Hydroxy ketones react with monosubstituted cyanamides under the influence of sodium hydroxide to yield derivatives of 2-aminooxazole (equation 125) (76S591). Oxazoles are obtained by the action of nitriles on a-diazo carbonyl compounds in the presence of Lewis acids, such as aluminum chloride or boron trifluoride, and the reaction is thought to involve the intermediacy of nitrilium salts (equation 126). Nitrilium salts are also the effective agents in the formation of oxazoles from a-chloro ketones and nitriles in the presence of tin(IV) chloride (equation 127). 

Cyanamide in methanolic ammonia converts 21-hydroxypregnan-20-ones (463) into 17j8-(2-amino-oxazol-4-yl)androstanes (464). The reaction proceeds equally well in the presence of a 17a-hydroxy-group. ... 

Oxazole itself has been prepared from its 4,5-diester, by hydrolysis then decarboxylation though this formally falls into the same category of synthesis, it is probable that the ring oxygen derives from the 2-hydroxy-ketone, and not from the formamide the reaction of acyloins with formamide can be looked on as a general approach to oxazoles. " The use of cyanamide gives 2-amino-oxazoles. ... 

Condensation with the appropriate components is widely represented in literature approach to fluoroaUcyl derivatives of oxazole. Fluoroalkyloxazoles are of interest due to their application as surface modifiers of hydrophilic polymers, polymeric films for second-order non-linear optics, effective herbicides, body-membrane penetration enhancers, and intermediates for the synthesis of unnatural a-amino acids [12]. Thus, the syntheses of the trifiuoromethylated 2-aminooxazoles 8 and 9 were performed by reacting commercially available trifiuorobromoacetone with five equivalents of urea or cyanamide in refluxing fe/t-butanol to afford the corresponding 4- and 5-trifluoro-methyl-2-aminooxazoles in 70 % and 14 % yields, respectively [13,14]. 

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