Carboxylic acid amid 0-aminoketones

Imidazolidine-4-carboxylic acid amides from a-aminoketones... 

Bromination of ketone 3.17 gives 3.18 which can be converted to azide 3.19. Hydrogenation of 3.19 in the presence of hydrochloric acid affords aminoketone hydrochloride salt 3.20. Such aminoketones are often isolated as the corresponding salts because the free aminoketones are prone to dimerisation, having both nucleophilic and electrophilic centres. (For a common alternative preparation of aminoketones, see the Knorr pyrrole synthesis, Chapter 2.) Liberation of the free base of 3.20 in the presence of the acid chloride affords amide 3.21 which is cyclised to oxazole 3.22. Ester hydrolysis then affords the biologically-active carboxylic acid 3.23. 

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