2 -oxazolonium perchlorates

A-Alkyl- and A-aryl-a-acylamino acids with a mixture of acetic anhydride and perchloric acid form 1,3-oxazolonium perchlorates... 

Cyclodehydration of l-carboxymethyl-2-pyridone with acetic anhydride and perchloric acid gave the corresponding 1,3-oxazolonium perchlorate which with triethylamine gave the dimer (72) directly. Similar dimerization of other meso-ionic l,3-oxazol-5-ones (66) have been reported. The monomer (71) could not be isolated, but acetyl (67, R = Me) and benzoyl (67, R = Ph) derivatives were prepared from a... 

Condensation products of 4(5//)-oxazolonium salts with aldehydes and orthoesters are the subject of a series of papers by Kosulina and co-workers Reaction of 2-methyl-4(5//)-oxazolonium perchlorates 44 with an ortho ester gives rise to an enol ether, which reacts with furanamides to afford the frani-eneamides 45 (Scheme 6.14). " Using electron deficient anilines in a three component condensation affords either 46 or 47 in 64-80% and 78-84% yields, respectively, depending on whether the reaction is performed in acetic acid or acetic anhydride. Electron-rich anilines are unreactive since they are merely protonated by the perchloric acid present in the reaction medium. ... 

TABLE 6.2. 2-[2-(a-HETEROARYL)ETHENYL]-4(5//)-OXAZOLONIUM PERCHLORATES FROM OXAZOLONIUM SALTS AND ALDEHYDES ... 

Figure 6.7. (E.Et-Dienes from a 2-methyl-4(5f/)-oxazolonium perchlorate.

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