Isoxazoles 2- -5-methyloxazoles

See Hydrogen peroxide 2-Amino-4-methyloxazole See related ISOXAZOLES... 

Radical bromination with fV-bromosuccinimide often succeeds. Thus, 2,5-disubstituted 4-methyloxazoles on bromina-tion give the 4-bromomethyl compounds, and methyl groups at the 4- or 5-positions of isoxazoles 568 and 569 can be brominated with NBS. Controlled mono- or dibromination of 3-aryl-5-methylisoxazole-4-carboxylates allows access to aldehydes <2004T2301>. 

Closely related to the aldoxime fragmentation is the base-catalyzed ring cleavage of C(3)-substituted isoxazoles. Quite recently a novel base-catalyzed isoxazole-oxazole ring transformation was realized in the conversion of ethyl 5-hydroxy-3-(5-methylisoxazol-4-yl)isoxazole-4-carboxylate (61) into ethyl 4-cyano-5-methyloxazol-2-ylacetate (62 Scheme 5). ... 

Vivona and co-workers also described an unusual base-catalyzed isoxazole-oxazole rearrangement. Here, treatment of 3-(aroylamino)-5-methylisoxazoles 122 with KOtBu/DMF effected rearrangement to 2-(aroylamino)-5-methyloxazoles 125 (Scheme 1.33). The authors proposed initial deprotonation of 122 to generate 123,... 

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