5-aryl-2-methyloxazoles

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>. 

The Stille coupling reaction is the most versatile method among all Pd-catalyzed crosscoupling reactions with organometallic reagents. By lithiation of 4-methyloxazole with H-BuLi and subsequent quenching with trimethyltin chloride, Dondoni et al. prepared 2-trimethylstannyl-4-methyloxazole [39], which was then coupled with aryl- and heteroaryl-halides to provide the expected 2-aryloxazole. Thus, 2-trimethylstannyl-4-methyloxazole was coupled with 3-bromo-pyridine to afford oxazolylpyridine 35. 

TABLE 1.72. 2-ARYL(HETEROARYL)-4-METHYLOXAZOLES FROM PALLADIUM-CATALYZED CROSS-COUPLING OF 4-METHYL-2-(TRIMETHYLSTANNYL)OXAZOLE ... 

Complexes of phenol with 5-aryl-2-methyloxazoles 205 and related azoles as well as 2-aryl-5-phenyloxazole 198, 2-(2-furyl)-5-phenyloxazole 206 and 5-phenyl-2-(2-thienyl)oxazole 207 have been investigated in different solvents... 

TABLE 1.76 2-ACYL-4-METHYLOXAZOLES AND 2-ACYL-5-ARYLOXAZOLES FROM 4-METHYL-2-(TRIMETHYLSILYL)OXAZOLE OR 5-ARYL-2-(TRIMETHYLSILYL) OXAZOLES AND ELECTROPHILES, 223... 

Jefferys has modified the Davidson oxazole synthesis by using phenacyl bromides and ammonium acetate to yield 2-methyl-4-(or 4,5-di-)-substituted oxazoles. He was also able to extend the syntheses outlined by Japp and Davidson to obtain 4,5-dialkyl and 4-aryl oxazoles. These oxazoles together with 2-methyloxazole were then quatemized and transformed into cyanine and merocyanine dyes. 

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