Thiazole 2-tert-butyl-5-methyl

The effect of the halogen of the aryl halide was also carefully studied using bromobenzene and chlorobenzene as the electrophile. When the arylation was performed on ethyl 4-oxazole carboxylate using di-tert-butyl(methyl)phosphine as the Ugand and cesium carbonate as the base, the product of C5 arylation B was obtained when bromobenzene was used as the electrophile. Conversely, the product of C2 arylation A was formed if chlorobenzene was employed (eq 16). Similar results were obtained for the arylation of tert-butyl 4-thiazole carboxylate when mbidium carbonate was used as the base (eq 16). Again, it should be noted that the regioselectivity is highly dependent on the choice of the base and the phosphine. 

Arylation of Thiazoles and Oxazoles. The protocol that was previously developed for the C-H activation of azine and diazine (V-oxides with aryl triflates was used to effect the arylation of flve-membered ring heterocycles, such as oxazoles and thiazoles. In contrast to another protocol that was previously reported by the same group, the transformation did not require an V-oxide function. However, in order to direct the arylation at the C4-position, to prevent the formation of a mixture of regioisomers, and to minimize the generation of diarylated products, a C5-chloride was used as a blocking group. The procedure, which is promoted by palladium acetate and di-tert-butyl(methyl)phosphonium tetrafluoroborate, uses an aryl bromide as the electrophile. 

The C5-arylation is usually preferred in the C-H activation of thiazoles. For instance, upon using di-tert-butyl(methyl)phosphonium tetrafluoroborate in conjunction with palladium acetate, theregioselectiveCS-arylation of unsubstituted thiazoles was observed (eq 15). ... 

Bis-[l,3-Benzothiazol-2-ylthio]-organo- 997 Bis-[4-tert.-butyl-1,3-thiazol-2-yl]- 71 Bis-[l,3-dimethyl-lH-pyrazol-5-yl]- 557 Bis-[4,5-diphenyl-l,3-thiazol-2-yl]- 71 Bis-[4-methyl-l,3-thiazol-2-yl]- 71 Bis-[5-nitro-l,3-thiazol-2-yl]- 244 Bis-[l,3-thiazol-2-yl]- 70, 71 Ethyl- 337... 

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