Diazines, functionalization by directed

The aforementioned method was employed to enable the direct arylation of pyrazine Af-oxides en route to tri-arylated diazines (eqs 9 and 10). In these two examples, aryl bromides were used as the electrophile and no additives were utilized. TheiV-oxide function was removed by performing a chlorination reaction with phos-phorus(V) oxychloride, leading to the 5-chloro derivative (eq 9). In another example, the Af-oxide was reduced under hydrogenol-ysis conditions (eq 10). ... 

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. 

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