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A general and efficient synthesis of 5-aryl imidazo[1,5- a]pyrazines by palladium-catalyzed coupling of the corresponding 8-substituted derivatives with aryl halides is described. The scope of this new reaction for the imidazo[1,5- a]pyrazine ring system was explored using three readily available 8-substituted precursors, X = NH 2, NMe 2, and OMe, as well as 8-aryl derivatives, X = Ar′. On the basis of these results as well as studies using a deuterated derivative, a Heck-like mechanism is proposed for this transformation. [ABSTRACT FROM AUTHOR]