The regiodivergent palladium-catalyzed C-H arylation of pyrazolo[1,5-a]pyrimidine has been achieved, wherein the switch in regioselectivity between positions C3 and C7 is under complete catalyst control. A phosphine-containing palladium catalyst promotes the direct arylation at the most acidic position (C7), whereas a phosphine-free catalyst targets the most electron-rich position (C3).

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4531820PMC
http://dx.doi.org/10.1002/anie.201502150DOI Listing

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