Oxidative Biaryl Coupling of Thiophenes and Thiazoles with Arylboronic Acids through Palladium Catalysis: Otherwise Difficult C4‐Selective CH Arylation Enabled by Boronic Acids

It adds up to 4! Thiophenes and thiazoles can be arylated in the 4- rather than the expected 5-position in a new CH functionalization reaction (see scheme; TEMPO: 2,2,6,6-tetramethylpiperidine-N-oxyl). The boronic acid proved to be the key to achieving the otherwise difficult C4 selectivity. The method was applied to a concise synthesis of a key pharmacological structure with potential for treatment of Alzheimer's disease.