Rhodium catalysis substitution, aromatic

Highly efficient rhodium-catalyzed direct arylations were accomplished through the use of 2,2, 6,6 -tetramethylpiperidine-N-oxyl (TEMPO) as terminal oxidant [17]. Thereby, a variety of pyridine-substituted arenes was regioselectively functionalized with aromatic boronic acids (Scheme 9.5). However, in order for efficient catalysis to proceed, 4equiv. of TEMPO were required. The use of molecular oxygen as terminal oxidant yielded, unfortunately, only unsatisfactory results under otherwise identical reaction conditions. However, a variety of easily available boronic acids could be employed as arylating reagents. 

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