Regioselectivity in alkenyl(aryl)-heteroaryl Suzuki cross-coupling reactions of 2,4-dibromopyridine.: A synthetic and mechanistic study

2,4-Dibromopyridine undergoes a regioselective Suzuki cross-coupling reaction at position 2 with several alkenyl(aryl) boronic acids to render 4-bromo-2-carbon substituted pyridines, difficult to be prepared otherwise, in good yields under palladium catalysis, either Pd(PPh3)(4)/TlOH or Pd(2)dba(3)/PCy3/K3PO4 at 25 degrees C. This behavior is explained on the basis of the electrophilic character of both C-Br bonds, being their relative reactivity in 2,4-dibromopyridine similar to that in the corresponding monobromopyridines. In addition, the dicoupled compound 6 is not formed through a double oxidative addition of 2,4-dibromopyri dine to Pd(PPh3). (c) 2006 Elsevier Ltd. All rights reserved.