A new catalytic cross-coupling approach for the synthesis of protected aryl and heteroaryl amidines.

[reaction: see text] A new method for the synthesis of protected benzamidines is described. The commercially available 1,3-bis(tert-butoxycarbonyl)-2-methyl-2-thiopseudourea guanidylation reagent, after SEM-protection, functions as an amidine-forming cross-coupling partner under Liebeskind-Srogl conditions. In the presence of copper(I) thiophenecarboxylate (CuTC), the palladium-catalyzed cross-coupling of the SEM-protected thiopseudourea reagent with boronic acids affords fully protected benzamidines in good to excellent yield (40-91%).