Gold versus Silver-Catalyzed Intermolecular Hydroaminations of Alkenes and Dienes

Comparative studies about the hydroamination of unactivated alkenes and dienes catalyzed by either cationic gold(I) triphenyl phosphite complexes or silver salts were performed using sulfonamides, anilines and carbamates as nucleophiles. Gold-catalyzed reactions generally, need lower loadings than those carried out with silver salts. Simple alkenes react only with sulfonamides and weak aromatic amines such as p-nitroaniline, whereas for conjugated dienes carbamates can also be used. Carbon-carbon double bond isomerization is observed only with gold similarly to when triflic acid was used, affording mixtures of regioisomeric products in the same cases. Silver-catalyzed hydroaminations failed with terminal alkenes, except with styrenes. Conjugate dienes can be hydroaminated either at 85 degrees C in toluene or at room temperature in dichloromethane. Non-conjugated 1,4- and 1,5-dienes suffer double hydroamination leading to saturated N-tosylated heterocyclic amines The catalytic cycle for the silver(I)-catalyzed hydroamination process has been computationally analyzed, resembling gold(I)-catalyzed processes, although with some significant differences.