Asymmetric hydroamination of aminoallenes catalyzed by titanium and tantalum complexes of chiral sulfonamide alcohol ligands

A series of bidentate sulfonamide alcohol ligands with varying steric and electronic properties was synthesized. The titanium and tantalum complexes of these ligands, prepared in situ from either Ti(NMe2)4 or Ta(NMe2)5, were used as catalysts for the asymmetric hydroamination of 6-methyl-hepta-4,5-dienylamine, giving exclusively the α-vinylpyrrolidine product. The titanium derived catalysts gave products with low stereoselectivity, up to 11%ee favoring (+)-2-(2-methyl-propenyl)-pyrrolidine, while the tantalum derived catalysts gave products with higher and opposite stereoselectivity, up to 34%ee favoring (−)-2-(2-methyl-propenyl)-pyrrolidine.