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.