A promising new catalyst family for enantioselective cycloadditions involving allenes and imines: chiral phosphines with transition metal-CH2-P: linkages

The racemic rhenium-containing phosphine (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂PPh₃) (3) catalyzes the 3+2] cycloaddition of H₂CCCHCO₂Et and N-tosyl imines ArCHNTs in C₆H₆ (RT, 1 d, 20 mol %) to give 2-aryl-3-carbethoxy-3-pyrrolines (Arp-C₆H₄X (X = H, NO₂, OMe, Me, Cl, Br), 2-furyl; 95-84% isolated). Similar reactions with enantiopure (S)-3 are conducted in C₆H₅Cl at −30 °C (8 d) to maximize enantioselectivities (60-51% ee; 93-90% isolated).