Enantioselective Binaphthophosphepine-Promoted [3+2] Annulations of N-Ts- and N-DPP-Imines with Allenoates and 2-Butynoates

The use of binaphthophosphepine la as a catalyst for the [3+2] cyclisation between allenoates or 2-butynoates and imines was investigated. The effects of the imine protecting group on both the catalytic activity and enantioselectivity were-determined by comparing the behaviour of N-tosyl- and N-DPP-imines. The N-DPP-imines displayed lower reactivity, but afforded the desired pyrrolines in higher enantiomeric excess (73-92% ee). The DPP protecting group was removed from the final pyrrolines under mild conditions to afford the corresponding secondary amines. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)