The use of binaphthophosphepine 1a as a catalyst for the [3+2] cyclisation between allenoates or 2-butynoates andimines 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
The use of chiral, binaphthyl-based phosphepines as catalysts improves previous results for the enantioselective [3+2] cyclisation reactions between allenic esters and N-tosylimines, both in terms of conversion rate and enantioselectivity. Pyrrolines bearing 1-naphthyl, phenyl, o-tolyl and p-MeO-phenyl substituents on the stereogenic alpha-carbon have been obtained with enantiomeric excesses up to 64-80%. (c) 2007 Elsevier Ltd. All rights reserved.