Towards phase-transfer catalysts with a chiral anion: inducing asymmetry in the reactions of cations

✍ Scribed by Christabel Carter; Sarah Fletcher; Adam Nelson

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 445 KB
• Volume: 14
• Category: Article
• ISSN: 0957-4166
• DOI: 10.1016/s0957-4166(03)00367-7

✦ Synopsis

The ability of chiral anions, for example bis[1,1%-bi-2-naphtholato]borate, to induce asymmetry in the reactions of prochiral cations was investigated. Ion-pairing of a borate anion with an aziridinium ion was demonstrated by NMR spectroscopy. The addition of N-methyl indole to an iminium ion (benzylidenedimethylammonium) and the ring-opening of an aziridinium ion (1,2-diphenyl-3-azonia-spiro[2.4]heptane) with benzylamine were studied. Low, but significant, (<15%) enantioselectivities were induced in the formation of the diamine benzyl-(1%,2%-diphenyl-2-pyrrolidin-1-yl-ethyl)-amine. The counterion of the additive was found to have a remarkable effect on the yield and the sense of enantioselectivity of these reactions.