Desymmetrization of Prochiral Phosphanes Using Derivatives of (−)-Cytisine

Historically, (−)-sparteine·sec-BuLi has been used to desymmetrize prochiral phosphanes. In this report, derivatives of an alkaloid extracted from the seeds of Laburnum anagyroides have been utilized to mimic (+)-sparteine, which is not readily available. In several cases, the enantioselectivities achieved with the (+)-sparteine surrogates outperformed (−)-sparteine itself in the deprotonation of alkyl-substituted (as well as aryl-substituted) prochiral phosphane derivatives. In addition, use of these surrogates allows a new methodology for a chiral switch in phosphorus chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)