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)