Hydroxyproline-Derived Pseudoenantiomeric [2.2.1] Bicyclic Phosphines: Asymmetric Synthesis of (+)- and (−)-Pyrrolines

We have prepared two new diastereoisomeric
2-aza-5-phosphabicyclo[2.2.1]­heptanes
from naturally occurring trans-4-hydroxy-l-proline in six chemical operations. These syntheses are concise
and highly efficient, with straightforward purification. When we used
these chiral phosphines as catalysts for reactions of γ-substituted
allenoates with imines, we obtained enantiomerically enriched pyrrolines
in good yields with excellent enantioselectivities. These two diastereoisomeric
phosphines functioned as pseudoenantiomers, providing their chiral
pyrrolines with opposite absolute configurations.