A Flexible Carbanionic Approach to Protected trans-(2R,3S)-2-Substituted 3-Aminopyrrolidines: Application to the Asymmetric Synthesis of (+)-Absouline

Based on the use of phenyl thioether (3S)-7 as a synthetic equivalent to the N- and (alpha)-dianions (3S)-2a, a new carbanionic approach to trans-(2R,3S)-2-substituted 3-aminopyrrolidines (10) is described. Application of the method to the asymmetric synthesis of 1-aminopyrrolizidine alkaloid (+)-absouline is also reported.