Self-reproduction of chirality on α-aminophosphonates: asymmetric synthesis of α-alkylated diethyl pyrrolidin-2-yl-phosphonate
摘要:
A simple method for the asymmetric synthesis of alpha-substituted diethyl pyrrolidin-2-yl-phosphonate is described. The chiral oxazolopyrrolidine phosphonate was alkylated diastereospecifically with an alkyl halide. The key intermediate is an alpha-phosphonate-stabilized carbanion that can be alkylated without loss of optical activity and a single enantiomer of product was formed exclusively in 10-80% yield. The configurational assignment of the products relied on H-1-H-1 NOESY analysis of the alkylated oxazolopyrrolidine phosphonates. This represents an unprecedented case of self-regeneration of stereocenters (SRS) of cyclic aminophosphonates. The enantiomerically pure alpha-aminophosphonate dietlhyl-(2S)-(2-methylpyrrolidin-2-yl)-phosphonate, a surrogate of 2-methyl proline, was obtained upon hydrogenolysis of the chiral auxiliary in 83% yield. (C) 2004 Elsevier Ltd. All rights reserved.