Synthesis of (2S,1 ' R,2 ' R,3 ' R)-2-(2 ',3 '-dicarboxycyclopropyl)-glycine via the stereochemically controlled cyclopropanation of (S)-glyceraldehyde acetonide-derived enones

The reaction of ethyl dimethylsulfonium acetate bromide with aromatic enone s 5a or 5b derived from (S)-glyceraldehyde acetonide under the action of DB U provides cyclopropanation products in excellent yield and good diastereos electivity (10/1). High geometry-selectivity (>95/1) can be reached when th e reaction is carried out at lower temperature in toluene. The cis-enone 5a gives better geometry-selectivity than trans-enone 5b. The ylides with ami de groups can also be used for cyclopropanation reaction but neither the yi elds nor the geometry-selectivity are satisfactory. Based on this reaction a new synthetic protocol for (2S,1'R,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl )glycine (L-DCG-IV), an isotype-selective agonist of metabotropic glutamate , is developed. (C) 2000 Elsevier Science Ltd. All rights reserved.