Enolate Alkylation of Polymer-Supported Evans Oxazolidin-2-one
R. Green, A. T. Merritt, S. D. Bull*
University of Bath and GlaxoSmithKline Research and Development, Stevenage, UK
19. März 2008 (online)
The enolate alkylation of the polymer-supported Evans’ oxazolidin-2-one was described. Thus, the oxazolidin-2-one 1 was treated with 2-chlorotrityl chloride polymer resin to give the polymer-supported oxazolidin-2-one 2. The N-acylation of 2 with carboxylic anhydrides afforded the polymer-supported Evans’ oxazolidine-2-ones 3. After the treatment of 3 with 10 equiv of LHMDS in THF, the solvent and excess amount of LHMDS was drained. Addition of the alkyl halide in THF to the resulting resin at 0 °C, followed by elevating the reaction temperature to room temperature gave the corresponding polymer-bound alkylation products 4. Treatment of 4 with LiOOH released the corresponding α-alkylated acids 5 in 42-69% yield over three steps from 2 with 87-99% ee.