摘要:
Epoxy mesylates 5 react with a variety of sodium alkoxides to produce the corresponding alpha-alkoxyketones in good yields. Evidence is presented for the involvement of transient allene oxides in these reactions. Enantiomerically enriched epoxy mesylates (2R,3S)-5a-c were prepared using the Sharpless asymmetric epoxidation reaction as the key step. These precursors rearrange to alpha-alkoxyketones without significant racemisation under modified reaction conditions (ROK, 18-crown-6, THF, -78 degrees C). The reactions are shown to proceed with stereochemical inversion at the epoxide centre. (C) 1998 Elsevier Science Ltd. All rights reserved.