| Abstract: | ABSTRACT The Witting reaction of (carbethoxymethylene)triphenylphosphorane with perbenzylated sugar δ-lactones and their 2-acetamido-2-deoxy derivatives is described. It is shown that this olefination occurred readily with the galacto and gluco derivatives, leading stereoselectively to Z-C-glycosylidenes in good yields. However, the same reaction with the perbenzylated 2-deoxy-D-arabino-hexono-1,5-lactone and the mannonolactones worked poorly. Reduction over Pd/C followed by acetylation of the obtained C-glycosylidenes led stereoselectively to peracetylated β-C-glycosides and amino β-C-glycosides. The olefin function could also be reduced selectively by Raney nickel or NiCl2/NaBH4, affording the perbenzylated C-glycosides and amino β-C-glycosides. Other transformation of the enol ether function is also reported. |
