Synthesis of Ribofuranosides by Catalysis with Lewis Acids. Glycosidation Versus Transacetylation

Several ribofuranosyl derivatives bearing trichloroacetimidoyl or acetyl leaving groups in a Lewis acid promoted ribosylation reaction were prepared and used in an attempt to improve the yield and to avoid donor → acceptor transacetylation. Trichloroacetimidates were excellent donors affording disaccharides with very high yields under mild conditions. The corresponding 1-O-acetylated analogs could also be used with out transacetylation in the presence of boron trifluoride etherate.