Reaction of pyranoside diol (equatorial) monotriflates with soft, nonbasic nucleophiles is a useful way to make axial heteroatom-substituted and “epimerized” pyranosides, particularly where a fused acetal ring inhibits ring contraction. Among the substrates examined (1, 2, 3, 4, 35), only 4 shows a strong tendency to give ring-contracted products. The reaction of 1-3 with more basic nucleophiles (P, t-BuO-) leads to the anhydrosugars 8, 25, and 26, ...
