REACTIONS OF SOME PYRANOSIDE DIOL MONOTRIFLATES WITH NUCLEOPHILES AND BASES

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 (F-, t-BuO-) leads to the anhydrosugars 8, 25, and 26, respectively. The S(N)2 reaction of 35 with tetra-n-butylammonium iodide forms the basis for a new synthesis of the Cerny epoxide 32.