Rearrangement reactions in the fluorination of d-glucopyranoside at the C-4 position by DAST

Attempts to synthesize 4-deoxy-4-fluoro-KRN-7000 (2), a potential immune adjuvant, by fluorination of 4-hydroxy of α-d-glucopyranoside using DAST, were not successful. Instead, the unusual 5-deoxy-5-fluoro β-l-altrofurnoside and the corresponding 4-deoxy-4-fluoro α-d-glucopyranoside with retained configuration were obtained. In the presence of polar solvents, the reaction afforded the epoxide product, suggesting the bicyclic oxiranium ion intermediate to be involved in this reaction. Compound 2 was eventually achieved by treating 4-methanesufonated glucopyranoside with fluoride ion and found to be a weak agonist for CD1d and NKT cell activation.