TBAF Effects 3,6-Anhydro Formation from 6-O-Tosyl Pyranosides.

3,6-Anhydro sugars are common structures in algal polysaccharides and occur in the furanodictine and sauropunol natural products. We have found that treatment of 6-O-tosylpyranosides with tetrabutylammonium fluoride provides a mild, high-yielding synthesis of 3,6-anhydro sugars. Using O-glycoside substrates, 3,6-anhydropyranosides are isolated and the use of N,O-dimethyl hydroxylamine glycosides yields 3,6-anhydrofuranosides. Applying this approach, concise synthetic routes to several 3,6-anhydro sugar natural products are reported, including furanodictine A and sauropunols A-D.