Synthesis and functionalization of bicyclic N,O-acetal scaffolds from furfural.

We have synthesized biologically relevant 6-aza-8-oxa[3.2.1]bicyclooctane scaffolds in a five-step procedure starting from furfural. Besides showing that these scaffolds are amenable to decoration via standard functional group interconversions, we also describe investigations for further functionalization via Lewis acid-mediated N,O-acetal opening, followed by nucleophilic trapping of the resulting intermediate cation. By using different nucleophiles, we have successfully prepared a modest library of 2,6-trans-disubstituted pyrans in good yields and in a highly diastereoselective manner.