Synthese mittlerer und großer Ringe, XXXIV. Stereoselektive Synthese überbrückter und verzweigter Methyl‐desoxyfuranoside aus 3,6‐Hexanooxepin‐4,5‐dicarbonsäure‐dimethylester

Syntheses of Medium and Large Rings, XXXIV[1,2]. – Stereoselective Synthesis of Bridged and Branched Methyl Deoxyfuranosides from Dimethyl 3,6-Hexanooxepine-4,5-dicarboxylate The stereoselective synthesis of the bridged methyl furanosides 4–8 with four, five, and six stereogenic centers is described. The reaction sequence starts with the addition of methanol to the oxepine 1. The photochemical electrocyclic ring closure of 2 gives the cyclobutene 3. Ruthenium tetraoxide oxidation of 3 leads to the title compound 4 that is further converted to 5–8 by stereoselective reductions.