Synthesis of C-furanosides from a D-glucal-derived cyclopropane through a ring-expansion/ring-contraction sequence

摘要

Gem-Dibromocydopropane 1, prepared from tri-O-benzyl-D-glucal, undergoes thermal and silver-promoted ring expansion in the presence of alcohols to give substituted oxepines. With further heating, ring contraction to highly substituted tetrahydrofurans follows. These represent C-furanosides, potentially useful as precursors to C-nucleosides and other carbohydrate mimics. Carbohydrates are valuable chiral pool reagents due to their degree of functionalisation and defined stereochemistries. Cyclopropanation of carbohydrate scaffolds enables the preparation of a diverse range of modified sugars, such as C-branched glycosides and septanoside precursors.