Synthesis of 4,4-difluoroglycosides using ring-closing metathesis

Area of Science:

• Carbohydrate Chemistry
• Organic Synthesis
• Fluorine Chemistry

Background:

• 4-Deoxy-4,4-difluoro-glycosides represent a novel class of carbohydrate analogues.
• The synthesis of fluorinated carbohydrates is challenging due to the unique properties of fluorine.

Purpose of the Study:

• To develop a novel synthetic route to 4-deoxy-4,4-difluoro-glycosides.
• To investigate the efficacy of different protecting group strategies in this synthesis.
• To explore the stereochemical outcomes of dihydroxylation reactions.

Main Methods:

• The synthesis involved a direct sequence of ring-closing metathesis (RCM) and indium-mediated difluoroallylation.
• Reactions were performed in water using 1-bromo-1,1-difluoropropene.
• Two protecting group strategies were evaluated: one protecting the C-6 hydroxyl group and another allowing deprotection before dihydroxylation.
• Dihydroxylation reactions were employed to introduce hydroxyl groups with stereochemical control.

Main Results:

• The study successfully synthesized 4-deoxy-4,4-difluoro-glycosides for the first time.
• Benzyl ether and pivaloyl protecting groups were found to be effective for different stages of the synthesis.
• Dihydroxylations proceeded with high stereoselectivity, influenced by the orientation of the glycosidic C-O bond.

Conclusions:

• A novel and direct synthetic pathway to 4-deoxy-4,4-difluoro-glycosides has been established.
• The choice of protecting group strategy is crucial for successful synthesis.
• The stereochemical outcome of dihydroxylation can be controlled by the glycosidic bond orientation.