Eosin-Y-Catalyzed Visible-Light-Driven Ferrier Rearrangement of Glycal C3-Imidates

Area of Science:

• Organic Chemistry
• Carbohydrate Chemistry
• Photocatalysis

Background:

• Ferrier rearrangement of glycals yields 2,3-unsaturated glycosides, crucial for synthesizing rare sugars and natural products.
• Classical methods use harsh Lewis/protic acids and high temperatures, posing sustainability challenges and leading to byproducts.

Purpose of the Study:

• To develop a sustainable and mild photoacid-catalyzed method for O-Ferrier rearrangements.
• To activate C3-imidates on glycals using visible light and an organic photoacid.

Main Methods:

• Utilized eosin-Y as an organic photoacid and Ph2S2 as a cocatalyst under blue light irradiation.
• Investigated the O-Ferrier rearrangement of glycals with C3-imidate leaving groups.
• Explored substrate scope with various alcohols and phenols.

Main Results:

• Achieved chemoselective generation of Ferrier adducts from both gluco- and galacto-configured glycals.
• Demonstrated mild reaction conditions compatible with acid-sensitive acetal protecting groups.
• Obtained desired products in good to excellent yields across a broad substrate scope.

Conclusions:

• The visible light-driven strategy offers a sustainable alternative to traditional Ferrier rearrangement methods.
• The C3-imidate leaving group and blue light are crucial for this photoacid-catalyzed transformation.
• This method provides efficient access to valuable glycosides and synthetic intermediates.