Magnetic Core-Shell Fe3O4@C-SO3H as an Efficient and Renewable ‘Green Catalyst’ for the Synthesis of O-2,3-Unsaturated Glycopyranosides

A magnetic core-shell solid-acid catalyst Fe3O4@C-SO3H was studied for synthesis of O-2,3-unsaturated glycosides through Ferrier rearrangement. The donors include 3,4,6-tri-O-acetyl-D-glucal and 3,4-di-O-acetyl-L-rhamnal. The acceptors consist of primary alcohols, secondary alcohols, tert-butanol, unsaturated alcohols, halogenated alcohol, sterol, sugars, and phenols. O-2,3-Unsaturated glycosides were obtained rapidly (<3 h) and efficiently (up to 98%) in good a selectivity (alpha/beta >5:1 to 19:1). Moreover, the catalyst can be easily separated from the reaction with an external magnetic force and reused for a minimum of five times without any significant decrease in the yields of the products after every recycle, suggesting it a promising green catalyst in 2,3-unsaturated glycosides syntheses.