Direct epoxidation of d-glucal and d-galactal derivatives with in situ generated DMDO

A multi-gram epoxidation of 3,4,6-tri-O-benzyl-d-glucal and d-galactal with dimethyldioxirane (DMDO) generated in situ from Oxone®/acetone in a biphasic system (CH2Cl2–aqueous NaHCO3) resulted in the formation of the corresponding 1,2-anhydrosugars in a 99% yield and 100% selectivity. In a similar way, 3,4,6-tri-O-acetyl-d-glucal afforded a 7:1 mixture of the corresponding gluco and manno derivatives in an 87% overall yield.