Glycosylated vinyl ethers by the Julia–Lythgoe–Kocienski olefination: application to the synthesis of 2′,5′-dideoxydisaccharides and carbohydrated β-lactams

α-Carbohydrated pyridinyl sulfones, prepared from commercially available d-(−)-ribose, d-(+)-galactose, and d-(+)-glucose through a five-step sequence, have been employed in the Julia–Lythgoe–Kocienski olefination with aldehydes. This one-pot protocol, using solid KOH at room temperature, affords the corresponding glycosidic enol ethers in moderate to excellent yields and (E)-stereoselectivities. These glycosylated adducts undergo hetero-Diels–Alder reactions with 2-formyl-1-malondialdehyde to afford 2′,5′-dideoxygenated disaccharides in good yields and complete regio- and endo-selectivity. Alternatively, the 2+2]-cycloaddition reaction of the glycosidic enol ethers with chlorosulfonyl isocyanate provided glycosylated β-lactams regioselectively and with only trans-stereoselectivity. The β-lactams could be converted to N-methylthio derivatives which show decent antibacterial activity toward methicillin-resistant strains of Staphylococcus aureus.