A Photoacid-Assisted Ag(I)-Catalyzed Glycosylation Based on <i>ortho</i> -Methoxycarbonylethynylphenyl Thioglycosides

-methoxycarbonylethynylphenyl thioglycoside donors has been developed. Catalytic AgOTf with eosin Y under visible light enables efficient glycosylations with diverse donors and acceptors resulting in high to quantitative yields and excellent stereoselectivities. The photoacid accelerates Ag(I) turnover without compromising stereoselectivity or acid-labile protecting groups. DFT calculations, gram-scale reactions, and synthesis of trisaccharide further support the proposed mechanism and practicality of this sustainable glycosylation protocol.