2-O-Propargyl Ethers: Readily Cleavable, Minimally Intrusive Protecting Groups for β-Mannosyl Donors

[reaction: see text]. The use of 2-O-propargyl ethers as protecting groups in 4,6-O-benzylidene-protected mannopyranosyl donors bearing either bulky silyl groups or glycosidic linkages on O3 overcomes the poor stereoselectivity achieved with the corresponding 2-O-benzyl ethers, due to a reduction of steric buttressing. Deprotection is conducted by treatment with potassium tert-butoxide followed by catalytic osmium tetroxide and N-methylmorpholine N-oxide.