An expeditious route to N-Acetyl-D-galactosamine from N-Acetyl-D- glucosamine based on the selective protection of hydroxy groups

GalNAc (1) was straightforwardly prepared from GlcNAc (2a) in six steps. Selective protection of the hydroxy groups on the C-1, C-3, and C-6 positions at the same time was performed by the treatment of TBDPS chloride (5.5 eq.) in DMF in 70% yield. The nucleophilic attack with CsOAc or KOBz on the chloromethylsulfonyloxy group at C-4 worked well (69-77% yield), accompanied by an unexpected rearrangement, to give the furanose products (6). The deprotection of all silyl and acyl groups under acidic conditions and the re-acetylation provided GalNAc (1) in 51% yield.