Sulfamate-Tethered Aza-Wacker Cyclization Strategy for the Syntheses of 2-Amino-2-deoxyhexoses: Preparation of Orthogonally Protected d-Galactosamines

We present a new strategy for the assembly of protected d-galactosamine synthons. Our route uses a sulfamate-tethered aza-Wacker cyclization as a key step and commences from d-erythrono-1,4-lactone. This stands in contrast to most literature syntheses of 2-amino-2-deoxyhexose derivatives, as these generally employ glycals or hexoses as starting materials. This strategy may serve as a template for the assembly of many other 2-amino-2-deoxyhexoses with protection patterns difficult to access by conventional methods.

Intramolecular Metal-Free C(sp3)-H Activation Enables a Selective Mono O-Debenzylation of Fully Protected Aminosugars

Carbamate-bearing benzylated aminosugars undergo an I₂/I(III)-promoted intramolecular hydrogen atom transfer (IHAT) followed by a nucleophilic attack to provide polycyclic structures. Thus, suitably positioned benzyl ethers are surgically oxidized into the corresponding mixed N/O-benzylidene acetals, which can be conveniently deprotected under mild acidic conditions to grant access to selectively O-deprotected aminosugars amenable for further derivatization. The scope of this strategy has been proven with a series of furanosic and pyranosic scaffolds. Preliminary mechanistic studies, including Hammett LFER and KIE analyses, support a reaction pathway with nucleophilic cyclization as the rate-determining step.