The synthesis of α-1-C-propyl-3,6-di-epi-nojirimycin and Polyhydroxyindolizidine alkaloids from readily available α-methyl-D-mannopyranoside is described. The key step in this process involves a regioselective and diastereoselective amination of anomeric acetal functionality using chlorosulfonyl isocyanate (CSI). © 2022 Elsevier Ltd