Concise synthesis of 1-epi-castanospermine

1-epi-Castanospermine (5) was synthesized from readily available 2,3,4,6-tetra-O-benzyl-1-deoxynojirimycin (11) in 9 steps and 21% overall yield, with selective debenzylation, Barbier reaction and reductive amination as the main reaction steps.