A Flexible Approach to Azasugars: Asymmetric Total Syntheses of (+)-Castanospermine, (+)-7-Deoxy-6-<i>epi</i>-castanospermine, and (+)-1-<i>epi</i>-Castanospermine
The asymmetric total synthesis of natural azasugars (+)‐castanospermine, (+)‐7‐deoxy‐6‐epi‐castanospermine, and synthetic (+)‐1‐epi‐castanospermine has been accomplished in nine to ten steps from a common chiral building block (S)‐8. The method features a powerful chiral relay strategy consisting of a highly diastereoselective vinylogous Mukaiyama‐type reaction with either chiral or achiral aldehydes