Regioselective Conversion of the Secondary Hydroxyl Groups of D ‐Glucuronic Acid without the Requirement of O ‐Protecting Groups

Trifluoromethanesulfonic acid anhydride (triflic acid anhydride) transforms the bicyclic thiazolidinlactam 1 a into the crystalline elimination product 2 , in which all four secondary hydroxyl groups of 1 a are differently functionalized. Compound 2 can then add nucleophiles with high chemo‐ and stereoselectivity. Altogether, the four secondary hydroxyl groups of D ‐glucuronic acid are selectively transformed without the need for any O ‐protecting groups. Minimizing the number of O ‐protecting groups is a prerequisite for the use of sugar scaffolds in molecular libraries. The hapalosin analogues 15 , 16 , 19 , and 22 outline the strategy towards O ‐diversified glucose derivatives.