High 1,3-trans stereoselectivity in nucleophilic substitution at the anomeric position and β-fragmentation of the primary alkoxyl radical in 3-amino-3-deoxy-ribofuranose derivatives: application to the synthesis of 2-epi-(-)-jaspine B.

The high inverse stereoselectivity in the nucleophilic substitution at the anomeric position of 3-amino-3-deoxy-ribofuranose derivatives is reported. This unprecedented stereoselectivity is explained in terms of preferential nucleophilic attack on the "inside face" of the respective five-membered ring oxocarbenium ion that orients pseudoequatorially to the benzylamine group placed at the C-3 position. In addition, an unusual β-fragmentation of a primary alkoxyl radical generated from its corresponding N-phthalimide derivative was achieved, and thus taking advantages of both reactions, the total synthesis of 2-epi-(-)-jaspine B was completed.