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.