Synthesis of novel Bi-, Tri-, and tetracyclic nucleosides by reaction of a common cyclic enamine derived from TSAO-T with nucleophiles.

We report here the efficient regio- and stereoselective synthesis of new polycyclic nucleosides using a common cyclic enamine (7) as the starting material. In fact, the reaction of 7, easily prepared by reaction of 5'-O-Tosyl TSAO-T under basic nonnucleophilic conditions (potassium carbonate), with different classes of nucleophiles, for example, nitrogen-, oxygen-, sulfur-, and carbon-based nucleophiles, or with amino acids afforded, with total regio- and stereoselectivity, new bi-, tri-, and tetracyclic nucleosides. This straighforward route represents an original and unambiguously regio- and stereoselective pathway to these compounds. Some of these polycyclic nucleosides may be useful intermediates for a second series of reactions that may lead to the generation of structurally new nucleosides.