Asymmetric Synthesis of Cyclohexene Nucleoside Analogues

The asymmetric synthesis of novel cyclohexene nucleoside analogues 12 and 15 is described. An enantiospecific DielsAlder reaction between (E,E)-diene 2 and (+)-5-(D-mentyloxy)-2(5H)- furanone 3 provided the cycloadduct isomer 4. Three additional steps yielded amine 8 allowing the constructions of the thymine and adenine moieties to afford intermediates 11 and 14, respectively. Amination or cyclization and removal of the protecting groups occurred in one step in the presence of ammonia, giving the target six-membered ring nucleosides