Synthesis of neplanocin A and its 3'-epimer via an intramolecular Baylis-Hillman reaction.

The key cyclopentenyl intermediate 1 1b was synthesized in 4 steps from D-ribose in 41% overall yield via an efficient intramolecular Baylis-Hillman reaction. This novel key intermediate can be modified easily and transformed to neplanocin A (1a) and its 3'-epimer (1b).