Concise total synthesis of (±)-cephalotaxine via a transannulation strategy: development of a facile reductive oxy-Nazarov cyclization.

A concise total synthesis of (±)-cephalotaxine (1) has been achieved from dioxolanone derivative 15 via a transannulation strategy. The key transformation is a facile reductive oxy-Nazarov cyclization as illustrated above, involving presumably a tethered 1,2-oxidopentadienyl cation species 7a or 7b, which represents a new variant of the oxy-Nazarov cyclization and constitutes an effective, regio- and stereospecific 5-hydroxy cyclopentenone annulation protocol under mild hydride reduction conditions.