Novel Formal Synthesis of Cephalotaxine via a Facile Friedel−Crafts Cyclization

A novel formal synthesis of cephalotaxine (CET), the parent structure of the antileukemia Cephalotaxus alkaloids, was achieved via a facile Friedel−Crafts cyclization of the amino (or amido) spiro-cyclopentenone precursor (A) mediated by a protic acid leading to tetracyclic ketone B. A remarkable stereoelectronic effect of the methylenedioxy substituent (R) and an interesting skeletal isomerization of the CET core ring system (B, X = H₂) were observed.