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.