Lignans and related phenols. Part XIII. Halogenated derivatives of podophyllotoxin

Abstract

Replacement of the alcoholic hydroxy-group by halogen in podophyllotoxin on treatment with phosphorus pentahalides is followed by halogenation of the pendant aryl substituent; this occurs either by substitution of a hydrogen atom or by displacement of a methoxy-group. The sequence ends with the halogenation of the methylene-dioxy-residue. The orientation and stereochemistry of the inserted halogen atoms have been largely assigned by n.m.r. spectroscopy.