Copper-Catalyzed Annulation: A Method for the Systematic Synthesis of Phenanthridinium Bromide

A novel procedure
for the Cu-catalyzed systematic synthesis of
phenanthridinium bromide is reported. This transformation was achieved
with direct construction of central pyridinium core by using an in
situ formed biaryl imine as a substrate. Tolerance of a very wide
variety of N-substituents is indicated; this has
never previously been disclosed by other reports. Application of this
method to synthesis of the natural alkaloid bicolorine, and its derivatives,
was also carried out in only three synthetic steps from commercially
available compounds.