A new approach to the 1,10-phenanthroline core

A protocol for the synthesis of substituted 1,10-phenanthrolines is reported. The phenanthroline scaffold has been obtained constructing the central cycle starting from two pyridine rings. The method is hinged upon the intramolecular coupling of cis-1,2-di(2-bromo-3-pyridyl)ethenes that are in turn obtained from the Wittig reaction of 2-bromonicotinaldehydes with phosphonium salts prepared from 2-bromo-3-(bromomethyl)pyridines. Yields up to 75% have been obtained.