Convenient and Multistep Preparation of Oligopyridines Bearing Multiple Dansyl and Nitroxide Radicals

A series of pyridine and bipyridine molecules combining dual fluorescent (dansyl) and magnetic (free radical) probes has been prepared by a linear multistep protocol from the corresponding monodansylated derivatives. The grafting of the flexible aliphatic radical is realized by the use of a chloromethylnitronyl nitroxide derivative under basic conditions and with KI as a mediator. The synthetic potential of 2-[(5-dimethylamino-1-naphthalenesulfon-amide)methyl]-6-formylpyridine is assessed by the construction, in a first step, of an aliphatic nitroxide radical and subsequently of an additional aromatic radical. The synthetic methods reported herein provide a practical approach to the rational design of ligands bearing various kinds of functionalities such as chromogenic and spin-labeled fragments. A significant merit of this method is that it allows the introduction of the fluorescent substituent onto the pyridine or bipyridine framework at the beginning of the synthetic protocol.