Facile and multistep synthesis of functionalized nitroxide radicals containing a bipyridine frame

The synthesis of stable bipyridine substituted nitronyl-nitroxide (NIT) or imino-nitroxide (IM) is reported. These methyl or ethynyl functionalized co mpounds have been prepared from the bromo-substituted analogues by a carboa lkoxylation reaction catalyzed by low valent palladium(0) using carbon mono xide in the presence of a primary alcohol as nucleophile and a tertiary ami ne as base. In the case of the 6,6'-dibromo-2,2'-bipyridine, a quite select ive mono-carboethoxylation reaction is achieved under mild conditions (70 d egreesC, 1 atmosphere CO). Stepwise reduction of the resulting esters with sodium borohydride, followed by Swern oxidation, affords the corresponding carbaldehydes in good yield. Furthermore, these derivatives were, used in a multistep protocol to prepare hybrid molecules bearing both an ethynyl gro up and a nitroxide free radical. The synthetic methods reported herein prov ide a practical methodology to the rational design of ligands bearing diffe rent kinds of functionalities.