α-Hydrogen Nitroxyl Radicals: Design, Synthesis and Properties

Hila Toledo, Organic, Technion, Haifa, Israel

The nature and use of nitroxide compounds as stable radicals and as reactive reagents and catalysts for redox reactions gives them a unique place in organic chemistry.^[1],[2] Designed nitroxide compounds have been used as radical trapping reagents, catalysts for oxidation of alcohols into carbonyl compounds and allylic transposition reactions. They also have applications in biology and medicine.

TEMPO, is one of the most efficient and widely used nitroxides exemplifies the archetypal nitroxide structure with its four flanking methyl groups. Unfortunately, the design of nitroxyl radicals with a more diverse set of substituents constitutes a significant synthetic challenge.  A logical way to diminish the steric congestion is to replace an α-alkyl substituent with a hydrogen. However, α-hydrogen nitroxyl radicals are extremely unstable and disproportionate to form nitrones and hydroxylamines.

We have developed a new concept for designing stable α-hydrogen nitroxyl radicals.  Following the guidelines of this concept we have prepared and studied two new families of nitroxyl radicals namely IAPNO 1 and IINO 2.

This poster will present the efficient and flexible syntheses of 1 and 2 as well as showcase the properties of these unique new radicals.[3]