Degradation of cobaloximes to derivatives of imidazo[1,2-a]pyridine

Abstract

Acetic anhydride in pyridine degrades several alkylcobaloximes to 2-[(E)-1-acetoxyiminoethyl]-3-acetylimidazo-[1,2-a]pyridine (5), the structure of which is established by direct X-ray crystallographic analysis of 3-acetyl-2-[(E)-1-hydroxyiminoethyl]imidazo[1,2-a]pyridine (6) derived from compound (5) by mild hydrolysis. Treatment of compound (6) with nitric acid gives 3-acetyl-2-(1,1-dinitroethyl)imidazo[1,2-a]pyridine (11). Spectroscopic properties of compounds (5), (6), and (11) confirm the assigned structures. Experiments concerning the mechanism of formation of compound (5) are reported, and the generality of the described degradation is indicated.

Compound (6) is orthorhombic, space group Pbca, with a= 16·402(10), b= 13·463(10), c= 9·735(10)Å, Z= 8. The structure was solved by direct methods and refined to R 0·089 for 520 observed reflections measured by diffractometer.