Theoretical study of the mechanism of formation of 4-aminoisoxazoles. 2*. An unusual rearrangement of oximinonitriles

The base-catalyzed cyclization of oximinonitriles in the presence of lithium ions leads to 4-aminoisoxazoles and, sometimes, to 5-aminooxazoles. Modeling using the density functional theory and the HF and MP2 methods indicated that both 4-aminoisoxazoles and 5-aminooxazoles are formed from the anion of one of the oximinonitrile lithium complexes. The formation of 5-aminooxazoles proceeds through an unusual anion rearrangement. The thermodynamic parameters of the transition states were calculated to explain the predominant formation of 4-aminoisoxazoles.