Structure and bonding in 3,3-dialkyl-2-phosphinoyloxaziridines by X-ray diffraction and nuclear magnetic resonance spectroscopy

Abstract

X-ray crystal structure determinations are reported for 2-diphenylphosphinoyl-3,3-dimethyl- and 3-ethyl-3-methyloxaziridines, 2a and 2b, prepared from acetone and butanone via the oximes. The P–N bond lengths, 1.722(3) and 1.702(5)Å, and the conformation about this bond, are consistent with an n–σ*π-bonding interaction. Steric interactions appear to influence the bond angles at the pyramidal nitrogen. Oxaziridine 2b is a mixture of cis and trans isomers (ratio ca. 1 : 3) in the crystal and in solution. The ¹H, ¹³C and ³¹P NMR spectra are discussed. The barriers to nitrogen inversion, ΔG^‡ 12.6–13.2 kcal (52.7–55.2 kJ) mol^–1 by dynamic ¹³C NMR, are the lowest yet reported for an oxaziridine.