Acyclic Imidate and Thiomidate Normal-Oxides: Nitrones of Esters and Thioesters (alpha-Alkoxynitrones, Alpha-Alkylthionitrones, Normal - Alkylthiohydroxamic Acids, X-Ray)

Abstract

Two N,O-dialkylacetimidate N-oxides and their hydrochlorides, and the hydrochloride of O-ethyl-N-methylpropionimidate N-oxide were prepared in dichloromethane solutions by the acid-catalyzed condensation of N-alkylhydroxylamines with aliphatic orthoesters. The (alpha)-alkoxynitrones and their hydrochlorides were characterized by ('1)H NMR spectroscopy and, in one case, by reaction with ammonia and aniline. In addition, a series of N,S-dialkylthioimidate N-oxides hydroiodides was synthesized by S-alkylation of N-alkylthiohydroxamic acids with methyl and ethyl iodide in acetone. The free (alpha)-alkylthionitrones were liberated from the corresponding hydroiodides with sodium carbonate or bicarbonate in water. The thioimidate N-oxides and their hydroiodides were characterized spectroscopically and their equilibrium ratios were determined in bromobenzene and acetone, respectively. The E/Z stereochemistry of the C-phenyl thioester nitrones is unambiguously established on the basis of an X-ray structural analysis on the N,S-dimethyl compound, and that of the C-alkyl counterparts is tentatively assigned on the basis of long range coupling, nuclear Overhauser effects, and chemical shift correlations. The reactions of (Z)-N,S-dimethylthiobenzimidate N-oxide, with methylmagnesium bromide and aqueous acid and base were investigated.