Thioimidate N-Oxides: Nitrones of Thio Esters

Article abstract of DOI:10.1021/jo00376a028

A group of three C-phenyl and three C-alkyl thioimidate N-oxides (nitrones of thio esters) was prepared by S-alkylation of N-alkylthiohydroxamic acids with methyl or ethyl iodide followed by basification of the resulting hydroiodide salts.An X-ray crystallographic analysis of S-methyl N-Methylthiobenzimidate N-oxide (9Z) established the Z stereochemistry for the more stable isomer.The 1H NMR, 13C NMR, IR, and UV spectral properties of the thio ester nitrones are reported.The E/Z stereochemistry of the C-alkyl derivatives is tentatively assigned on the basis of NOE measurements, long-range coupling, and chemical shift correlations.Thermal equilibration in bromobenzene-d5 at 80 deg C gave the following E/Z ratios: C-phenyl, 5:95; C-methyl, 46:54; C-ethyl, 53:47; C-isopropyl, 83:17.The equilibrium values are rationalized in terms of a balance between electronic stabilization and steric destabilization of the Z isomers.Hydrolysis of 9Z in aqueous acid at 100 deg C gave S-methyl thiobenzoate and N-methylhydroxylamine, whereas basic hydrolysis at 100 deg C afforded N-methylbenzohydroxamic acid as the principal initial product.