Lawesson's reagent for direct thionation of hydroxamic acids: Substituent effects on LR reactivity

Abstract

To explore the generality and scope of direct thionation of hydroxamic acids (HAs), the reaction of various structurally diverse HAs with Lawesson's reagent was investigated. The yield of thiohydroxamic acid (THAs) is poor when HAs possess bulky acyl and/or N-substituents, acidic ␣-hydrogen atoms, or an N-phenyl ring. THAs yields were correlated withBrown sigma parameter. The relative rates of two subsequent processes k T 2 and k R 2 were also measured. Correlation was also found for methine proton chemical shifts of N-isopropyl benzothiohydroxamic acids.

Ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides

“…Spectral data were consistent with those reported previously [31]. Compounds 1h and 1i were prepared in the same manner.…”

Conformational analysis of N-isopropylbenzohydroxamic acids: crystal structure, DFT, and NMR studies

“…As previously reported [10], the chemical shifts for 2 correspond to average signals for Z and E isomers in solution. A population of both isomers could depend on the electronic character of ring substituents, the concentration, as well as on the solvent used.…”

“…On this basis, we should be able to estimate relative populations of isomers for 2a and 2b of in solution and to clarify the differences in reactivity reported previously [10] for 2 containing substituents of opposite electronic character.…”

“…According to a proposed reaction mechanism [9] electrophilic Lawesson's reagent attacks both carbonyl (O1) and hydroxyamino (O2) oxygen atoms, but electronodonor substituents (EDG) prefer reaction to proceed at O2. On the other hand, good linear correlation between methine protons chemical shifts and Hammett substituent parameters (negative slope) [10] and between 15 N chemical shifts and Brown's parameters (positive slope) [11] was found.…”

On the reaction of bis(phosphothioyl)disul‐fanes with hydroxamic acids, part I: Ionic versus radical reaction pathways

“…Disulfanes 1a [20], 1b [21], 1c [22], 1d [22], and 1e were obtained from the corresponding phosphodithioate salts by using the reported method [23]. N-Methyl- [24], N-isopropyl- [25], N-tertbutyl-4-chlorobenzohydroxamic acid [26], and the corresponding benzamides 9b-c [27] are known compounds and were prepared by acylation of the respective N-alkylhydroxylamine or alkylamine with 4-chlorobenzoyl chloride. Diisopropylphosphorochloridothioate was obtained according to the described procedure [28].…”