Lawesson's reagent for direct thionation of hydroxamic acids: Substituent effects on LR reactivity
作者:Witold Przychodzeń
DOI:10.1002/hc.20259
日期:——
To explore the generality and scope of direct thionation of hydroxamicacids (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 α-hydrogen atoms, or an N-phenyl ring. THAs yields were correlated with Brown sigma parameter. The relative rates of two
that the inductive effect of the hydroxyl group rather than steric hindrance is responsible for non‐additivity of the effect of substituents. Additionally, N‐hydroxyl diminishes the effect of aromatic ring substituents on the 15N chemicalshifts in the thiohydroxamic acids 3 which is approximately half that in the respective thiobenzamides 6. The chemicalshift values correlate best with Brown's σ+