Disubstituted or sterically hindered hydroxylamines react with bulky S-thioacyl dithiophosphates yielding O-thioacylhydroxylamines. The reaction of O-thioacylhydroxylamines with dithiophosphoric acids yields acyl thiophosphoryl disulfides and ammonium dithiophosphates. The influence of radical traps on the reaction yield strongly suggests that radicals are involved in the mechanism of the process. The low redox potential of dithiophosphates, the observed photochemical stability of O-thioacylhydroxylamines and the influence of light on acyl thiophosphoryl disulfides yield imply involvement of a single electron transfer process in the investigated reaction.
Recently we have developed a convenient method for the synthesis of S-thioacyl dithiophosphates 1, excellent thioacylating reagents. When hydroxylanzines with one bulky group or two substituents on the nitrogen atom are treated with S-thioacyl dithiophosphates I O-thioacyl hydroxylamines 3 are produced exclusively. What is more important, compounds 3 undergo interesting reaction with dithiophosphoric acid 4 yielding amine and acyl thiophosphoryl disulfide 5. The disulfide 5 can be formed as a product of thiophilic attack of the dithiophosphate anion on the thiocarbonyl group in protonated O-thioacyl hydroxylamine 3. On the other hand, it is well known that dithiophosphate anions easily undergo one electron oxidation. Hence the dithiophosphate anion can act as single electron donor and disulfide 5 can be formed as a product of the SET reaction. The influence of light and radical traps strongly suggests that the second possibility operates in the reaction in focus.
S-Thioacyldithiophosphates in the Synthesis of Thiohydroxamic Acids and O-Thioacylhydroxylamines
作者:Leszek Doszczak、Janusz Rachon
DOI:10.1055/s-2002-31957
日期:——
S-Thioacyldithiophosphates proved to be excellent thioacylating agents. They are easily available from carboxylic acids. Due to their low reactivity towards oxygen nucleophiles and high reactivity towards nitrogen ones they found application in the synthesis of thiohydroxamic acids directly from hydroxylamines without protection on the hydroxy group. However, in cases of steric hindrance O-thioacyl hydroxylamines are formed and can be isolated with high yield.
thio and seleno analogs of phosphoric acid 1b–f with O-thioacylhydroxylamine 2 was examined. The experimental evidence for the proposed mechanism involving an N—O bond cleavage and a single electron transfer process (SET) from phosphate anions was collected. The influence of phosphoric acids 1 structure and their oxidation potentials on the course of the reaction and products 3, 4, 6, 7 distribution