Reaction of Carbodiimides with Phosphorothioic, Phosphorodithioic, and Phosphoroselenoic Acids: Products, Intermediates, and Steps

Article abstract of DOI:10.1021/jo00179a028

The reaction of the title acids with dicyclohexylcarbodiimide (DDC) used in a 2:1 ratio was found to give a complex mixture of products consisting of thio(seleno)pyrophosphates, thiolo(selenolo)phosphates, thiono(selenono)phosphates, dicyclohexylthiourea (DCTU), and a polymeric alkyl metaphosphate.When both reaction components are mixed in a 1:1 ratio, N-phosphoryl-N,N'-dicyclohexylthio(seleno)ureas (B) were formed.The formation of equimolar adducts (B) was also observed with other dialkyl- and diarylcarbodiimides.The spectral properties (especially the value of ³J_P-H) and reactivity of these adducts are strongly dependent on their conformation.The distinct conformational differences between the adducts B derived from DCC and diisopropylcarbodiimide (DiPC) and those obtained from dibenzylcarbodiimide (DBC) and diarylcarbodiimides were revealed by X-ray analysis of the selected N-phosphorylthioureas.By means of low temperature FT 31P NMR spectra it was demonstrated that the adducts (B) arise from the first formed unstable S(Se)-phosphorylisothio(seleno)ureas (A) as a result of S(Se)->N-phosphoryl migration.The differences in ability of the phosphoryl group to undergo S(Se)->N and O->N 1,3-shifts are briefly described.N-Phosphorylthio(seleno)ureas (B) obtained from DCC and DiPC, in contrast to those prepared from DBC and diarylcarbodiimides, reacted with a second thio(seleno)acid molecule.Crossover experiments and the use of O,O-diethyl phosphorothioate containing 35S-labeled sulfur showed that the adducts (B) are in equilibrium with their unstable isomers (A), the latter being active phosphorylating agents.The formation of the final reaction products was rationalized in terms of the threedirectional attack of the thioacid anion at the phosphorus, alkoxy carbon, and central carbon atoms of the protonated adduct (A).