Synthesis, Crystal Structure, and Diastereomeric Transfer of Pentacoordinated Phosphoranes Containing Valine or Iso-Leucine Residue

Abstract

Pentacoordinated phosphoranes containing valine or iso-leucine residue (2-phenyl-2,75-spiro[1,3,2-phenanthrodioxaphosphole-2,2′-1,3,2-oxazaphospholan]-5′-one) were synthesized through sequential two-step reactions, whereby the reaction products of phenyldichlorophosphine with N,O-bis(trimethylsilyl)valine or iso-leucine were followed by the addition of phenanthrenequione, and the crystals of 4a and 4b were obtained from benzene and hexane mixed solution. The x-ray structure of the crystals 4a and 4b revealed that they are distorted TBP, exhibiting RP absolute configuration. The 31P NMR spectra showed that the SP diastereomer could transfer into the other one RP that came out from the solution during crystallization. Correspondingly, when it was dissolved in solvents the RP diastereomer transferred into the other one SP, and the pair of diastereomers changed each other in solution at room temperature through a phosphonium carboxylate zwitterions intermediate. The work was supported by the National Natural Science Foundation of China (No. 29902003), the National Science and Technology Committee of China, the Chinese Education Ministry, and Tsinghua University.