³¹P NMR and Computational Studies on Stereochemistry of Conversion of Phosphoramidate Diesters into the Corresponding Phosphotriesters

Abstract

³¹P NMR spectroscopy was used to investigate a stereochemical course of a nitrite-promoted conversion of phosphoramidate diesters into the corresponding phosphotriesters. It was found that this reaction occurred with almost complete epimerization at the phosphorus center and at the C1 atom in the amine moiety. On the basis of the ³¹P NMR data, a plausible mechanism for the reaction was proposed. The density functional theory calculation of the key step of the reaction, i.e., breaking of the P–N bond and formation of the P–O bond, suggested a one-step S_N2(P) process with retention of configuration at the phosphorus center.

Keywords:

• Phosphoramidates
• nitrite-promoted rearrangement
• phosphotriesters
• DFT calculations
• edge attack
• SN2(P)

Acknowledgments

Financial support from the Swedish Research Council is gratefully acknowledged. The authors dedicate this article to the late Professor Vladimir Efimov, our friend and great chemist.