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α-Ketophosphonates in the Synthesis of α-iminophosphonates

[ Vol. 7 , Issue. 2 ]

Author(s):

Petro P. Ony`sko*, Tetyana I. Chudakova, Vladimir V. Pirozhenko and Alexandr B. Rozhenko   Pages 226 - 238 ( 13 )

Abstract:


The potentialities of condensation of α-ketophosphonates with primary amines for direct synthesis of α-iminophosphonates have been revealed. Diesters of α-ketophosphonic acids react with the primary amines by two competitive pathways: with a formation of α-iminophosphonates or a C-P bond cleavage resulting in a hydrogen phosphonate and an acylated amine. In many cases, the latter undesirable pathway is dominant, especially for more nucleophilic alkyl amines. Using metallic salts of α-ketophosphonates avoids the C-P bond cleavage, allowing direct preparation of α-phosphorylated imines by the reaction with primary amines. This strategy provides an atom economy single-stage synthesis of iminophosphonates – precursors of bio relevant phosphorus analogs of α-amino acids. Methyl sodium iminophosphonates, bearing aryl or heteryl substituents at the imino carbon atom exist in solutions at room temperature as an equilibrium mixture of Z- and E-isomers. A configuration of the C=N bond can be controlled by the solvent: changing the aprotic dipolar solvent DMSO-d6 by water or alcohols leads to the change from a predominant Z-isomer to almost an exclusive E-form. In contrast, diesters of the respective iminophosphonates exist in non-protic solvents predominantly in Econfiguration. The solvent effect on E-Z stereochemistry is demonstrated by DFT calculations.

Keywords:

α-Iminophosphonates, α-ketophosphonates, aminophosphonates, aminophosphonic acids, E-Z isomerism, DFT calculations.

Affiliation:

Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmans’ka str., Kyiv 02660, Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmans’ka str., Kyiv 02660, Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmans’ka str., Kyiv 02660, Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmans’ka str., Kyiv 02660

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