Phenyl(seleno)phosphonic Dichloride1

[39078-30-3]  · C6H5Cl2PSe  · Phenyl(seleno)phosphonic Dichloride  · (MW 257.94)

(reagent for effecting oxygen-selenium exchange reactions of polarized carbonyl groups;1 exchanges O for Se in some O-heterocycles1)

Physical Data: bp 60 °C/0.01 mmHg; suffers progressive decomposition into PhPCl2 and Se on being heated.

Solubility: sol most inert solvents; most useful are xylene, toluene, benzene, dichloromethane.

Preparative Methods: PhPCl2 is treated at ambient temperature with ca. 6 mol % Aluminum Chloride under dry N2 followed by Selenium powder. The resulting PhP(Se)Cl2 is distilled in a good vacuum.2 More convenient is to heat PhPCl2 with a 20 mol % excess of powdered black Se at 170-175 °C under dry N2 for 40 min.1 The PhP(Se)Cl2, which is formed quantitatively, is cooled and dissolved in dry xylene. The mixture is filtered through a glass frit to remove the excess Se and sufficient additional xylene is added to give a 2 M solution. Other inert solvents may be used in place of xylene.

Handling, Storage, and Precautions: PhP(Se)Cl2, alone or in solution, is sensitive to moisture. Solutions of PhP(Se)Cl2 should be stored in dark bottles which are tightly closed by crown or screw caps fitted with a septum. Required volumes are transferred by means of graduated syringes. For best results, PhP(Se)Cl2 and solutions thereof should be used within 2-3 days after preparation. Reactions involving prolonged times should be carried out in a dry inert atmosphere.

Oxygen-Selenium Exchange Reactions.

Various types of carbonyl compounds in which the carbonyl group is highly polarized undergo O-Se exchange reactions with PhP(Se)Cl2. The carbonyl substrate is allowed to react with an aliquot of a 2 M solution of PhP(Se)Cl2 in xylene, either with or without addition of more xylene or a different inert solvent. Tertiary amides of aliphatic1, aromatic1, and electron-rich heterocyclic carboxylic acids3 are converted into the corresponding selenocarboxamides (eqs 1-4), and N-substituted lactams yield the corresponding N-substituted selenolactams (eq 5).1

A recommended workup procedure for small-scale (<25 mmol) reactions is to add chromatographic alumina (activity I-II) to the reaction solution, transfer the resulting slurry to a column of alumina (activity II-III), and elute. Unreacted PhP(Se)Cl2 and its reaction product PhP(O)Cl2 are retained on the basic column.

Indolizine-1- and 3-carbaldehydes are converted into the corresponding indolizineselenocarbaldehydes at room temperature (eq 6).1 In one case a 1,2-dithiol-3-one was converted into the corresponding 1,2-dithiol-3-selone (eq 7).1

Conversion of Oxygen Heterocycles into Selenium Heterocycles.

1-Oxa-6,6al4-dithiapentalenes and 6-oxa-6al4-thia-1,2-diazapentalenes, which are masked carbonyl compounds, react at room temperature with PhP(Se)Cl2 in the presence of Triethylamine to give the corresponding Se-containing heterocycles (eqs 8 and 9).1 The Et3N suppresses acid-catalyzed side-reactions of the substrates.

1. Michael, J. P.; Reid, D. H.; Rose, B. G.; Speirs, R. A. CC 1988, 1494.
2. Roesky, H. W.; Kloker, W. ZN(B) 1973, 28, 697.
3. (a) Nonoyama, M.; Nonoyama, K. Polyhedron 1989, 8, 2517. (b) Nonoyama, M.; Nonoyama, K. Polyhedron 1991, 10, 2265.

David H. Reid

University of the Witwatersrand, Johannesburg, South Africa

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