Seleno-phosphonic/-phosphinic acids

The synthesis of phosphonic acid derivatives by the direct oxidation of those of the corresponding phosphonous acid has been afforded very little interest (Chapter 2, Section VI.c), unlike the more controllable synthesis of derivatives of the thio- or seleno-phos-phonic acid derivatives (Chapter 5, Section II.B.4). In the present instance, the oxidation of A -protected (fmoc) (l-aminoalkyl)phosphinic esters has been carried out with NaI04 with high yields. Quantitative yields of (aminoalkyl)phosphonic acids were obtained in oxidation reactions with bromine water and with HgCl2-H20. In an alternative approach (Scheme 59), the A -protected (cbz) ethyl(l-aminoalkyl)phosphinate is initially converted into a (l-aminoalkyl)phosphonous acid diester, which is then subjected to the Atherton procedure to achieve change in valence at phosphorus. ... 

III. INTERCONVERSIONS OF THE MONOTHIO(OR SELENO) -PHOSPHONIC AND -PHOSPHINIC ACIDS AND THEIR... 

The replacement of one or more oxygen atoms in a phosphonic or phosphinic acid, or a derivative thereof, by an atom of a higher chalcogen affords a series of mono-, di- or even trithio- or -seleno-substituted acids (or their derivatives). Those rare substances which contain tellurium are rather unstable (even if only monoatomic with respect to that element) and cannot be readily purified, but have been characterized spectroscopically. 

The only comprehensive and readily-available surveys of thio- and seleno-phosphonic and -phosphinic acids appear to be those in the compilation by Kosolapoff and Maier which appeared during the 1970s, and those in the Houben-Weyl volumes. Some further information relevant to heterocyclic systems which possess endo- or exo-cyclic phosphorus-sulphur bonds has been surveyed by Mann Gefter has also provided a useful compilation of syntheses and data for unsaturated thiophosphonates and related compounds. As in the preceding chapters concerned with the synthesis of the various classes of phosphonic and phosphinic acids, literature surveys have been presented for individual compounds and the field, as a whole, is surveyed annually". In addition. Hall and Inch reviewed the mechanistic implications of changes in stereochemistry following displacement reactions at phosphorus in cyclic phosphorus(V) esters and amides, and in so doing discussed the reaction s of many such thiophosphoryl compounds. 

C. Chirality in Thio- and Seleno-phosphonic and -phosphinic Acid Derivatives... 

The mono-thio, -seleno and -telluro analogues of phosphonic and phosphinic acids are tautomeric (equations 1, 2 and 4). In the case of the sulphur-containing compounds, an attempt has been made to estimate the equilibrium compositions of a variety of acids by means of physicochemical measurements. The alkali metal salts of phosphonothioate and phosphinothioate acids possess anions which are mesomeric and, theoretically, it is possible for such ions to act as sources of both O-and S-substituted products. The same products can be obtained through reactions between the free acids and diazoalkanes, and because these reactions are relatively fast, it might be expected that the composition of the product mixtures might be a reflection of the tautomer composition of the acids. 

IV. SYNTHESES AND REACTIONS OF Dl- AND TRI-THIO(SELENO)-PHOSPHONIC ACIDS AND DITHIO(SELENO)PHOSPHINIC ACIDS... 

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