Tervalent Phosphorus Esters

Once again, the drive for improved performance in transition metal ion-catalysed processes has continued to stimulate the synthesis of new types of organophosphine and tervalent phosphorus-ester and -amide ligands. Activity in the chemistry of heteroaromatic phosphorus ring systems and low-coordination number p -bonded systems has also remained at a high level. New mechanistic insights into the Mitsunobu reaction have been reported, and interest in synthetic applications of Staudinger/Mitsunobu procedures has continued to develop. 

As this chapter covers two years of the literature relating to the above area, it has been necessary to be somewhat selective in the choice of publications cited. Nevertheless, it is hoped that most significant developments have been noted. As in previous reports, attempts have been made to minimise the extent of overlap with other chapters, in particular those concerned with the synthesis of nucleic acids and nucleotides to which the chemistry of tervalent phosphorus esters and amides contributes significantly, the use of known halogen-ophosphines as reagents for the synthesis of phosphines (see Chapter 1), and the reactions of dialkyl- and diaryl-phosphite esters in which the contribution of the phosphonate tautomer, (R0)2P(0)H), is the dominant aspect, which are usually covered elsewhere in these volumes. 

As in recent years, the synthesis of new chiral phosphines and related chiral tervalent phosphorus esters and amides continues to be a major preoccupation, being driven by the need for improved performance in metal-catalysed processes. It is very pleasing to note that two of the recipients of the 2001 Nobel Prize for Chemistry, William S. Knowles, and Ryoji Noyori, are honoured for their work in the synthesis and application in catalysis of chiral phosphine ligands. Interest in the structures of metallo-organophosphide systems, noted in the previous volume, has continued to develop. The chemistry of heteroaromatic ring systems, notably that of phospholes, and of low coordination number p -bonded compounds, also remain active areas. 

The reactions between tervalent phosphorus esters and chlorochioformamides or thlochloroformates yield the thioamides (185) or the thio esters (186) respectively. 

Oxaphospholans.—Full details have appeared of the reactions of the lactone and dione dimers of dimethylketen with a series of tervalent phosphorus esters and amides, and the postulated quinquecovalent intermediate (49) from the lactone dimer has been isolated in one case. Of potential mechanistic significance is the preferred migration of exocyclic substituents in the steps corresponding to (49) (50). 

Two highly unusual procedures for the preparation of trialkyl phosphates have been described. In the first, alkanes are made to react with trimethyl phosphite in a medium consisting of FeCl2.4H2O Zn(0) O2 in pyridine - acetic acid. The essential reaction appears to be one of Fe(II)-catalysed oxidation of the tervalent phosphorus ester by an alkyl hydroperoxide to afford an alkyl dimethyl phosphate. In the second procedure, described in considerable detciil, a Cu(II) catalyst aids in the interaction of red... 

Among tervalent phosphorus esters, phosphite-type compounds represent a noteworthy breakthrough in the field of catalysis, as thq usually present low sensitivity to air and to other oxidising agents. During the year of 2014 several new ligands and their metal complexes were reported in literature. Furthermore, it is worth mentioning the many reports on the use of known phosphites and/or their metal complexes in a diversity... 

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