Phosphine Oxides and Sulphides

A somewhat featureless year s literature, with a decided lack of new reactions, and little advance in our understanding of old problems Perhaps the most interesting papers have been on the synthesis of bicyclic and polycyclic structures, and on the pathways of two rearrangements which appear to involve hydride transfer. 

Two of the elusive pimpernels of organophosphorus chemistry, the acyldiphenyl-phosphine oxides (1), have been isolated and adequately characterized for the first time. Thus careful oxidation of the corresponding phosphines yields the oxides (la) and (Ib). Deliberate hydrolysis of the latter yields the bis-oxide (2), and hence permits a fuller rationalization of the formation of (3) in earlier experiments on this system.  

Simple, but potentially useful, alkoxymethyl(diphenyl)phosphine oxides (6) are produced in good yields from benzene. A series of diphenylphosphinoyl acetals (7) has been prepared, and their n.m.r. spectra have been described.  

Addition of chlorodiphenylphosphine to aldehydes in the presence of carboxylic acids or of aqueous acids has long been used as a preparative route to a-hydroxyalkyl-(diphenyl)phosphine oxides (15). A re-examination of this reaction, using benzalde-hyde and acetic acid, has revealed that although (15 R = Ph) is the initial product, the final products are the acetate (16) and the bis-ether (17). It seems that (17) was first isolated by Conant and his colleagues, but that the analytical methods of fifty years ago failed to distinguish (15) from (17). 

Other carbonyl addition reactions of phosphorus(m) derivatives have been used to prepare the oxides (18)—(20). - The oxide (20) is of interest because of its ability to form stable copper(n) complexes.  

Reviews have appeared on synthetic uses of a-diazoalkylphosphoryl compounds,1 and on the synthesis and complexing properties of alkylenediphosphine dioxides.2 

The diversity of the reactions of a-diazoalkylphosphine oxides is further demonstrated by work from Regitz s group.8 Treatment of diazomethyldiphenylphosphine oxide with aldehydes yields the oxides (1), which have been converted into a range of other oxides3 as shown. 

Compounds possessing a yPH part-structure undergo a general condensation 

Ferrocenylphosphines and their oxides (3) have been prepared by standard routes,7 and the properties of diferrocenylphosphine oxide (3 n = 2) reported.8 Derivatives of diphenyl(ferrocenylmethyl)phosphine oxide (4) have been prepared by a metallation-alkylation sequence,9 as shown for the oxide (5). 

Synthetic studies of various cyclic phosphine oxides continue to be published. Thus a methanolic work-up leads to an 88% yield of 1-methylphospholen 1-oxides (6) from dichloro(methyl)phosphine, and detailed S1P n.m.r. and mass spectra have been described.10 The oxides (7) and (8) have been prepared11 as shown. Structural 

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Two contrasting conclusions have been reported in the reactions of lithium aluminium hydride in THF with phosphine oxides and phosphine sulphides respectively. The secondary oxide, phenyl-a-phenylethylphos-phine oxide (42), has been found to be racemized very rapidly by lithium aluminium hydride, and this observation casts some doubt on earlier reports of the preparation of optically active secondary oxides by reduction of menthyl phosphinates with this reagent. A similar study of the treatment of (/ )-(+ )-methyl-n-propylphenylphosphine sulphide (43) with lithium aluminium hydride has revealed no racemization. These results have been rationalized on the basis of the preferred site of attack of hydride on the complexed intermediate (44), which, in the case of phosphine oxides (X = O), is at phosphorus, and in the case of the sulphides (X = S), is at sulphur. Such behaviour is comparable to that observed during the reduction of phosphine oxides and sulphides with hexachlorodisilane. ... 

Higher Hydrogen Phosphides—Hydroxyphosphides—Alkylphosphines, Alkyl-phosphine Oxides and Sulphides. 

General.—brief report indicates that phenylthiocarbamoylphosphonates (48) rearrange, evidently rather readily, to phosphate esters phosphinates are obtained from phosphine oxides and sulphides. ... 

Conjugate addition reactions to activated olefins have also been used to prepare phosphine oxides and sulphides. In general these reactions have been quite standard, as illustrated by the syntheses of the oxides (21), (22), and (23). 

From Secondary Phosphine Oxides and Sulphides.—A novel reaction of phosphinates with sodium bis-(2-methoxyethoxy)aluminium hydride has been used to synthesize phosphine oxides, The complex hydride is believed to generate a secondary phosphine oxide anion from the phosphinate, and this ion may be trapped by an alkyl halide to give a phosphine oxide. The reaction is general for tetrahedral esters, and is... 

Interestingly, while 2-hydroxyalkylphosphines undergo Rabbit gastric lipase-catalysed acylation, the corresponding phosphine oxides and sulphides either react more slowly or not at all.39... 

The method can be used preparatively. Other examples include the selective demethylation of triethylmethylammoniiun chloride with sodium benzenethiolate. A somewhat analogous reaction is observed in the reaction of alkoxytri(dimethylamine)phosphonium chloride (33) with thiolates forming a phosphine oxide and sulphide. ... 

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