Phosphonate-phosphate rearrangement

A phosphate-phosphonate rearrangement process has also been explored in which a strong base is used to abstract a proton from the position adjacent to an aryl phosphate ester linkage. The product, an or f/io-phosphonopheno I, is generated in excellent yield (Figure 6.16).70 Further exploration of the variability of structure for this type of reaction seems desirable. 

By contrast, the similar phosphate-phosphonate rearrangement proceeds with retention, whether it proceeds via a tertiary56 or a secondary57 organolithium 57 or 58, as does the related amide-ketone rearrangement of 59.58 These retentive rearrangements presumably involve C=0-Li or P=0-Li coordination not possible in the Brook rearrangement. 

It has been shown that metallation of diisopropyl phosphates derived from primary aliphatic alcohols, except methanol, takes place at the alkyl as well as the isopropyl group in a ratio which is strongly influenced by steric effects. It was proposed that short-lived alkyllithium compounds were configurationally stable up to — 50°C and rearrange, with retention of configuration, into the corresponding a-hydroxyphosphonates (phosphate-phosphonate rearrangement) (Scheme 21). ... 

Jackson, J.A., Hammond, G.B., and Wiemer, D.F., Synthesis of a-phosphono lactones and esters through a vinyl phosphate-phosphonate rearrangement, J. Org. Chem., 54, 4750, 1989. 

The possibility of P-C bond biosynthesis for AEP through a phosphate-phosphonate rearrangement has been tested in Tetrahymena thermophila by growth on a medium containing (D)-[6,6-D2]glucose and isolation of the labelled AEP. The latter, labelled 1,1-D2, was isolated in amounts not consistent with an enzymic phosphate-phosphonate rearrangement of... 

Dhawan and Redmore have explored the scope of the isomerization. Thus, the (2-hydroxyaryl)phosphonate ester 255 may itself be 0-phosphorylated and a second rearrangement carried out, with the resultant formation of 257 from 256 in addition, the rearrangement of 260 into 261 and that of 262 into 263 were carried out. The diaryl phosphates 264 rearrange to the bis(2-hydroxyaryl)phosphinates 265 whilst the use of mixed alkyl aryl phenylphosphonates (266) affords mixed diarylphosphinates... 

When the preparation of alkali metal enolates derived from alkanoylphosphonates was attempted by treatment with strong anhydrous bases such as lithium diisopropylamide or sodium hydride, the formation of phosphate phosphonate-type products was observed. This was interpreted in terms of fragmentation of the enolate formed in the first step to ketene and dialkyl phosphite anion (equation 75), and addition of the latter to the carbonyl group of an unreacted acylphosphonate molecules to form a bisphosphonate. Such molecules are known to rearrange to phosphate phosphonates ... 

Salicylaldehyde and triethyl phosphite upon heating gave, instead of the expected diphosphonate (20), the rearranged phosphate-phosphonate (21). A new method to obtain 1-aminoalkylphosphinic acids (22) has been published it involves addition of bis(trimethylsilyl) phosphonite to Af-trityl imines, followed by hydrolysis. A similar reaction of bis(trimethylsilyl) phosphonite with 1-pyrroline trimer gave 2-pyrrolidinylphosphinic acid in 90% yield. Bis(trimethylsilyl) phosphonite with carbamoyl chlorides and triethylamine gave fair yields of the carbamoylphosphonites (23). ... 

Orthophosphoric and benzylphosphonic acids have been selectively alkylated with triethyl phosphite in a new synthesis of mono-, di-, and triethyl phosphates and of mono- and di-methyl phosphonates.62 A-Methylol carboxamides and sulphonamides react with trialkyl phosphites to give the phosphonate derivatives (78) and (80), respectively.63 However, the mechanism appears to be quite different in each case while the carboamides react by a transesterification-rearrange-ment pathway, the sulphonamides undergo elimination-addition via the imine (79). 

Another example is the electrocatalytic reaction between aromatic carbonyl compounds and dialkyl phosphonates. Here, rearrangement of the product anion leads to a phosphate as the product [136]. 

A comparison has been made" of various monoterpenoid rearrangements cataiysed by either zirconium phosphates or by zirconium organo-substituted phosphonates, and acid-catalysed rearrangements of a-trans- and /3-cis-3,4-epoxycaranes have been described." It has been observed" that on exposure to Li (OBu )3AlH, perhydro-naphthalene-l,4-diol monosulfonate ester (269) rearranges to the 11-oxatricyclo-[5.3.1.0.2,6]undecane derivative (270) (see Scheme 88). 

Phosphate-derived a-oxycarbanions can rearrange into a-hydroxy phosphonates. This class of rearrangement is known to proceed with retention of configuration at the carban-ion terminus. The enantioselective version of this rearrangement has been developed using a chiral lithium amide as a base (equation 115) . The reaction of benzyl dimethyl phosphate 182 with amide R,R)-63 in THF gave the hydroxy phosphonate (5 )-183 in 30% in enantioenriched form (52% ee). 

Hammerschmidt, F. Hanninger, A. Enantioselective deproto nation of benzyl phosphates by homochiral lithium amide bases. Configurational stability of benzyl carbanions with a dialkoxyphosphoryloxy substituent and their rearrangement to optically active a-hydroxy phosphonates. Chem. Ber. 1995, 328, 823-830. Avolio, S. Malan, C. Marek, I. Knochel, P. Preparation and reactions of functionalized magnesium carbenoids. Synlett 1999, 1820-1822. 

Acylphosphonates generate acyl anion equivalents with cyanide via phosphonate-phosphate rearrangement. These anions react with aldehydes to provide cross-benzoin... 

First ( 1 ), we have shown that O-benzylic phosphoric acid derivatives 2 treated with a strong base produced phosphate oarba-nions which immediately rearranged into a-hydroxy phosphonate oxanions 3. ... 

A mechanism, via a 6-hydroxy phosphorothiolate 8-mercapto-phosphate rearrangement, will be shown, and these new synthons will be compared with the phosphonate analogs (Wittig -Horner reagent). 

The formation of phosphates 90 can be explained by phosphonate-phosphate rearrangement catalyzed by bases [84], The authors of [82] were able to show that phosphonates 89 react with isatin (in the presence of sodium alkoxide), leading to compounds 90. 

The procedure of isotope effect studies will be illustrated on several examples. First one concerns studies of phosphonate-phosphate rearrangement (Scheme 1). Phosphite 3 reacts in the presence of triethylamine with o-nitrobenzaldehyde (Pudovik reaction) to form 1-hydroxyphosphonate 4 as mixture of two diastereo-isomers, 1 1. Amine also catalyses the reverse refro-phospho-aldol (retro-Abramov) reaction of 1-hydroxyphosphonate to phosphite and aldehyde and rearrangement to phosphate 5. In acetonitrile at 65°C Pudovik reaction is much faster than of retro-Abramov reaction and phosphonate-phosphate rearrangement, which rates are comparable. Important fact for the mechanism elucidation was experimental evidence that rearrangement occurs with retention of configuration at phosphorus atom.49... 

Because the phosphonate-phosphate rearrangement requires P-C bond breakage and formation of the P-O bond kinetic isotope studies by means of 13C NMR were chosen.50 13C KIEs were derived from NMR analysis of substrate-o-nitro-benzaldehyde or product-phosphate. Samples of aldehyde were prepared using the dead-end method. To the solution of phosphite 3 and triethylamine in acetonitrile an excess of aldehyde was added and solution was heated at 65°C to complete conversion of phosphonate 4 to phosphate 5 monitored by 31P NMR. The aldehyde conversions 0.2-0.8 were calculated from the balance of concentrations. The changes of 13C composition were determined for carbonyl carbon atom using signal of meta aryl carbon as an internal standard. KIE 1.0223(14) was calculated from the slope of linear relationship of isotopic ratio R and fraction of reaction,... 

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