Aryl phosphates 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. 

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,... 

The LDA catalyzed rearrangement of dialkyl aryl phosphates (99) to dialkyl (2-hydroxyaryl)- phosphonates has been known for some time and the use of the di-tert-butyl esters, now reported, offers advantages in the ease of preparation of the respective free (2-hydroxyaryl)phosphonic acids. The sequence (Scheme 7) has also been extended to include further phosphorylation and rearrangement steps to yield the 2,6-bis(dialkoxyphosphinyl)phenols (100). ... 

The rearrangement of the aryl phosphate esters 254 into esters 255 of (2-hydroxyaryl)-phosphonic acids under the influence of a strongly basic agent was discovered by Melvin who employed Ida and independently, and almost by accident, by Cambie and Palmer, who treated the phosphate ester 258 with BuLi and so obtained the phosphonate ester 259. 

Partitioning of carbocations between addition of nucleophiles and deprotonation, 35, 67 Perchloro-organic chemistry structure, spectroscopy and reaction pathways, 25, 267 Permutations isomerization of pentavalent phosphorus compounds, 9, 25 Phase-transfer catalysis by quaternary ammonium salts, 15, 267 Phenylnitrenes, Kinetics and spectroscopy of substituted, 36, 255 Phosphate esters, mechanism and catalysis of nucleophilic substitution in, 25, 99 Phosphorus compounds, pentavalent, turnstile rearrangement and pseudoration in permutational isomerization, 9, 25 Photochemistry, of aryl halides and related compounds, 20, 191 Photochemistry, of carbonium ions, 9, 129... 

Scheme 6.12 Rearrangement to C-aryl glycosides from aryl O-glycosides following a-selective synthesis using glycosyl phosphates.

The utility of glycosyl phosphates in the synthesis of C-glycosides was demonstrated in the synthesis of the natural product 8,10-di-O-methyIbergenin 39. Utilizing the O-to-C rearrangement, the key C-aryl linkage was installed and further elaboration afforded the product in good yield. 

The cyanophosphates resulting from a,p-unsaturated ketones are readily transformed into conjugated allylic phosphate via a BF, FtiO-catalyzed allylic rearrangement (Scheme Similarly, the cyanophosphates derived from 1,4-benzoquinones react with aromatic and heteroaromatic compounds to give 3-aryl-4-hydroxybenzonitriles. ... 

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... 

---