Phosphoryl migration

The full paper has appeared on the solvolysis of the dibenzyl ester (28) of phosphoenolpyruvic acid and on the related phosphonate ester (29). Reversible phosphoryl migration from the enol oxygen to the carboxy-group occurs readily in (28) and (29) but only to a small extent - and probably not reversibly-in the monoanion (30) and phosphoenolpyruvic acid itself. These observations are readily accounted for in terms of the expected ease of pseudorotation between the various configurations of the... 

Evidence has already been mentioned which indicates the presence of some ester groups at the 5-position,48 198 and it must be pointed out that, since no phosphoryl migration to or from the 5-position is expected to occur, these conclusions are still valid. Similar conclusions have been reached through studies of the nature of ribonuclease action. 

Example 27 Sekine and associates have used bis-0-(2-cyano-l,l-dimethy-lethyl)-iV,Ar-diethylphosphoroamidite in their studies on steric and electronic control of 2 -3 phosphoryl migration in 2 -phosphorylated uridine derivatives [57]. 

Intramolecular five-membered ring formation occurs in the alkaline-catalyzed hydrolysis of a series of esters of 2-hydroxypropylphosphate, where a linear free-energy relationship is found for the rate of alkoxide expulsion as a function of the pKa of the alcohol. No evidence for phosphoryl migration was obtained consistent with the fact that pseudorotation of the presumed intermediate leading to ring opening would be inhibited (50), viz. 

This process appears to be an additional example of a phosphoryl migration mediated by a pentacovalent species131. 

The acyl migration was found to be both base catalyzed with a second order rate constant of k2 = 160 M 1 s l and acid catalyzed, however much more slowly, with a second order rate constant of k2 = 4 x 10-4 M-1 s-1 (calculated between pH 1 and 2). The pH-rate profile is shown in Figure 1. At basic pH, the hydrolysis of the fatty acyl group is approximately 6500 times slower than migration. The equilibrium mixture in base contains approximately 90% of the 1-acyl isomer and 10% of the 2-acyl isomer. The phosphoryl migration was found to be too slow to measure, except at very acidic pH. Under these conditions, however, a variety of hydrolytic reactions also take place on a similar time scale so that the quantitation of the phosphoryl migration is complicated. 

Recent investigations in this standard synthetic procedure have featured the use of LDA (3 eq) or t-BuLi in the presence of HMPA at low temperature for promotion of the 1,2-phosphoryl migration conducive to fonnation of diethyl l-(alkoxycarbonyl)methylphosphonates in satisfactory yields (58-74%, Scheme 8.13). ... 

Rearrangements in the naphthalene series are exemplified by that of dialkyl 1 -naphthalenyl phosphates into dialkyl (2-hydroxynaphthalenyl)phosphonates and, more surprisingly, that of dialkyl 2-naphthalenyl phosphates into dialkyl (3-hydroxy-2-naph-thalenyl)phosphonates. The most recent extension of the rearrangement is in the pyridine series. In a series of diethyl pyridinyl phosphates, phosphoryl migration occurred from oxygen on C(3) to C ), or if the latter position was blocked, to C(2), and from oxygen... 

Ring-opening reactions brought about by alkoxides are more complex. The formation of the initial product(s), i.e. those which are kinetically preferred, may be followed by a phosphoryl migration fromm C(4)0 to C(6)0 or from sulphur to oxygen. The compounds 607ax (A = Ph or Me, Z = O or S) react quickly with NaOMe in MeOH after 2 h the products consist of the 4-substituted esters 608 formed with inversion (a tentative assumption)... 

As a result of an unexpected metal-induced phosphoryl migration reaction from carbon to nitrogen, ligand 47 can display different isomeric forms that lead to the formation of a cationic bis-chelated platinum complex containing a rearranged and an intact ligand 47 as part of a six-membered and a four-membered chelate (Scheme 14.26). 

---