Phosphatoxy migrations

Table 3 Activation barriers for 1,2-phosphatoxy migration and syn-, 3-elimination in radicals 13a-e (in kJ/mol)...

This selection includes transition states from chlorine, acyloxy, and phosphatoxy migration reactions as well as three-and five-membered ring transition states in order to illustrate, how broadly the charge density /spin density space is covered in 1,2-migration reactions. That one and the same process can substantially change its characteristics as a function of solvent polarity and substitution pattern is, of course,... 

Figure 7.6 Rearrangement of 2-acyloxy and related glycopyranosyl radicals (a) tetra-O-acetylglucopyranosyl, (b) tetra-O-acetylmannopyranosyl, (c) a phosphatoxy migration note how the a-face of the sugar is (d) reverse migration where the anomeric centre is stabilised, (e) failure of migration of a 5-thio radical.

Scheme 18. Photolytically induced carbohydrate-based phosphatoxy migrations AcO AcO-. AcO— QnrS...

Scheme 19. Carbohydrate-based phosphatoxy migrations coupled with glycosylation reactions...

A 1,2-shift has been observed in radicals bearing an OCOR group at the p-carbon where the oxygen group migrates as shown in the interconversion of 36 and 37. This has been proven by isotopic labeling experiments and other mechanistic explorations. A similar rearrangement was observed with phosphatoxy alkyl radicals such as 38. ... 

The chemistry of radical sites adjacent to phosphatoxy centers elicited interest because of the involvement of such species in DNA degradation processes. These species can give rise to rearrangement, elimination, and substitution products, and for some time concerted eliminations and migrations as well as heterolysis to a radical cation and a phosphate anion were considered to be involved (Scheme 2). Recently, experimental studies of the l,2-dibenzyl-2-(diphenylphosphatoxy)-2-phenylethyl radical and complementary theoretical studies of l,l-dimethyl-2-(dimethylphosphatoxy)ethyl radical have been interpreted as indicating that a radical cation/anion pathway with initial formation of 49 is favored. ... 

Beckwith, A. L. J., Crich, D., Duggan, P. J., and Yao, Q. W., Chemistry of beta-(acyloxy)alkyl and beta-(phosphatoxy)alkyl radicals and related species radical and radical ionic migrations and fragmentations of carbon-oxygen bonds, Chem. Rev., 97, 3273, 1997. 

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