Phenyl Migrations

Phenyldiazonium salts react with malonaldioxime to produce a 2-isoxazoline (7 IGEPl 920245), and the diazo ketone (484) when photolyzed gave a mixture of 2-isoxazoline and an isoxazole by a 1,5 carbon-hydrogen insertion. A phenyl migration was apparently not involved (Scheme 124) (66CC689). 

Migration to the developing electron sextet at nitrogen is not restricted to hydrogen. In (79) there is methyl migration with formation of methylamine and acetone in the acid-catalyzed decomposition of (80), phenyl migration leads to aniline and acetaldehyde. 

The mechanism of the reaction is unknown. The stereospecificity observed with (E)- and (Z)-l-methyl-2-phenylethylene points to a one-step reaction. The very low Hammett constant, -0.43, determined with phenylethylenes substituted in the benzene ring, excludes polar intermediates. Yields of only a few percent are obtained in the reaction of aliphatic alkenes with (52). In the reaction of cyclohexene with (52), further amination of the aziridine to aminoaziridine (99) is observed. Instead of diphenylazirine, diphenylacetonitrile (100) is formed from diphenylacetylene by NH uptake from (52) and phenyl migration. 

Kim and coworkers introduced silyl radical mediated addition of alkyl radical to silyloxy enamine 76. The silyloxy enamine moiety is readily accessible from a variety of functionalities. The mechanistic concept is illustrated in the Scheme 12 and involves the addition of R radical to 76 to give the radical adduct 77 and the subsequent homolytic cleavage of N-O bond to yield the desired product 78 and a silyloxy radical 79. The latter undergoes 1,2-phenyl migration to give the silyl radical 80 that abstracts halogen from the alkyl halide to regenerate the R radical. 

Tenney, Boykin and Lutz<58) labeled carbon 1 with either 14C or deuterium and showed that a hydrogen or phenyl migration was not involved in the rearrangement ... 

In addition, it was observed that the sensitized photolysis produced the same distribution of products with the same efficiency (fingerprint characteristic of the triplet state). From quenching studies the specific rate constant for the rearrangement could be obtained. Phenyl migration rearrangement is of intermediate efficiency, interposed between the more efficient and less efficient type A processes (Table 7.4). The type of mechanism proposed for this transformation is as follows ... 

Again the di-7r-methane reaction is regiospecific but this time it is competing with phenyl migration,... 

Casey et al. have studied the decarbonylation reactions of [cis-(OC)4M(MeCO)(PhCO)], in which M is Mn or Re (16,17). These complexes lose a carbonyl ligand to form five-coordinate intermediates of the type [(OC)3M(MeCO)(PhCO)]. Reversible methyl migration proceeds much more rapidly than does phenyl migration. In the course of these studies, a phosphine substituted rhena-/3-diketonate complex, [fac-(OC)3(Et3P)Re(MeCO) (PhCO)], was prepared. 

In the presence of ferrous salts the hydroperoxide decomposition goes by way of an oxygen monoradical intermediate, with different migration aptitudes. Para nitrophenyl rather than phenyl migrates under the radical conditions. Although the oxygen cation resembles the carbonium ion both chemically and in charge type, it may also be a diradical ... 

From synthetic point of view, the 1,5-phenyl migration discussed above (Reaction 42 44 in Scheme 6.12) has been successfully applied to the synthe-... 

When a phenyl group is linked at a vicinal position to tellurium, the replacement of tellurium by the methoxy group is accompanied by phenyl migration. - ... 

---