Carbanions phenyl migrations

The basic hydrolysis of the bisphosphonium salt (80) gave a phosphonium salt (81) and a phosphine oxide (82) in a ratio which depended upon the acidity of the solvent used. The reaction is presumed to proceed via a carbanion from which the phosphonium salt arises by protonation by the solvent and the phosphine oxide by phenyl migration from phosphorus. The mechanism of the unexpected formation of 2-methyl-2 T-benzopyran from the phosphonium salt (83), under normal Wittig conditions, has been discussed in some detail. ... 

It was suggested (66) that anionic polymerization of methyl methacrylate terminated by isomerization of the carbanion into a carboxylate ion by migration of a methyl carbonium ion. However, the authors later stated (73) that the methyl methacrylate used was not sufficiently well purified. Schreiber (59) pointed out that methyl methacrylate reacts with phenyl lithium in the following manner ... 

MisceUaneous.—The carbanions (94), formed from the reaction of the corresponding phosphonium salt with sodium ethoxide and the sodium salt of t-butyl hydroperoxide, decompose in a number of ways. Migration of a phenyl group to oxygen yields the phosphine oxide (95) and formation of the alkyl ethyl ethers may be due to the intermediacy of a carbene, which is trapped by solvent. ... 

The results suggest that the anionic rearrangement proceeds essentially to completion, so that very little carbanion is present at equilibrium. It is not necessary to have a phenyl group present on the carbon for it to be metalated. As seen in Eq. (28), a methylthiosilane anion also undergoes rearrangement with migration of silicon. 

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