11-13 (a) Carbon-to-carbon rearrangements of carbanions are rare, but they have been observed, as exemplified by the reaction shown [J. Am. Chem. Soc. 1961, 83, 412, 2537]. When lithium is used as the metal, the rearrangement takes place only above 0°C. Provide a reasonable rationalization for the formation of the product in this reaction.
Ph
Ph
K
Ph
K
Ph CI -66°C
Ph
Ph
(b) When the corresponding anion is generated from the methylated analog shown, preferential migration of the phenyl group is observed. How does this modify your answer to part (a)?
Ph
Ph
Ph
1) K, THF
Me
2Hg 2) CO2
HOâ‚‚C
Me
Ph
(c) The Grignard reagent, the alkyllithium, and the alkylpotassium with the same alkyl group as in part (b) show very different propensities to rearrange: the Grignard reagent does not rearrange, even in refluxing dioxane, the alkyllithium is stable at 0°C but rearranges at 40°C, and the alkylpotassium rearranges rapidly at room temperature. What does this tell you about the species actually rearranging? [J. Am. Chem. Soc. 1961, 83, 1196]
