Alkyl groups rearrangements

You may have noticed that only one of the three alkyl groups of a trialkyl-borane is converted to an aldehyde by the carbonylation-reduction-oxidation sequence. To ensure that carbonylation takes the desired course without wasting the starting alkene, hydroboration is achieved conveniently with a hindered borane, such as 9-BBN, 12. With 12, only the least-hindered alkyl group rearranges in the carbonylation step ... 

Sigman, M. E. Barbas, J. T. Leffler, J. E. Supercritical Carbon Dioxide. 5. Carboxyinversion Reactions of Diacyl Peroxides. Alkyl Group Rearrangements and C02 Exchange. J. Org. Chem. 1987, 52, 1754-1757. 

However with 2,4,6-trisubstituted phenols electron-transfer occurs followed by nucleophilic attack by nitrile solvent. Alkyl group rearrangement or loss ultimately leads to benzoxazole products. 

Alkyl Group Rearrangements and Reactions Involving Dealkylation and/or Transalkylation (Disproportionation). 

In some cases, as with pentamethylbenzenes, the alkyl group rearrangement is... 

The ready reduction of acyl- to alkylarenes also provides a way to synthesize alkyl-benzenes without the complication of alkyl group rearrangement and overalkylation. For example, butylbenzene is best synthesized by the sequence of Friedel-Crafts acylation with butanoyl chloride, followed by Clemmensen reduction. 

---