2
$\begingroup$

enter image description here

Phenyl has greater migratory power. However, why did methyl migrate in step 2 of the reaction?

$\endgroup$
  • $\begingroup$ What makes you think the reaction depicted is right? $\endgroup$ – Zhe May 2 '18 at 15:25
  • 2
    $\begingroup$ ^ In other words, what is the source for this mechanism? Note that your thought may possibly be correct as well. $\endgroup$ – Gaurang Tandon May 2 '18 at 16:02
  • $\begingroup$ One might compare the stabilities of the cations formed from phenyl vs. methyl migration. $\endgroup$ – user55119 May 3 '18 at 16:37
1
$\begingroup$

In general, migratory aptitude of different groups follow following order: $\ce{-Ph} > \ce{-C(CH3)3} > \ce{-CH(CH3)2} > \ce{-CH2CH3} > \ce{-CH3} > \ce{-H}$

For example, 2,3-diphenylbutane-2,3-diol (1) was allowed to react under homogeneous (25 mol% of p-toluenesulfonic acid) or heterogenious (20 mol% of graphene oxide) catalytic conditions using toluene as a solvent at $\pu{100 ^\circ C}$. Under both conditions, only pinacol rearrangement with phenyl migration was observed affording 3,3-diphenylbutan-2-one (2) in a 90 and 95% conversion. Methyl migration has not been observed [Reference].

Pinacole

Reference:

Pinacol Rearrangement and Direct Nucleophilic Substitution of Allylic Alcohols Promoted by Graphene Oxide and Graphene Oxide $\ce{CO2H}$: M. Gomez-Martinez, A. Baeza, D. A. Alonso, ChemCatChem, 2017, 9, 1032–1039 (https://doi.org/10.1002/cctc.201601362)

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.