Migratory aptitudes: pinacol

In order to answer the question about inherent migratory aptitudes, the obvious type of substrate to use (in the pinacol rearrangement) is R RC—CRR since the... 

A number of experiments have been carried out to determine the relative migratory aptitude of groups in pinacol/pinacolone type rearrangements, and in general the relative ease of migration is found to be ... 

Since the symmetrical pinacol can give only a single R, the product is determined by the greater migratory aptitude of C H,. 

Intermolecular migratory aptitudes in the pinacol rearrangement have been determined by comparing the rates of rearrangement of different pinacols, each with four identical substituents of the type 37. 

We have already mentioned that migratory aptitudes are dependent on the reaction and on the conditions under which the reaction is carried out. An example of the latter type of variation is that in the pinacol rearrangement of triphenylethylene glycol, the phenyl/hydrogen migration ratio may vary by a factor of 180 (from 7.33 to 0.41) when the catalyst is changed from concentrated sulfuric acid to HC1 in water/dioxane.48... 

Explain why the migratory aptitude of the o-anisyl group is only 0.3 in the pinacol rearrangement. 

The migratory aptitude of the substituents in the bicyclic triazoline (Scheme 163) is the same as in the pinacolic rearrangement. In addition to the aziridine, which is always minor, a ring-enlarged imine is formed when R1 =CH3.100... 

Nakamura, K., Osamura, Y. Theoretical study of the reaction mechanism and migratory aptitude of the pinacol rearrangement. J. Am. 

Diols obtained by osmium tetroxide treatment of porphyrins constitute some of the more complex structures which have been subjected to pinacol rearrangement. These reactions left the polycyclic framework intact, and the oxochlorin products were formed by rearrangements which followed normal migratory aptitudes (e.g. H, Et > Me). 

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