Migratory aptitude of alkyl groups

The study of relative migratory aptitudes of alkyl groups (Shubin et al., 1970b) began with the preparation of 9,10-dimethyl-9-ethylphenanthrenium ion [309] which was prepared from both 9-ethyl-9-methyl-10-methylene-[310] and 9,9-dimethyl-10-ethylidene-dihydrophenanthrene [311]. As shown... 

Harger, M. J. P., Westlake, S. Photolysis of some unsymmetrical phosphinic azides in methanol. Relative migratory aptitudes of alkyl groups and phenyl in the Curtius-like rearrangement. Tetrahedron 1982, 38, 3073-3078. 

Pilkington, J. W., Waring, A. J. Cyclohexadienones. Use of the dienone-phenol rearrangement in measuring migratory aptitudes of alkyl groups. J. Chem. Soc., Perkin Trans. 21976,1349-1359. 

Slayden, S.W. (1981) Relative migratory aptitudes of alkyl groups in the iodination of lithium ethynyltrialkylborates. 

Electrolysis of /J-hydroxy carboxylic acid (90) gave ketone (91) as the main product, which was converted to dl-muscone (Scheme 34) [113]. The migratory aptitude of alkyl substituents at the fi-position in the intermediate -hydroxy carbenium ion was scrutinized to show that vinyl, cyclopropyl, and benzyl groups rearrange predominantly. 

Answer. Three aspects of the scheme shown in Figure 13.2 may be examined by orbital interaction theory (a) the binding of CO compared to ethylene (b) the reactivity of coordinated carbonyl compared to ethylene with respect to reactivity toward intramolecular nucleophilic attack and (c) the migratory aptitude of alkyl versus carbonyl groups. 

The greater migratory aptitude of aryl groups over the alkyls during the Baeyer-Villiger oxidation and related processes is due to the participation of the soft 7T system. 

The carbocations generated by non-Kolbe electrolysis can rearrange by alkyl, phenyl or oxygen migration. The migratory aptitudes of different alkyl groups have been studied in the rearrangement of a-hydroxy carboxylic acids (Eq. 34) [323]. 

It is considered that [1,5] alkyl shifts usually require temperatures above 330 °C and proceed with free energies of activation greater than 180 kJmol-1. The 1,5-migratory aptitude of the formyl group is comparable with that of a trimethylsilyl group. However, 5-acetyl- and 5-ethoxycarbonyl-PMCPDs under the same conditions show a temperature-invariant XH NMR spectra, i.e. the migratory aptitude decreases in order CHO COMe COOMe114. 

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