1,3-Sigmatropic-alkyl migration

Stemming from the studies on the oxonia [3,3]-sigmatropic alkyl migration of branched homoallylic alcohols by Loh et al. (see Section 8.15, Figure 8.132), the same group had also found that In(OTf)3 catalyzes the formation of tetrahydrofu-rans and tetrahydropyrans from homoallylic alcohols in the presence of aldehydes, developing their initial observations to generate crossed Prins cyclization products... 

Sigmatropic [1,5] shift of the imido-group, rather than alkyl migration, is found to occur in the sterically stabilized o-quinodimethanes (305) and (306), since thermolysis of these compounds gives (307) and (308) respectively. ... 

Sigmatropic migration involving alkyl group shifts can also occur ... 

When an alkyl group migrates, there is an additional stereochemical feature to consider. The shift can occur with retention or inversion at the migrating center. The analysis of sigmatropic shifts of alkyl groups is illustrated in Fig. 11.7. The allowed processes include the suprafacial 1,3-shift with inversion and the suprafacial 1,5-shift with retention. Sigmatropic rearrangements of order [3,3] are very common ... 

These are suprafacial sigmatropic shifts of order [1,5] and should occur with retention of configuration at the migrating carbon. This stereochemical course has been established for the 1,5-alkyl shift that converts 16 to 17. The product which is isolated, 18, results from a subsequent 1,5-hydrogen shift, but this does not alter the stereochemistry at the migrating... 

Sigmatropic migrations of alkyl or aryl groups" are less common than the corres-... 

In addition to the migration of hydrogen atoms in sigmatropic rearrangements, alkyl shifts also take place. A large number of such reactions occur... 

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