Migration group rearrangement

The reaction is strictly intramolecular the migrating group R is never completely released from the substrate. The driving force is the formation of the more stable rearranged carbenium ion 4, that is stabilized by the hydroxy substituent. The... 

When the migrating group is allyl, an additional concerted ([2,3] sigmatropic) pathway for rearrangement becomes available. In this an allylic shift must also occur. Nevertheless, the radical pathway is not always excluded. For example, rearrangement of ylids such as 36 (R = CHs.CO) leads to product 37 (R = CH3.CO) in which the allylic protons adjacent to the amido-nitrogen atom appear in emission (D. G. Morris, 1969). No polarization is observed in the much readier... 

In a rearrangement reaction, a group moves from one atom to another in the same molecule. Most are migrations from an atom to an adjacent one (called 1,2 shifts), but some are over longer distances. The migrating group (Y) may move with its... 

CD3COCD3 D2 0, besides about 20% of allene, the sole product was the unrearranged ketone 228, with no detectable amounts of 229. Presumably in this case the j3-methyl group is not an adequate migrating group for participation and rearrangement. 

A related method was applied in the course of synthesis of a precursor of a macrolide antibiotic, protomycinolide IV. The migrating group was an a-trimethylsilylalkenyl group.68 In this procedure, the DiBAlH first reduces the ketone and then, after rearrangement, reduces the aldehyde to a primary alcohol. 

The migrating group retains its configuration. Some reaction conditions can lead to syn-anti isomerization at a rate exceeding rearrangement, and when this occurs, a mixture of products is formed. The reagents that have been found least likely to cause competing isomerization are phosphorus pentachloride and p-toluenesulfonyl chloride.283... 

Similarly, if rearrangements in which there is a hydride shift (cf. p. 109) are carried out in a deuteriated solvent (e.g. D20, MeOD, etc.), no deuterium is incorporated into the new C—H(D) bond in the final rearranged product. In both cases the rearrangement is thus strictly intramolecular, i.e. the migrating group does not become detached from the rest of the molecule, as opposed to intermodular where it does. 

The acid catalyzed rearrangements of peroxides, in which the migrating groups show the same migration aptitudes as in carbonium ion rearrangements, may be represented as rearrangements of oxygen cations.89-91... 

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