Rearrangements alkyl migration

The syrc-isomer (272) is less specific in its secondary rearrangements alkyl migration in (270b) would be expected to trap the twisted cation less efficiently than double bond participation in (270a). 

Rearrangement of an enamine to a Sehiff s base through N- to C-alkyl migration was reported 729). These authors also found that enamines, rather than aminals, were formed from butyraldehyde and seeondary amines (730). Chloramines and aeetylenes reacted to give chloroenamine intermediates, which hydrolyzed on work-up of the reactions (731). 

In the case of an appropriate substrate structure, the carbenium ion species can undergo a 1,2-alkyl shift, thus generating a different carbenium ion—e.g. 4. The driving force for such an alkyl migration is the formation of a more stable carbenium ion, which in turn may undergo further rearrangement or react to a final product by one of the pathways mentioned above—e.g. by loss of a proton to yield an alkene 3 ... 

The most widely used route to l-benzazepin-2-ones involves the Beckmann or Schmidt reaction of the easily accessible 1-tetralones. Many biologically active compounds described in this review have been prepared on the basis of these reactions they have been fully reviewed [2], In the Beckmann reaction of 1-tetralone oximes, polyphosphoric acid is used as a catalyst-solvent in most instances. Aryl migration generally takes precedence over alkyl migration under these reaction conditions, and various 1-tetralone oximes substituted on the aromatic and/or aliphatic rings can be converted to the appropriate 2,3,4,5-tetrahydro-l//-l-benzazepin-2-ones (51) [5, 20-23, 36, 59, 65, 80, 107-112]. Both courses of the rearrangement occur in some instances, yielding l-benzazepin-2-ones (51) and the isomeric 2-benzazepine-l-ones, probably due to electronic effects of the substituents [90, 113, 114]. 

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

Taken together, these observations suggest a reaction pathway involving an intermediate dialkyl alkynylzinc species which rearranges to the allenylzinc reagent by alkyl migration from zinc and internal Sjv2 displacement of the mesylate (equation 20). 

A Chapman-like rearrangement has been observed in an attempt to prepare imidoyl fluoride 9. Instead, carbamoyl fluoride 10 is formed by an oxygen to nitrogen 1,3-alkyl migration."... 

---