Beckmann rearrangement groups

The stereochemical course of the Beckmann rearrangement often allows for the prediction of the reaction product to be obtained in general the substituent R anti to either the hydroxy or the leaving group will migrate ... 

Unlike the Beckmann rearrangement, the outcome of the Neber rearrangement does not depend on the configuration of the starting oxime derivative E- as well as Z-oxime yield the same product. If the starting oxime derivative contains two different a-methylene groups, the reaction pathway is not determined by the configuration of the oxime, but rather by the relative acidity of the a-methylene protons the more acidic proton is abstracted preferentially. ... 

The reaction that normally occurs on treatment of a ketoxime with a Lewis or proton acid is the Beckmann rearrangement (18-17) fragmentations are considered side reactions, often called abnormal or second-order Beckmann rearrangements. Obviously, the substrates mentioned are much more susceptible to fragmentation than are ordinary ketoximes, since in each case an unshared pair is available to assist in removal of the group cleaving from the carbon. However, fragmentation is a side reaction even with ordinary ketoximes and, in cases where a particularly stable carbocation can be cleaved, may be the main reaction. ... 

Thus, in most Beckmann rearrangements called anti) to the hydroxyl group migrates ... 

The assembly of the benzazepane framework 2-338 (e. g., found in cephalotaxine [187]) starting from 2-336 has been achieved by the group of Schinzer [188] utilizing a combination of a Beckmann rearrangement to give the iminiumion 2-337 and an allylsilane cydization (Scheme 2.79). 

The oxime nitrogen can also participate in cycloamination reactions to give pyrroles. Thus, treatment of oxime esters such as 185 with Pd(Ph3P)4 readily affords 186 [129]. The pentafluorophenyl group is necessary for good results otherwise a Beckmann rearrangement can unfavorably enter the picture. The oxime stereochemistry makes no difference on the outcome of the reaction. In addition to 186, pyrroles 187 and 188 were also prepared in this study (among others) [129]. 

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