Beckmann rearrangement synthetic utility

The rearrangement of ketoximes to amides was discovered more than a century ago, by Beckmann in 1886 , but remains a topic of current interest and stiU retains great synthetic utility. During the last century the Beckmann rearrangement has been frequently reviewedalthough the last major review was almost two decades ago. 

However, the stereochemistry of the oxime cannot be easily controlled and this may be a drawback for the synthetic utility of the Beckmann rearrangement. When a mixture of oximes is obtained from the ketone and when the isomerization of the oxime cannot be prevented during the rearrangement reaction, a mixture of amides is obtained. In other less favourable cases, the intended oxime cannot be obtained and the wrong amide will result from the rearrangement reaction. 

N.S. Mani and co-workers utilized the organoaluminum promoted modified Beckmann rearrangement during their efficient synthetic route to chiral 4-alkyl-1,2,3,4-tetrahydroquinoline. (4R)-4-Ethyl-1,2,3,4-tetrahydroquinoline was obtained by rearrangement of the ketoxime sulfonate of (3R)-3-ethylindan-1-one. The resulting six-membered lactam product was reduced to the corresponding cyclic secondary amine with diisobutylaluminum hydride. 

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