The Beckmann transposition as a strategy in the retrosynthesis

The rearrangement of oximes in an acid medium, called the Beckman rearrangement, produces an amide or lactam if the starting ketone is linear or cyclic, respectively.

To improve the performance of this type of reaction, various catalysts and acid media have been studied. Thus, for example, new acid media used as catalysts, with the indicated purpose, are: TCT/DMF, DAST/CH 2 CL 2 , CF 3 SO 3 H, PCl 5 , HgCl 2 /MeCN   and the ZnO.







diethylaminosulfide trifluoride

The migratory fitness of the groups is the same as in the Baeyer-Villiger reaction. Propose a synthesis design for each of the following molecules:

MOb 62


mob 63


MOb 64


MOb 62 . Retrosynthetic analysis. The   MOb 62 is an amide that could be prepared by   the Beckmann rearrangement of an oxime. Subsequent disconnections of the aromatic ketone lead to simple starting materials


Synthesis.   The reaction of the intermediate aromatic ketone with NH 2 OH and its subsequent treatment with an aqueous solution of sulfuric acid and ZnO, allows the formation of the   aromatic amide MOb 62.


MOb 63. Retrosynthetic analysis.   The synthesis strategy the   MOb 63, begins by treating it as a lactam formed by the Beckmann rearrangement of an oxime. The remaining simple disconnections lead to a cyclohexene as starting material for the synthesis.


synthesis .   The synthesis of MOb 63, according to the assumed strategy, does not present any reaction of special care. The last reaction shows the proper use of the Beckmann rearrangement reaction for the formation of lactams.


MOb 64. Retrosynthetic analysis. Beckmann's rearrangement strategy, for the phase of disconnection of the mob 64, greatly simplifies the synthesis of the lactam.


Synthesis.   Benzene is a suitable starting material for the synthesis of the mob 64. The reactions involved in the proposed design are sufficiently clear about their scope.