Recent Advances in the Synthesis of Amides via Oxime Rearrangements and its Applications

Background: Amide bond formation reactions are the most important transformations in (bio)organic chemistry because of the widespread occurrence of amides in pharmaceuticals, natural products and biologically active compounds. The Beckmann rearrangement is a well-known method used for the preparation of secondary amides from ketoximes. But, most of the traditional protocols used for the Beckmann rearrangement create enormous amount of wastes. Thus, the atom economical synthesis of amides has got high priority among the chemists. However, under classical Beckmann conditions, aldoximes do not rearrange into the corresponding primary amides. Indeed, reactions of aldoximes lead to nitriles. In recent years, it has been demonstrated that the aldoxime rearrangements can be carried out efficiently and selectively with the help of metal catalysts. Objective: This review focuses on the recent progress in the amides synthesis via ketoxime and aldoxime rearrangements. Applications of the rearrangements in the synthesis of heterocycles and natural products are also covered in this review. Conclusion: In the first part of the review, relevant pathways of oxime rearrangements are discussed and it is shown that several catalytic systems have been developed for the atom-economical synthesis of N-substituted amides from ketoximes. But similar reactions with aldoximes are, however, more challenging. The advances reached in the aldoxime rearrangement are also covered in this review. It is revealed that a large variety of homogeneous and heterogeneous metal catalysts have been developed to affect aldoxime rearrangements.