Abstract
Amide bonds are among the most interesting and abundant molecules of life and products of the chemical pharmaceutical industry. In this work, we describe a method of the direct synthesis of amides from carboxylic acids and amines under solvent-free conditions using minute quantities of ceric ammonium nitrate (CAN) as a catalyst. The reactions are carried out in an open microwave reactor and allow the corresponding amides to be obtained in a fast and effective manner when compared to other procedures of the direct synthesis of amides from acids and amines reported so far in the literature. The amide product isolation procedure is simple, environmentally friendly, and is performed with no need for chromatographic purification of secondary amides due to high yields. In this report, primary amines were used in most examples. However, the developed procedure seems to be applicable for secondary amines as well. The methodology produces a limited amount of wastes, and a catalyst can be easily separated. This highly efficient, robust, rapid, solvent-free, and additional reagent-free method provides a major advancement in the development of an ideal green protocol for amide bond formation.
Highlights
Amide bonds are among the most widely abundant and fascinating types of linkages in organic synthesis and nature [1,2,3,4]
Arguably the biggest drive to investigate these methods came from the success of solid-phase peptide synthesis (SPPS) [11]
We report a microwave-assisted synthetic protocol for the preparation of amides directly from carboxylic acids and amines in very good to excellent yields at reaction times significantly shorter than those of many previously reported direct amidations
Summary
Amide bonds are among the most widely abundant and fascinating types of linkages in organic synthesis and nature [1,2,3,4]. They constitute the backbone of peptides and proteins and are important elementary linkages in many natural products and polymers. The translation of mRNA to proteins in ribosomes, which is one of the key processes in biology, is catalyzed by peptidic transferase, which extends the peptide chain by linking a new amino-acid in the form of aminoacyl-tRNA with an N-terminus of the peptide through an amide bond [9,10]. Common coupling reagents (e.g., carbodiimides, phosphonium, or uronium salts [14,15,16]) are often rather expensive, toxic, and are used in stoichiometric quantities
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