Significant Self‐Acceleration Effects of Nitrile Additives in the Rhodium‐Catalyzed Conversion of Aldoximes to Amides: A New Mechanistic Aspect

Abstract

It was found that the catalytic activity of rhodium complexes was highly sensitive to the type of N-heterocyclic carbene (NHC) ligands in the conversion of aldoximes to amides. Among those species examined, the (cyclooctadiene)rhodium chloride-carbene complex RhACl exhibited the highest reactivity when it was employed in combination with a Brønsted acid, thus allowing mild reaction conditions. A significant rate acceleration effect resulting from the addition of nitrile additives was also observed. With the new protocol, the substrate scope of aldoximes has been widely expanded to include sterically congested and electronically varied derivatives. On the basis of detailed mechanistic studies, it is proposed that the reaction proceeds mainly via intramolecular electrophilic addition of aldoxime to rhodium-bound nitrile, which is different from the generally postulated two-step route: dehydration of aldoxime to nitrile followed by hydration of the latter intermediate.

Cu/SBA-15 is an Efficient Solvent-Free and Acid-Free Catalyst for the Rearrangement of Benzaldoxime into Benzamide

“…As it is reported by several authors [6][7][8][9][10][11], benzaldoxime transforms into benzonitrile (nitrile), benzaldehyde (aldehyde) and benzamide, of which benzamide is the main (desired) product. Indeed, the transformation of benzaldoxime into benzamide is a two-step process, wherein, the selective dehydration of benzaldoxime leads to benzonitrile, which on hydrolysis converts into benzamide.…”

“…Williams and his co-workers revealed the successful conversion of aldoximes into primary amides using Ru and Ir metal complexes [4,5]. It is proved that Rh complexes are good candidates for the rearrangement of aldoximes to primary amides [6][7][8]. However, Rh, Ir, and Rh containing catalytic materials are highly expensive and in addition, usage of these catalysts requires laborious workup procedure to separate the product.…”

Mechanistic Studies into Metal‐Catalyzed Aldoxime to Amide Rearrangements

“…Specifically, in the rearrangement of benzaldoxime into benzamide using a supported rhodium catalyst, the reaction profile showed the initial formation of benzonitrile before subsequent formation of benzamide. [10] Additionally, the universal inertness of O-alkylated aldoximes and ketoximes towards rearrangement suggests that the transformation requires the presence of both a hydrogen and a hydroxy group.…”

“…Chang et al have reported that nitrile additives have a self-acceleration effect on aldoxime rearrangements. [10] Within Changs study, reaction profiles were obtained for the rearrangement of benzaldoxime into benzamide, which indicated that the initial reaction rate was significantly increased in the presence of nitrile additives. Additionally, it was observed that the total concentration of nitrile remained almost constant throughout the reaction, with the amount of nitrile derived from the aldoxime increasing as the amount of nitrile additive decreased.…”

Emeraldine Base Form of Polyaniline Nanofibers as New, Economical, Green, and Efficient Catalyst for Synthesis of Z-Aldoximes

“…Oximes and their derivatives are important intermediates in the synthesis of amides [1][2][3][4], nitro compounds, hydroximinoyl chlorides, nitrones [5], amines, azoles, nitrile oxides, chiral -sulfinyl oximes, nitriles [6][7][8], and isoxazolines [9].…”