Mild and eco‐friendly chemoselective acylation of amines in aqueous medium using a green, superparamagnetic, recoverable nanocatalyst

Abstract

Copper-grafted guanidine acetic acid-modified magnetite nanoparticles (Fe 3 O 4 @GAA-Cu(II)) as a green, superparamagnetic and recoverable nanocatalyst is found to promote quantitative N-acylation of various amines in a very short time with an equimolar amount of thioacetic acid in water at room temperature. This method is found to be highly selective for amines and not sensitive to other functional groups. Mild reaction condition, high selectivity, efficiency, simple workup and excellent yields are some of the major advantages of the procedure.

CO2‐Promoted Direct Acylation of Amines and Phenols by the Activation of Inert Thioacid Salts

“…Effective formation of the amide bond relies on the activation of inert thioacid salts through suitable selection of activating reagent [9,[13][14][15][16][17] or reaction conditions. [18,19] As reported, K + can interact with the oxygen atom of carbonyl group, and such interaction can lead to the activation of a carbonyl group.…”

“…In recent years, thioacids have emerged as N ‐acylation reagents for their unique reactivity and selectivity but often require activation reagents [12] . For this purpose, a multitude of activation reagents were developed including Sanger reagents, [13] Mukaiyama reagents, [13] oganoisonitriles, [14] Cu II ‐reagents, [15] carbon disulfide, [9] organonitrites, [16] and nanocatalysts [17] (Scheme 1b). In addition, the use of thiocarboxylate salt as acylation alternative source to inherently irritant thioacid has attracted interest, but synthetically useful procedures could only be obtained by means of photo‐ or electrochemical methods (Scheme 1c) [18,19] .…”

Amide Synthesis from Thiocarboxylic Acids and Amines by Spontaneous Reaction and Electrosynthesis

“…So far, there are two main strategies for the formation of amide bonds from thioacids. One is that thioacids react with some chemical reagents such as Sanger reagents & Mukaiyama reagents, organoisonitriles, Cu II reagents, carbon disulfide, organonitrite, and nanocatalysts to form more reactive thio‐intermediates, which can react with amines to give the amides (Scheme a). The other one is that thioacids can be converted to disulfides, which can be nucleophilically substituted by amines to form the corresponding amides .…”

“…A good yield was obtainedb yu sing nBu 4 NAc (entry 4), but it was also able to provide ag ood yield if no acyl source was involved.N one of the other electrolytes achievedt he yield observed with nBu 4 NBF 4 .T he electrosynthesis with aqueous electrolytes( KCl) in MeCN was also tested, which gave 57 %y ield (entry 7). Next, other commonly used solvents were also screened( entries [8][9][10][11], and the yield was significantly increasedt o9 7% if EtOAcw as used as the solvent (entry 11). There was no reactionw ithout the electrolyte because the conductivity of the solution was not high enough for our equipment( entry 12).…”