Manganese Catalyzed Direct Amidation of Esters with Amines

Abstract

The transition metal catalyzed amide bond forming reaction of esters with amines has been developed as an advanced approach for overcoming the shortcomings of traditional methods. The broad scope of substrates in transition metal catalyzed amidations remains a challenge. Here, a manganese­(I)-catalyzed method for the direct synthesis of amides from a various number of esters and amines is reported with unprecedented substrate scope using a low catalyst loading. A wide range of aromatic, aliphatic, and heterocyclic esters, even in fatty acid esters, reacted with a diverse range of primary aryl amines, primary alkyl amines, and secondary alkyl amines to form amides. It is noteworthy that this approach provides the first example of the transition metal catalyzed amide bond forming reaction from fatty acid esters and amines. The acid–base mechanism for the manganese­(I)-catalyzed direct amidation of esters with amines was elucidated by DFT calculations.

An Environmentally Benign, Catalyst‐Free N−C Bond Cleavage/Formation of Primary, Secondary, and Tertiary Unactivated Amides

“…N ‐Phenylpivalamide [15c] (3C) : Using the experimental procedure EP‐1 , the product was obtained as white solid in 54 %; 1 H NMR (400 MHz, CDCl 3 ) δ 7.52 (d, J =8.3 Hz, 2H), 7.31 (t, J =7.7 Hz, 3H), 7.10 (t, J =7.4 Hz, 1H), 1.32 (s, 9H). 13 C NMR (100 MHz, CDCl 3 ) δ 176.73, 138.16, 129.02, 124.29, 120.17, 39.68, 27.72.…”

“…N ‐(4‐Methoxyphenyl)benzamide [15c] (5 f) : Using the experimental procedure EP‐2 , the product was obtained as white solid in 88 %; 1 H NMR (400 MHz, DMSO‐d 6 ) δ 10.12 (s, 1H), 7.96 (d, J =7.8 Hz, 2H), 7.69 (d, J =8.8 Hz, 2H), 7.61–7.47 (m, 3H), 6.94 (d, J =8.8 Hz, 2H), 3.75 (s, 3H). 13 C NMR (100 MHz, DMSO‐d 6 ) δ 165.06, 155.53, 135.02, 132.20, 131.29, 128.27, 127.48, 121.96, 113.69.…”

Manganese-N-heterocyclic carbene (NHC) complexes – An overview

“…Very recently, Wei, Liu and co-workers reported the synthesis of a series of new Mn(I) complexes bearing bidendate NHC-N and NHC-C ligands (Fig. 7) [40]. These complexes were studied for the direct amidation of esters with amines (see section 6.6).…”

Direct Amidation of Esters by Ball Milling**

“…To this end, one such avenue that has flourished is the direct amidation of carboxylic esters [6] . Examples of powerful contemporary methods include, among many others, Newman and co‐workers’ Ni 0 ‐catalyzed direct and redox‐neutral amidation of esters using NHC ligands, [6m,n] which can also be achieved by palladium‐catalysed processes, [6o–q] and Szostak and co‐workers’ direct amidation of simple esters using stoichiometric quantities of LHMDS (Scheme 1 B). [6r–t] …”