TaCl₅‐Catalyzed Amidation of Carboxylic Acids with Amines

Abstract

The reaction of alkyl-and aryl-substituted carboxylic acids with primary and secondary amines under the action of 0.2 equiv. TaCl 5 leads to selective formation of carboxylic acid amides of various structures. TaCl 5 -catalyzed formation of amides was demonstrated to proceed equally selectively both in toluene and methylene chloride, hexane, diethyl ether and 1,4-dioxane solutions.

The TaCl5-Mediated Reaction of Dimethyl 2-Phenylcyclopropane-1,1-dicarboxylate with Aromatic Aldehydes as a Route to Substituted Tetrahydronaphthalenes

“…The carbonyl bond length decreases in the order of the following complexes: Ester–GaCl 3 (1.246 Å) > Ester–TaCl 5 (1.244 Å) > Ester–ZnCl 2 (1.239 Å) > Ester–SnCl 4 (1.238 Å) > Ester–TiCl 4 (1.236 Å), which indicates the decreasing strength of the Lewis acid towards the carboxyl group in the sequence GaCl 3 –TaCl 5 –ZnCl 2 –SnCl 4 –TiCl 4 . We recently demonstrated the effectiveness of TaCl 5 in activating carboxylic acid esters for the amidation reaction with amines [ 26 , 27 ]. Thus, if the Lewis acid is sufficiently strong, it promotes the rapid rearrangement of DAC 1 to intermediate H (route II).…”

“…The B3LYP/6-31G(d)/LanL2DZ method was used to calculate the geometric parameters of the complexes TaCl 5 , TiCl 4 , SnCl 4 , ZnCl 2 and GaCl 3 with methyl acetate (MeC(OMe)=O→MX n complex). The carbonyl bond length decreases in the order of the following complexes: Ester-GaCl 3 ( We recently demonstrated the effectiveness of TaCl 5 in activating carboxylic acid esters for the amidation reaction with amines [26,27]. Thus, if the Lewis acid is sufficiently strong, it promotes the rapid rearrangement of DAC 1 to intermediate H (route II).…”

TiF4-catalyzed direct amidation of carboxylic acids and amino acids with amines

“…10,11 However, in addition to the reagent cost, the need for additional equivalents of amines and excess reagents adds to the difficulties in the separation of the amides from stoichiometric quantities of the side products. Leading the intense activity in developing alternate catalyzed direct amidation protocols 12,13 are boron- 14 and siliconbased 15 catalysts as well as transition metal salts, particularly those of Ti, [16][17][18] Mn, 19 Fe, 20 Zn, 21,22 Zr, 17,23,24 In, 25 Hf, 26 Ta, 27,28 etc. Indeed, some of these reactions are carried out in sealed tubes and are effective only for aliphatic acids and several of these protocols are inefficient for amidation with anilines.…”