New substituted mono-and bis(imidazolyl)pyridines and their application in nitroaldolisation reaction

Abstract

New chiral nitrogen ligands based on the substituted mono-and bis(imidazolyl)pyridines have been prepared and characterised. Their complexes with cupric acetate were used as catalysts in the nitroaldolisation reaction. In the case of optically pure complexes of mono(imidazolyl)pyridine, the isolated products were 2-nitro-1-(2-nitrophenyl)ethanols or 2-nitro-1-(4-nitrophenyl)ethanols in overall yields of 49-93 % and with the maximum enantiomeric excess of 15.6 %. The complexes of bis(imidazolyl)pyridine also catalyse the nitroaldol reaction, the yields being 64-90 %, but with zero enantioselective excess. Keywords: imidazolylpyridines, catalysis, copper complex, aldolisation reactionIn recent years, the development of new chiral ligands and their complexes with transition metals has been dynamically increasing [1,2]. These complexes are predominantly exploited as homogeneous catalysts within a broad spectrum of asymmetrical syntheses [3]. The ligands prepared in this study on the basis of mono-and bis(imidazolyl)pyridines are formally similar to the ligands with oxazolines "Pymox" [4] and "Pybox" [5], which belong among the best-known and widely applied nitrogen ligands. One of the most advantageous reactions for creating new C-C bonds at mild conditions is nitroaldolisation reaction [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. It is a reaction of carbonyl compound and nitroalkane having α-hydrogen atom, which is usually catalysed by metal complexes in the presence of bases (tertiary amines, sodium acetate) [6][7][8][9][10][11][12]. Another possibility consists in the catalysis by weak Lewis acids, which are components in complexes with mildly basic ligands (carboxylates) that can act as bases and deprotonate nitroalkane [13][14][15][16][17][18][19][20][21]. The product of nitroaldolisation reaction is β-hydroxynitroalkane, which can further be reduced to 1,2-amino alcohol, can undergo the Neff reaction to give the respective carbonyl compound, or can be dehydrated to nitroalkene [19,22]. In the previous paper, the synthesis and characterisation of (R,S)-, (R,R)-, (S,S)-2,6-bis(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-on-2-yl)pyridines and their complexes with ferric chloride was described [23].The aim of the present paper is the synthesis and characterisation of new chiral optically pure 2-(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-5-on-2-yl)pyridine (I ) and 2,6-bis(4-isopropyl-1,4-dimethyl-4,5-dihydro-1H-imidazol-5-on-2-yl)pyridine (II ). These ligands were prepared by Nmethylation of the optically pure 2-(4-isopropyl-4-methyl-4,5-dihydro-1Himidazol-5-on-2-yl)pyridine or 2,6-bis(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-on-2-yl)pyridine (Scheme 1).

Synthesis, copper(II) complexes and catalytic activity of substituted 6-(1,3-oxazolin-2-yl)pyridine-2-carboxylates

“…Finally this work represents a continuation and supplementation of our previous studies concerning Cu(I)/Cu(II) complexes of 4,5-dihydro-1H-imidazol-5-ones, which were used as homogeneous catalysts in some asymmetric reactions [14][15][16][17].…”

2-Amino-2-alkyl(aryl)propanenitriles as key building blocks for the synthesis of five-membered heterocycles

“…The prepared aminonitriles were partially hydrolyzed to give the respective aminoamides, which were acylated with aromatic acid chlorides; the acylation products were cyclized to prepare several series of substituted 4,5-dihydro-1H-imidazol-5-ones. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] The substituted 4,5-dihydro-1H-imidazol-5-ones prepared in this way were used in studies of their physico-chemical properties [20][21][22][23][24][25][26][27][28] also including studies of kinetics and mechanism of their formation and decomposition. [23][24][25] The substituted 4,5-dihydro-1H-imidazol-5-ones attached to a benzene ring or to a pyridine ring at 2-or 2,6-position(s) were used for preparation and characterization of the corresponding coordination [29][30][31][32][33][34][35][36] or organometallic 37 compounds with the following transition metals: Fe(III), 29,[30][31][32][33]…”

Stereoselective Electrochemical Reduction of Imazapyr in Aqueous Media Without Chiral Auxiliaries

“…Further studies demonstrated that this type of chemical exhibits anticonvulsive activity, antimicrobial efficiency over infectious diseases, 2 and the ability to act as chelating ligands with various metal ions. [3][4][5] Their organometallic complexes may show specific chiral catalytic activity in the homogeneous asymmetrical syntheses 6 or spin-crossover characteristics 7 that make them suitable for developing molecular switches, sensors, organic displays, or data storage devices.…”