Silica-supported LiHSO4 as a highly efficient, heterogeneous and reusable catalytic system for the solvent-free synthesis of β-enaminones and β-enamino esters

Abstract

A highly efficient, simple and green procedure for the synthesis of ȕ-enaminones and ȕ-enamino esters is described. The reaction of aromatic and aliphatic amines with ȕ-dicarbonyl compounds using catalytic amount of silica-supported LiHSO 4 (LiHSO 4 /SiO 2 ) under solvent-free conditions at 80 °C affords the title compounds in high to excellent yields and in short reaction times.

Silica supported Fe(HSO4)3 as an efficient, heterogeneous and recyclable catalyst for synthesis of β-enaminones and β-enamino esters

“…They even served as synthons for ␥-aminoalcohol, ␤-aminoacids which are a class of very stable compounds useful in asymmetric catalysis as a chelating agent [9]. Condensation reactions of carbonyl compounds with amines in the presence of various acid catalysts like Yb(OTf) 3 [10], Zn(O 4 Cl) 2 [11,12], InBr 3 [13], CoCl 2 [14], and LiHSO 4 ·SiO 2 [15] are well reported for the synthesis of ␤-enaminones and enamino esters. Additionally, non-conventional techniques such as microwave and ultrasound are also reported [16][17][18].…”

Fe(HSO4)3·SiO2 as an efficient, heterogeneous and recyclable catalyst for the synthesis of bis-(β-enaminones) and bis-(β-enamino esters)

“…The most well-known route for the synthesis of b-enaminones involves the direct condensation of b-dicarbonyl compounds with amines in refluxing aromatic hydrocabones with azeotropic removal of water [18]. Several catalysts have been applied to achieve this transformation, including P 2 O 5 /SiO 2 [19], I 2 [20], LiHSO 4 / SiO 2 [21], NaAuCl 4 [22], Bi(TFA) 3 [23], Sc(OTf) 3 [24], Yb(OTf) 3 [25], ZrOCl 2 Á8H 2 O [26], HClO 4 /SiO 2 [27], and silica chloride [28]. Recently, we used silica-supported ferric hydrogen sulfate [29] as an efficient, heterogeneous and recyclable catalyst for the synthesis of b-enaminones and b-enamino esters.…”

“…However, bis-(b-enaminones) are missing in most of the above procedures. Only a few narrow examples are reported in the literature [19][20][21]30,31].…”

Zeolite (ZSM‐5) as a Highly Efficient and Heterogeneous Catalyst for the Synthesis of β‐Enaminones and β‐Enamino Esters

“…Out of these methods, most of them suffer from various disadvantages such as long reaction time and unspecified yields, use of expensive reagents, tedious work-up and lack of general applicability etc. The reaction has recently been reported to be catalysed by heterogeneous catalysts such as silica sulfuric acid 32 and silica-supported LiHSO 4 33 .…”